Biology
Evidence for evolution
Fossils, similar bones, and shared body plans show that all living things are related to each other.
That life has changed over many millions of years is not just a guess. Researchers rely on clear evidence that can be read from fossils, from body structure, and from many further traces. Together this evidence forms a consistent picture of the kinship of all living things.
Fossils as witnesses of time
Fossils are the petrified remains or imprints of living things from the past, for example bones, shells, or the print of a leaf in stone. Because they lie in layers of rock, their age can be worked out. As long as the layers have not been shifted by movements of the ground, this holds: older species lie deeper, younger ones further up. In this way one can trace how living things changed step by step.
Homologous organs
If you compare a human arm, a bat's wing, and a whale's flipper, you find the same bones in the same arrangement: first one strong upper arm bone, then two forearm bones, then the many small hand bones. Upper arm, forearm, and hand: you find these three sections in all three of them, even though one of them grips, one flies, and one swims. Such organs with the same basic plan are called homologous. They point to a common ancestor from which all three inherited the plan.
After 0 generations: 50 % camouflaged
The environment selects, the beetle does not decide: camouflaged beetles are eaten less often.
Similarities in the body plan
Early in development, too, many animals resemble each other strongly. The embryos of a fish, a chicken, and a human look astonishingly alike at a middle stage of development. The more closely two species are related, the longer this similarity lasts. The shared body plan reveals the shared origin.
Many pieces of evidence form one picture
No single piece of evidence stands on its own. Fossils, homologous organs, and similar body plans all point in the same direction. Today a fourth piece of evidence joins them: the comparison of DNA, the genetic material. The more alike the DNA of two species is, the more closely they are related. When quite different traces lead to the same result, the explanation becomes very strong. That is exactly why the kinship of living things is so well supported.
Exercises
0 of 6 solvedTime to try it yourself. You can't break anything, every attempt counts.
What are fossils?
What do homologous organs like arm, wing, and flipper point to?
The homologous organs arm, wing, and flipper are compared with each other. How many organs is that?
Match each piece of evidence for evolution with the right example.
In a deep layer of rock lies a fossil that is 200 million years old. A second one is 50 million years younger. How old is the second one in millions of years?
Order the fossils by their age, from oldest to youngest. Use how deep they lie in the rock.
- 1Fossil in the deepest layer of rock
- 2Fossil in the topmost layer
- 3Fossil in a middle layer