CompuServe Thread

Don I have reviewed information in Vertebrate Paleontology and Evolution by Robert L. Carroll for references to specific cases of gradual evolution within a species. Sadly, I must report that no clear and decisive evidence was found. However, there is some very interesting commentary that is germain to our discussion. Haldane, in 1946, established the darwin (d) as a unit for measuring evolutionary change. It is defined as a change by a factor of e per million years. The apparent rate of change differs significantly over different time ranges. A rate of 0.1 darwin is common for vertebrates measured over a period of million years. For a period of 10 million years, the rate is about 0.02 d. Measures of change during the Pleistocene glaciation averages 4 d. Contrast that to the 60,000 d resulting from laboratory selection experiments The conclusion drawn from this is that species remain stable after an abrupt change. In fact, the fossil record supports episodic changes, often coupled with dislocations of a population from its customary habitat or local environment. While not exactly cataclysmic, the disruptions may markedly decrease population, isolate groups, or remove serious competitors. Nearly all published rates of evolution refer to a small number of characters, not necessarily indicative of the entire organism. Molecular evidence suggests that only a small portion of the genome is concerned with anatomical features. An example: Between humans and chimpanzees, the amino acid sequence of 12 varied proteins differ only by 1 percent. Hmmmm. To end…"If a single word is to be used to describe evolutionary rates, it is certainly neither gradual nor punctuational, but irreg- ular or opportunistic." For those seriously interested in Evolution, the above mentioned text is a must read. Not for the timid. Michael

In the March Scientific American, there's an "Overview" of the "punctuated equilibrium" theory of how species evolve. Apparently there's a good little controversy amongst the paleontologists about whether species usually change gradually or usually change suddenly. Apparently there's no controversy over "they change at different rates at different times" and "lots of species survive because they're lucky, not because they're strikingly more adapted to the environment than other species."