Oldest vertebrate fossil found in Australia, scientists say

Selected excerpts from above referenced link emphasis added

"Natural selection can maintain or deplete genetic variation depending on how it acts."

The most common action of natural selection is to remove unfit variants as they arise via mutation. [natural selection: differential reproductive success of genotypes] In other words, natural selection usually prevents new alleles from increasing in frequency."

"Natural selection can maintain or deplete genetic variation depending on how it acts. When selection acts to weed out deleterious alleles, or causes an allele to sweep to fixation, it depletes genetic variation. When heterozygotes are more fit than either of the homozygotes, however, selection causes genetic variation to be maintained."

"Balancing selection is rare in natural populations. [balancing selection: selection favoring heterozygotes] Only a handful of other cases beside the sickle-cell example have been found. At one time population geneticists thought balancing selection could be a general explanation for the levels of genetic variation found in natural populations. That is no longer the case. Balancing selection is only rarely found in natural populations. And, there are theoretical reasons why natural selection cannot maintain polymorphisms at several loci via balancing selection."

"Natural selection favors traits or behaviors that increase a genotype's inclusive fitness."

"The opportunity for natural selection to operate does not induce genetic variation to appear -- selection only distinguishes between existing variants."

Correct, but neither do individuals evolve independently of their populations.

Only rarely, if ever, would a gene change in an individual make it distinctly different without damaging its core design. What's far more likely is that a seemingly innocuous trait which was distributed within the population would begin to benefit reproduction (such as long haired mammoths) due to environmental change (like an ice age).

In this way, variation can occur all the time without having any direct benefit (or detriment) at all. It's only later, as populations press into different environments, or as the environment presses into them, that whatever variations match the environment will begin to accumulate in the population.

DISCUSSION OF THE PROBLEM

"The opportunity for natural selection to operate does not induce genetic variation to appear -- selection only distinguishes between existing variants."

The modified lottery model computes the probability that genetic variation is caused by random number picking events. It does this by first computing the ratio of [the number of numbers in subset of a set of numbers] to [the number of numbers in the entire set of numbers.] It then multiplies that ratio by the [total number of times numbers are picked at random from the entire set]. That product is equal to the probability that at least one number picked at random will be a number also found in the original subset.

Natural selection, itself, as described in my previous post appears to play no role whatsoever in influencing what numbers shall be picked at random. Natural selection influences only which of the picked numbers shall be subsequently maintained and which numbers shall be depleted.

However, which numbers are actually picked may be significantly influenced by which numbers have previously been picked and subsequently maintained. In that regard, the picking of numbers may not be a random process as is often alleged, since natural selection may actually indirectly influence which numbers are picked. Then this influence of natural selection, while not deterministic in itself, may play a major roll in influencing what does evolve as well as what doesn't.

Even that probability is not consistent across the board. Mutations in genes that are highly conserved throughout kingdoms -- anything involved in catabolism, for instance -- are very likely to kill the organism, if indeed it makes it beyond the zygotic stage. Other traits -- such as hair length in the mammoth example -- aren't as critical to the fitness of the individual, though one or another allele may be crucial for a population under different selective pressures. It may be possible to categorize the genome according to in what genes are more likely to survive mutation.

Wouldn't this phenomenom be one of the many characteristics of natural selection. Isn't it natural selection, whether the mutation causes a germline genome to die before meiosis, or it goes beyond the zygotic stage but the fetus dies before birth, or the baby dies before it matures and procreates, or what is subsequently procreated by that grown baby doesn't survive?




I tend to put all cosmetic (e.g., hair, eye, or skin color; size of skeleton, etc.) forms of evolution in a lesser category of evolution. My primary interest is the evolution of the mammal brain from CA to H, and CA to M. The complexity of even the simplest mammal brains over those periods is great enough that even now we cannot understand how they (let alone our own brains) actually performed their functions. I expect the differences in the respective brain specifying portions of genomes are likewise extremely complex.

An interesting article, somewhat related: http://www.guardian.co.uk/uk_news/story/0,3604,1105438,00.html

An interesting investigation! I'll follow it to see what they learn. Thanks.

Keep in mind that the common ancestor of humans and chimps was nor a chimp but something else. chimpanzees have there own 5 or 6 million year evolutionary history and that should be kept in mind when making comparisons.