On 10/3/2018 7:09 AM, MarkE wrote:
> Hi Ron, good summary. My question here concerns the status of NS in view of the modern synthesis (and extensions of it), i.e., does NS nevertheless remain the only mechanism responsible for the creation of new functionality, information and complexity? For the “appearance of design”?
First off Natural selection is just that, something selected for by
nature. Your concept of design only comes in because evolution builds
on what came before. The organism still survives, but new things emerge
and people call these designs, but they are usually just variants of
duplicated genes that do something a little differently and result in
the organism being a little different.
They just gave the Nobel prize to researchers who started using
"directed" evolution.
https://www.the-scientist.com/news-opinion/directed-evolution-phage-display-nab-chemistry-nobel-64890
Original paper:
http://www.pnas.org/content/pnas/90/12/5618.full.pdf
They call it directed evolution because it is artificial selection. The
researchers still use random mutations, but they have an assay that
allows them to select the genes that are better at what they want to
select for, so they have artificial generations where they take an
existing functional enzyme or antibody that binds things and introduce
random mutations, selected out of the thousands of variants that they
produce and mutate again and select again until they get to whare they
want to go.
Nature doesn't know where it is going with any selection. If the
mutation has some advantage more organisms with that mutation will be
produced in the next generation, and other mutations can build on what
came before. So nature can only select for what works. The researchers
can have some goal in mind, and still use random mutations to get there.
as long as they can select for what they want. The researchers do not
have to know what mutations will work, they let their selection
procedure identify those mutations. Nature can only select for a
mutation if it has some type of reproductive advantage.
Natural selection is only the selection part. Other factors produce the
genetic variation. As you indicate genetic drift is a major factor in
accumulating genetic variation in a population, and some biologist think
that it might be more important to what the organism ends up looking
like than natural selection. If you take a population like Europeans
you can see a wide range of phenotypic variation (what the individuals
look like). Some look more like each other, but there is a broad range
of phenotypes drifting in the population. There may be some selection,
but it has been too weak to make everyone look the same. The variation
that makes each person an individual can drift in the population for a
long time and it might be fixed by chance and the population would have
to build what comes next on that foundation.
So before genetic drift or selection you have mutation. In terms of
base-pair substitution mutations, every site in the human genome has
been hit on the order of 100 times by new mutations in the existing
generation of humans. So there is a lot of new mutations, but when we
talk about the standing genetic variation in a population we talk about
the variants that have risen to the level of 1% allele frequency in the
population (over 100 million people have the same variant). It takes
selection or drift for a variant to reach this allele frequency. The
human population suffered a population bottle neck within the last
100,000 years so we have around 1/5 the standing genetic variation that
the average species has. Chimps have around 3 times more standing
genetic variation than humans.
Genetic recombination is an important factor in genetic variation. Your
chromosomes get shuffled as the homologous chromosomes recombine to form
new haplotypes (order of alleles along a chromosome). Recombination is
important because you have just a few chromosomes, but thousands of
genes. Recombination allows different combinations of existing genetic
variants to be inherited.
You can see the evidence of genetic recombination in our genomes by
looking at the Neanderthal DNA that modern humans that made it out of
Africa around 80,000 years ago have in their genomes. Europeans, Asians
and native Americans have a couple percent Neanderthal DNA. The first
hybrids had one set of intact Neanderthal chromosomes, but in the time
since the hybridization event (soon after modern humans left Africa)
recombination has happened and the Neanderthal chromosomes have been
recombined with modern Human chromosomes so that the bits of Neanderthal
chromosome are only around 50,000 base-pairs. The rate of decrease in
size has gone down because at this point the Neandethal bits only have
around 1 in 5,000 chance to be involved in a recombination event. The
Neanderthal chromosomes started out on the order of 100 million
base-pairs and recombination has chopped them up to their current size.
Ron Okimoto
>
> It seems to me it is, by definition. The other factors provide the chance variations, the undirected experiments, but NS does the heavy lifting.
>
> If this is the case, what can made of this claim?
>
> “Neo-Darwinism ignores important rapid evolutionary processes such as symbiogenesis, horizontal DNA transfer, action of mobile DNA and epigenetic modifications. Moreover, some Neo-Darwinists have elevated Natural Selection into a unique creative force that solves all the difficult evolutionary problems without a real empirical basis.”
>
http://www.thethirdwayofevolution.com/
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