A characteristic that helps an animal survive is called an adaptation.
Let's take a frog, for example.
It has strong leg muscles to be able to jump out of the water, snatch prey, and return quickly. It has cameoflague to hide itself from predators and sometimes even poison. It has a see-through eyelid of sorts that acts like goggles to let it see underwater and still keep debris out of its eye...et cetera.
As he traveled, Darwin noticed three distinctive patterns of biological diversity: (1) Species vary globally, (2) species vary locally, and (3) species vary over time. Darwin noticed that different, yet ecologically similar, animal species inhabited separated, but ecologically similar, habitats around the globe.
