Biological Influences on Human Behavior: Genetics & Environment

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  • 0:02 Human Behaviors
  • 1:09 Twin Studies
  • 2:29 Genetics & Behavior
  • 4:28 Lesson Summary
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Lesson Transcript
Instructor: Sarah Friedl

Sarah has two Master's, one in Zoology and one in GIS, a Bachelor's in Biology, and has taught college level Physical Science and Biology.

Humans are a product of both our genetic makeup and our environmental surroundings. Does one influence our behavior more than the other? It can be difficult to tell, but there are ways that scientists can better understand why we do the things we do.

Human Behaviors

Sometimes I wonder if my sister and I are really part of the same family. We have the same parents and we definitely look alike, but our personalities are so different! This is because even though we have a similar genetic makeup, our external environment also plays a substantial role in shaping us as individuals.

Twins are even more interesting than regular siblings because even identical twins, who have the exact same DNA, can look and act differently from one another. Because different aspects of our behaviors are influenced by our genes, the environment, or a combination of the two, it can be difficult to determine which is more influential for specific behaviors.

For example, your natural features, such as your hair and eye color, are determined by genetics. But how you style that hair and what kind of sunglasses you wear over those eyes, well, those may be part of your genetic personality, but they're also likely influenced by the people you hang out with and other social cues in your 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.

Genetics & Behavior

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.

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