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Evolution of sexual reproduction

Discussion of everything related to the Theory of Evolution.

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Postby dmehling » Fri Mar 19, 2010 10:02 pm

That kind of evolutionary process seems quite dubious to me. It sounds like a lot of speculation regarding an extremely complicated process which has never been observed. I would certainly believe a conclusive report that puts forward a likely mechanism. However, no such evolutionary mechanism is really known. This is one of the most challenging areas of evolutionary science and present explanation seems so far out of the realm of science.
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Re:

Postby Riddles » Mon Jun 21, 2010 11:31 am

dmehling wrote:I still don't think you guys are really understanding my point. I'm not really asking how sexual reproduction originated or how it actually works. Rather I am interested in how sexual compatibility is maintained between the sexes of a species, as a species proceeds down a particular evolutionary path. Consider primates for example. They would have arisen from a single common ancestor. For a new species to develop (I'm assuming a species cannot interbreed with its parent species) would you not have to have simultaneous changes occurring in the reproductive systems of each sex? As you have these primates evolving into separate groups of humans, chimpanzees, gorillas, etc. there would have to be considerable evolution within each species since the biology of each sex is significantly different from its counterpart. Is there some kind of mechanism that would cause the reproductive systems of both sexes to undergo changes that are complementary to each other?


It is difficult to follow what your specific issue is here.

On the one hand it is reproductive incompatibility that leads to speciation so reproductive incompatibility is not something that has to be avoided as there would then be no speciation.

On the other hand you are asking why the males and females can remain compatible and therefore of the same species. It would also help to know what specifically you are referring to re. "simultaneous changes occurring in the reproductive systems of each sex". What specific sex differences of the primates are you concerned about?

Males and females of the same species share the same genome. How that genome is expressed differently in the two sexes is due to selection on that genome in females and selection on that same genome in males. For shared traits there can be a 'tug-of-war' where neither sex can move towards it's own optimum. But over time other mechanisms evolve to produce sex-linked expression of genes. Hormones are the main mechanism, afaik, so genes can be expressed differently in the two sexes.

If we consider the basic reproductive systems the basic mechanisms evolved with the first divergence of two sexes. From a parent body able to produce both sperm and eggs and having the two reproductive systems to do so there evolved those producing only one type of sex cell. With sex determination mechanisms and sex-linked gene expression selection could act on the same genome separately in both males and females. So, if selection acted on the genome when in males to, for example, evolve a structure to deposit sperm inside the female rather than simply expel sperm, selection acted on that genome when in females to deal with that internally deposited sperm (and often in an antagonistic way, see eg female cryptic choice).

Each sex is part of the environment for the other sex and therefore, just like the rest of the environment, creates selection pressures. It is like asking how do organisms manage to evolve in a complementary way with their environment. Each sex is a reproductive resource for the other sex. It is a coevolution process much like other coevolution processes. And the differences between the sexes in the basic reproductive anatomy is no different from the differences is size or colour or appendages or behaviour.
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Re: Re:

Postby JackBean » Tue Aug 10, 2010 7:29 am

dmehling wrote:I still don't think you guys are really understanding my point. I'm not really asking how sexual reproduction originated or how it actually works. Rather I am interested in how sexual compatibility is maintained between the sexes of a species, as a species proceeds down a particular evolutionary path. Consider primates for example. They would have arisen from a single common ancestor. For a new species to develop (I'm assuming a species cannot interbreed with its parent species) would you not have to have simultaneous changes occurring in the reproductive systems of each sex? As you have these primates evolving into separate groups of humans, chimpanzees, gorillas, etc. there would have to be considerable evolution within each species since the biology of each sex is significantly different from its counterpart. Is there some kind of mechanism that would cause the reproductive systems of both sexes to undergo changes that are complementary to each other?


