From: lip@s1.gov (Loren I. Petrich)
Newsgroups: soc.women,soc.men,sci.bio,sci.skeptic
Subject: Biological Sex Differences?
Date: 31 Jul 92 08:47:04 GMT
Organization: LLNL


	There is a school of thought that states that men are
biologically predisposed to, and women are biologically predisposed
not to, exhibit what is variously called "aggressiveness" or
"dominance behavior"; one leading advocate of this school of thought
is Steven Goldberg, and as is typical, he does not define his terms
clearly enough to be terribly helpful.

	But let us look around the animal kingdom, and beyond, to see
what we find.

	First of all, why are there two sexes? It is a much-debated
question why genome-scale gene mixing takes place so widely. One
hypothesis is that it has a significant probability of bringing
together lots of "good" genes, that would not be brought together
otherwise.

	One simple way that gene-mixing can take place is by two
organisms exchanging genetic material, as in the conjugation practiced
by Paramecia.

	Another way is for two cells to fuse. Some organisms, such as
some one-celled flagellate green algae (_Chlamydomonas_ is one
example, I think) go through haploid and diploid phases. When in the
diploid phase, the organism reproduces by meiosis: XX -> XXXX -> XX XX
-> X X X X and produces haploid organisms. Two haploid organisms may
then fuse to form a single diploid one: X X -> XX.

	This system is more "practical" for a multicelled organism,
since the organism can contribute special cells for the purpose of
reproduction.

	The simplest system would be for all the gametes to be alike,
but there is a tradeoff between the food supply a cell can have (a
head start helps) and how mobile it is. So one strain may specialize
in having being big (and necessarily immobile) and another strain may
specialize in being mobile (and necessarily small). Thus arises the
female and male sexes. How many times this division of labor has
arisen from the presumed original state of "isogamy" is an interesting
question, one that may be answered by molecular evolutionary biology.

	This may be taken as "proof" of male dominance (consider the
swimming sperms) or else that female power is evil (consider the
sperm-swallowing egg). Or else it may be concluded that the male sex
is fundamentally parasitic (it is the egg, not the sperm, that
supplies the bulk of the food). And egg cells are not exactly passive;
they release pheromones that attract sperm cells to them (after all,
sperm cells have to know which way to go :-).

	Let us next consider the question of full-organism size; if
members of one sex are bigger than members of the other, then why is
that so? This question can be answered with the help of "sequential
hermaphrodites", natural sex changers. In the animal kingdom, it is
universally one-directioned: male->female or female->male. But in the
Jack-in-the-Pulpit plant, the sex change can go in both directions.
When the plant is small, it is male. When it grows big enough, it
turns female. But if it is partially eaten or shaded, it shrinks, and
can turn male again. The plant is male when it is small because it
saves its resources for pollen, which are cheaper for it to produce
than ovules. When it gets big, it can produce ovules without too much
cost. This same rule applies to the oysters illustrated in Stephen Jay
Gould's article _Sex and Size_ -- the oysters turn male->female as
they grow because sperm cells are cheaper to produce than egg cells.
In predatory arthropods like mantises and spiders, the female can
actually be dangerous to the male, since to the female, the smaller
male looks suspiciously like potential prey.

	But what about the reverse? That takes place among social
animals, like certain fish in which the largest of a group is male,
while the rest are female. When the male is removed, one of the bigger
females changes into a male. But why the male the biggest here?
Because a male has less investment in gametes, he has more resources
left over than females, thus males can compete with each other for
exclusive rights to mating with a group of females. This is very
common behavior among social animals, with the males sometimes
fighting each other.

	But can females enter this game? Yes, they can. Among
Australian bush crickets and related insects, it is the females who
compete for access to the males. How is that so? The male inserts
their sperm into the female inside of a "spermatophore", a sperm
capsule. But female crickets like eating sperm capsules, and the males
put blobs of jelly on them to give the sperm time to enter the
females. This blob of jelly is a major source of nutrition for the
eggs, got there by the female eating it and digesting it. Thus, it is
the male who makes the biggest contribution, and the females who have
resources to spare for competition.

	This male competitiveness hardly equals male domination. For
instance, among wild horses, there are two kinds of herds, one of
mostly mares with a stallion, and one of mostly stallions without
mares. The mostly-mare herds follow regular migration routes, while
the "bachelor" stallion herds wander irregularly. This is connected
with the most effective strategy for producing colts; for stallions,
it is to keep other stallions from mating with a group of mares and to
dethrone other stallions who are currently enjoying this privilege if
one is without mares. Thus, a stallion can afford lean times in his
wanderings. A mare, on the other hand, has to be well-fed in order to
successfully bear and nurse a colt. Thus, it is advantageous for her
to know where all the green pastures are. The result: The stallions
follow the mares around.

	While males can be competitive, females can be choosy. Thus,
female African widowbirds are known to have a preference for males
with very long tail feathers. This selection for seemingly troublesome
features of males in many bird species is an admittedly perplexing
problem, and several solutions have been proposed. One of them is
runaway natural selection. But that leaves out the question of what
started off the trend that ran away. Many of the various proposed
"starters" boil down to some form of conspicuous consumption,
something that a bird that doesn't have to lay eggs can certainly
afford. Presumably, the most lavish of the conspicuous consumers can
demonstrate that he is strong and healthy enough to be able to get
away with it, and thus have lots of strong and healthy offspring.

	Can female animals form hierarchies? Yes, they can. In a pack
of wolves, one male -- and one female -- do most of the breeding.
Presumably, they keep the others under stress and keep them infertile.
That appears to happen for mongooses, where one female stresses the
others and disrupts their ovulation cycles.

	The social insects provide good examples of females dominating
other females; in some social species, usually those with the smaller
colonies, if one removes the queen, one of the workers takes her place
as the reproducing female. The same happens among the Naked Mole Rats,
where the queen dominates the others, often by shoving them. She is
also the one who initiates mating with the fertile males in the
colony.

	So this analysis proves that it is wrong to perform simplistic
extrapolations from animal behavior to what "human nature" supposedly
is. In many cases, it is a simple matter of economics. And this
also explains many arrangements of human societies, rather than some
supposed biological imperatives.

	And one last thing. Internal fertilization. It has appeared
several times among animals, and at least once among plants, and in
most cases, it is the male who injects gametes into the female,
instead of vice versa. The only exception I know of is the seahorse.
Why might the rule be so? Because, especially for land animals and
plants, it is much easier to transfer a sperm cell (or even LOTS of
sperm cells) than an egg cell, which can be quite big. For land
plants that make seeds, a pollen grain sprouts a thin tube that grows
toward the ovules. But even this does not imply male dominance, for
the two sexes can be essentially cooperative, or it can be the female
who initiates mating.
Newsgroups: soc.women