[quote]wufwugy wrote:
Chris (NZ) wrote:
uh what? what, then, is responsible for evolution?
Random genetic mutation.
randomness? is there any proof that our genes arbitrarily mutate?[/quote]
Yup, loads of proof. Here’s a brief intro to mutations and natural selection:
[i] At the genetic level, the signs of natural selection are surprisingly subtle.
More knowledge doesn’t necessarily translate into less confusion. In 1953, when James Watson and Francis Crick discovered the double-helix structure of DNA, biologists were poised for all the pieces of evolutionary theory to fall quickly into place. Darwin had shown how natural selection could transform anatomy and patterns of behavior, and now scientists looked forward to detecting the fingerprints of natural selection at the molecular level. But it turned out that natural selection was not the only force that could significantly alter DNA, and no one knew how to identify the source of any given change. It has taken decades to figure out a way.
This predicament took many biologists by surprise, because once the structure of DNA was understood, they thought they had a good handle on how natural selection works, Researchers determined that a gene consists of a stretch of DNA–a sequence of molecules called nucleotides that serves as a blueprint for the synthesis of a protein. If the nucleotide sequence somehow mutates, it may produce a different protein. The new protein may turn out to be so defective that the individuals who inherit the mutation die or become infertile; either way, such harmful mutations may end up being almost completely weeded out of a species. But some mutations may give their owners a reproductive edge, and before long those mutations will become widespread–even universal–in a species. In the course of thousands and millions of years, a series of such beneficial changes could thus rework the genome of a species.[/i]
Aaaaaaand nope, not exactly randomly:
Another problem was that the models of evolution used by biologists for detecting natural selection assumed that mutations were random, which is not entirely true. For example, the chemical nature of DNA makes certain nucleotides more likely to mutate into certain other ones.
Here’s another little blurb, less technical this time:
[i]A gene mutation is a permanent change in the DNA sequence that makes up a gene. Mutations range in size from a single DNA building block (DNA base) to a large segment of a chromosome.
Gene mutations occur in two ways: they can be inherited from a parent or acquired during a person?s lifetime. Mutations that are passed from parent to child are called hereditary mutations or germline mutations (because they are present in the egg and sperm cells, which are also called germ cells). This type of mutation is present throughout a person?s life in virtually every cell in the body.
Mutations that occur only in an egg or sperm cell, or those that occur just after fertilization, are called new (de novo) mutations. De novo mutations may explain genetic disorders in which an affected child has a mutation in every cell, but has no family history of the disorder.
Acquired (or somatic) mutations occur in the DNA of individual cells at some time during a person?s life. These changes can be caused by environmental factors such as ultraviolet radiation from the sun, or can occur if a mistake is made as DNA copies itself during cell division. Acquired mutations in somatic cells (cells other than sperm and egg cells) cannot be passed on to the next generation.
Mutations may also occur in a single cell within an early embryo. As all the cells divide during growth and development, the individual will have some cells with the mutation and some cells without the genetic change. This situation is called mosaicism.
Some genetic changes are very rare; others are common in the population. Genetic changes that occur in more than 1 percent of the population are called polymorphisms. They are common enough to be considered a normal variation in the DNA. Polymorphisms are responsible for many of the normal differences between people such as eye color, hair color, and blood type. Although many polymorphisms have no negative effects on a person’s health, some of these variations may influence the risk of developing certain disorders.[/i]
I think your question might have been going along the lines of “if it’s good for us to be stronger, then our genes will mutate accordingly to make us stronger.” This isn’t the case. Mutations occur, if they’re beneficial, they’ll spread throught the population down the generations; if they’re detrimental, the individual will most likely not reproduce and the mutation dies with him/her.