Basically. If the two sexes became incompatible, how would they reproduce? :D
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Re: Evolution of sexual reproduction

Postby jevg » Tue Aug 17, 2010 4:25 pm

As dmehling points out
Consider primates for example. They would have arisen from a single common ancestor. For a new species to develop (I'm assuming a species cannot interbreed with its parent species) would you not have to have simultaneous changes occurring in the reproductive systems of each sex? As you have these primates evolving into separate groups of humans, chimpanzees, gorillas, etc. there would have to be considerable evolution within each species since the biology of each sex is significantly different from its counterpart. Is there some kind of mechanism that would cause the reproductive systems of both sexes to undergo changes that are complementary to each other?

Well lets try and understand why there is this understanding that humans and apes are biologically related.

According to the modern synthetic theory of evolution
“ Very likely an explosion of gene duplications 7-12 million years ago led to the branching off of gorillas and then chimpanzees from the evolutionary line that ultimately became modern humans.”
http://anthro.palomar.edu/synthetic/synth_3.htm

Simply put the process of this evolutionary change is the mutation in many forms of the gene pool that is then passed on to the next generation.
In order for a mutation to be inherited, it must occur in the genetic material of a sex cell.

In the case of human lineage therefore, there must have occurred a mutation in the sex cell of an ancestor that led to the branching off of the ape line.
It is for this reason that apes and humans are related, so the story goes.

The question therefore is whether the biological evidence supports this understanding.

Some of the latest evidence on this matter is a paper in 2007 entitled:-
The Evolutionary History of Human and Chimpanzee Y-Chromosome Gene Loss.
http://mbe.oxfordjournals.org/cgi/reprint/24/3/853

This research compares human and chimpanzee Y-chromosome (a sex chromosome) and finds that 4 genes present in the human Y-chromosome are not functional in the chimpanzee Y chromosome.

In particular the gene “(USP9Y) is critical for spermatogenesis in humans, with any gene disruptive mutations at this locus resulting in azoospermia or the absence of sperm in seamen. Thus the potential loss of this specific gene in the chimpanzee lineage is especially puzzling.”

Why is it puzzling?

From the modern evolutionary perspective, a gene that was present in the last common ancestor of humans and chimpanzees has been damaged somewhere in the chimpanzee line. This mutation therefore occurred sometime after the human chimpanzee branching. In humans this gene is critical for the production of sperm cells and any disruption of this gene results in male infertility.

Now if in this hypothetical ancestor this gene had a similar function and was therefore vital for reproduction, how could the chimpanzee’s ancestor have lost it given that chimpanzee are naturally fertile.

It must be assumed that the chimps have another gene(s) that provide the function USP9Y has in humans.

These genes must therefore have been present before the loss of USP9Y in the chimpanzee line or otherwise this loss could not have survived in their genome.

However if USP9Y was still functional how could the alternate have evolved while there was no need for it.

Questions of this nature remain unanswered by the modern theory.

As dmehling rightly states, there a great deal of speculation and virtually no evidence put forward in support.

That is why a considerable amount of rethinking is taking place in biology.
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Postby Darby » Thu Aug 19, 2010 2:57 pm

The mutation doesn't have to happen in a sex cell, just in the lineage of the sex cell, which means a lot of embryonic alterations will get passed on as well...
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Re: Evolution of sexual reproduction

Postby jevg » Mon Aug 23, 2010 10:03 pm

by Darby » Thu Aug 19, 2010 2:57 pm
The mutation doesn't have to happen in a sex cell, just in the lineage of the sex cell, which means a lot of embryonic alterations will get passed on as well...



Sorry for the delay in responding but I have been busy elsewhere.

Of course mutation doesn’t have to happen in the sex cell, but however and wherever it happens it must appear in the sex cell for that mutation to be inherited.

With respect you appear to be missing the point the data is revealing.

Common decent is a fundamental pillar of Darwinian theory whether neo or classical.
The so called tree of life (TOL) is the explanation for all the diversity we see in nature. Please check the illustration here
http://tolweb.org/tree/

If you look at this TOL, at it’s root is the origin of this diversity of life.
At the top of this diversity there are the different biological divisions, the frog, butterfly and flower representative of the different phyla (body plans).
Between these bookends we see the branching out of organisms as life became more complicated and varied. The driving force for this diverse change being random mutation filtered by Natural Selection. The whole process being gradual.

