Evolution through variation and natural selection

In this video, we are going to focus even more on the idea of evolution. We introduced it in other videos, but here we're really going to focus on what it is and what it isn't. As I've mentioned before, it's a super important idea. If you were to try to understand life on another planet, well, you would have to understand how evolution works.

So, evolution as we know it is based on two underlying principles. It's based on a principle that in a population of a species, there is variation; that there's variation in the phenotype, in the traits that that population has. Now, the other idea that's related to that variation is that you have natural selection. Natural selection—if someone tries to explain evolution without variation and natural selection, they might not be explaining evolution; they might be explaining something else.

So this idea—if I have a population of circles, some of the circles are blue circles, some are yellow circles, some are pink circles. There are, for sure, traits; there are phenotypes that might not have any bearing on an organism's ability to survive or reproduce. In that case, that variation would probably continue. But there will be some variations; some phenotypes—remember, phenotypes is what's expressed versus genotypes, which are the actual genes, the actual alleles that an organism has.

But evolution occurs because depending on where we are in our environment and the time and space of our environment, certain phenotypes might be slightly more advantageous than others. They might make it slightly more likely that the organism will survive and reproduce, slightly less likely that it will die or not be able to reproduce.

So, if we said these circles were living things, and let's say the environment that they happen to be in right now, it's that much more likely for them to reproduce and survive if they are warmer colors—if they are an orange or a pink versus a blue. So then, in your next generation, the yellows and the pinks are more likely to reproduce. They might reproduce a little bit more—let me put some of the pinks in there. They're going to reproduce a little bit more, and the blues might have a lower probability, or would have, based on the situation I described, of reproducing.

So you'll still have some blues, but you might have fewer blues. This process could keep going on for a very, very, very, very long time, and at some point, you might see only pinks and yellows. This is just one phenotype that we're talking about being selected for. There might be another one—if we're talking about circles, it might be roundness or whatever else.

So the key thing is you need that variation, and depending on where in time and space you are in that environment, some of those variations, some of those phenotypes, the exhibited traits, might make you more successful at reproducing and passing on that trait to your offspring.

I really want to contrast this with what some people think of when they think of evolution. Some people think that evolution is a process of going from basic to advanced. The reason why we sometimes think this is we think of many of the early organisms on Earth maybe being unicellular organisms, and now we have these complex animals like ourselves that we consider much more advanced than those things. We have trillions of cells. But remember, unicellular organisms continue to be very successful even today, and some of them aren't a lot more advanced than things that might have existed, say, 500 million years ago or even a billion years ago.

So, even though these things might be the product of evolution, all it says is that over time, you have this variation. Based on which variations, which phenotypes were more suited to their environment, those are the ones that were able to pass on their traits.

Another place where this misconception comes from is you might have seen these diagrams where you have these apes, where the first apes are kind of hunched over, and then they get upright or more and more upright, and eventually, you see a walking person. We are officially apes as well, and we tend to think that we are pretty advanced. We do things like wear hats and things, so we say, "Oh yeah, it's going from primitive to advanced, or from basic to advanced." But that is not the case.

Remember, even in today's world, we aren't the end of evolution. Even in our world, there are many animals in the animal kingdom that are at all different levels of either complexity or, if we want to think about intelligence or sophistication. There could for sure be a reality where you could imagine a human colony goes to another planet, and it's actually suitable to be more hunched over, in which case the animal, the human beings, the variations of humans who are better at hunching over might be more successful. Maybe they need to go into these tunnels to find some animals to eat or whatever else, or to farm.

Then, on that planet, that variation might be the one that wins out. Now, another misconception that people have with evolution is when they hear it, they kind of think, "Hey, this might be due to the effort of an animal over its lifetime." Some of the early explanations that folks gave before Darwin of why a giraffe, for example, has a long neck—some people believe that hey, some of the early giraffes might have been straining to get leaves on tall trees, and that straining somehow stretched out their necks.

Somehow, they might have been able to pass that on to their offspring. This is not the case. The explanation consistent with our understanding of evolution is that you would have had a population of giraffe ancestors, and they would have had variation in their neck length. Because of the environment that they happened to be in for that population, the variants that had longer neck lengths would have been able to have a slightly higher probability of reproducing and surviving.

So over time, those longer necks became more predominant in the population. At some point, you might say, "Well, why don't giraffe neck lengths become indefinitely tall?" Well, that's because at some point, the variations that had super long necks—even longer than the giraffes we have today—that might have created some other difficulties, making it harder for them to survive and reproduce. Maybe their hearts weren't strong enough, and so they died of heart attacks, or maybe it was more difficult to escape predators for the variations where the necks were too long.

It's really important to recognize that evolution is a byproduct of variation that happens in populations and then natural selection due to the environment on those variations. They act on the phenotype; they act on the exhibited traits that are shown. Evolution is not necessarily a process going from basic to advanced, and it's not due to an individual organism somehow exercising or training itself to the environment that it's in.