21. Evolution
Natural Selection
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In this example, it says, how do giraffes get such long necks? Is a classic question in an evolution. We want to use the observations and inferences of natural selection to describe in simple terms how long necks could evolve in giraffes. Alright. So we have this little illustration here showing we have maybe some shorter neck giraffes, and over time these giraffes get longer necks, the long neck giraffes that we see today. Alright. So remember, we start with variation. Natural selection needs variation to work. So what would be the variation that you see here? Alright. I'm just gonna go with neck length. Right. It's perfectly reasonable that there are some ancestors of the giraffe that in that population, some had a little bit longer neck, some had a little bit shorter necks. Alright. Well, what about overproduction? What are we gonna say there? Well, we'll just say more giraffes born then can reproduce. Alright. That we said is true for really all organisms. Alright. Well, what's the selection gonna be in this case? Well, we'll say that longer necks get more food. Right? That's sort of the classic story. You have this very tall tree here and the the drafts with the longer necks will be able to get those leaves up in that high tree easier. That means they're more likely to survive, because they're less likely to starve to death. If you survive, you reproduce. Alright. Well, that means evolution. What's gonna happen to this, population? Well, average neck length increases. Right? If the individuals with shorter necks are not reproducing, they're not passing on that variation. Those individuals with longer necks are reproducing. They're passing on that variation and the population changes. The average neck length gets longer. Alright. Practice this more and problems after this. I'll see you there.
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