The question is whether the data, be it biological or fossil support this hypothesis.

Darwin himself acknowledged that the data in his day could be interpreted differently. The reason - he was aware of the fossil record and in particular the record of what is known as the Cambrian radiation. That is why he took the view that the fossil record was incomplete and therefore could not be relied upon.

Despite the common perception that the fossil record provides confirmation for the neo-Darwinian account of the origin of new biological forms, the data of the Cambrian radiation actually contradict the expectations of neo-Darwinism at nearly every point. Even Richard Dawkins himself, in his book the Blind Watchmaker acknowledged
“It is as though they [the invertebrate phyla] were just planted there, without any evolutionary history.”

According to neo-Darwinism, biological change occurs as natural selection acts on random genetic changes and mutations, selecting those changes that favor the survival of the organisms that possess them. Over time, small-scale advantageous genetic changes accumulate, eventually resulting in large-scale changes in the morphology of organisms. Thus complexity should accumulate in a gradual bit-by-bit fashion over vast periods of geologic time resulting in new body plans (Phyla)

However contrary to the predicted patterns above, the Cambrian radiation
and subsequent variation occurs after and not before the basic body plans appear in the fossil record.

In other words the TOL starts at the top and diversifies down to species level.
The so-called "inverted cone of diversity."

As stated above, the fossil record shows a hierarchical “topdown” pattern in which phyla-level disparity of body plans appears first followed only later by species-level diversity. Major innovations in body plans precede minor variations on basic designs.

This is what the fossil data reveals, and this along with the genetic data emerging is all running contrary to the Darwinian thinking of common decent.

Science always goes where the evidence leads.
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Re: Evolution of sexual reproduction

Postby JackBean » Tue Aug 24, 2010 7:13 am

jevg wrote:In other words the TOL starts at the top and diversifies down to species level.
The so-called "inverted cone of diversity."

As stated above, the fossil record shows a hierarchical “topdown” pattern in which phyla-level disparity of body plans appears first followed only later by species-level diversity. Major innovations in body plans precede minor variations on basic designs.


Can you explain this? I didn't get it much...
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Re: Evolution of sexual reproduction

Postby jevg » Tue Aug 24, 2010 7:21 pm

I assume you are familiar with the term Cambrian (radiation) Explosion that describes the geologically sudden appearance of multi-cellular animals in the fossil record during the Cambrian period of geologic time. During this event, over forty separate phyla first made their appearance on earth. Phyla constitute the highest biological categories or taxa in the animal kingdom, with each phylum exhibiting a unique architecture or structural body plan.
http://www.pbs.org/wgbh/evolution/libra ... 34_02.html

Familiar examples of basic animal body plans are cnidarians (corals and jellyfish),
mollusks (squids and shellfish), arthropods (crustaceans, insects, and trilobites),
echinoderms (sea star and sea urchins), and the chordates (animals with backbones), the phylum to which all vertebrates including humans belong.

Recent dating has shown that this radiation occurred within a very narrow window of about 5 million years, some 530 million years ago and that represents a very small fraction of earth’s history.

The other noticeable feature of this sudden appearance is that in almost all cases, the body plans and structures present in Cambrian period animals have no clear morphological precursers in earlier strata.
In other words as Richard Dawkins put it “It is as though they were just planted there, without any evolutionary history”.

Darwin’s hypothesis of common decent, as illustrated by the TOL states that the higher taxa arrive by a process of gradual increase in diversity and complexity from simple beginnings, i.e. a bottom up progression from a single common ancestor, diversifying by branching off as more complex structures evolve. The frog, butterfly and flower in the illustration are representations of these phyla at the top of the tree.

