Natural selection is “a mechanism by which individuals inherit beneficial adaptations to create more offspring than others. There are four main principles that allow natural selection; variation, overproduction, adaptation, and descent with modification. There are countless examples of all these principles in the evolution of prokaryote, eukaryote, and most living organisms, but just to give an example here is how they all tie into reptiles turning into mammals. First, variation of these reptiles meant that there was a difference in the physical traits of each individual, even if just slight. This variation must have given a feature that was an advantage for that animal that allowed it to better survive in the environment, or an adaptation. Due to overproduction, survival of the fittest kicked in and only the strongest survived, and since this trait has an advantage it survives and then is able to reproduce. Then what is known as descent with modification comes as more individuals have this feature or trait every following generation. Natural selection like this is what led to the evolution of species from the start until today
There are many examples in the history of Mertens where selective pressures came into play with evolution. An example of when selective pressures could be seen was once when a huge volcano named “Terry” erupted on the supercontinent (on Mertens the only land is one huge island continent of 7.692 million km²). After the eruption, the neon yellow rat species which used to survive well in the bright jungle almost completely died out, however due to natural selection there were a few black rats with mutations who were able to survive in the now black and burnt jungle. This caused the individuals with the black fur trait to have higher fitness and due to evolution caused this trait to become dominant, which is what directional selection does. In the same explosion, the trees in the area were burned down, causing the green birds to not be able to hide in trees anymore to hunt land animals. Because of this, the birds had to turn to hiding next to rocks while hunting, however the rocks on Mertens were all black or white so only birds with white feathers and black feathers were able to hunt, survive, and reproduce. This is Disruptive selection as individuals at each end of the curve survive better than the ones in the center. Then for the next 100 or so years, the environment remained stable and nothing really happened, leading to stabilizing selection as the fittest bird and rats remained the fittest and kept reproducing
Now that you are an expert on evolution, go to "Witselonians Emerge" under the "LIFE" tab to learn about how our species came about due to it.