Jake Young is a 
Scientists have just documented (another) inheritable change in a species that occurred in response to a change in the environment -- in this case a parasite. Hence they have observed the process of natural selection.
In the latest issue of Science, Charlat et al. observed that the sex ratio in a species of Polynesian butterfly -- Hypolimnas bolina -- changed from 99:1 favoring females to parity in less than 10 generations. The sex ratio favored females because there is a parasite -- a bacteria called Wolbachia -- that selectively kills the male embryos.
However, in the space of ten generations the scientists observed that some of the butterflies had restored parity between males and females. Clearly the butterflies had evolved some resistance to the parasite during that period. They also must have evolved it incredibly quickly in comparison to most known examples of natural selection.
To confirm that the restoration of parity was because of a inheritable change in the butterflies' genes, the researchers back-crossed the resistant butterflies with butterflies that were not resistant to the parasite. They found that they could restore susceptibility to the parasite within three generations and that the sex ratio returned to 99:1.
This data confirms that the switch in the sex ratio is the result of a inheritable genetic change in the butterflies that allowed the male embryos to resist to the parasite. In short, it confirms the process of natural selection.
Charlat has the money quote:
Natural selection typically moves very slowly, sometimes over hundreds of years, they said, but when under severe attack, this process was accelerated."It is the speed of the process that demonstrates the intensity of the selection," Charlat said.
"The take-home message is that evolution can be really, really fast." (Emphasis mine.)
Comments
In the case of newly emergent polyploids, evolution can happen in about a day. That's pretty fast, when you think about it.
Posted by: Gork | July 13, 2007 10:37 AM
If you think about it, it makes sense that it happened so fast in this case: once a resistant male butterfly has the gene he's practically guaranteed to mate many times, which will all result in half resistant males and so on. very interesting
Posted by: MaxPolun | July 13, 2007 11:09 AM
Adaptation is even faster with viruses and bacterias. Hence our current problem with antibiotic-resistant strains which can arise within a few years of a new antibiotic coming out.
Posted by: romeo vitelli | July 13, 2007 12:24 PM