mark kennedy said:
Assuming that natural selection is a quantifiable event, how is it measured?
Maybe someone who is more knowledgeable in the mathematics of biology can answer that. I am not sure if the darwin is the relevant unit or not.
Natural selection eliminates mutations through genetic drift most of the time.
Actually genetic drift refers to the fixation of alleles that is not due to natural selection. Natural selection is the most important driver of evolution, but not the only one.
Some times one will slip through and become inheritable even having an effect on the gene flow.
Please clarify. One [what?] will slip through [what?] and become inheritable?
What do you mean by "have an effect on the gene flow".
As far as I can see, none of this relates to natural selecion.
For millions of years they shared the same environment in equatorial Africa. The migration of apes from that area of our supposed ancestors was 1 million years ago. They, like virtually all the Homo species coexisted for extensive periods of time.
But note that it was the other Homo species that became extinct, not the chimpanzees. This indicates that competition was more intense among the various Homo species than between humans and chimpanzees. This is what we would expect when natural selection is applied to inter-species competition.
We now now what the divergance is,
Knowing what the level of divergence is is a different matter than understanding the process of divergence. You need to understand the process before you can make proclamations as to whether the level of divergence outruns the capabilities of the process.
The process is what I am concentrating on. I will leave the more mathematically inclined to figure out whether the process is capable of producing the observed level of divergence between chimps and humans in the available time-frame.
What I do know is that if you do not relate the level of divergence to the process of divergence, there is no framework within which to judge whether or not the level of divergence is possible or not.
So, back to process...
Changing alleles sounds like the genes have been altered
Correct. Note that the gene alteration occurs only in one cell/organism out of the total population. This means that none of the other members of the population have an altered gene. Just the one individual in whom the alteration occurs.
What this means for the population as a whole is that this gene now exists in the gene pool in two forms, each form being called an allele. One of these alleles is located in one member of the population. The other shows up in all other members of the population.
Now, supposing the altered gene confers a benefit on the one member of the population who carries it, how does it spread from a single member of the population to all the other members of the population?
while change in distribution means a rearrangment of existing alleles.
Possibly, but given your past record, I don't think so. Where are you supposing that this re-arrangement of existing alleles takes place?
Meiosis and recombination,
No, this is not the process of changing the distribution of alleles in a
population. And given your reverence for Mendel you should know better. Mendelian inheritance, when unaffected by natural selection, preserves the status quo distribution of alleles. It does not change it.
The recombination of genetic material in meiosis only affects the distribution of the alleles in the germ cells to the gametes, and the probable proportional distribution of those alleles in the offspring of the parents whose germ cells were transformed into gametes.
This recombination which takes place in individual parental germ cells is not sufficient to affect the distribution of alleles in the gene pool of the whole population.
Evolution is a
species-wide phenomenon. The change in distribution you need to look at is not the re-arrangement which occurs in meiosis, but the redistribution of alleles in the gene pool of the whole population.
How does that occur? Hint: it has nothing to do with dominanct and recessive alleles. Both dominant and recessive alleles can spread through a population when they are beneficial and can be purged from a population when they are harmful.
One of the goals of hybrids is to make the recessive traits more dominant.
No, the goal of hybridization is to bring together desirable alleles which currently exist in separate breeds. It seems to me that you are confusing "dominant and recessive" with "more or less prevalent" and even with "more or less beneficial". "Dominant and recessive" refers only to which allele is more likely to be expressed in an individual which is heterozygous i.e. carries both the dominant and recessive allele of a gene. In a population it is possible for the dominant allele to be very rare. Especially when its effect is deleterious.
That's selective breeding and supposedly nature does something simular.
Hybridization is part of selective breeding, but the reason it is called selective breeding is because a selection is made among candidates for breeding as to which will be allowed to breed and with whom. Hybridization is not effective in producing a new breed unless it is followed up by selection.
Similarly in nature. Hybridization occurs, but it is rarely the means of producing a new breed or species. Most natural hybrids are incapable of viable reproduction. So most production of new species does not rely on hybridization at all, but only on selection. And even when hybridization is a factor, it has to be supported by selection.
When it becomes fixed it is no longer subject to genetic drift the way mutant alleles have to be.
This is insufficiently explicit for me to decide whether it answers the question. The elaboration, re polar bears does not help. But lets use it to set up the question again.
Today all polar bears are born with white fur. You agree that probably their ancestors did not have white fur. Would you agree this implies a transition period from a population in which white fur was rare, possible even non-existent, to one in which white fur is the fixed trait of the species? In short, the appearance of white fur must have changed over generations from rare, to occasional, to about equal with darker fur, to more frequent than darker fur, to predominant, to sole existing fur colour in the species.
If you agree with this scenario, how does this happen?
Through some genetic mechanism the way these genes are expressed changed in distribution and now have become fixed.
The genetic mechanism is mutation. A mutation in the genes producing melanin and/or other pigments for fur colour suppressed the production of the pigment. Result: white fur.
Now what mechanism changed the distribution of the mutated gene so that this mutation became fixed?
98% of mutations are neutral, the vast majority of the balance are deleterious with a rare few being beneficial in their effect.
Ok. This is the rate of neutral:deleterious:beneficial mutations among all mutations. But the 5% I was referring to is a different rate.
It is a rate at which one mutation may show up in a population. Different mutations, such as those for albinism or microcephaly or six fingers instead of five each turn up consistently at a measurable rate in the human population. Each turns up at a different rate. Possibly as high or even higher than 5%, possibly as low or even lower than 0.5%.
In any case, how often a mutation, or more precisely, a trait based on a mutation, shows up in a population is a totally different concept from how often a mutation is deleterious or beneficial.
Are you clear on the difference?
The ones that effect populations probably effect less then 5%, good, bad or neutral.
No, you have tried to assimilate one rate with one application to a totally different rate applying to a different matter. The rate of deleterious mutations per all mutations is not correlated to the rate at which one deleterious mutation may occur in a population. Keep your rates separate.
That is why I asked you to be specific about which rate you were referring to.
It effects only 5% because only 5% have it to begin with. I think what you are trying to say is the natural selection is screening harmfull effects out.
No, natural selection does not screen out harmful effects. An organism carrying a mutation with deleterious effects will experience the deleterious effects. But natural selection does affect the distribution of the mutation.
So the question is: if a deleterious mutation is found in 5% of the population now, what keeps it from spreading to 6% of the population in the next generation, and 10% a few generations later, and even to more than 50% of the population eventually. Why do deleterious mutations not become more common generation after generation?
(Again, note, this is not a question about the overall rate of deleterious mutations vis-a-vis neutral and beneficial mutations. It is a question about the rate of occurance of one mutation on a population basis.)
Bottlenecks tend to cut down the gene flow,
I am not sure that is true, but in any case it is irrelevant. It does make me wonder if you understand what gene flow refers to. Would you care to explain gene flow as you understand it?
adaptation is much more likely the result of triggered responses.
Can you clarify what a triggered response is and what the "trigger" would be?
There are genetic mechanisms that adapt living creatures to their environments.
Mutation is such a genetic mechanism. But on its own, it does not produce adaptation. Natural selection is needed to make the adaptation effective in the species.
What other genetic mechanisms did you have in mind?
I need to break this response into two parts. Sorry.
Sorry, it's just how I work. I'm a numbers person and numbers make scientific predictions tangible for me.
