Hi, it's Mr. Mazurkiewicz and in this video I'm going to be talking to you guys about mechanisms of evolution or in other ways how can we get evolution to occur. So I just wanted to start off by kind of defining what we mean by evolution. Most of the time when we talk about evolution, we're talking about a type of evolution that is referred to as macro evolution.
Macro meaning big. So when you think about evolution, you're probably thinking about species giving rise to new species and things changing over the course of long-scale time. So here's an example of how the dinosaurs came to be. Even though they all share a common ancestor, over the course of time, they gave rise to a bunch of different species or types of dinosaurs.
This is macro because this takes a very long time to occur. It's not like all these dinosaurs were born overnight. What gives rise to macroevolution are these small-scale changes in the gene frequency.
So if you have a species, small little changes can add up over time to then eventually give rise to new species. So these smaller-scale changes are things that we refer to as Microevolution, micro meaning small. So imagine I have a species of insect here.
The small changes that are happening in its population over time are eventually going to lead to a type of macroevolution. So we say that microevolution leads to... macroevolution. So when we talk about these mechanisms, we're mostly going to be focused on those small-scale changes in allele frequency in the population. So what really is evolution in these terms?
Well, imagine we have that insect. Let's say within that species of that insect, we have some blue and some green. And in this example, we're going to have equal amounts.
We have five of each type. Well, evolution will be occurring if over the course of time, let's say that a certain one is thriving more than the other. So in this case, Blue seems to be more prominent than the green ones over a course of, let's say, a few years.
Now, if you look at this, if you already know about natural selection, which I'm sure you do, you'd probably look at this and say, sure, evolution is occurring because the blue ones are better adapted to their environment. So those are the ones that are surviving. They're reproducing more than the green. What we're really going to be focused on, though, is what other things can make this happen. So when we define evolution, though, in these terms, what we're talking about is that evolution is any change in the frequency of alleles in a gene pool.
Anything that causes... certain alleles to become more frequent while other ones become less frequent, we're going to say that evolutionary change is happening. It's more small-scale, so it's type of micro, but it is evolution nonetheless. So again we're going to be focused on how can evolutionary change, or these changes in allele frequency, how can they occur outside of natural selection? You already know about natural selection, what other forces can cause this sort of change to happen.
The first one we're going to look at is genetic drift. So in my class, what we did was a lab using these different colored beans. We had black ones and white ones.
And we used that to simulate different types of moths, light moths and dark moths. And what students did to start was they took a population size of 100, 50 of each, and they randomly selected out 50 lucky survivors. The other 50 would die. And they did this for a course of, let's say, three different trials to make three new generations.
And what most groups saw is that the population didn't really change much. In other words, it didn't evolve. They still had, after three times of doing this, just around 50-50 of white ones to black ones.
That's because when you take a large sample size, a good probability is going to be that it's going to be half of each as long as they start off equal like we did. But then what students did is then they took a small sample size. They said, okay, instead of 50 surviving, only five are going to survive this time. And this is where they started to see evolutionary change happen.
What you should have seen is that if you choose five, it is more likely that you can choose out five of one color. or five of the other or maybe three and two. But either way, it is more likely that we can get that change in allele frequency to happen.
So this is called genetic drift because this change that you saw is not due to natural selection, not due to adaptations, but rather just due to random chance. You randomly chose out five to survive and those five ones might have all been black or all white. So what we saw is the same sort of change happening, but again, the key thing is due to random chance.
The other thing... Another thing that we need to notice is that genetic drift is really going to only occur in small populations. So again, when you chose out 50, you don't really get a change to happen.
When we only chose out 5, that's where change started to happen. Think about it with the probability of flipping a heads or tails. It's a 50-50 shot. So if I asked you to flip a coin 100 times, do you think you could ever get 100 heads in a row? Probably not.
probably end up with about a 50-50 between the two. But if I said, okay, flip a coin only two or three times, could you get all heads or all tails? You probably would say, yeah, it's more likely.
That's because when it comes to probability and random occurrences, it is more likely to get a sway in smaller sample sizes, or in this case, smaller populations. So how can this sort of change happen in the real world? What things are going to cause this random change in allele frequency? One way is going to be through something known as a bottleneck effect. So if you think about the neck of a bottle, it's very narrow.
So this is going to be some sort of event that's going to cause my population to narrow or reduce in size. So imagine I have a bottle here with different colored beads that are going to simulate or represent different genes inside my population. Well, let's say that I let only a few through the neck of that bottle. In this case, a couple of blue make it out, one orange, the red ones don't.
So everyone that's left inside that bottle dies. They vanish. So now when this population repopulates...
and reproduces, eventually my new population looks nothing like the original. I've had a change in allele frequency. So evolutionary change has occurred.
