Resumen de cómo Darwin construyó la idea de selección natural y el rol de Malthus. Transcript: Speaker 1 So Darwinism in 1838, he came up with three ideas, just in his shows up in his notebook that basically drove the rest of his thinking. And it came up right after rereading or I don’t know whether he read the whole thing before this, but certainly reading Malthus on population. This whole problem that Malthus realizes is that reproduction outpaces resources. And Malthus, of course, had this dire prediction that this would lead to terrible things in England and Europe because populations were growing so fast and resources were not growing Fast enough. Darwin sees this and says, aha, but in the natural world, this is going to be the case. And that means there’s going to be selection that favors a few over the others, those that fit better with the contexts, they can do better, they can outpace the others. And so this sort of drives his theory and he comes up with three ideas. He says, the first thing is that I noticed that everybody realizes that the grandchildren are like grandparents. As basically, the traits are inherited, they’re passed on down. And he says, but in fact, the second thing is that there is a great variety in offspring. That is, although they carry some of those traits, there’s a lot of variety. So that’s his second story. That’s the variation problem. Then the third one is he says, but then there’s this great overproduction with respect to the support of those offspring. But those three things together and you get natural selection. That’s Darwin’s basic idea. (Time 0:04:40)
definición evolución selección_natural teoría
Transcript: Speaker 1 We primates need to eat vitamin C. We need to eat a scorpic acid in fruit. Whereas almost no other mammal, in fact, very few other animals in general, need it because they have a gene that produces it. We actually have a pseudo gene that somewhere back in our evolutionary past, we think somewhere than 50 million years ago, actually produced vitamin C in all primates. But the anthropoid primates, the monkeys and apes, lost this capacity. And they lost this capacity probably because they were eating fruit. And the fruit provided it from the outside world. So in effect, it masked natural selection on the gene, and it allowed it to just sort of pick up noise. So in fact, what we see now in most anthropoid primates is not only noise in the gene, we have to stop codons in the gene and so on. But in fact, there’s a major frame shift so that it’s just complete nonsense now. And yet that means that we’re addicted to vitamin C. We have to eat it. We can’t make it ourselves like your dog or your cat can. So as a result, a number of other things have happened. We have changes in taste receptors so that we actually have this pleasing interest in sweets and sour, that is the acidic nature in vitamin C. But we also, subsequent to this in monkeys and apes, duplicated the options. That is the genes that are involved in producing light-receptive pigments in our retina. And so what amounted to the central pigment, a green sort of central frequency pigment, duplicated, got plugged right next to itself in the end of the ex-promisone. And that one began to degrade. And as a result, it reduced its sensitivity to free to higher frequency, became more and more red in its reception. Now we have this sort of red-green distinction, which of course is critical to determine the ripeness of fruit. Fruit is ripening and giving a color signal to birds mostly, initially, that says, okay, now green, we’re camouflaged. You can’t see it very edible yet. But now I’m going to make a clear change. And now you can eat me. Well, that’s a good thing to know if you’re a primate and you need fruit, you need to have this capacity. So one of the things that happened here is that now a duplication outside the body is not just like a gene inside the body, but now it’s outside the body, created a whole bunch of other changes Elsewhere in the body. So many genes are now contributing to the fact that we’re getting enough vitamin C, getting enough ascorpic acid. (Time 0:13:25)