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Books sometimes say, "Our genes want us to have as many children as possible", or "Evolution wants the fittest to survive". But genes are not conscious entities who can want things. So, why do we anthromorphize genes, evolution, and nature?
After his seminal work in developing theories of natural selection, Charles Darwin devoted much of his final years to the study of animal emotions and psychology. He wrote two booksThe Descent of Man, and Selection in Relation to Sex in 1871 and The Expression of the Emotions in Man and Animals in 1872 that dealt with topics related to evolutionary psychology. He introduced the concepts of sexual selection to explain the presence of animal structures that seemed unrelated to survival, such as the peacock's tail. He also introduced theories concerning group selection and kin selection to explain altruism.  Darwin pondered why humans and animals were often generous to their group members. Darwin felt that acts of generosity decreased the fitness of generous individuals. This fact contradicted natural selection which favored the fittest individual. Darwin concluded that while generosity decreased the fitness of individuals, generosity would increase the fitness of a group. In this case, altruism arose due to competition between groups.  The following quote, from Darwin's Origin of Species, is often interpreted by evolutionary psychologists as indication of his foreshadowing the emergence of the field:
In the distant future I see open fields for far more important researches. Psychology will be based on a new foundation, that of the necessary acquirement of each mental power and capacity by gradation.
Darwin's theory inspired William James's functionalist approach to psychology.  At the core of his theory was a system of "instincts."  James wrote that humans had many instincts, even more than other animals.  These instincts, he said, could be overridden by experience and by each other, as many of the instincts were actually in conflict with each other. 
In their Evolutionary Psychology Primer Tooby and Cosmides make note of James' perspective, and also quote him:
"We do not realize that 'normal' behavior needs to be explained at all. This "instinct blindness" makes the study of psychology difficult. To get past this problem, James suggested that we try to make the "natural seem strange": It takes. a mind debauched by learning to carry the process of making the natural seem strange, so far as to ask for the why of any instinctive human act. To the metaphysician alone can such questions occur as: Why do we smile, when pleased, and not scowl? Why are we unable to talk to a crowd as we talk to a single friend? Why does a particular maiden turn our wits so upside-down? The common man can only say, Of course we smile, of course our heart palpitates at the sight of the crowd, of course we love the maiden, that beautiful soul clad in that perfect form, so palpably and flagrantly made for all eternity to be loved! And so, probably, does each animal feel about the particular things it tends to do in the presence of particular objects. . To the lion it is the lioness which is made to be loved to the bear, the she-bear. To the broody hen the notion would probably seem monstrous that there should be a creature in the world to whom a nestful of eggs was not the utterly fascinating and precious and never-to-be-too-much-sat-upon object which it is to her. Thus we may be sure that, however mysterious some animals' instincts may appear to us, our instincts will appear no less mysterious to them. (William James, 1890) In our view, William James was right about evolutionary psychology. Making the natural seem strange is unnatural -- it requires the twisted outlook seen, for example, in Gary Larson cartoons. Yet it is a pivotal part of the enterprise. Many psychologists avoid the study of natural competences, thinking that there is nothing there to be explained."
According to Noam Chomsky, perhaps Anarchist thinker Peter Kropotkin could be credited as having founded evolutionary psychology, when in his 1902 book Mutual Aid: A Factor of Evolution he argued that the human instinct for cooperation and mutual aid could be seen as stemming from evolutionary adaption. 
William McDougall made a reference to "evolutionary psychology" in his 1919 book An Introduction to Social Psychology: "It is only a comparative and evolutionary psychology that can provide the needed basis (for psychology) and this could not be created before the work of Darwin had convinced men of the continuity of human with animal evolution as regards all bodily characters, and had prepared the way for the quickly following recognition of the similar continuity of man’s mental evolution with that of the animal world." (p. 16)
While Darwin's theories on natural selection gained acceptance in the early part of the 20th century, his theories on evolutionary psychology were largely ignored. Only after the second world war, in the 1950s, did interest increase in the systematic study of animal behavior. It was during this period that the modern field of ethology emerged. Konrad Lorenz and Nikolaas Tinbergen were pioneers in developing the theoretical framework for ethology for which they would receive a Nobel prize in 1973.
Desmond Morris's book The Naked Ape attempted to frame human behavior in the context of evolution, but his explanations failed to convince academics because they were based on a teleological (goal-oriented) understanding of evolution. For example, he said that the pair bond evolved so that men who were out hunting could trust that their mates back home were not having sex with other males. 
In 1975, E. O. Wilson built upon the works of Lorenz and Tinbergen by combining studies of animal behavior, social behavior and evolutionary theory in his book Sociobiology:The New Synthesis. Wilson included a chapter on human behavior. Wilson's application of evolutionary analysis to human behavior caused bitter debate.  
With the publication of Sociobiology, evolutionary thinking for the first time had an identifiable presence in the field of psychology.  E. O. Wilson argues that the field of evolutionary psychology is essentially the same as "human sociobiology". 
Edward H. Hagen writes in The Handbook of Evolutionary Psychology that sociobiology is, despite the public controversy regarding the applications to humans, "one of the scientific triumphs of the twentieth century." "Sociobiology is now part of the core research and curriculum of virtually all biology departments, and it is a foundation of the work of almost all field biologists" Sociobiological research on nonhuman organisms has increased dramatically and appears continuously in the world's top scientific journals such as Nature and Science.The more general term behavioral ecology is commonly used as substitute for the term sociobiology in order to avoid the public controversy. 
The term evolutionary psychology was used by American biologist Michael Ghiselin in a 1973 article published in the journal Science.  Jerome Barkow, Leda Cosmides and John Tooby popularized the term "evolutionary psychology" in their 1992 book The Adapted Mind: Evolutionary Psychology and The Generation of Culture.  The term is sometimes abbreviated "EvoPsych" or "evo-psych" or similar. 
In contrast to sociobiology and behavioral ecology, evolutionary psychology emphasizes that organisms are "adaptation executors" rather than "fitness maximizers."  In other words, organisms have emotional, motivational and cognitive adaptations that generally increased inclusive fitness in the past but may not do so in the present. This distinction may explain some maladaptive behaviors that are the result of "fitness lags" between ancestral and modern environments.  For example, our ancestrally developed desires for fat, sugar and salt often lead to health problems in modern environment where these are readily available in large quantities.
Also, in contrast to sociobiology and behavioral ecology (which mostly study non-human animal behavior), rather than focus primarily on overt behavior, EP attempts to identify underlying psychological adaptations (including emotional, motivational and cognitive mechanisms), and how these mechanisms interact with the developmental and current environmental influences to produce behavior.  
Before 1990, introductory psychology textbooks scarcely mentioned Darwin.  In the 1990s, evolutionary psychology was treated as a fringe theory,  and evolutionary psychologists depicted themselves as an embattled minority.  Coverage in psychology textbooks was largely hostile.  According to evolutionary psychologists, current coverage in psychology textbooks is usually neutral or balanced. 
