Using the words "selection pressure" and "fitness", explain how natural selection causes populations to change over time.

Environment and competition is the leading cause of evolution. It's an instinct to want to live, but trying to survive is difficult when other animals have the same goal. An ecosystem is a cycle, but every generation of this ecosystem slightly changes, and so do the animals. Every bug that has fitness can start overpopulating the ecosystem, leading to a surge of resources for what preys on the bug. Now bird's population goes up, so do other animal populations. Or the bug becomes an invasive species, and birds are being hunted too often to decrease the population.

In a different scenario, bugs are evolving because of the selection pressure that the environment is giving them. The birds have become better over the generation, and now have a more suited beak to catch the bug off the ground. The bug population maybe be decreasing, but the ones who live through the crisis are populating with bugs that certain gene that helped them out. But it's not over, the bug population isn't declining but it wasn't as big as it was before. The bird will find more ways to find and capture the bugs. But then bugs will keep surviving through the selection pressure and become much harder to find since they figured out camouflage. The bug that was neon yellow was dying since they were easy to see. Now they can range from green to black to hide in the environment. Now the birds are facing the selection pressure, it's a cycle.

(look, im not good at gammar, so you should get this looked at before entering it. I put it through gammarly if that helps.

sorry to break it to ya but no one can answer your question it's just

jk but i am serious about the part that most people cant answer it beacuse you did not mention the section you are talking about. but it would if you added some detail and were a bit more specific.

in a chemical reaction, the atoms and molecules produced by the reaction are called products. no new atoms are created, and no atoms are destroyed. in a chemical reaction, reactants contact each other, bonds between atoms in the reactants are broken, and atoms rearrange and form new bonds to make the products.