Devolution in biology, sometimes also called degeneration, is a theory that suggests that over time, some species or organisms may evolve to become less complex or advanced than their ancestors or their counterparts. This could happen when an organism loses certain features or abilities or when mutations occur that result in a loss of function or adaptation.
Think of it like playing a game of Jenga. You and your friends build a big tower by stacking blocks one on top of the other. But if you start removing blocks from the bottom, the tower may become unstable and start to crumble. In biology, "removing blocks" can happen when an organism stops using certain features or abilities, or when mutations occur that cause certain functions to disappear or become less efficient.
In some cases, devolution can cause an organism to become less adapted to its environment, which can ultimately lead to its extinction. For example, in the ocean, some fish species that once had eyes to help them navigate in the dark depths eventually lost their sight because they no longer needed it in their new environment. But then, as the water began to clear up again, these fish became more vulnerable to predators and had a harder time finding food.
That being said, it's important to understand that not all organisms experience devolution. In fact, many continue to evolve and adapt to their environment, developing new traits and abilities to better survive and thrive. Devolution is just one of many factors that can influence the way species have evolved over time.