Evolution and natural selection biology lesson for kids: 1st, 2nd, 3rd, 4th, 5th, 6th and 7th grades biology lesson.
Life on Earth is constantly changing. Over thousands and even millions of years, the many species of plants, animals, and other organisms on this planet accumulate changes so that they do not look or behave the same as they once did. This change in a species over time is called evolution, and it happens by way of another process called natural selection.
In order to understand how evolution and natural happen, let us take a look at a classic example. Although whales and dolphins spend their entire lives in the water, they are not fish. In fact, they are mammals, just like humans are: they breathe air, have very tiny hairs, and even produce milk for their young.
Millions of years ago, a species of four-legged mammals started spending a lot more time in the water. Here’s where natural selection comes in. Variation, especially genetic variation, is crucial for this process to happen. The individuals who, because of their genes, were better able to swim and get to their food in their aquatic environment were more likely to survive and mate, passing on their genes to the next generation.
This is where the concept of “survival of the fittest” comes in. This doesn’t mean the strongest will outlive the weakest, though. What it means is that the individual with the traits that are best suited to the environment will be more likely to live on and produce its own offspring. Said another way, natural selection isn’t like Mother Nature is deliberately pointing her finger and choosing who would survive; rather, natural selection is the, well, natural result of specific traits being better suited for the environment. The ancestors of whales and dolphins had to lose the traits that made them suited for life on land, and new traits were selected for to make them better able to survive in water.
Maybe one of them had really short fur while everybody else had longer fur. This shorter fur would have allowed them to swim without as much drag. So, the ones that had longer hair were more likely to be caught and eaten by predators, while the one with shorter hair survived, and could mate. It had more babies, and the babies with short fur had more babies, until short fur spread through the entire species, and, eventually, the species’ hair got so short it was almost impossible to see.
Over time, new traits like these accumulate, and can result in some drastic changes. The ancestors of whales and dolphins became more streamlined, so they could swim more easily. Their legs got shorter, and even turned into fins. Their nostrils even moved from the front of their snouts to the top of their heads, so they could breathe without lifting their heads too far out of the water.
Evolution is very important for life to survive, especially when the environment changes, or when the species enters a new environment. Without it, no life on Earth would be able to stay around for long, in this ever-changing world.