cricket

We see gender differences in sexual strategies -- generally speaking, men have evolved a different set of behaviors than women. Men can sire numerous children, therefore their strategy for evolutionary success is to be randier - less monogamous - than women. Also they are attracted to young (fertile) women. Yadda yadda. Women can bear a limited number of children, hence they are more selective about their sex partners. Yadda yadda. We all know these theories. They make sense to me.

How exactly does it work though, from generation to generation? Is it that it's a sex-linked tendency, like baldness? and that's why these tendencies evolved step-by-step through the generations? And the result, over time, is then that men are randier and women are selective about mates?

But... other tendencies don't 'know' which gender they're supposed to evolve to in the descendents. If one particular ancestor had the "risk taking" set of genes, for example, his daughters and sons would be equally likely to inherit this. But if he had the "randier" set of genes, how is it his sons inherit this but his daughters do not?

I realize his randier-gened daughters would be disadvantaged somewhat, and their children may not grow to reproduce. But his sons will have daughters too who have this tendency (or will daughters NOT inherit such a tendency? ie will they not inherit it BECAUSE they are daughters?)

OR will they, through all the generations, inherit the tendency -- but then be less successful in terms of reproductive success?

No, of course not (sorry i'm talking to myself).. people are born with these tendencies; they aren't still being weeded. Well wait yes they are... damn this gets confusing.

So were the tendencies always sex-linked? If not, the tendencies would have to have been sex-linked since long ago, right?

OTOH, most tendencies that are inherited are inherited by sons and daughters both, right? (or, not?)

Risk-taking. ADD. Heart disease. Etc.

Do hormones alter the *effects* of one's genetic legacy? So that men and women react to the same genes in different ways?

Am I completely off track? How does this work? <img src="confused.gif" border="0">

[ April 06, 2002: Message edited by: cricket ]</p>

liquid

The only genetic difference between men and women is that on the last pair of chromosomes, women have an X and an X chromosome, and men have an X and Y chromosome. The Y chromosome is shorter than the X chromosome. (this is a common method of distinguishing the male sex - in some insects it is even XO, meaning just a single X, not a pair.).

It is this difference that causes development to be gender-specific. For instance, take the case of colour blindness. This requires a faulty allele (i.e. a 'version' of a gene) on an x chromosome. Because women usually have a back-up copy on their other X chromosome, and it is not present on the Y chromosome, men tend to get this fault several times as often as women. It is the same with many genetic conditions. The effect of the genetic difference is especially marked because several of the genes on these chromosomes are controller genes, that can affect the expression of yet other genes.

Anyway, this genetic difference is important, but there is more to it than this. As you correctly identified, the different sexes produce different hormones as a result of their genetic differences. These hormones actually chemically promote or inhibit the effects of even more genes in the body.

Interestingly, you can get the odd case where the chromosomes are mixed up. XYY men, XXX women... some of these conditions produce very odd people, some have little noticeable effect.

Viti

I remember readin about XXX women. Apparently they are almost cartoonishly feminine as they produce almost no testosterone.

cricket

Really?! I'd be curious to read more about that as well. What are XXX women called? I can't do a search for XXX; I'll never find it wading through all the porn!

Writer@Large

cricket, it's called "Triple X syndrome." Type it into Google, and a lot of info pops up. Here's a thorough overview:

<a href="http://www.aaa.dk/TURNER/ENGELSK/TRIPLEX.HTM" target="_blank">http://www.aaa.dk/TURNER/ENGELSK/TRIPLEX.HTM</a>

--W@L

Mageth

(this is a common method of distinguishing the male sex - in some insects it is even XO, meaning just a single X, not a pair.).

IIRC, in birds it is the female that is "XY" (actually ZW), while the males are ZZ. (edited to add: and possibly all reptiles as well)

Interestingly, you can get the odd case where the chromosomes are mixed up. XYY men, XXX women... some of these conditions produce very odd people, some have little noticeable effect

Not to mention XY females, who have the exterior appearance of a female, no ovaries or uterus, and internal testicles, IIRC.

[ April 07, 2002: Message edited by: Mageth ]

[ April 07, 2002: Message edited by: Mageth ]</p>

cricket

bump

RufusAtticus

Sexual determination in humans uses two different things. Some things, like external male genitalia are trigered by the "male-factor" on the Y chromosome.

Other sexual traits are trigered by gene counting. If you have one gene (XY), then male features develop. If you have two genes (XX), then female features develop. The number of genes is determined by using a biochemical pathway to compare gene products from autosomal chromosomes and gene products from the X-chromosome.

Links:

<a href="http://www.people.virginia.edu/~rjh9u/sexdev.html" target="_blank">Sexual Development in Humans</a>
<a href="http://www.news.harvard.edu/gazette/1999/02.11/femaledevel.html" target="_blank">A Female Gene</a>

-RvFvS

Mageth

Note, however, that fetal development anomalies may result in an XY fetus developing female external features/genitalia.

[ April 10, 2002: Message edited by: Mageth ]</p>

Vorkosigan

Do most men father so many children? I suggest that men's sexual strategies may be more closely related to other factors besides siring children. After all, someone as rich as Donald Trump or Bill Gates could easily father 700 or 800 children and care for them. Perhaps men are interested in the social status given by conquests, or in variety, or something. I have never known a man in a one-night affair to insist that his partner NOT use birth control so she can father his child....

Hmmm...

Michael