Introduction to Human Development: Biological Perspective
Thursday, October 18th, 2007The biological perspective looks at how our genes influence our development. However, since the issue of how much influence genes have is rarely discussed without also considering how much influence the environment has, it makes little sense to try to look at either side in isolation. So what we’ll look at here is the age old argument of nature versus nurture.
How do genes and the environment affect development?
One way of looking at how genes and the environment affect development is through these three patterns of interaction:
- Active
The active pattern is one in which you choose to do things which compliment your genetic disposition. So if you’re really tall, you might choose to play basketball. - Passive
This pattern is followed if your environment is set up for you in a way which compliments your genetic make up. In this case your highly intelligent parents may surround you with books and other educational material, including educational toys. - Reactive
In this pattern you’ll behave in a way that compliments your genetic endowment, and this will lead people to react to you in a way which reinforces that behaviour. So your Aunt sees you running around the backyard and says, “Oh look at little Timmy, running around just like his Dad. He’s going to grow up to be a sprinter too isn’t he?” Hearing this you gleefully run a little faster.
Another approach is to look at how genes result in the development of specific traits, where a trait could be eye colour, type of personality, level of intelligence, genetic disease, etc. It used to be thought that specific genes meant specific traits, and indeed many people still think that’s how genes work.
A more recent theory is that genes only indicate a likelihood of developing a specific trait, and that environmental factors play a significant part in determining whether or not that trait is expressed. The more complex the trait, the more factors involved, the harder it is to figure out the likelihood that having specific genes will mean having a specific trait. So for example, if you have genes which make it easy for you to put on weight, it’s no guarantee that you will put on weight, unless your environment allows it. Yes, put down that donut, pick up that carrot. Better yet, give me the donut!
How much of an effect do genes and the environment have?
One way of measuring the effect of genes on a particular trait is to look at it’s heritability. Heritability is a measure of how much variation there is between people. For example there is not much variation in the number of fingers people are born with, so we can say that the heritability of number of fingers is low. If you have fewer fingers it’s probably because a drinking game involving power tools went horribly wrong.
Compare this to the heritability of height. Height varies a lot, and as with the number of fingers, it’s mostly due to genetic factors. Some variation in height can be accounted for by environmental factors, though arguably if you ask someone who hunches over a computer all day to stand up straight so they can be measured, they probably won’t standing as straight as most people would. So it’s unlikely that being short is due to anything but genes. After all, if a drinking game goes horribly wrong and it affects your height, well, at best you won’t be a foot model any more. At worst… Well, let’s not go there.
But one thing to keep in mind when thinking about heritability is that it’s really just an estimate of variation across people in general. It doesn’t actually say much about genetic contribution to a specific trait in an individual. For that we need to look at the research.
How do we know how genes and the environment affect development?
Much of the most conclusive research on the influence of genes versus the environment has been done by studying twins, both identical and fraternal twins.
Various studies on IQ have produced some interesting results. Some early studies showed that identical twins were clearly more similar in intelligence than were fraternal twins. Yet these studies didn’t account for how identical twins may be treated almost identically, as opposed to more varied treatment of fraternal twins, though the effect of the differences in treatment was probably small.
Even more interesting are studies which looked at the difference in intelligence of identical twins who shared a placenta compared to identical twins who had separate placentas. Sharing a placenta resulted in more similar levels of intelligence, showing that even the pre-natal environment has at least some influence on development in contrast to the influence of genes.
Finally, a study of adopted children looked at the differences in their IQ, paying particular attention to the socio-economic status (SES) of both biological and adoptive parents. It turns out that genetic and environmental influences were about equal. Children of biological and adoptive parents of low SES had the lowest IQs, while children of low SES adoptive parents and high SES biological parents were similar to children of low SES biological parents and high SES adoptive parents, with children of both adoptive and biological parents of high SES having the highest IQs. So if you can follow that (sorry, the graph is under copyright), while you might not think the SES of biological parents would matter to a child’s IQ, it does, but as far as IQ of adopted children is concerned, both genes and the environment have comparable effects.
Onwards
The debate has gone back and forth for a long time, but for now it seems clear both genes and the environment have an influence on our development, with neither one nor the other necessarily having the greater influence in general. More research will let us figure out just how much each has an influence over specific traits, but for now we can rest assured that for many of the issues which may bother us, regardless of our genetic make up we can alter our environment to give us a good chance of expressing the kind of traits we’d prefer, rather than the ones we might think we’re stuck with.
Most of the info I’ve presented has come from books or papers which require a subscription for access, but a quick search for “nurture vs nature” will give you plenty of info, such as the wikipedia page or the about.com page. The BBC also have a good article on the topic, though being short it doesn’t say much more than you’ve just read.
Next up is the socio-emotional perspective which looks more closely at how behaviour develops in response to social and local environmental interaction, as well as emotion, temperament and attachment.
Related entries:
- Introduction to Human Development
- Introduction to Human Development: Psychoanalytic/Psychosocial Perspective
- Introduction to Human Development: Social-Emotional Perspective - Part 1
- Introduction to Human Development: Social-Emotional Perspective - Part 2
- Introduction to Human Development: Cognitive Perspective
- Introduction to Human Development: Socio-cultural Perspective
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