Back To CourseAP Biology: Tutoring Solution
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Steph has a PhD in Entomology and teaches college biology and ecology.
Are you who you are because of genetics or because of how you grew up? This old question of how much of a trait is genetically determined versus environmentally determined is referred to as the nature versus nurture debate. Nature generally refers to genes, nurture refers to environment.
This is an old debate. The dichotomy of nature and nurture is referenced in ancient Greek texts, and the English-language comparison of 'nature' and 'nurture' is a turn of phrase you can find in the works of Shakespeare.
Because of his 1690 work, Essay Concerning Human Understanding, the philosopher John Locke is generally regarded as the founder of the modern idea that we are a 'blank slate' on which our environment 'writes' our personality.
Locke's ideas were controversial even in his own time, but garnered occasional support throughout the centuries.
Darwin's theory of natural selection swung the pendulum towards 'nature' in the late 1800s after his famous work Origin of Species described natural selection. He used the word 'gemmules' as a sort of space-filler to describe the units of inheritance, which we would later discover to be genes, further backing up the nature side of things. Darwin didn't quite have it all correct though, Darwin thought that traits pass on included acquired traits during an organism's lifetime. This last bit was later rejected, at least in the way he was thinking of it, as traits acquired during one's lifetime (like a scar from an injury or gained intelligence) are not passed down biologically.
Behaviorists in the mid 20th century revived 'nurture' and claimed that all human behaviors were acquired through conditioning. It was an important school of thought in psychology because it placed emphasis on factors that could be measured (like your actions, unlike, say, your mind, mood, or free will).
Behaviorism founder John Watson in 1930 put it this way: 'Give me a dozen healthy infants...and I'll guarantee to take any one at random and train him to become any type of specialist....'
This idea has since been criticized for ignoring important genetic factors entirely, as well as things like your mood and mental state (which are certainly real, even if you can't measure them).
Altruism was long thought to be unexplained by biology and therefore evidence for 'nurture'. However, in the 1970s Richard Dawkins popularized gene-centered evolution with his book The Selfish Gene, which proposed that genes could explain altruism. Geneticists worked out mathematically that altruism could be explained by its degree of relatedness to the beneficiary. In other words, you're more likely to rescue your brother than a second cousin, and more likely to rescue a cousin than a stranger. The model had a good deal of explanatory power and is still in use today.
After that, genes ('nature') became so entrenched in our thinking that some scholars argued that we were unable to see past it. By the 2000s, most scholars agreed that the simplistic form of the 'nature versus nurture' debate is outdated; that our behaviors and appearance are influenced by a combination of genes and environment. Psychologist Donald Hebb said, 'Which contributes more to the area of a rectangle, its length or its width?'
Okay, so they are both factors. There are a lot of mysteries left though in teasing out where nature come in to play vs nurture.
Some well documented examples of nurture at work is shown in phenotypic plasticity, when our phenotype, or traits, can change depending on the environment.
Epigenetics is the relatively new study of traits that are inherited, but not because of genes. In other words, the traits that genes express change even though the DNA instructions are still the same. For example, in methylation as it relates to epigenetics, a single carbon is added to the outside of a strand of DNA, which does not change the genetic information within the DNA but has the effect of 'turning off' a gene, preventing it from being expressed.
Epigenetics is an interesting modern form of the nature versus nurture debate, because, traditionally, 'nature' meant 'genes only.' With epigenetics, changes can be acquired during the individual's lifetime (nurture) or even acquired from parents (nature).
Sexual orientation is a big topic these days. For a long time, many believed that it was a choice or strictly an effect of environmental factors (nurture). However, there are now studies suggesting that orientation may in fact be linked to certain chromosomes, or even to the hormonal circumstances of the womb.
A 2015 study of identical twins showed that some epigenetic markers acquired in utero might predict men's sexual orientation. However, these and other studies have been somewhat contested, so we will have to wait for the scientific method to take its course to get more insight on the nature vs nurture debate in this case.
Nature versus nurture is a debate about whether our characteristics are because of genetics or because of environment.
Darwin's theory of natural selection made our nature seem deterministic. Twentieth-century psychologists called Behaviorists, on the other hand, argued that anything about human behavior could be taught in the proper environment (nurture).
The book Selfish Gene by Richard Dawkins then made behavior seem deterministic again in the 70s by arguing that even altruistic behavior could be explained by genetics. Current science has come to the consensus that nature and nurture both affect individuals, but the interplay can be hard to tease out.
Examples of the nature v nurture can be seen in the wild and in human sexual orientation. Phenotypic plasticity is the flexibility of our traits as determined by our environment, like rabbits that change color in winter or temperature determining the sex of alligators.
Epigenetics is the study of mechanisms outside of our genes that shape our traits and get passed down to the next generation.
Sexual orientation in humans is one example of a trait that almost certainly has biological causes, but their nature, whether genetic, epigenetic, or hormonal, are not fully understood.
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Back To CourseAP Biology: Tutoring Solution
27 chapters | 344 lessons
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