Biological Influences on Human Behavior: Genetics & Environment

Twin Studies

Because identical twins have the same DNA, they are often used to help scientists understand which behaviors may be determined by genetics and which may be influenced by our environment. As exact copies of each other, sets of identical twins can be compared with other sets of identical twins to see how the environment affects their individual behaviors.

For example, scientists may compare identical twins that were separated at birth to identical twins that grew up in the same household. This allows them to examine how different environments influence the same genetic makeup. Other studies may compare identical twins that were raised together to fraternal twins, who, like normal siblings, only share about half of their DNA.

While there are no definitive answers, what these studies do generally show is that neither genetics nor the environment is more important than the other when it comes to some of the more complex behaviors. For example, genetic makeup accounts for about half of the variation we see in human personalities and intelligence. But this means that the other half of the variation we see in people comes from their environmental surroundings. So for some behaviors, both our genes and the environment play an equally important role.

It may be tempting to think that genetically influenced behaviors come from specific genes. However, just because a behavior has a genetic basis doesn't mean that there is a gene that 'controls' that trait. Genes don't actually control behaviors, they just facilitate certain reactions to our environment.

For example, many animals in nature are monogamous, which is a genetically influenced behavior. But there is no specific gene that causes monogamous behavior in these animals. Instead, certain genes produce proteins with receptors that respond positively to the scent of their mate. And it's this positive response that began with genetics and then is triggered by the environment that keeps the couple close to each other.

Humans have similar responses to other people; we like being around others for a reason! Human brains are genetically programmed to respond to social recognition and bonding with others. We are a very social species and we form complex relationships with friends and family. However, what we don't know much about is how our brains do this. Hormones and hormone receptors are major players, but the jury is still out on just how those mechanisms are involved in forming relationships and bonding with others.

One thing that separates us from other animals is how much longer it takes us to develop after we're born. We spend a very long time learning how to talk, walk, and interact with the world around us. During this time we are involved with many different people: our parents, siblings, and schoolmates, just to name a few. This allows us to be involved in a variety of complex social networks, which scientists think may have led to our unique success in the Animal Kingdom. As you can see, even from very early in life, both our environments and our genetics are important factors in determining how we behave.

Human behaviors are complex. Our social networks, personal interactions, and relationships are determined by both our genes and the world around us. Some behaviors may have a genetic basis, but genes do not actually control behavior. Rather, our genetic makeup influences how we interact with and respond to our surroundings.

While we do not fully understand the mechanisms behind human behaviors, we do have some insight into whether certain behaviors are influenced more by our genes or our environment. Twin studies are helpful for this because identical twins have the same DNA. Comparing sets of identical twins in different environments allows scientists to more closely examine how genetics and the environment shape us as individuals.

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Biological Influences on Human Behavior: Genetics & Environment