Also, from Jan 06 issue of Science,iansmith said:All species evolve but not all evolution is perceivable in human life spam.
Species with smaller generation time will appear to evolve quicker. The best example are bacteria vs. human. Human have a 20-30 years generation whereas bacteria have 20-30 minutes generation time. So over 20-30 years a specie of bacteria will accumulate more genetic variation than a human.
and also, another quoteA favorite, if unlikely, subject for evolutionary studies is the
small fish called the stickleback. Repeatedly, sticklebacks have
moved from the sea into fresh water. When that happens, the fish
shed the rather heavy armor plates that protect them from marine
predators, freeing themselves to enjoy la dolce vita fresca. New species have been generated in each invasion,
always in the same way: by rapid evolutionary selection of the same rare and ancient gene.
This year field biologists recorded compelling examples of that process, some of which featured surprisingly rapid evolution in organisms' shape and behavior. For example, birds called European blackcaps sharing breeding grounds in southern Germany and Austria are going their own ways—literally and figuratively. Sightings over the decades have shown that ever more of these warblers migrate to northerly
grounds in the winter rather than heading south. Isotopic data revealed that northerly
migrants reach the common breeding ground earlier and mate with one another
before southerly migrants arrive. This difference in timing may one day drive the two populations to become two species. Two races of European corn borers sharing
the same field may also be splitting up. The caterpillars have come to prefer different plants as they grow—one sticks to corn, and the other eats hops and mugwort—and they emit different pheromones, ensuring that they attract only their own kind. Biologists have also predicted that these kinds of behavioral traits may keep incipient species separate even when geographically isolated populations somehow wind up back in the same place. Again, examples have been few. But this year, researchers found that simple differences in male wing color, plus rapid changes in the numbers of chromosomes, were enough to maintain separate identities in reunited species of butterflies, and that Hawaiian crickets needed only unique songs to stay separate. In each case, the number of species observed today suggests that these traits have also led to rapid speciation, at a rate previously seen only in African cichlids.
Other researchers have looked within animals' genomes to analyze adaptation at the
genetic level. In various places in the Northern Hemisphere, for example, marine stickleback fish were scattered among landlocked lakes as the last Ice Age ended. Today, their descendants have evolved into dozens of different species, but each has independently lost the armor plates needed for protection from marine predators. Researchers expected that the gene responsible would vary from lake to lake. Instead, they found that each group of stranded sticklebacks had lost its armor by the same mechanism: a rare DNA defect affecting a signaling molecule involved in the development of dermal bones and teeth. That single preexisting variant—rare in the open ocean—allowed the fish to adapt rapidly to a new environment.