Sexual Selection, Stasis, Runaway Selection, Dimorphism, & Human Evolution

Actually, viruses are already emerging as natural mechanisms of genetic transformation, not just human manipulated ones.

On-going work by one of my colleagues is showing that sorghum plants naturally-infected with certain plant viruses can have their entire genome 'scrambled' by the infection, and in a way that gives rise to heritable changes in the progeny. The progeny represent a startling array of divergent morphologies, each with heritable genetic differences. Although many are, of course, non-viable, certain others have unique and potentially desirable characteristics.

Interestingly, the same work shows that the genetic sequence of the virus itself can be permanently changed by passing it through a particular host plant.

It is almost Lamarckian (but not quite).

RAZD writes: Interesting too, are the hermaphrodite species like some snails that can be either {sperm\giver} or {egg\reciever} and their mating behavior (tag-your-it).

Yes, hermaphrodites are the "special cases" of sexual evolution.

Two kinds exist:

simultaneous herm's (like your snails and earthworms)
sequential herm's (first one sex, then the other)

Simultaneous hermaphrodites are thought to arise in sexual species when the organism has very low mobility and may occur at very low population densities. So the advantage is, you can mate with any conspecific you encounter - even if you only encounter one in your entire reproductive life.

Sequential hermaphroditism is a bit more tricky and may have a sexual selection component to its evolution.
There are 2 kinds: protogynous (beginning as female) and protandrous (beginning as male - much rarer)

It occurs in certain fish species, and a few other taxa. In the case of the fish, female fitness increases as a linear fucntion of age, simply because large females can produce more eggs.

The female fish all prefer to spawn with large males for qualitative reasons: large males are 'proven' fit by virtue of their age alone. Thus male fitness is a non-linear (actually sigmoidal) function of age. This means the best way to maximize lifetime fitness is to start out female when you are small and then 'switch' to being male once you reach a certain size, because big males can achieve much more fitness than females of the same size.

The interesting thing is that when you have a school of these fish in a tank and remove the male, the largest female will then turn into a male. It has been shown that male aggressive behavior, posturing, coloration, and other signals actually suppresses the development of 'maleness' in the females.

Here are a couple of good links:

http://www.ptmsc.org/science/topics/fish_tales.htm

http://www.reefscapes.net/articles/articles/2002/hermaphroditism.html

(editted for typos - EZS)

This message has been edited by EZscience, 05-04-2005 01:37 PM

Amazing! Goodbye phylogenetic trees, hello phylogenetic cobwebs!

Well it is questionable what degree of interchange of genetic information occurs between plant and virus, so phylogenies of the actual organisms will probably still remain independent of one another.

However, it kind of deflates arguments objecting to 'genetic engineering' of crops as an unnatural process.
Apparently, genetic engineering by viruses is a natural phenomenon.

What it does show is that extrinsic forces (such as a virus infection) can produce heritable genetic changes in an organism - hence my comment about Lamarack.

there is also the argument that DNA sharing occured early in evolution and contributed to diversity, if not to the more advanced cell form with mitochondria being inclusions of another species. speculative but interesting.

Actually, the theory of 'endosymbiosis', first advanced by Lynn Margulis in 1981 to explain the origin of mitochondria *and* chloroplasts in eukariotic cells remains the most appealing explanation to date regarding the origin of these cellular organelles.

After all, both these organelles have double, rather than single, membranes suggesting they were phagocyticly engulfed by the ancestor cell, but never consumed. There is little in the way of direct evidence, apart from the double membranes and both possessing autonomous DNA, but no better explanation has yet been put forward.

This message has been edited by EZscience, 05-05-2005 03:45 PM

yep, thats the one.

perhaps that was the first "sex" ?

if you consider sex to be a sharing of DNA between two parents to make an offsring with features that come from both parents ...

the question left for me, though, is whether the {mitochondrial donor} was a willing (injecting?) participant or an unwilling (consumed) participant, and one that evolved a defence against being digested.

