Natural selection is a big part of how species change and evolve over time. It happens through some important ideas.

First, there are differences inside a group of living things. For example, in a group of beetles, some are green and some are brown. These differences often come from genetics, which is like the instruction manual for how living things are made.

Next, these beetles have to compete for what they need. They are searching for food and partners to mate with. If there are predators around, they might see the green beetles more easily against a brown background. This puts the green beetles in trouble.

Then, we have the idea of "survival of the fittest." This means that the brown beetles are more likely to live longer and have babies. They pass their helpful traits to the next generation. Over time, we will see fewer green beetles and more brown beetles in the population.

Lastly, this slow change is called adaptation. If the environment changes, like when trees are cut down, what was once helpful may not be so good anymore. For instance, if the background becomes lighter because more sand is visible, the green beetles might start to do better again. This shows how natural selection is always at work, changing species over time.