Animals will generally choose where to live based on food and mates. Some organisms will actually, in their lifetime, move very great distances, and this is known as migration. This is a long-distance movement of a population, and it's usually associated with seasonal changes. However, organisms will migrate for a variety of reasons, like the availability of food sources, differences in climate, or for mating purposes. Now we'll actually see 3 interesting types of migration, what we call piloting, which is basically the use of familiar landmarks to find their way: compass orientation, where the organisms have their movement oriented to a specific direction, and true navigation, which is the ability of animals to find their way as if they were looking at a map, like as if they had GPS or something. One example of this is with sea turtles that have the ability to sense the magnetic field of the Earth and use that sense of the magnetic field to orient themselves. Basically, you know, blindfold a sea turtle, drive it around, take it in a bunch of back streets for a while, throw it in the ocean, and it'll still find its way because it has that ability of true navigation. And here you can see a herd of wildebeests migrating, and here you can see some migratory patterns of birds, and hopefully you realize how astounding some of these distances are that these birds will travel.
Altruism is an interesting type of behavior because it seems counterintuitive in some ways. It's a behavior that actually has a fitness cost to the actor that exhibits it. So the organism that exhibits the behavior receives a fitness cost, meaning there's a detriment to their fitness, and the recipient of this behavior will actually receive a fitness benefit. So, why would an organism do this if it's not seemingly in its own self-interest? Well, part of the explanation for this is something known as kin selection, which is an evolutionary strategy that favors the reproductive success of an organism's relatives. And you can see this in organisms like bees, for example. Now, Hamilton's rule is a way of looking at altruistic behavior, and it basically says that when certain conditions are met, you're more likely to have an altruistic behavior. These conditions are that the benefit to the recipient is going to be high, the cost to the actor is going to be low, and it's also going to factor in something known as the coefficient of relatedness, which is the average number of genes that are shared between the individuals.
This is represented with the equation: r > c b where: r is the coefficient of relatedness, c is the cost, b is the benefit. The idea is that the benefit is high enough, and the coefficient of relatedness is high enough that it outweighs the cost to the actor.
So, if you're still wondering why we would see this type of behavior, why we'd see altruism, Hamilton developed this idea. It's sort of a different way of looking at fitness, and he calls it inclusive fitness. This is basically a way of looking at fitness where you're looking at the evolutionary success of an organism based on the number of offspring it produces, which is pretty standard in how we look at fitness, but it also includes how that individual helps its relatives produce more offspring than they otherwise would be able to on their own. It's believed that these behaviors are seen because they might not directly spread an organism's genetics, but because it's happening with relatives, those relatives are going to share a portion of that organism's genes, and so the organism is helping to pass on a portion of its own genes by helping its relatives, though it's not directly passing on all of its genes.
Now an interesting idea that has sort of been extrapolated from this thinking is the idea of reciprocal altruism. This is going to be seen between organisms that are not related. This is when an actor is going to temporarily reduce its fitness to benefit the recipient, under the assumption that the recipient will return the favor someday. This is seen, for example, in communities of chimpanzees. It's thought to explain some aspects of human behavior and altruism amongst humans.
One nice example that I want to leave you with of all this altruism, all of this thinking is with prairie dogs. Prairie dogs are numerous, they live in big communities with lots of relatives, and prairie dogs exhibit this behavior you see here, where they kind of like scream, basically, to alert their community of the presence of a predator. I don't know if you can tell, but there are some feathers back here. Prairie dogs have to watch out for birds of prey, which love to eat them. So this is an example of altruistic behavior because by alerting their community, by making this noise, these prairie dogs actually draw attention to themselves. So they put themselves at a greater risk of predation, but it helps warn all their brothers, and so that means their brothers are more likely to survive, and this is going to help with their inclusive fitness. That's all I have for this one. See you guys next time.