The presence that evolutionary theory holds in psychology has been steadily increasing.  According to its proponents, evolutionary psychology now occupies a central place in psychological science. 
DNA and Evolution
WHAT IS DNA?
DNA, or deoxyribonucleic acid, is a molecule found in the nuclei of cells. DNA contains genes, the building blocks of all organisms.
THE STRUCTURE OF DNA
The most important function of DNA is its ability to replicate itself repeatedly. DNA must be copied when new cells are formed, when genetic material is passed from parents to offspring, and when coding for RNA (ribonucleic acid) to make proteins. The structure of DNA – a double helix – allows DNA to be copied successfully many times over with very few errors.
DNA’s double helix (which looks like a twisted ladder) is made of units called nucleotides. Each nucleotide consists of a phosphate, sugar, and base. The phosphates and sugars form the sides of the ladder, while the bases form the rung. A base from a nucleotide on one side of the ladder will chemically bond with a nucleotide from the other side, forming the rung. Certain bases always pair together adenine always pairs with thymine and guanine always pairs with cytosine. These four bases have different chemical structures, causing them to pair in this specific manner.
When DNA replicates, the bonds between bases break and the DNA “unzips” itself. New nucleotides are joined to either side of the broken ladder by the work of DNA polymerase, an enzyme. Enzymes are proteins that mediate and initiate chemical reactions. When the polymerase has traveled the entire length of the DNA, it will have formed two new ladders from the original single ladder. Now the DNA has been perfectly copied from one strand into two. Some enzymes will even “proofread” the DNA to try to catch any errors!
When errors do occur during copying, mutations arise. Some mutations are beneficial, and some are not. If the mutations occur in sex cells, they can also be passed from parents to offspring. The existence of random mutations is essential for evolution theory. Populations will naturally vary some individuals may have certain mutations while others do not. Those with beneficial mutations may be more likely to survive and produce offspring, passing their mutation to some of their offspring. Those with detrimental mutations may not be less likely to survive and produce offspring. (IMAGE from http://evolution.berkeley.edu/evosite/ evo101/images/dna-mutation.gif demonstrating a mutation)
Several scientists were responsible for the eventual discovery of DNA’s structure. Erwin Chargaff and his colleagues noticed in the mid-20th century that the amount of adenine always equaled the amount of thymine and that the same was true of guanine and cytosine. Rosalind Franklind and Maurice Wilkins performed X-ray crystallography of DNA, and the resulting image suggesting a helical shape. By putting these pieces of information together, Francis Crick and James Watson developed the double-helix model of DNA.
HOW DOES DNA PRODUCE PROTEINS?
The other major feature of DNA is its ability to make proteins. Proteins provide structure for our bones and other tissues, transport materials like iron throughout our bodies, help materials move from one cell to another, function as hormones that regulate our body’s functions, act as enzymes in chemical reactions, and fight diseases in the form of antibodies. In short, proteins are among the most important cells in the body.
A protein, at its most basic level, is a chain of amino acids. Amino acids are made from codons, sequences of three nucleotides in the DNA. There are 20 amino acids found in humans. While some amino acids can be made from more than one codon, each codon can only produce one amino acid. This feature of amino acids is called redundancy.
The process of making proteins is complicated, but to summarize here, the making of proteins begins with the unzipping of DNA, as if it were going to copy itself into two DNA strands. Instead, the nucleotides join the now open side of the ladder to form mRNA, or messenger RNA. This molecular has a slightly different chemical structure than DNA, allowing it to take the genetic code from the nucleus to the cytoplasm. In the cytoplasm, mRNA will bind with a structure called a ribosome. In the ribosome, each codon of mRNA is matched with the amino acid for which the codon codes. As the codons are read in sequence, the amino acids are also assembled in the same order, forming a protein. In this way, different sections of DNA can eventually make different kinds of proteins.
An older theory of genetics maintains the principle of “one gene, one protein.” However, modern genetics has discovered that oftentimes, proteins are determined by the coordinated activities of several genes.
WHAT IS A GENE?
A gene is a section of DNA responsible for a certain trait. Often, these traits are physical like the color of our hair or the length of our toes. However, genes can also produce subtler traits, like whether we have a propensity to develop cancer or what our blood type is. We inherit our genes from our biological parents.
Gregor Mendel, a monk living in the 19th century, was the first scientist to describe our modern understanding of genes. He noticed that different pea plants had different characteristics, and he rigorously bred them to see how offspring inherited the traits of their parents.
Many earlier scientists thought that offspring were a “blending” of their parents you can see in yourself that you may look sort of like your mom and sort of like your dad. However, if you look closer, you may notice that you are not just a blending of their features. Instead, some parts of you (like your eye color) may be more similar to one parent than the other. Mendel noticed this in pea plants, too.
He realized that genes came in versions, producing different traits. For example, one gene codes for color in pea plant flowers. It may produce a purple or white color these different versions are called alleles. It might help to think of them as “flavors” of ice cream – whether strawberry or vanilla, it’s still ice cream. However, unlike when you mix strawberry and vanilla ice cream, when Mendel bred a purple and white pea plant together, he did not get light-purple offspring. Instead, he got all purple plants. He realized that the purple allele was dominant over the recessive white allele. If a plant inherited a purple allele from one of its parents, it would be purple. It could only be white if it inherited two white alleles, one from each of its parents.
In this way, Mendel discovered several important principles of inheritance. First, an offspring inherited exactly half of its genetic material from each parent. Second, genes came in alleles and some alleles could be dominant over other alleles. Finally, he also noticed that traits independently assorted – just because a plant was purple did not also mean it had yellow seeds. These traits were inherited from different genes. You can already see how important these principles are to evolution. Traits can be inherited from parent to offspring, and the natural occurrence of different alleles creates variation within a population.
A Punnett Square is a model used by scientists to demonstrate this kind of inheritance. The genotypes – the genetic codes – of the parents are on the sides of the square. They each have two alleles – one from each of their own parents. One allele is selected from each parent and the resulting genotypes are then combined (like a multiplication table). These show the possible genotypes of a single offspring. Since genes independently assort each time parents procreate, each offspring has a possibility of being one of the four genotypes produced. A dominant allele is always written in capital letters, and a recessive allele is always written in lowercase. To determine the phenotype, or physical trait, of the possible offspring, just look at the genotype. If there is a capital letter, even just one, the offspring will have a dominant phenotype. If it has two recessive alleles, it will bear the recessive phenotype.
This was the earliest form of genetics, which is still called Mendelian (or Classical) genetics. In reality, scientists have discovered that genes are much more complicated. Some traits require the combined action of multiple genes, like hair color. Others have more than two alleles, like blood type, which has three alleles – A, B, and O. To make matters more complicated, the A and B alleles of blood are codominant. An individual who inherits an A from one parent and a B from another has AB blood type. Some genes are regulated by other genes, and some genes will not function if a mutation is present.
