Natural Selection A mechanism that adapted organisms use to survive and produce a greater number of viable offspring.
In a beetle population there are some brown ones and some black ones. The brown beetles can camouflage better than the black colored beetles. This is because of genetic variation.
The black beetles struggle to survive in their current environment and many of them are getting eaten by predators. Many black beetles are not able to survive long enough to reproduce.
Now the surviving brown beetles are able to reproduce more and have brown colored baby beetles. They are able to survive long enough to reproduce unlike the black beetles and they pass their beneficial traits to their offspring.
Over time, there can be a change in the gene pool if this continues. Then, the beetle population in this environment will all be brown colored.