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we are limited in our ability to understand
by our ability to understand

RebelAAmerican.Zen[Deist
{{{Buddha walks off laughing with joy}}}

Razd writes: perhaps that was the first "sex" ?

Ah, but this was not a combining of *conspecific* genomes, but rather *heterospecific* genomes, chromasomes that had never functioned in tandem before.

It was an act of predation (phagocytic engulfing) that ultimately resulted in a 'truce' between predator and prey.

Razd writes: one that evolved a defence against being digested.

That would have likely been the first step. In the case of mitochondria, the 'prey' was capable of generating ATP, and if an opportunistic 'predator' happened to be able to avail itself of this energy source, and also provide some raw materials for the process, it would have benefited much more from sharing fortunes with its prey than by consuming it.

Possibly some lessons there for our politicians today.

But can we seriously expect those currently in power to grasp the relevancy of these concepts to human destiny ?

This message has been edited by EZscience, 05-07-2005 09:52 PM

Here is a perfect example of what we were discussing earlier in this thread. In this case, its all about female choice - no male combat involved.

"A study of mosquitofish — guppy-like creatures that feed on mosquito larvae — shows that females definitely prefer well-endowed males to their shrimpier brothers."

"But sex aside, being bigger isn't necessarily better. Male mosquitofish with large genitalia have a greater risk of dying — even if it is with a smile. That's because mosquitofish with large genitalia — known as a gonopodium — can't swim as quickly..."

"All females had the same preference..."

-as predicted by the Fisherian 'runaway' model-
fixation of a female preference in a population leading to exaggeration of a male trait that is then ultimately limited by natural selection when it reaches the point where it reduces survival.

I wonder how an ID theorist would model this?

Good stuff again. Doesn't seem to be on the PNAS (Proceedings of the National Academy of Sciences) website yet.

I am still waiting to see if any IDist (like Jerry) can identify a specific {just created} stage in the fossil record and then demonstrate devolution from that point on. But that's another thread.

{{edited to correct typo ... wegsite? perhaps a freudian link to wigsite? lol}}

This message has been edited by RAZD, 05*13*2005 08:24 PM

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we are limited in our ability to understand
by our ability to understand

RebelAAmerican.Zen[Deist
{{{Buddha walks off laughing with joy}}}

Addendum #1

In the original post on this thread I introduced a number of features that I felt fit the pattern of run-away sexual selection.

Possibly the most contentious of these was the Skin hair thinness issue at the end.

Let's look at this issue in a little more detail.

From Human Thermoregulation and Hair Loss (click)

Body hair is one of the most important features of the mammal thermoregulatory system. Hair can act as an important heat retention and heat prevention device in mammals. By trapping a layer of dead air against the skin, a layer of hair can act as an extremely efficient insulation, reducing the rate of convective heat loss to the environment. However, this exact same system acts as a way to prevent heat gain from the environment by the same principle; by using this layer of dead air to reduce the rate of convective heat gain from the environment to the skin. Besides insulation, the layer of hair on mammals is important in reducing the radiation from direct and indirect sunlight, and can thus act to reduce heat gain from the environment in two ways.

If loss of hair was an important variable in thermoregulation then we would expect {evolutionary pressure \ natural selection} to show a broad trend of hair thickness variations that could be correlated with the need to {retain\dissipate} heat.

We do see this. From the same source, here discussing the need of larger bodies to {retain less \ dissipate more} heat due to the increase in volume as the cube but skin area as the square of a size dimension:

The obvious solution to this situation is decreased body hair with increasing body size, which is exactly what is seen in anthropoids. When the number of hair follicles present in species per unit of area is compared with body size, all primates (including humans) fit along a regular log linear regression line, along which the density of hair per unit of area decreases as body size increases. Species like chimpanzees and gorillas have relatively fewer hair follicles per unit area of skin compared to the smaller monkeys. Humans fall along this line, and have a relative hair density almost the same as seen in chimpanzees, gorillas and orangutans.

