Evolution and Natural Selection
|
|
Snurfle Island Virtual Lab
Evidence - FAMED
Fossil Evidence
Anatomical Structures
Sharks and dolphins are not closely related. However, dolphins and humans are. One piece of evidence that supports the idea that dolphins and humans come from a common ancestor is their limbs. Dolphins have front flippers that help reduce friction in water as they swim. However, by looking at the bones within the flipper, it is easy to see how similar in structure it is to the human arm. This is one of the ways scientists use to classify organisms into groups that branch off from a common ancestor.
|
Molecular Evidence- DNA
All life carries the same DNA components, and scientists have found the same DNA sections in bacteria as in humans. Biologists have put patches of DNA controlling one part of an animal into another animal to find that it performs the same job. For example, a DNA section that controls how eyes are formed in mammals like mice was put into a fly, and it produced a normal eye. Further evidence for how DNA supports evolution is reflected in closely related organisms. The closer the relation, the more similar their DNA. The DNA sequences of humans and chimpanzees are about 97 percent identical. |
Embryonic Evidence
Humans, dogs, snakes, fish, monkeys, eels (and many more life forms) are all considered "chordates" because we belong to the phylum Chordata. One of the features of this phylum is that, as embryos, all these life forms have gill slits, tails, and specific anatomical structures involving the spine. For humans (and other non-fish) the gill slits reform into the bones of the ear and jaw at a later stage in development. But, initially, all chordate embryos strongly resemble each other.
|
Distribution of Organisms
Another clue to patterns of past evolution is found in the natural distribution of related species. It is clear that major isolated land areas and island groups often evolved their own distinct plant and animal communities. For instance, before humans arrived 60-40,000 years ago, Australia had more than 100 species of kangaroos, koalas, and other marsupials but none of the more advanced mammals such as dogs, cats, bears and horses. Land mammals were entirely absent from the even more isolated islands that make up Hawaii and New Zealand. Each of these places had a great number of plant, insect, and bird species that were found nowhere else in the world. The most likely explanation for the existence of Australia's, New Zealand's, and Hawaii's unique creatures is that the life forms in these areas have been evolving in isolation from the rest of the world for millions of years.
|