Traits and fitness

0:00- [Instructor] You look very different from your friends or your siblings, right? Maybe your hair is curlier or your earlobes are shaped differently, or maybe you have dimples when you smile. In fact, even identical twins will have some differences. And it's not just in humans.

0:16The same is true for animals and plants. But the question is, why do individuals of the same species often differ from one another? Well, to answer this, we need to understand the idea of traits. Okay, so what's a trait? Think of traits as any characteristic of a living organism.

0:37For example, in humans, traits could include eye color or hair texture or, you know, the shape of your earlobes or the fact that you have dimples and so on. Other animals can have traits too. For example, a cheetah's spot pattern is a trait. The coloring of a frog is a trait.

0:54Dog's coat or fur texture, all examples of traits. And by the way, traits not only describe what an organism looks like, it's not just about looks. It can also be about how their bodies function or even how they behave. For example, a frog's ability to breathe through its skin, that's a trait.

1:14A dog wagging its tail when it's happy or it's excited, that's a trait. So any characteristic of a living organism, that's a trait. And it's this combination of the traits that make you or any individual unique. Okay, so where do these traits come from? Well, traits can either be inherited, can be acquired during your life, or they can be learned behaviors.

1:42Let's look at each one in detail. Let's start with the inherited traits. These are characteristics that are passed down from parents to offsprings during reproduction. For example, hair texture is an inherited trait. Dimples tend to be an inherited trait. These traits are directly passed down during reproduction.

2:05You don't have to do anything to get these traits. That's why they're called inherited. And of course, they can also be further passed down, you know, to the future generations. And animals inherit traits too. For example, the spots on a deer, that's an inherited trait.

2:21The deer must have inherited that spot pattern from its parent during reproduction. And of course, they can be also passed down to future generation. Okay, next up, acquired traits. What are these? Well, acquired traits are physical changes that happen during an organism's lifetime.

2:43For example, imagine you scrape your knee while riding a bike and later develop a scar. That scar is an acquired trait. You acquired it during your lifetime. It was not inherited. It was not passed down from your parents. No, no, no. It was acquired. Similarly, a guitarist who practices for years could develop calluses on their fingertips.

3:05Those calluses are also acquired traits. An athlete may develop strong muscles through training. Acquired traits. Notice none of this was passed down. They were all physical changes that happened during your lifetime. Acquired traits affect the individuals, but they are not passed down to the next generations.

3:28They're not inherited. Okay, that brings us now to the third category, learned behaviors. Learned behaviors are behaviors or skills that an organism gains through experience or by watching others. For example, think about riding a bike. It's a skill that you learn through experience, for example.

3:50Think about reading or cooking or writing. All experiences, they're all learned behaviors. And animals have learned behaviors too. For example, a young dolphin learns to hunt fish by looking at its mother, for example. It's a learned behavior. Can learned behaviors be inherited?

4:10No. Nobody's born knowing how to ride a bike or how to read or cook or how to hunt, for example. They are learned behaviors. They are learned through experiences. They are learned by watching others. So they too cannot be inherited. Okay, so both of these cannot be inherited, right?

4:31But what's the difference between them? Well, notice acquired traits are physical changes; scars, big muscles, calluses. Whereas learned behaviors are, well, behaviors or skills that you learn; riding a bike or for example, reading or hunting. But wait a second, why do we even care about traits in the first place?

4:52Well, because they help us understand an important concept in biology, the idea of fitness. Now in everyday life, fitness might make us think about exercise or muscles or sports, but in biology, fitness means something different. Biological fitness is about how well an organism survives and reproduces.

5:14For example, let's say there are two groups of animals living in the same habitat, but one group has inherited an especially keen eyesight. That means they can spot dangerous sooner and they can find food more easily. So this specific trait can increase their chances of survival and increase the chances of having offsprings compared to the other group.

5:41And so because of their sharp eyesight trait, they're more likely to have more offsprings and they're more likely to pass down that trait in the future generations. So in biology, we would say that these animals have a higher fitness compared to these because they survived and reproduced more successfully.

6:05So you can see traits help us understand fitness and it helps us understand chances of, you know, a population survival and the chances of a population reproducing and so on. Okay, now coming back to our original question, why do people look different from one another?

6:27Well, because we have inherited different traits. For example, some may inherit curly hair while others inherit straight hair. Some may inherit attached earlobes while others inherit detached ones, and so on. So look, as a result, even within the same species, individuals differ from one another in their inherited traits.

6:54And that's why we are all different. This idea is called trait variation. And this is true even within siblings, even within identical twins. They don't inherit exact same combination of traits. That's why there's trait variation even within a family. And again, this is not specific to just humans.

7:19Trait variations exist in all kinds of populations. So for example, in litter of puppies, some may have inherited different coat patterns. In a field of flowers, some may inherit slightly different petal shapes or colors. They're all examples of trait variation.

7:37It's the trait variation that makes every single individual unique. All right, so let's put it all together. A trait is any characteristic of a living organism, and the traits can either be inherited, meaning they're passed down from parents to offsprings during reproduction and they can be further passed down to future generations, or they can be acquired.

8:02These are physical changes that happen during an organism's lifetime. Or they can be learned behaviors or skills that you gain through experience or by watching others. Acquired traits and learned behaviors cannot be passed down to future generations. They cannot be inherited.

8:20And these traits, especially the inherited traits, help us understand the idea of fitness, which is not about being physically fit or about exercise or anything, but it's about how well an organism survives or reproduces in its environment. And finally, trait variation refers to the fact that every individual differs from one another in their inherited traits.