To drive this point home, the number of hairs on the human body are precisely what they should be for the human body size. We are not displaced on the scale. There is no special loss of hair required for thermoregulation, and thus there is no special mechanism needed to provide for the loss of hair: no mutation is needed for the explanation of amount of human body hair. ⁽¹⁾ Let's continue:

The difference between the thick pelage of the Great Apes and humans is not in terms of the density of hair, but in its length and thickness and the production of vellus hair in most humans to the exclusion of terminal hair on the body. Humans are not "hairless", but are merely covered by thinner, smaller and unpigmented hair (Schwartz & Rosenblum 1981; Schultz 1931).

This may seem like an obvious point (although 'underpigmented' might be better than unpigmented: it's not albinoism).

Now to better understand the distinction here, we need to know what vellus hair is and how it differs from terminal hair.

Types of Hair (click)

There are three types of hair: *lanugo: fetal hair *vellus: replace lanugo hairs in the peripartum period, unmedullated *terminal hairs: long, coarse, medullated; typified by scalp and pubic regions

And from Hair Growth, Classification of Hair (click):

Human hair varies with respect to texture, color, and length. *Lanugo hairs cover most of the fetal skin and shed perinatally. These lightly pigmented hairs are fine in texture. *Thicker and darker than lanugo hairs, vellus hairs cover most of the glabrous skin surface except palms, soles, palmar and plantar surfaces of fingers and toes, inner aspect of the prepuce, and the glans penis. *Darkly pigmented terminal hairs are long and thick and most commonly are located on the scalp and the facial areas of men. These hairs can reach a preprogrammed length based on length of the anagen phase. Ultimately, terminal hairs undergo involution and convert to catagen and then to telogen phase. The mechanism and factors that induce the hair to terminate growth and involute are largely unknown.

And from Wikipedia: http://en.wikipedia.org/wiki/Vellus_hair

Vellus hair is a very soft and short hair that grows in most places on the human body in both sexes. In Caucasians it is often colourless, or blonde. It is best seen in women and children, as they have less terminal hair to obscure it. Vellus hair is also found in pre-adolescents (Tanner stage 1) as well as in male pattern baldness.

Vellus hair is juvenile hair that is best seen in women? Other than facial hair, is there really that much difference in hair patterns between males and females? See information about a medical 'condition' called Masculine Hair Distribution (in a female):

This is excessive hair growth in an androgen dependent pattern. It is applied to females who complain of hair growth in the beard area, around the nipples and in a male pattern on the abdomen. Androgens induce the transformation of fine vellus hair into coarse terminal hair.

Female vellus hair that is transformed into terminal hair in a male pattern. As a bad thing.

Put this together with the "baby-faced-ness" and the issue of run-away sexual selection of
Human Skin hair thinness is seen as two results of the same process: juvenile features selected for in the female of the species. And considering that the bareness of the human female could not get much further developed without some mutation to actually decrease the numbers of hairs on the human body, I would say that it has been carried to the extreme condition that is characteristic of a fully developed run-away mechanism.

Enjoy.

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⁽¹⁾ -- This is for those that followed the {evolution of clothes) thread or that have seen a particular message of mine referring to sexual selection "blocking" the selection of a mutation for less hair in non-human species. I had claimed that a mutation was not necessary to explain the apparent bareness, just selection of already occurring variations within the population.

Jar please take note, as this specifically addresses the point you raised in msg 86 (click) of that thread: mutation is not needed to explain human body hair.

But I also could have been clearer on what was being "blocked" and why: normal sexual selection revolves around the 'norm' of the species (tendency for stasis) and abnormalities are rejected, sometimes viciously, sometimes just by refusal to mate. Albinism is a recurring condition due to a recessive gene mutation. Usually albinos do not have high success in mating. A similar mutation in a dominant gene is not observed, although it has likely occurred in the past: failure to observe it is possible evidence of acute selection against it in mating success. You also have the Greenish Asian Warbler ring species where two subspecies do not mate (even though each other subspecies does around the ring) because they are viewed as just too different.

