High school biology - NGSS
Evolution of group behavior
Group behavior has evolved because membership can increase the chances of survival for individuals and their genetic relatives. Created by Sal Khan.
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- [Instructor] In our journey, studying evolution and natural selection, we often index on individual organisms. If we look at a species or population of a certain species, we've talked about how there could be variation in that population, which I will depict by these colors and these shapes over here. And sometimes the variation really doesn't confer any advantage or disadvantage for reproduction, but sometimes it might. And if a certain variation maybe because the environment changed or maybe this population finds themselves in a new ecosystem confers an advantage, well, that variant will be more likely to multiply. And the genes which produce that phenotype are more likely to become a larger and larger part of the gene pool. Similarly, if there's some disadvantage, maybe because the environment has changed some way, well, that might select out certain variants and the underlying genetics that cause it. But this is when we're thinking about traits that primarily affect an individual's chances of survival and reproduction. But what we're going to do in this video as this title implies, is focus on... it's not just about individual traits. There is also evolution of group behavior, and we see that right over here in a school of fish. Why does it make sense for these fish to ball up into this huge school? It might seem like it makes it very easy for a predator to just go right into the middle of that and open its mouth and get as much as it wants, an all you can eat buffet, so to speak. Well, it turns out that this type of behavior does confer a benefit. The benefit is yes, this shark that I just drew might be able to get a mouth full of fish, but the great majority of the fish are going to be protected. And by being in a big ball like this, instead of just having your own eyes, looking for a predator, as soon as any one of these tens of thousands, or maybe hundreds of thousands of fish spot a predator, well, the whole school will know it. So they're able to share information. Also, even though some fish might get eaten up, the probability that any one will be eaten by this shark is actually lower versus if there was just one of these fish, just swimming by itself, that one is much more likely to be picked off. And we see this type of behavior in many, many, many types of animals. This right over here is a herd of wildebeest. And once again, if you have an individual wildebeest, it would be easy to be surrounded by say, hyenas, by predators, that could be caught by surprise. The younger of the wildebeest would be easy to pick off if they were by themselves. But if they're in a herd, maybe they can be in the middle of the herd. Here's an example of adult elephants protecting their young when they see a threat approaching. And notice, more than just the parents are protecting the young. These elephants are probably related to each other. And so even though one elephant might sacrifice themselves, maybe from some type of a threat, if they're able to protect the young, even though it might not be their child, it might be their nephew, it might be their cousin, their shared genetics are more likely to be passed on. You've sometimes heard people say things like I'd be willing to die for two brothers or eight cousins. And that would actually make sense from a genetic point of view, but it's not just about protection, where we see the evolution of group behavior. We could also see it in terms of predation. So this right over here as a pack of wolves that are attacking this bison here, and first of all, you can see how much more vulnerable this bison is when it's alone than if it were part of a herd. If it was part of a herd, it would be much harder to surround it. You'd have a ton of these other bison all around that could run and chase individual wolves. But when this bison is surrounded like this, when it's outnumbered, it is more vulnerable. And these wolves, which are much, much smaller individually than this bison have a decent chance of taking it down. So once again, this group behavior of these wolves to not hunt by themselves, but to hunt together, to surround animals, to coordinate with each other, that allows them to prey on animals much, much larger than themselves. So I encourage you to think about this idea because it's happening all around us, including in human beings. We are social animals. This is occurring through out the animal kingdom. And it's a really fascinating thing to observe all around you.