DO MY GENES DETERMINE WHO I AM?
The short answer is, yes, our genes determine our bodies. They provide the biological information that makes us who we are. Although future developments in science and medicine may allow us to change parts of ourselves, right now we cannot change our genetic code. For example, we cannot change the genes that give us our natural hair color. Instead, if we want to change our hair color, we would have to dye it. The same is true for many disorders and diseases that have a genetic origin we cannot change them once we inherit them from our parents.
Genes may also determine certain parts of our personalities. Research has demonstrated that genes may relate to our sexuality, the development of addictions, how our moods change, and many other elements of human psychology. However, if you know identical twins, you may already realize how difficult these studies are. Even with the same genetic code, identical twins often form distinct personalities. A lot remains to be learned in this field.
Finally, although earlier theories of genetic determination maintained that all human features were determined by genes, modern scientists understand that environment also plays a role in forming many of our physical traits, personality characteristics, and illnesses. Additionally, epigenetic effects may cause genes to turn off or on, downregulate, or upregulate. Changing how a gene is expressed will change the trait produced, even if it does not change the basic DNA sequence of the gene.
Nash JM. 1998. The Personality Genes. Time. Monday April 27.
Stanford C, Allen JS, and Anton SC. 2009. Biological Anthropology: The Natural History of Humankind. Upper Saddle River, New Jersey: Pearson Prentice Hall.
So it's all about Sex?
Why are evolutionary psychologists so obsessed with sex? Isn't that rather juvenile? And why have they put forward those politically awkward arguments about the innateness of behavior differences between men and women? The answer is that evolutionary theory tells us that if there is anywhere that we would expect to find a strong selective influence on behavior it will be in behavior related to reproduction itself, and sex is a crucial part of human reproductive behavior. Humans have quite a few peculiarities in their reproductive strategies which evolutionary psychologists have connected to differences in male and female behavior (see Sex Differences).
To many it seems nonsensical to propose that having lots of grandchildren is the intention underlying all human behavior because:
Evolutionary psychologists reply that:
E.O. Wilson's Theory of Altruism Shakes Up Understanding of Evolution
In 1975 Harvard biologist E. O. Wilson published Sociobiology , perhaps the most powerful refinement of evolutionary theory since On the Origin of Species . Darwin’s theory of natural selection postulated a brutal world in which individuals vied for dominance. Wilson promoted a new perspective: Social behaviors were often genetically programmed into species to help them survive, he said, with altruism— self-destructive behavior performed for the benefit of others—bred into their bones.
In the context of Darwinian selection, such selflessness hardly made sense. If you sacrificed your life for another and extinguished your genes, wouldn’t the engine of evolution simply pass you by? Wilson resolved the paradox by drawing on the theory of kin selection . According to this way of thinking, “altruistic” individuals could emerge victorious because the genes that they share with kin would be passed on. Since the whole clan is included in the genetic victory of a few, the phenomenon of beneficial altruism came to be known as “inclusive fitness.” By the 1990s it had become a core concept of biology, sociology, even pop psychology.
So the scientific world quaked last August when Wilson renounced the theory that he had made famous. He and two Harvard colleagues, Martin Nowak and Corina Tarnita, reported in Nature that the mathematical construct on which inclusive fitness was based crumbles under closer scrutiny. The new work indicates that self-sacrifice to protect a relation’s genes does not drive evolution. In human terms, family is not so important after all altruism emerges to protect social groups whether they are kin or not. When people compete against each other they are selfish, but when group selection becomes important, then the altruism characteristic of human societies kicks in, Wilson says. We may be the only species intelligent enough to strike a balance between individual and group-level selection, but we are far from perfect at it. The conflict between the different levels may produce the great dramas of our species: the alliances, the love affairs, and the wars.
When you published Sociobiology in 1975, you faced enormous resistance, especially to the implication that human nature was genetically based. Now your colleagues are defending one of key tenets in your book—kin selection—while you try to dismantle it. What do you make of the shifting attitudes in your field? Interesting, isn’t it? But I’m not so sure I pivoted that much on kin selection in Sociobiology . If you look at the opening pages, I had a diagram showing how a future science of sociobiology would be built. Kin selection was a nice little part of it in 1975, but Sociobiology went way beyond that. It goes into demography: how groups are formed, how they compete, how communication evolves. Together with ecology and population genetics, it all formed a framework to help explain the origin of social behavior.
Yet a generation of sociobiologists built their research around the idea of kin selection. How did that happen? They were enchanted by kin selection because it appeared to have a basis in mathematics. It seemed solid and it looked good. It was glamorous.
Your new paper states that the mathematical underpinning of kin selection, called the Hamilton inequality, does not work. Why not? When analyzed to the bottom of its assumptions–when we ask under what conditions it could hold—it applies only to a very narrow set of parameters that don’t actually exist on Earth. Inclusive fitness turns out to be a phantom measure that cannot be obtained.
If inclusive fitness is wrong, how do you explain “eusociality”—when individuals reduce their ability to have offspring of their own to raise the offspring of others? It turns out that there’s only one condition that has to be reached in the course of evolution for eusociality to emerge: A mother or father must raise their young within reach of adequate resources at a defensible nest. Getting from the solitary lifestyle to one that includes a defensible nest can be done in one evolutionary step—one gene change. This turns the concept of inclusive fitness on its head, because the gene change and the social behavior came first. Kinship is a consequence of that, not a cause.
How do these ideas play out in the natural world? Let’s take the example of a bird with helpers at the nest. Supporters of inclusive fitness point to a correlation between the amount of help that the young birds give when they stay at home and how closely they are related to the parents and each other. But the young birds are looking after their extended family only until they have families of their own. By analogy, you might stay home and baby-sit for younger siblings after college, but it’s not out of a sense of kinship toward them. It’s because it makes financial sense until you find a job and move out. What these researchers unwittingly do not mention in their studies is that cases of inclusive fitness are quite unusual in an important way. Each of the bird species lives in an area where nest sites and territories are very scarce, very hard for young birds to get.
There are three related problems at the intersection of philosophy and science that are fundamental to our understanding of our relationship to the natural world: the mind–body problem, the free will problem, and the nature–nurture problem. These great questions have a lot in common. Everyone, even those without much knowledge of science or philosophy, has opinions about the answers to these questions that come simply from observing the world we live in. Our feelings about our relationship with the physical and biological world often seem incomplete. We are in control of our actions in some ways, but at the mercy of our bodies in others it feels obvious that our consciousness is some kind of creation of our physical brains, at the same time we sense that our awareness must go beyond just the physical. This incomplete knowledge of our relationship with nature leaves us fascinated and a little obsessed, like a cat that climbs into a paper bag and then out again, over and over, mystified every time by a relationship between inner and outer that it can see but can’t quite understand.
