Created by Ryan Scott Patton.
So the past videos of this series have been a pretty continuous discussion about our genes, so our genes and our environment related to our behavior. And to say that the genes and the environment are both important is really true. But really more specifically, they interact. And so I've alluded to this previously with the tea in the hot water example. But I'm going to get really specific with the language here because not only do our genes and our environment both effect our behavior, their effect is really dependent on each other. OK. So say you have two babies in a nursery of a hospital. One, we'll say, is genetically predisposed to be much more attractive than the other one. So we have this attractive baby and we have this really hideous baby. And as a result, the beautiful baby over here, it receives more affection and more attention. And it grows up to be generally more sociable and well adjusted. But suppose even further that at birth, both of these babies share a combination of genes that predisposes depression. As we've learned, the environment activates those genes. So in this case, maybe the genes are activated by environmental stressors. So both babies have these genes. But throughout life, this cute and ultra-lovable baby is surrounded by this great and supportive network and it has reduced stress. So its genes aren't stimulated to create the combination of neurotransmitters and other proteins that are involved in depression. But over here, this ugly baby is cranking out these proteins like crazy. And maybe that's because this baby is getting made fun of all the time or maybe it's because it has less friends. So I guess the cute baby's genes are somewhat responsible for setting up the environment. But really also the environment is responsible, at least to some degree, in keeping those depression genes at bay. Similarly, the less fortunate baby over here, his genes play a role in his tough life. And that tough life is activating the genes that are associated with creating the neurotransmitters of depression. So this is kind of a crude example of gene and environment interacting with each other. But a more specific example is the genetic condition PKU or phenylketonuria-- so PKU. And phenylketonuria is a genetic condition in humans that's caused by mutations to a gene that code for a liver enzyme. And that liver enzyme is phenylalanine hydroxylase-- so PAH. But because the enzyme is missing the amino acid phenylalanine, it doesn't get converted into the amino acid tyrosine during one of the metabolic pathways in our body. And so this causes a build-up of phenylalanine in the body, which can cause problems for brain development and even other problems. So PKU, it affects one in about 15,000 babies in the US. But most of these babies grow up without any major problems. And it turns out that during infant screening, these babies are identified and are placed on a special phenylalanine-free diet. So because they're not taking in all of this phenylalanine, it's resulting in a less problematic build up of the phenylalanine in the body. So it's really an interaction again between our genes and our environment that initiates the body's responses and behavior. So we see that the environment is dependent on genetic predisposition. But gene expression is also dependent on the environment. And this is the phenomenon that we're referring to as gene/environment interaction. So this idea is going to shift our vocabulary away from phrases like nature versus nurture. It's going to bring us to a more correct phraseology, nature through nurture.