|
Mountaineer -> RE: Stasis as criticism of evolution (2/11/2008 10:30:29 PM)
|
I'm not sure how someone can think this is evidence against evolution. First of all, there are several species of horseshoe crabs. Second, what is meant by "it's a good plan" is referring to the body 'plan'. The shape of the crab has remained largely unchanged for a half billion years. No change to the phenotype does not necessitate no change to the genotype. Think of how we look similar to our ancestors from 10,000 years ago yet there are some fundamental changes. Lactose tolerance comes to mind first, but there are plenty of other examples (for instance, the fossil of an American Indian would be indistinguishable from that of a European a few hundred years back, yet the European had a higher resistance to small pox). The idea that this presents a problem for evolution because mutations occur at regular intervals and rates is boggling. First, many mutations are either neutral or deleterious. The neutral ones are a non-factor for obvious reasons. The deleterious ones are weeded out by natural selection. Second, beneficial mutations are quite evidently extremely rare for the horseshoe crab. In other words, what leads to more adaptability would need to be extremely specific at this point due to the fact that the crab is already so highly adapted to its environment. But again, it's important to remember that a beneficial mutation need not necessarily have a result in the phenotype. It is a true stretch to claim stasis presents any issues for evolution. It would be surprising to discover a majority or even a relatively large number (1%, say) of species that remained unchanged for such long periods of time, but to find a few is not so surprising. All that is needed is a relatively stable environment. This means that when the Earth faces large scale changes to most of its species that not every species will be forced to go through a period of great change. This is because a horseshoe crab doesn't necessarily need to change its shape if it can eat various species of clams and worms that are going through great changes. In other words, its environment hasn't actually changed. It is still obtaining a food source and the method it currently uses is the best available.
|
|
|
|