It may seem obvious that we are born with certain characteristics while others are acquired, and yet of the three great questions about humans’ relationship with the natural world, only nature–nurture gets referred to as a “debate.” In the history of psychology, no other question has caused so much controversy and offense: We are so concerned with nature–nurture because our very sense of moral character seems to depend on it. While we may admire the athletic skills of a great basketball player, we think of his height as simply a gift, a payoff in the “genetic lottery.” For the same reason, no one blames a short person for his height or someone’s congenital disability on poor decisions: To state the obvious, it’s “not their fault.” But we do praise the concert violinist (and perhaps her parents and teachers as well) for her dedication, just as we condemn cheaters, slackers, and bullies for their bad behavior.
The problem is, most human characteristics aren’t usually as clear-cut as height or instrument-mastery, affirming our nature–nurture expectations strongly one way or the other. In fact, even the great violinist might have some inborn qualities—perfect pitch, or long, nimble fingers—that support and reward her hard work. And the basketball player might have eaten a diet while growing up that promoted his genetic tendency for being tall. When we think about our own qualities, they seem under our control in some respects, yet beyond our control in others. And often the traits that don’t seem to have an obvious cause are the ones that concern us the most and are far more personally significant. What about how much we drink or worry? What about our honesty, or religiosity, or sexual orientation? They all come from that uncertain zone, neither fixed by nature nor totally under our own control.
Researchers have learned a great deal about the nature-nurture dynamic by working with animals. But of course many of the techniques used to study animals cannot be applied to people. Separating these two influences in human subjects is a greater research challenge. [Image: Sebastián Dario, https://goo.gl/OPiIWd, CC BY-NC 2.0, https://goo.gl/FIlc2e]
One major problem with answering nature-nurture questions about people is, how do you set up an experiment? In nonhuman animals, there are relatively straightforward experiments for tackling nature–nurture questions. Say, for example, you are interested in aggressiveness in dogs. You want to test for the more important determinant of aggression: being born to aggressive dogs or being raised by them. You could mate two aggressive dogs—angry Chihuahuas—together, and mate two nonaggressive dogs—happy beagles—together, then switch half the puppies from each litter between the different sets of parents to raise. You would then have puppies born to aggressive parents (the Chihuahuas) but being raised by nonaggressive parents (the Beagles), and vice versa, in litters that mirror each other in puppy distribution. The big questions are: Would the Chihuahua parents raise aggressive beagle puppies? Would the beagle parents raise nonaggressive Chihuahua puppies? Would the puppies’ nature win out, regardless of who raised them? Or. would the result be a combination of nature and nurture? Much of the most significant nature–nurture research has been done in this way (Scott & Fuller, 1998), and animal breeders have been doing it successfully for thousands of years. In fact, it is fairly easy to breed animals for behavioral traits.
With people, however, we can’t assign babies to parents at random, or select parents with certain behavioral characteristics to mate, merely in the interest of science (though history does include horrific examples of such practices, in misguided attempts at “eugenics,” the shaping of human characteristics through intentional breeding). In typical human families, children’s biological parents raise them, so it is very difficult to know whether children act like their parents due to genetic (nature) or environmental (nurture) reasons. Nevertheless, despite our restrictions on setting up human-based experiments, we do see real-world examples of nature-nurture at work in the human sphere—though they only provide partial answers to our many questions.
The science of how genes and environments work together to influence behavior is called behavioral genetics. The easiest opportunity we have to observe this is the adoption study. When children are put up for adoption, the parents who give birth to them are no longer the parents who raise them. This setup isn’t quite the same as the experiments with dogs (children aren’t assigned to random adoptive parents in order to suit the particular interests of a scientist) but adoption still tells us some interesting things, or at least confirms some basic expectations. For instance, if the biological child of tall parents were adopted into a family of short people, do you suppose the child’s growth would be affected? What about the biological child of a Spanish-speaking family adopted at birth into an English-speaking family? What language would you expect the child to speak? And what might these outcomes tell you about the difference between height and language in terms of nature-nurture?
Studies focused on twins have led to important insights about the biological origins of many personality characteristics.
Another option for observing nature-nurture in humans involves twin studies. There are two types of twins: monozygotic (MZ) and dizygotic (DZ). Monozygotic twins, also called “identical” twins, result from a single zygote (fertilized egg) and have the same DNA. They are essentially clones. Dizygotic twins, also known as “fraternal” twins, develop from two zygotes and share 50% of their DNA. Fraternal twins are ordinary siblings who happen to have been born at the same time. To analyze nature–nurture using twins, we compare the similarity of MZ and DZ pairs. Sticking with the features of height and spoken language, let’s take a look at how nature and nurture apply: Identical twins, unsurprisingly, are almost perfectly similar for height. The heights of fraternal twins, however, are like any other sibling pairs: more similar to each other than to people from other families, but hardly identical. This contrast between twin types gives us a clue about the role genetics plays in determining height. Now consider spoken language. If one identical twin speaks Spanish at home, the co-twin with whom she is raised almost certainly does too. But the same would be true for a pair of fraternal twins raised together. In terms of spoken language, fraternal twins are just as similar as identical twins, so it appears that the genetic match of identical twins doesn’t make much difference.
Twin and adoption studies are two instances of a much broader class of methods for observing nature-nurture called quantitative genetics, the scientific discipline in which similarities among individuals are analyzed based on how biologically related they are. We can do these studies with siblings and half-siblings, cousins, twins who have been separated at birth and raised separately (Bouchard, Lykken, McGue, & Segal, 1990 such twins are very rare and play a smaller role than is commonly believed in the science of nature–nurture), or with entire extended families (see Plomin, DeFries, Knopik, & Neiderhiser, 2012, for a complete introduction to research methods relevant to nature–nurture).
For better or for worse, contentions about nature–nurture have intensified because quantitative genetics produces a number called a heritability coefficient, varying from 0 to 1, that is meant to provide a single measure of genetics’ influence of a trait. In a general way, a heritability coefficient measures how strongly differences among individuals are related to differences among their genes. But beware: Heritability coefficients, although simple to compute, are deceptively difficult to interpret. Nevertheless, numbers that provide simple answers to complicated questions tend to have a strong influence on the human imagination, and a great deal of time has been spent discussing whether the heritability of intelligence or personality or depression is equal to one number or another.
Quantitative genetics uses statistical methods to study the effects that both heredity and environment have on test subjects. These methods have provided us with the heritability coefficient which measures how strongly differences among individuals for a trait are related to differences among their genes. [Image: EMSL, https://goo.gl/IRfn9g, CC BY-NC-SA 2.0, https://goo.gl/fbv27n]
One reason nature–nurture continues to fascinate us so much is that we live in an era of great scientific discovery in genetics, comparable to the times of Copernicus, Galileo, and Newton, with regard to astronomy and physics. Every day, it seems, new discoveries are made, new possibilities proposed. When Francis Galton first started thinking about nature–nurture in the late-19th century he was very influenced by his cousin, Charles Darwin, but genetics per se was unknown. Mendel’s famous work with peas, conducted at about the same time, went undiscovered for 20 years quantitative genetics was developed in the 1920s DNA was discovered by Watson and Crick in the 1950s the human genome was completely sequenced at the turn of the 21st century and we are now on the verge of being able to obtain the specific DNA sequence of anyone at a relatively low cost. No one knows what this new genetic knowledge will mean for the study of nature–nurture, but as we will see in the next section, answers to nature–nurture questions have turned out to be far more difficult and mysterious than anyone imagined.