Any randomly occuring mutation for bareness would run into this problem. And such mutations do occur: we have the hairless cat (click) as a result of such a mutation and selective breeding by humans.

{{edited subtitle and first line to make room for a followup addendum, added line above footnote}}

Enjoy.

{{added by edit: the next addendum is

Addendum #2 Message 65- Enabling Mechanisms

end edit}}

This message has been edited by RAZD, 06*02*2005 07:57 AM

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we are limited in our ability to understand
by our ability to understand

RebelAAmerican.Zen[Deist
{{{Buddha walks off laughing with joy}}}

btw jar, no offense, but I felt that because you were involved in the other discussion(s) that another view would be appropriate. I have also added an addendum that would have made the OP even bigger, and have another one planned to finish my presentation on this topic.

Please note that I also address your question about mutations in the addendum in greater detail (see the footnote).

cheers.

Hey Raz - good stuff.

I enjoy your posts because they make me think beyond the hexapoda of my daily existence !

I think you have a very well substantiated story on how the evolution of 'bareness' in humans
has evolved in response to thermoregulatory constraints and the cultural evolution of 'clothing' etc.

You have convinced me that we are approaching the biological limits of nakedness.
Now if we could just get rid of the clothes, heh heh ...NO - wait, please, not *everyone* !

But seriously, what is lacking in your thesis is tying this into some sort of mating advantage for hairless as opposed to hairy men.

(we can safely assume that with mammals, only males usually benefit from polygamy because females are far more tied to the offspring because of lactation and thus more subject to abandonment than vice versa.

For the hairless trait to be useful to females in SS, it would have to affect their fitness via the quality of their offspring.

The only way to make this argument work would be if it was a male choice situation, but then you would need to show that males giving birth to hairless daughters achieved greeater reproductive success than those giving rise to hairy daughters.

While this might seem logical on the surface, we need to rememeber that reproductive success in human females varies little.
Even the uglist are sometimes the most fecund !

Otherwise, for this to be truly categorized as Fisherian 'runaway' SS you need to demonstrate a minimum of two things:

1. Females choose mates based on degree of hairlessness in males.

Hmm... opening a recent copy of GQ magazine one might expect that to be the case...but no.

Rationale human beings have more cerebral mate choice criteria (one would certainly hope !).

2. Hairless males leave more progeny (or more fertile progeny) than hairy males. Not likely, I think you will agree.

So a great story, but not a Fisherian Runaway story.

minor content added in edit - EZ

This message has been edited by EZscience, 05-13-2005 10:39 PM

put the shoe on the other foot: the females are being selected for mating based on their bareness, not the males.

the evidence is (1) greater expression of the feature in females than in males and (2) greater consistency of expression in females than in males

if males are not being selected for bareness (while females are) then they should exhibit more variation in hairiness than females: they do.

this also correlates with babyfacedness being selected for in females but not in males.

this was part of my point on sexual dimorphism in the OP, if you remember.

the next question on whether Fisherian Runaway is involved is if any disadvantage can be identified and whether any possible compensatory mechanisms become involved (the answer here is yes, but that is the next addendum...)

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we are limited in our ability to understand
by our ability to understand

RebelAAmerican.Zen[Deist
{{{Buddha walks off laughing with joy}}}

OK - now I owe you an apology.

My edit on the post added that possibility, but not fast enough to head off you reply.

So we can go from here on what it would take to make the male choice model work....

As stated below:

1. Females would have to vary significantly in reproductive success based on degree of hairiness (No evidence, I suggest)

2. Males would have to gain fitness by selecting hairless females via the increased fitness of their hairless daughters.

Entirely contingent on No. 1, but could be true if No. 1 is true.

EZ