Re: Why cooled testicles?

Aaron Denney wrote:
On 2006-03-11, sorensonian@xxxxxxxxx <sorensonian@xxxxxxxxx> wrote:
Erik Max Francis wrote:
Peter Knutsen (usenet) wrote:
How likely is it that non-terrestrial life forms may have a similar need
to keep mobile procreative cells cool?

Doesn't sound like a given to me.

I have to agree. Extraterrestrial physiologies are a complete blank. We
have no reason to assume that there will be significant similarities
with terrestrial life - on the other hand we cannot rule such
similarities out, either. I don't believe in parallel evolution, but
some mechanisms could certainly be similar. No harm in taking what we
know from our own planet's animal evolution and applying it to the
fauna of fictional alien planets. As far as likelihood goes, however,
we simply can't put a value on that. There's nothing to qualify such an
estimate.

As for your alien species, Peter, is it originally unisexual, or is it
a hermaphroditic species evoled from earlier bisexual species? I would
suggest - based on the evolutionary mechanisms we know from Earth,
which of course in the case of alien life may be apocryphal - that it
has to be the latter, in order for it to have gametes at all. If it
were originally unisexual, its mode of reproduction would probably be
more vegetative, like natural cloning. The kind of genetic variation we
see in gametes owe directly to bisexual reproduction; it is practically
certain that bisexual reproduction evolved in the first place as a
method of increasing genetic diversity, which was a great evolutionary
advantage.

It seems far more likely to me that the two sexes evolved from
hermaphroditism.

Well, obviously there was a unisexual form of reproduction prior to the
evolution of bisexual reproduction (this was back when there was
nothing more complex than micro-organisms). But by hermaphroditism I
specifically meant the presence of actually male and female organs,
which would thus have needed to evolve first. Some fish and at least
one species of lizard are capable of changing gender temporarily, in
case there is a shortage of a necessary gender. But they spend most of
their lives as normal, gendered individuals, from which they have also
clearly evolved. Thus, I opine that it is quite likely to have a
hermaphroditic species, even a complex one, as long as it's evolved
from gendered ancestral species. Peter's aliens specifically have both
male and female sexual organs, so they would fit my description (and
the evolutionary history I suggest) of a hermaphroditic species. If, on
the other hand, the aliens were classically unisexual, and had been so
throughout their evolutionary history, not using male and female organs
for reproduction, then I would argue that there would need to be some
other strong explanation - a description of some mechanism of achieving
significant genetic variation - for how they would ever reach a genetic
complexity rivalling humans, since unisexual evolution proceeds
immensely slowly.

I don't want to make the "less like humans, less
evolved, more primitive and older fallacy", but there are, for example,
bacteria that exchange DNA with other bacteria, and then split, and a
whole host of species such as various earthworms, snails, and so forth
that are hermaphroditic. Hermaphroditism has a clear path to the two
sexes: just don't bother with one of the steps in the exchange. Males
are easy to develop -- if you don't gestate a kid (the more expensive
part), your genes still get passed on, while hugely cutting the cost.
From there, there are a couple paths to getting some pure females.

I'm not quite sure of your meaning and context here, so I'll just
comment on something you seemed to touch on. Most animals are females
by genetic default (and have been so since long before the evolutionary
advent of gestation), requiring certain "abnormal" parts of the male
chromosome to kick in in order to create a male individual. As far as I
know, the original unisexual genetic basis became the foundation for
the female genes, while the masculine genes were separately "attached"
chromosomally as modifiers. Disengaging these modifiers in early fetal
development, you end up with a female individual. This state of affairs
stems, of course, from the early evolutionary history of bisexual
reproduction, and may suggest that the two genders emerged as a
consequence of two different organisms entering into a new symbiotic
relationship, where one provided the modifying genes that proceeded to
comprise the DNA (or ABC, if you will) of masculinity. :-)

- Tue

.

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