Evolutionary Psychology and Fundamental Human Needs
Our prehistoric ancestors needed to belong to groups in order to protect themselves against those who might harm them, and to find a suitable mate.
Five Fundamental Human Motives
One primary place where evolution seems to have played a role is in people’s motives and goals. Think for a moment about what motivates your behavior on a daily basis—what does your behavior seem designed to achieve for you?
When evolutionary psychologists look for consistencies in what most people strive for in their daily lives—what they focus on, what they think about, and what they respond to—they conclude that it boils down to about five basic things.
First, all people want to be accepted—not by everybody, but by certain other people. And a great deal of what we do each day helps us to be accepted—or at least avoid being rejected—by other people.
So, we try to be nice. We cooperate when we work with others. We do our share. We try to get others to perceive us positively. We work on our close relationships, and so on.
Second, people the world over belong to cooperative groups of various kinds: work groups, committees, hunting parties, sports teams, political groups, civic organizations, and so on. Belonging to groups is a feature of human nature. It is uncommon to find many otherwise well-adjusted people who never join groups.
Third, people are motivated to influence other people. We want other people to act in certain ways, and we do what we can to get them to behave as we wish.
We also want other people to think certain things, to hold certain beliefs, and to agree with us so we spend time trying to persuade them. The quality of our life depends on other people treating us in certain ways we are therefore invested in influencing others.
Fourth, all of us have our antennae up for people who might harm us in one way or another—not just for people who might hurt us physically, but also for those who may treat us unfairly, take advantage of us, cheat us, or fail to do their share. And we react very strongly to being mistreated by other people. It’s part of human nature to guard against being hurt and exploited.
And, finally, at many points in their lives, people focus on mate selection and retention—having intimate sexual relationships with others.
Much of what we do every day of our lives seems to be in the service of these five primary motives. That’s not to say that all of your behavior is due to these motives, rather that they consistently exert a very strong role in what you do and how you feel.
The influence of these motives may not always be obvious. You might want to make money or learn new things or retire early.
But those specific goals are often in the service of these five broader motives. These motives are so central to human nature that it’s hard to even imagine how behavior might look without them. We simply don’t find otherwise normal, well-adjusted people who have the opposite motives.
How Our Ancestors Have Influenced Our Basic Motives
Why does human nature consistently emphasize these five basic motives?
The answer is that these are the motives that would have promoted survival and reproduction during the evolutionary past. What did our prehistoric ancestors need to do in order to survive and reproduce?
They needed to be accepted by other people, belong to groups, influence other people, protect themselves against those who might harm them, and find a suitable mate.
Prehistoric humans that belonged to groups were more likely to survive and reproduce.
That’s pretty much it. If an individual accomplished those five things, his or her chances of surviving and reproducing would have been much higher than if he or she didn’t accomplish those things.
So, we are the descendants of generations and generations of beings who sought acceptance, belonged to groups, tried to influence others, protected themselves, and had successful mating relationships.
Individuals who weren’t motivated to do those things—or worse, wanted to do the opposite—didn’t fare as well in their own lives, and they weren’t as successful passing their genes to future generations.
The bottom line is that much of what you are motivated to do each and every day, you are motivated to do because evolution built those motives into human nature.
Evolutionary Purpose of Fear
One of the topics to which Charles Darwin himself applied evolutionary ideas was the topic of emotions. Emotions evolved because they provided an adaptive benefit for our ancestors.
The most obvious example perhaps is fear. Fear alerts us to dangers and leads us to avoid things that might hurt us.
Of course, people can learn to be afraid of things that don’t pose any real danger, but, fundamentally, fear evolved to help us respond to threats to our well-being. In other words, the emotion of fear is related to the fundamental human motive to protect ourselves.
It’s informative to look at the fears that are more or less universal—the things that human beings tend to be afraid of without much learning—because those fears probably evolved.
One such fear involves snakes. During the course of human evolution, while we were wandering around on the African savannah, snake bites were a real threat.
In fact, even today in Africa and Southeast Asia, thousands of people die from venomous snake bites each year.
Our prehistoric ancestors who feared snakes were much more likely to survive and reproduce than those who weren’t afraid of snakes, or worse, those who tried to play with snakes. Prehistoric people who weren’t cautious around snakes tended not to have many offspring.
Because we descended from individuals who were afraid of snakes, it’s a feature of human nature to dislike snakes. You can override that normal wariness, but anxiety about snakes appears to be part of human nature.
That’s why you’re probably more nervous about snakes than you are about cars, even though in the United States cars are far, far more dangerous. You aren’t naturally afraid of riding in cars because our species doesn’t have millions of years of experience dying in car accidents.
The same is true of how people react to spiders, and even to the feeling that something is crawling along their skin. Think of how you react when you have the sense that something is creeping up your leg that’s an evolved reaction.
Why Do We Overreact to Threats?
Snarling animals are upsetting to most people, particularly when they are showing their fangs. And what’s really interesting is that many people have negative emotional reactions when they simply see pictures or movies of snakes, spiders, or snarling animals.
When you think about it, that negative reaction is weird. Why would we be afraid of a picture or a movie? That’s totally irrational!
The answer is that throughout the entire course of evolutionary history, anytime you saw a snake, spider, or ferocious animal, it was really there. Your brain isn’t designed to distinguish automatically between real threats and pictured threats in photographs or movies.
One of the interesting things about evolved fear responses is that they often appear overly responsive, if not totally unnecessary. All animals, including human beings, are far more likely to overreact to something that’s not actually threatening than they are to under-react, or have no reaction at all, to a real threat.
Think of a deer in the forest. Deer startle and run away far more than is necessary. In the same way, people get upset over little things, and they worry about things that turn out to be nothing.
During the course of your life, you have likely worried about things that didn’t really hurt you more often than you failed to worry about things that posed a real threat to you.
You were probably more likely to worry about medical tests that came out fine, than you were to be cavalier about medical tests that showed a serious problem. Late at night, you’ve probably been more likely to have concerns about noises in your house that were nothing, than you were to ignore signs that there was a real intruder.
When you were a student, you probably worried more about tests on which you ultimately that you did fine, than you were relaxed about tests that you failed.
This overreaction to possible harm is also an evolved feature of the brain. Evolution seems to operate on the idea that it’s far better to be safe than sorry—that it’s better to experience unnecessary fear and anxiety, and to react as if something is dangerous when it’s not—than to fail to react to a real threat.
