Behavior and genetics
Temperament, heredity, and genes
All right. So here we have three babies. And if you've been around babies very much, you know that babies are often pretty unique in the way that they respond and the way that they react to their parents and to other people and to their environment. And so we might give this baby on the left here a big old grin. And we could say that this baby is really cheerful and really relaxed and fairly predictable in its sleeping and in its feeding. And we might characterize this baby as easy. And then we have this baby in the middle, and maybe we'll give it a real sad face here. And maybe this baby is really irritable or intense or less predictable in its sleeping and in its feeding. And we might characterize this baby as pretty difficult. And then we have this baby on the end, and maybe we'll just give it a really flat affect. Maybe we can't tell if she's smiling or if she's frowning. But maybe this little girl is kind of resistant to change and maybe withdrawn from new people or new scenarios. And we might characterize her as withdrawn. And there are other ways that we might differentiate between these and other children. But we call these differentiations temperament. And temperament is a pretty broad term and is actually quite difficult to define. But to get your intuition rolling, you might be thinking words like "personality." But temperament is really a little bit broader than that. And we might say that it's a person's characteristic emotional reactivity and intensity. So maybe words like their "sociability" or their "shyness." But the real interesting thing about temperament is that, as psychologists study this idea, they find that temperaments seem to be pretty well established before babies are exposed to much of their environment. And even more interesting, to me at least, is that as these studies continue, and as psychologists continue to look at this temperament, it seems to be fairly persistent as a person ages. So I'll write, "persists." And what I mean by that is that maybe this inhibited or withdrawn child on the right here, this little girl, as she grows up, studies have found that she is more likely to be inhibited and withdrawn as an adult. And so combined, these two ideas-- this idea that the temperament is fairly established at birth and that it also persists as people age-- leads us to believe that, really, this temperament, this idea that kind of defines us, is fairly hardwired into us at birth. And so that leads us to develop further curiosities. If our temperament is hardwired into us, what about our personality? Is that hardwired into us? And is it persistent as we age? And how about our gender identity? Does that come predetermined and hardwired? And are there are certain folks that are hardwired, maybe, to have higher intelligence or to be geniuses or even super athletes? Well, hopefully we can dissect some of these ideas, or at least begin to dig into them as we talked about-- really a field, called behavior genetics, looking at the genetic component or the hardwiring component to behavior. So when we talk about hardwiring, what we're really talking about is heredity. And heredity is the idea of passing traits from parents or ancestors to offspring. There's the father. And then we'll have a mother. And we said these parents are passing traits. So let me draw that. They're passing traits. And as a review, traits are essentially the distinguishing qualities or characteristics that compose us. Maybe a better word would be our "attributes," so things like our eye color, or even our temperament. And these inherited traits that we get from our mother and from our father-- these characteristics that define us-- are actually controlled by genes. And so as I get a little bit deeper into the biology, I need a better picture, and I've pre-drawn an image that will help me talk about some of these ideas. But genes are actually the little, individual units of heredity. They're actually segments of DNA, right here, that's capable of synthesizing a protein. So this strand, this double helix, is DNA. And let me write that real big for us. And DNA is-- I guess continue in what is now becoming almost a vocabulary lesson-- but DNA is deoxyribonucleic acid. And it's actually a molecule in us that contains all the instructions used in our development and in the function of our organisms and, really, in the function of our personage. But it contains all of our genetic material. That's what DNA is-- our genetic material. So, many of these genes, these little units of heredity right here, are linked together to form a long strand of DNA called a chromosome. So we have maybe a gene there, and maybe a gene here, and a lot of little genes link together as we go down. But they form this long strand of DNA, and it coils up really tightly. And this long strand-- all of this whole structure right here-- is one strand of DNA coiled up called a chromosome. And as humans, we have 46 chromosomes full of genes that make us who we are. And we get 23 of these chromosomes from our father, through his sperm, and 23 of these chromosomes from our mother, through her egg. And in the end, we end up with this nice collection of genetic content-- 46 chromosomes in its entirety-- that resides in almost every single cell in our body right here in the nucleus. And we refer to this collection of genes, compiled in this list of chromosomes, as our genome. So I guess it's kind of like this-- we have approximately 30,000 genes, and if we consider them to be words in a story, that story would be about as long as The Old Man in the Sea by Ernest Hemingway-- so kind of a short novel. But continuing that theme, I guess that story would have 46 chapters, and the title of that entire story would be our "Genome." So our genome is really just this entire collection of genes that make us who we are. Some of the more simple traits can be traced fairly specifically to certain genes, like eye color or hair color. Relatively simple traits can be traced back to specific genes. We can actually see which genes are controlling those specific traits. But most of our traits-- especially the complicated ones like intelligence or happiness or aggressiveness or all of those characteristics that play into our temperament, the ones that are heavy hitters in our behavior-- are traced back to groups of genes. And those groups of genes are actually interacting with each other and with our environment. You see, these genes can either be active or inactive. And the environment actually plays a major role in turning them on or off, determining whether they're going to code for these proteins or not code for these proteins. And so you can think of this idea like a tea bag. Let me draw a cup here. And in this cup we have a tea bag here. So we've got this tea bag. It's kind of hanging off the side right there with its label. And in this tea bag are all of the makings for the tea that we're going to drink. And so all of the little leaves, and all of the things that are characteristic of this tea, and all the makings of the tea-- so its flavor, it's caffeine, its smell-- are contained within this little tea bag. But they're actually coaxed into expression as hot water is poured over it. So as water gets poured over it, especially hot water, it pulls from these leaves the flavor. And it pulls the caffeine out, and it pulls that aroma. And that tea that was contained in this bag begins to spread and express itself in this glass so that we can enjoy it. And while all of the contents were originally contained-- everything about the tea, its characteristics, were determined by that tea bag-- ultimately its expression was dependent on the hot water. And so what becomes really challenging is separating the effects of our genes and our environment and ultimately determining which ones, and to what degree, these genes and these traits end up affecting our behavior. But I'm running out of time in this video, and so in the next video, I'm going to talk about how, as scientists, psychologists begin to tease apart these effects of environment and our genetic background in ultimately determining who we are and how we respond.