The fossil data however is showing that these top biological complex structures( plyla) represented by the frog etc in the Darwinian TOL arrived suddenly and separately and then branched into the various species we have today, showing of course a top down progression.
This is the exact reverse of Darwinian theory.

One of the outstanding features of this diversification being “stasis.”
Each phyla down to species level is also isolated from all others.
So instead of having a single Tree of Life (TOL) there are several trees each one remaining isolated from all others.

I hope this explains matters a little bit better.

There have been attempts to try and explain this data through Darwinian theory but it is proving an impossible task. I have come across two or three attempts and I would be happy to put them up for discussion.
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Postby Darby » Tue Aug 24, 2010 9:41 pm

As more fossil beds are found, the Cambrian Explosion is looking more artifactual. The changes were pretty quick, but following the Snowball Period reradiation, some rapid changes are to be expected.

Darwin was a uniformitarian, but that hasn't been the prevailing attitude for half a century.
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Re: Evolution of sexual reproduction

Postby jevg » Wed Aug 25, 2010 9:47 pm

As more fossil beds are found, the Cambrian Explosion is looking more artifactual


(1) If I understand you correctly you are stating that the Cambrian radiation (explosion) is of human origin. Is that correct? Because that is what artifactual means.
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(2)
“As more fossil beds are found…


Well there is the famous Burgess shale in Canada, the Chengjiang strata in China perhaps the two most studied sites.
There of course other sites, North West Scotland, the Bastian formation of East Greenland, Siberia and others.

Can you be a little more precise? To what Cambrian strata are you referring.?

(3)
following the Snowball Period reradiation, some rapid changes are to be expected.


The snowball earth hypothesis is considered to have come before the Cambrian period
and you are suggesting this may have triggered the evolution of multi-cellular life that we see in the Cambrian strata. Have I understood you correctly?
If so, can you provide any data that would show how multi-cellular life emerged, or are you simply echoing another hypothesis?

(4)
Darwin was a uniformitarian, but that hasn't been the prevailing attitude for half a century

Darwin’s theory was based on gradualism. Dawkins, Coyne, Orr, Jones and others continue to have that view. Read Dawkins “ Climbing Mount Improbable”

Eldridge and Gould have rejected gradualism with their Punctuated Equilibrium theory, with the Cambrian Radiation forming the basis of the data that led them to that view.

This debate has been going on for some decades now, so perhaps, can you explain more clearly what the “prevailing attitude” has been for half a century.

That having been said do I assume you agree with me at least in part when I say that Darwin’s theory is being falsified, at least on the point of gradualism.
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Postby newscctv » Wed Sep 15, 2010 9:03 am

I still don't think you guys are really understanding my point. I'm not really asking how sexual reproduction originated or how it actually works. Rather I am interested in how sexual compatibility is maintained between the sexes of a species, as a species proceeds down a particular evolutionary path. Consider primates for example. They would have arisen from a single common ancestor. For a new species to develop (I'm assuming a species cannot interbreed with its parent species) would you not have to have simultaneous changes occurring in the reproductive systems of each sex?
As you have these primates evolving into separate groups of humans, chimpanzees, gorillas, etc. there would have to be considerable evolution within each species since the biology of each sex is significantly different from its counterpart. Is there some kind of mechanism that would cause the reproductive systems of both sexes to undergo changes that are complementary to each other?
Last edited by canalon on Wed Sep 15, 2010 4:34 pm, edited 1 time in total.
Reason: spam removed, author banned
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Re:

Postby Geokinkladze » Sat Sep 18, 2010 9:16 pm

Darby wrote: Darwin was a uniformitarian, but that hasn't been the prevailing attitude for half a century.


What is the prevailing view currently? I'd hate to be left behind.

jevg wrote:(1) If I understand you correctly you are stating that the Cambrian radiation (explosion) is of human origin. Is that correct? Because that is what artifactual means.


I think by artifactual he means to say that some factor causing the fossil record's incompleteness accounts for lack of precambrian ancestors, ie there were ancestors, we just don't have fossils for them. At least I think thats what he means?
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