Our threat detection system is built in a way that makes false positive errors much more common than false negative errors.
It’s like the smoke detector that you probably have in your home. Smoke detectors are designed to be certain that they warn you about a possible fire.
You may have had smoke detectors go off when there really wasn’t a fire, but rather you burnt the toast or you took a steamy shower. But that false alarm is not a bad price to pay to be sure that your smoke detector never misses the smoke from a real fire.
Animals with very sensitive threat-detection systems were more likely to survive and reproduce, so that became a part of human nature, making us much more reactive than we often need to be.
Nature vs nurture: how does our personality develop?
In psychology, there has been always been a long standing debate as to how our personality develops. Do humans act, behave and interact in the way we do because of nature, such as our genes inherited from our parents, or nurture, such as our environment, culture, religion or childhood interactions.
Personality is a key part of every single one of us, it determines our moods, our behaviours, how we interact with each other and the decisions we make. Effectively, our personalities make us who we are. This is why, it is crucial to study whether our personality is caused by our ancestors, the environment we grew up in, on perhaps, even both.
Research has found that personality changes and adapts throughout our whole life, but the reasons as to why is still up for debate. Could it be that our environment constantly changes and adapts us? Or could it be that our genetics influence when and how our personality changes?
How many times have you heard the saying “oh, she’s definitely her mother’s daughter!’ or “like father, like son” - perhaps it’s because 50% of your DNA comes from each of your parents and this inherited genetic makeup could influence your personality.
If our personality was influenced solely by nature, then we would have inherited genes from our ancestors that influence how our personality is shaped. It’s just the same as how we inherited physical factors such as our eye or hair colour from previous generations, we also could inherit our internal drive and spur that influences our behaviours.
Genes within a species are all the same - the DNA within you genes is most likely 99.9% similar to mine. This allows use to develop characteristics that come naturally to us. However, some of us are better at things than the other. We all have the instincts to learn language and to walk - why do some of us do it better than others?
“The biological theories of personality assume that differences in personality are partly based in differences in structure and systems in the central nervous system such as genetics, hormones, and neurotransmitters" - suggesting that our personality differs due to the genes we develop and how our body regulates these.
Research into twins and adoptive children has shown that our genetic make up has a stronger influence on our personality that child rearing providing support for the 'nature' side of the argument. It has also been found that all the traits we inherit, including personality traits, are greatly influenced by our genetics and biology - further supporting the nature argument.
Other, perhaps less scientific theories, have suggested our personality is caused by our recent ancestors. It wouldn’t surprise me if you’ve heard of ‘psychodynamic theory and therapy’ or of the term the ‘unconscious’ and it also would surprise me if you haven’t heard of any other psychodynamic theorists apart from the notorious Freud.
Well, one of Freud’s colleagues, Carl Jung believed that our unconscious mind, which the psychodynamic theory argues drives our behaviours, interactions and therefore forms a fundamental part of our personality, is partly comprised of memories from our ancestors and these then influence our personality and behaviour.
Overall, the idea that our personality is caused by our genetic makeup is quite a believable one. Often, babies who are relaxed and ‘easy going’ tend to become adults who are equally as laid back and easy going. Similarly, the babies, much like myself, who are born screaming and spend much of their infant years throwing tantrums, tend to grow up to be the drama queens of the world. So, there’s a high chance our personality is in fact influenced by our genetics.
However, when arguing that our personalities are developed by our genetics, a factor that is out of our control, it raises issues. If our personalities are really caused by our genetics, then can we be held accountable for anything we ever do? Or is it our great, great, great, great, great grandparents faults? So, it is important to consider the opposing factor - our environment.
Our environment does play a crucial part in our life some people are rich, some people are poor. Some people grew up in Kensington, whilst others in rural towns miles away from any fast moving cities. Some people have four sisters, whilst others have no siblings at all. Some people have it easy, whilst others don’t. But, does this really influence our personality and our later behaviour?
It is often argued that our personality is in fact influenced more so by our environment than by our genetics. Much of our personality is based on the adaptation of our abilities, cognitive abilities and social interests. This adaptability that shapes and forms us can only be learnt from the interaction with our environment.
Think about children who are bullied, it has often been suggested that the children grow up to be the Introverts of the world - they are perfried of human interaction due to the experiences they had with other children when they were younger.
Studies have shown that personality is caused by the cultural development and the interactions we have with others and our environment when we are a child. Similarly, evidence from studies that have found that children raised in foster homes were influenced greater by their foster parents child raising, than by their genetics.
As I used the example of psychodynamic therapy above, I will use a contradicting theory to argue the opposing point. Freud, the father of the psychodynamic theory, argued that our unconscious mind, which as I said above determines our behaviours and personality, is influenced and developed by our childhood experiences and interactions. This theory, although it has little empirical evidence, is still well regarded today and it the crucial point of psychodynamic therapy.
Finally, if you have siblings your birth order may well have affected your personality. Alfred Adler, a famous psychologist, described the eldest child to feel superior and powerful, the middle child to be competitive and the youngest to be dependent on others.
So, a child is being born into a situation which causes them to react as described in the stereotypes of birth order, and therefore the environment has influenced our personality. However, little scientific evidence has been found to support this theory, so maybe personality is due to genetics.
Overall, many psychologists are starting to adopt the view that all aspects of humans are influenced by nature and nurture. Yes, our genetics are inherited, but it has been suggested that they do not determine our behaviour.
Our personalities, and humans in general, are too complicated to be whittled down to one specific cause and we will be influenced by many aspects of ourself and our environment. We are much too complicated to be one of the other.
If you are looking to discover your personality type through test then I have written a very comprehensive list of the best personality tests which you will find useful.
Heather Harper is a psychology student from the University of Lincoln. She currently works as an intern for WorkStyle and is studying a Masters in Occupational Psychology at the University of Manchester.
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A leading genetic expert tackles the nature vs. nurture debate
Robert Plomin is no stranger to controversy. It comes with the territory, he tells me, for someone who has spent over four decades studying the role genetics play in making us who we are.
That question is at the heart of a field of science known as behavioral genetics, or the study of the interplay of genetic and environmental influences on human behaviors. The question of how much of a role genetics play in making us who we are is controversial, not just because no one seems to be able to agree on an answer, but also because figuring out how we become who we are is filled with social, historical, and political minefields.
In the past, the belief that genes exclusively determine who we are has led humanity down some dark paths, including social Darwinism, a belief that people were subject to survival-of-the-fittest laws of nature, which was used by some political theorists to justify laissez-faire capitalism and political conservatism. That, in turn, spawned eugenics, a pseudoscience used by various authoritarian regimes to rationalize inhumane policies like selective breeding, sterilization, and even genocide. It’s sensible, then, that social scientists are hesitant to embrace any line of thinking that, in their minds, might lead history to repeat itself.
