Evolution explains how the planet's present-day species developed from earlier, different species through natural selection. It works because of the genes, sections of DNA, found in the cells of all living things. Organisms with similar genes belong to the same species, but many variations in genes can exist within that one species. Dogs, for example, from tiny Chihuahuas to Great Danes, are all variations of the same species, Canis familiaris. As we mentioned earlier, fossils provide evidence for evolution. More evidence is found in the existence of what we call "vestigial organs" in many animals. These are small, seemingly useless organs that were once useful for tasks an organism no longer performs. For example, some snakes still have a tiny bone tip on their bodies where an earlier species had feet. Also, the fact that our human DNA is very similar to that of all other living organisms on Earth, from amoebas to turkeys to poison ivy vines, indicates that everything has evolved from the same place. How do vestigial organs provide evidence for the theory of evolution?

A
Vestigial organs show differences between our DNA and the DNA of amoebas.

B
Vestigial organs show traits that a species once needed to have to perform certain tasks.

C
Vestigial organs show the variation in genes that can exist within one species.

D
Vestigial organs show how many cells organisms of a species once had.