Trait variation and environmental changes

0:00- [Instructor] Look at the grasshoppers in this field. Some grasshoppers are green while others are brown. This difference in the color can dramatically affect their ability to survive and reproduce. Let's find out how. Now, before we get into that, let's first quickly review the idea of traits.

0:16Remember that a trait is any characteristic of a living organism. For example, eye color, hair texture, whether you have a dimple or not. All examples of traits. A cheetah's spot patterns and the dog's coat texture, they're all traits. The combination of traits is what makes an individual unique.

0:37Now, inherited traits are characteristics passed down from parents to offspring, like the grasshopper's color. That's an inherited trait. It's passed down from the parents to offspring, right? And trait variation is the fact that individuals in the population don't inherit the same traits.

0:54Again, just like the colors in the grasshopper, not all are green, some are green, others are brown. That's a variation in the trait. Okay, let's go back to our green field now. Suppose a bird is flying over looking for lunch. Which grasshoppers do you think are easier to spot, the green ones are the brown ones?

1:13Well, that's easy to answer. I mean, the green ones are even harder for us to spot over here because they blend in so nicely with the green field, right? In contrast, the brown ones, well, they're much easier to spot. This means the green color works in the grasshopper's favor.

1:31They are more likely to survive and reproduce in this environment. So, traits like these that help an organism survive and reproduce, we call them advantageous traits. So, the green color over here is an advantageous trait for grasshoppers over here. What about the brown color?

1:51Well, this color is making them easier to spot. They're becoming easier prey, and therefore, this color is making them harder to survive and to reproduce. So, such traits that make it harder for an organism to survive and reproduce, we call them disadvantageous traits.

2:10So, in this particular example, the brown color is a disadvantageous trait for the grasshoppers. So, does this mean for grasshoppers, green is always the advantageous trait, green is the best trait to have? No, not necessarily. Why not? Suppose a drought hits.

2:30Over time, the field dries out and the grass turns from green to brown. Now look, it's the brown grasshoppers that blend nicely into this brown grass, right? But it's the green ones that are now easy to spot. So, look at what happened. Now, the brown color has become the advantageous trait.

2:56It's helping them survive and reproduce because it's harder to spot them, and the green color has now become a disadvantageous trait because now because they can be easily spotted, they can easily become lunch, and so it's harder for them to survive and reproduce now.

3:13So, why did this happen? Why did the green suddenly become a disadvantageous trait? Well, not because something in the grasshoppers changed, but because the environment itself changed. So, the lesson here is that there's no single best trait. Whether a trait is advantageous or disadvantageous completely depends on the environment.

3:39A trait that helps in one environment could be very harmful in another. Okay, so now, let's think about this question. What if there was no trait variation among these grasshoppers? What if all the grasshoppers over here had the same color? Let's say green. Well, at first, it looks like that's awesome, because look, all the grasshoppers have advantageous traits, which means very high chance of survival, right?

4:14Not really, because when the drought hits, look, all of them now have disadvantageous traits, which means their entire population is at risk. So, we can now see why variation in traits are so important. Because some grasshoppers were already brown to begin with, they were already well-suited for the drought conditions.

4:44This is why trait variation is so important for the survival and not just survival, for their ability to reproduce and continue to grow their population, for example. It's so important because the trait variation acts like a buffer. It ensures that when the environment itself changes, and they always do, sometimes slowly, sometimes quickly, but the environment will always change, and when it does, the trait variation ensures that there will always be some individuals, or there's a high chance that there'll be some individuals or a group of individuals which will already have some traits that would be advantageous in that new environment.

5:28And so the whole population is more likely to survive through the different environmental changes. That's pretty awesome if you think about it. So, let's summarize what we've learned. An advantageous trait helps an organism survive and reproduce, and a disadvantageous trait makes it hard for an organism to survive and reproduce.

5:52And whether a trait is advantageous or disadvantageous depends on the environment. A trait that's advantageous in one environment could become disadvantageous in another. And that's why trait variation matters, because it increases the chances that some individuals in a population will survive when conditions change.