Plomin, a psychologist and professor of behavioral genetics at King’s College in London, has little patience for this argument. His research tells him that genes account for about half of the differences between us, and that the rest is mostly attributable to random experiences, not systemic forces like the family you are born in. Accepting that, says Plomin, can free us of the anxieties that come from believing everything we do—as parents, as teachers, as friends and neighbors—can irreparably harm our fellow man. That’s why he wrote his book, Blueprint: How DNA Makes Us Who We Are.
Quartz spoke with Plomin about behavioral genetics, what it means to be “us,” and whether we can control our own destiny.
This interview has been lightly condensed and edited for clarity.
Quartz: Let’s start with the basics. Why did you write this book, and why now?
Plomin: I was asked to write this book 30 years ago. But I realized at the time that more research was needed. It was a dangerous time to put your head above the parapet and say “genetics is important.” I had just started graduate school, and psychology was dominated by environmentalism that’s the view that you are what you learn. Genetics never got mentioned.
[But] in these 40 years I’ve been working in the field, the evidence has accumulated and accumulated, so that most scientists now accept that inherited DNA differences account for a lot of the differences between us. I would say, on average, it’s about half of the differences between us in personality, in psychopathology (mental health and illness), and also in mental abilities and disabilities. The other thing that no one anticipated, though, is the DNA revolution. It changes everything, because now we can use DNA itself to predict psychological propensities from birth.
What difference has that made in your field?
That really will change how we do psychology, how we do clinical psychology, and even parenting and education, and society as a whole. I think it will actually change our understanding of ourselves. Because it becomes very real now we’re not saying “in the abstract, on average, genetics is important.” You could say “yeah, yeah.” But, when I say, “here is your DNA. Here is your sister’s DNA. You’re at risk for alcoholism your sister isn’t,” it really is going to be a transformation. So, I’m very glad I waited, because now that the evidence is there, people are more accepting.
We need to have this discussion, and to get that conversation going, and that’s why I launched the book. Also, to give people the DNA literacy that they need to join the conversation, because I am amazed about how little people really know about genetics and DNA.
Let’s talk about that. For people who haven’t read your book, what are the basic concepts that anyone trying to understand your work needs to know?
The main message is that these are not mysterious it’s just dumb chemicals. But they are the molecule of life. And that’s because [DNA] replicates itself very reliably. That’s why you start life as a single cell, a fertilized egg, and the DNA in that cell is the same DNA as the fifty trillion cells in your body now. And 99% of the steps in the spiral staircase of the DNA…are identical for all of us. The 1% that differs is what we’re talking about.
The biggest problem I have is to stop people from using the word “determine” oh, genes determine who you become. But they don’t! They influence you. They’re like nudges, and other things being equal, they’ll push you in one direction or another. But that doesn’t mean you can’t change.
It’s hard to understand these concepts. But I find one thing that helps people get it is I say: “If you were adopted away at birth, raised in a different family, gone to a different school, had different friends, had a different occupation, I would say, you’d be essentially the same person.” [Editor’s note: This is the subject of a recent documentary film, Three Identical Strangers.]
Just so readers understand: You’re talking about variations across a group of individuals, not genetic variations in an individual person. Can you clarify that?
That is such a critical issue. The short hand is: Height is 90% heritable. What does that mean? It means, of the individual differences between people [when it comes to] height, 90% of the differences are due to inherited genetic differences, on average, in the populations we studied.
And it’s not to say, then, that for an individual, 90% of your height is due to genetics. That’s a completely different issue. And it could be that, although on average, 90% of the differences between people in height is due to inherited genetic differences, any one individual, their short height could be due to environment they could’ve had a childhood illness.
So, I think most people can get behind the idea that genetics influence height, or weight—but not things like intelligence or kindness. You’ve worked a lot on proving the link between genetics and intelligence. Can you explain your findings?
I started out doing work 45 years ago in personality, and then I kind of moved into cognitive development, language development, and then as my kids grew up in my sample, I studied education attainment—how they do at school.
And I’m keen to keep my hand in until I make a difference in education. Because education is the last bastion of anti-genetic thinking—it’s not even just ignoring genetics, I mean they’re really quite hostile. And I think it’s a bit like clinical psychology 30 years ago, where they thought…it’ll put them out of business if things are genetic. But no one thinks that way anymore. They realized it’s a good thing for clinical psychologists to know “this is particularly heritable,” and the main point is that causes and cures aren’t necessarily related. So you could have a disorder that’s entirely genetic, but it doesn’t mean that you have to fix it genetically.
Education hasn’t gotten that message yet, so they’re still quite hostile, which is surprising, because the problems teachers are worried about are among the most heritable ones around.
How could information about a student’s genetic background help teachers?
Teachers recognize that students differ in how well they learn… and, when pushed, they’ll probably say they think it’s genetic, to some extent. It doesn’t mean you don’t teach kids, it just means some kids are going to have a hard time learning.
If there are teachers or parents who don’t recognize genetics, then it’s important they read this book, because it does have an effect. In the past, if kids didn’t do well in school, the first thing the governments would do is blame the schools, blame the teachers. But that doesn’t pan out very well empirically. So then, what do you do? You blame the parents, and then if you fail there, you blame the kids. But I think it’s very important to recognize that kids differ a lot genetically, even in terms of learning ability. And then to respect those differences to a greater extent.
Concretely, what does this mean for teachers?
The big example is personalized learning, which I get a lot of pushback on, but I just don’t get it. It’s the idea that it shouldn’t be a one-size-fits-all education system. It should be personalized. We recognize that kids are different and we try to give them the best boost we can to try to maximize their strengths and minimize their weaknesses. And genetics is part of that.
I think maths is the best example, because they have these wonderful computer programs that do what’s called “adaptive learning.” [Editor’s note: Adaptive learning is a personalized online course, tailored to a student’s strengths, weaknesses, goals, and engagement patterns, and that adapts in real-time to the student’s activity, performance, and interest level.] Computers are perfectly set up for personalized learning.
Aren’t you worried that will lead to lower expectations for kids who have genetic indicators that they are, say, likelier to be bad at math, and that in turn will lead them to underperform? Won’t that be a self-fulfilling prophecy?
It’s not as simple as that, really. You can make a difference, but kids aren’t stupid. You can push and get kids to do this stuff, but at what cost? It’s more appetites than aptitudes. We think of genetics as being hardwired I think it’s a matter of finding what you like to do, and then you do it a lot, and you do it better, because it’s self-rewarding, as opposed to the old model of education, or tiger moms, where you pre-ordain what your kids are going to do. It just can’t be the right way to go. It doesn’t mean you can’t do it you can make a kid who has very little mathematical skills get pretty good at math. But it’s going to be such an uphill battle why not find something that the kid likes to do, and is better at?
The positive spin is “yeah, anyone can be president, and we can all do anything we want to do, all you need is a growth mindset, or 10,000 hours of practice [Editor’s note: Plomin is referring to a rule based on research by psychologist Anders Ericsson but made popular by the writer Malcolm Gladwell in his book Outliers, that 10,000 hours of dedicated practice can make anyone gifted in a particular field], or grit.” But I just don’t believe those things. You can make a difference, but why not go with the flow rather than swimming upstream?