Remember before we had equal amounts of red, blue, and orange. Now we have mostly blue. And it's not because blue was better adapted. They just got lucky and passed through that event.
So a bottleneck effect is going to be any event that reduces the size of a population small enough. Okay, remember it's got to be small. And therefore it's going to reduce the variation of the gene pool. I now have less alleles in my population.
But But again, this is not good because it's not like with natural selection the blue ones are adapted. Maybe the blue ones are less adapted. We don't know.
But either way, evolutionary change has occurred. So a real-world example of this would be with the Florida panther. What we've seen is that the gene pool of the Florida panther has been reduced because of a bottleneck effect.
The bottleneck effect in this case was humans. We've come in, we've encroached on their land, and through hunting and traffic and through just competition between the males killing each other, there's been a reduction in their gene pool. So evolution has been occurring in that sense. but not in a good way. It's not because they're more adapted, it's just because of a bottleneck effect.
Another way we can get genetic drift to happen is through something known as the founder effect. So if we think about what the term founder means, who's the founder of Facebook, Mark Zuckerberg, well he's the person that started the company. So the founder effect is when let's say we have our population of greens and blues here, let's say a small amount of them are the founders of a new population for whatever reason.
Maybe they got separated, maybe they decided to leave and start a new colony. But either way, so now my new population here, when they reproduce, looks nothing like the original. Now I have more blues than greens.
This was not because blues were more adapted. It's just because the new population started off different from the original because, again, it was a small sample size. So the founder effect is going to be when a new population is started or founded by a small number of individuals.
Again, it's got to be small, resulting, again, in a loss of genetic variation. So another real-world example of this is in humans. There are actually a group of humans that...
that settled German people who settled in Pennsylvania here in the United States, and they started the Amish populations in Pennsylvania. And what we notice is that there is a higher than normal percentage of people with this condition here known as polydactylism, having six fingers or six toes. Now, it's not because for them it's beneficial to have that.
It's just because the founders of that population, when only a few hundred people started it, some of them had that condition so that when they reproduced and started that colony, we see that sort of trait more abundant in that population. So, one thing to realize about genetic drift is it's not as good as natural selection because it's not necessarily selecting for the best trait. It's just through random lucky chance. Another way we can get this happen, so another way we can get a change in allele frequency is through what we know as gene flow.
So, this is not the same as genetic drift. Think about this word flow. To flow means to be able to move. So in gene flow, what's going to happen is we can get alleles moving into and out of my population.
So here's my starting population. What if some red ones decide they're going to move in? So now I've got a change in my allele frequency. That's evolution. Maybe some of my blue ones move out.
that also can change my allele frequency. So you notice my starting population looks nothing like my ending population. So again, evolution has occurred. So with gene flow, gene flow's gonna be immigration and emigration, moving in and moving out.
Of individuals, it's gonna result again in a change in that allele frequency. So to stop and think for a second, does gene flow increase variation or does it decrease variation like what happens with natural selection and with genetic drift? And really, it could happen either way.
You saw here how we could increase variation by introducing new alleles in, or if some of them leave, then we can decrease variation. Either way, we call this evolutionary change because we're getting a change in the number of alleles inside that population. One last way we can get evolution to occur is through something known as sexual selection, or sometimes referred to as non-random mating.
So let's again go to my beetle population or insect population here and say we have equal amounts of green and equal amounts of blue. What might happen in this population is that for some reason, individuals start choosing, let's say, blue ones as mates. They only want to reproduce with the blue ones. So over the course of time, we have a change in allele frequency. There are more blues than greens.
But it's not because the blues are more adapted. It's just for some reason that trait is being selected for in reproduction. So with sexual selection, we're going to get those changes to happen due to non-random mating.
They're not randomly choosing mates. They're looking for a specific trait. An example of this, my favorite example, is in the case of peacocks. If you've ever seen a male peacock, peacock before, you see its beautiful elaborate tail and you might think to yourself, how did this occur? And even Darwin might look at this and say, there's no way that natural selection would allow this to happen.
They're slower, it's a lot easier to catch them if you're their predator. So how is this being selected for? How did this evolve? And it was actually through sexual selection. What it turns out is peahens, the females, prefer males with more beautiful elaborate tails because it signifies to them health.
So they want those genes to be passed on to their offspring. So over the course of time, we can get that evolutionary change to happen. happen.
So if we revisit our less than essential question, how can this evolutionary change occur outside of natural selection, you should be able to by now think about how genetic drift or these random changes in allele frequency can occur. Gene flow can just be the movement of these alleles into and out of a population, or just through sexual selection, non-randomating how certain individuals will choose for certain traits to reproduce with, how all these things can cause evolutionary change. If you can do that, I think you're in great shape. You got it. If not, feel free to go back and watch certain parts.
But I thank you guys so much for watching.