That’s why you say that both teachers and parents matter but….
…but they don’t make a difference. And I know that’s a really hard one for people to accept.
I understand why! It seems fatalistic, and goes against a huge body of research, for example in early childhood development, that targeted interventions can reverse the course of someone’s life. You’re saying that’s not true.
I don’t think it is, no. There [are] several problems. One is effect size people talk about these new interventions that really make a difference, [but] you have to ask, how much of an effect does it really have? Does it have a long-term effect?
People are looking for either quick fixes or magic-bullet interventions that will make a difference. I’m very skeptical, because the history of these [experiments] is that these things don’t replicate and they don’t make a difference in the long run.
It’s important to realize that a lot of what we think is environmental, isn’t. It’s disguised genetic. Not to say that the environment isn’t important, because it is. It accounts for about half of the differences that we see. But it’s not the environment of nurture that we always thought was so important. An intervention could make a big difference, but that’s could make a difference. Experiments are about what could be that doesn’t mean it makes a difference in the real world.
All of your theories are pretty radical. What are the policy implications, for parents, teachers, and schools?
There’s no necessary policy implication. So, you could have the right-wing view [of education], which might be something stupid like “educate the best, forget the rest.” Or you could have a left-wing point of view, which would be to identify the kids who are going to have trouble, and realize we need to put as much resources as we need to get them up to some minimal level. That is being done—it’s called the Finnish model. And that works pretty well.
Another thing where people get confused is that this doesn’t mean parents can’t do anything. Parents can control the behavior of their children. If you have an aggressive child who is hitting another child over the head, you can say “that is not acceptable.” You’re not changing the aggressiveness, but you can control the behavior. And where we see that really works is zero-tolerance bullying policies in schools they really work. You knock out the bullying behaviors, but it doesn’t mean you change the bullies.
Parents can have an effect, but what I’d like to argue for is that…it’s good for parents to relax. You can’t make much of a difference in the long run anyways.
Are you saying parents should just stop trying?
That is a possible problem, but I don’t think it works that way. You can work with the behavior. And if you love somebody, you don’t love them to change them. And I think it should be that way between parents and children to a larger extent. We should watch [our children] become who they are we shouldn’t pre-ordain who they become.
The Biological Approach
The biological approach attempts to explain behaviour as the direct product of interactions within the body.
Key assumptions of the biological approach:
- There is a direct correlation between brain activity and cognition
- Biochemical imbalances can affect behaviour
- Brain physiology can affect behaviour
- Behaviour can be inherited (as it is determined by genetic information)
Evolution and the genetic basis of behaviour
Charles Darwin’s publication – On the Origin of Species (1859) – described the process of natural selection characteristics that are not suited to a species’ environment will die out as it struggles to survive, and with time will evolve over generations so that only adaptive characteristics remain in future offspring.
Genes are the genetic information carried by DNA in chromosomes, found within a cell’s nucleus they are passed on through generations of a species if individuals survive and successfully reproduce. In line with Darwin’s theory of evolution, it might also follow that genes form a basis of behaviour, as both behaviour and genes appear to be heritable. An example might be aggressive behaviour, in light of obvious survival benefits such as warding off predators and competing for resources.
The genotype describes the genetic configuration of an individual, whereas phenotype describes the combined effects of genetic makeup and surrounding environment on behaviour. The nature-nurture debate highlights a key argument in psychology, over the relative influence of biology and environment on the characteristics of an individual an extreme biological approach assumes that these are determined solely by nature.
Effects of brain physiology and neurochemistry
Interactions between regions of the brain help to control different functions, which biological psychologists assume to be significant in determining our actions. For instance, the occipital lobe is involved heavily in processing sight, along with the frontal lobe, which is thought to be involved in control and attention.
Electrical impulses enable an important means of internal communication that directs our behaviour, travelling around the brain and to/from the body via the nervous system. Impulses are transmitted between neurons (nerves) at synapses, junctions where neurotransmitters are released that inhibit or excite other neurons to achieve different responses. Neurochemical imbalances in the brain are often associated with abnormal behaviour – for instance, evidence suggests that imbalances of dopamine (a neurochemical linked with the brain’s natural ‘pleasure’ system) are associated with mood disorders such as depression.
The endocrine system is a slower-acting communication system that regulates the circulation of hormones, released by glands into the bloodstream. For example, cortisol and adrenaline are key hormones that facilitate the fight or flight response, a key evolutionary survival mechanism whereby the body primes itself for imminent danger (e.g. increasing heart rate, initiating sweating to cool down, dilation of pupils, sharpened sense of hearing).
Research methods used by the biological approach
Animal studies – used to investigate biological mechanisms that govern human behaviour, often where ethical guidelines would not allow human participation. Many species (e.g. rats) are thought to have a similar biological makeup to humans, such that studies’ conclusions can be generalised to humans. However, this methodology still raises ethical debate, and some argue that complex human behaviour cannot be replicated in non-human animals like rats, and thus cannot be investigated.
Case studies – can investigate normal behaviour by observing behavioural abnormality alongside corresponding changes in biology. A very early example is the apparent personality alteration observed in Phineas Gage (mid 1800s) after a railroad construction accident drastically changed his physiology by forcing an iron rod through his brain’s frontal lobe.
Drug therapy – behaviour can be manipulated by altering an individual’s biochemistry, a research method that can ultimately lead to developing drug applications to improve health and wellbeing. Initial phases of research are usually conducted on non-humans.
Scans – physiology and activity across the brain can be gauged using various techniques (e.g. MRI, PET, CAT), helping researchers to identify the functions of specific regions (known as localisation of cortical function).
Twin/family studies are useful for investigating the heritability of behaviour. For instance, research can investigate the likelihood that both of two twins develop a characteristic, known as a concordance rate. However, these studies can be time-consuming, due to long delays often required before follow-up data is collected. It is also difficult finding a large samples of participants for twin studies.
Example: Evidence has suggested that if one identical twin (monozygotic [MZ], with near-identical genetic information to the other) develops schizophrenia, there is a roughly 48% chance of the other also developing schizophrenia, whereas this is only about 17% with non-identical twins (dizygotic [DZ], who share about 50% of their genes). Such findings support that genetics play a significant part in the disorder.
Evaluation of the biological approach
- Scanning research techniques are useful for investigating the functions of the brain: an organ with obvious involvement in our behaviour that would otherwise be unobservable.
- The approach presents the strong nature viewpoint of the nature-nurture debate.
- The experimental methods used (gathering empirical [i.e. observable] evidence) make this approach very scientific.
- The approach is considered reductionist complex behaviour, thoughts and emotions are all equally explained by low-level biological mechanisms such as biochemicals and nerve impulses.
- Biology alone has been unable to explain the phenomenon of consciousness.