Why is there male and female?
badgerboy
answers to my last question, but I've got a new one, which is probably
a lot less obvious:
I can imagine organisms developing into two sexes because of the
massive advantage from variation in the gene pool (organisms can
evolve to adapt to an environment FAR quicker if they mix up and
recombine their genes with each other) - but why is it that we ended
up with two sexes that can't breed with other members of the same sex?
Surely it wouldn't be too difficult for an organism to evolve a
mechanism whereby either sex can produce offspring (having the sperm
and egg combined, being produced by any member of the species). The
advantages for this, not least in terms of preventing inbreeding,
would be great. I'm sure it goes on in some organisms (in a way), but
why is there any survival advantage of making sure that an organism
can only breed with half of its own species?
Walter Bushell
Specialization. "To be an error and be cast our is part of God's
design." W. Blake
Male genes that are not the best can be excluded from reproduction, I
believe that even in humans more females than males reproduce. Males can
specialize in signs of fitness that are expensive to maintain like
bright colors in birds and fish which make one more susceptible to
predation.
--
Reality has been corrupted. Please insert new system disk.
Sleighwhitaker
>> mechanism whereby either sex can produce offspring (having the sperm
>> and egg combined, being produced by any member of the species). The
>> advantages for this, not least in terms of preventing inbreeding,
>> would be great. I'm sure it goes on in some organisms (in a way), but
>> why is there any survival advantage of making sure that an organism
>> can only breed with half of its own species?
Well if one individual is producing both types of gametes what's to prevent
those gametes from fertilizing each other? If I remember correctly many
organisms that produce both male and female gametes have also evolved some sort
of self fertilization barrier (although some organisms can self fertilize). It
is possible that the evolution of sexually distinct gametes (small and
generally mobile sperm, and large and generally less mobile ova) may have been
at least partially to limit self fertilization.
Leigh
Richard S. Norman
>can only breed with half of its own species.
Sexual dimorphism is very widespread among animals and plants although
some organisms can reproduce sexually without sperm and egg -- the
gametes look the same (isogamy). But most sexually reproducing
organisms have heterogamy, producing sperm specialized for motility
and eggs specialized for food storage.
The plants show the evolutionary strategy much more clearly than
animals. The gametes are produced by a multicellular
haploid generation, the gametophyte, which is not found in animals.
The structures that produce sperm and eggs are different but some
plants have different gametophyte individuals, male and female.
Gametophytes are produced from spores and some plants have different
types of spores, male and female (actually microspores and
megaspores). And the structures that produce spores can also be
specialized so you have male pine cones or flower parts producing
microspores which grow into male gametophytes (pollen grains) which
produce a sperm cell. On the other hand, you have female cones or
flower parts praoducing a megaspore which grows into a female
gametophyte which produces an egg cell. Sexual dimorphism actually
crosses generations in this case. Since plants don't have behavior
the way animals do, the role of this dimorphism is much clearer than
in animals, where social roles can be very complex. Males disperse
the genetic material, females nurture the next generation both with
stored nutrients and with physical protection from the envirnoment and
predators.
In social animals, the role of an individual may well go far beyond
this particular reproductive function. Human societies in particular
have culturally conditioned roles for individuals that transcend any
evolutionary antecedent. So when simplistic "evolutionary
psychologists" claim that evolution decrees thuman males should run
around impregnating anything that moves while human females should
stay home tending to the kids, they are far out of line.
The cost of not being able to mate with half your conspecifics is not
very great. Males (or male-type structures) are motile enough to find
the few females that exist. Where even this can be a problem, many
species (plant and animal both) revert to various methods of asexual
reproduction.
Tim Tyler
: In social animals, the role of an individual may well go far beyond
: this particular reproductive function. Human societies in particular
: have culturally conditioned roles for individuals that transcend any
: evolutionary antecedent. So when simplistic "evolutionary
: psychologists" claim that evolution decrees thuman males should run
: around impregnating anything that moves while human females should
: stay home tending to the kids, they are far out of line.
I don't believe I've ever heard any sort of evolutionary psychologists
claiming that humans "should" do anything.
The "should" word is very loaded. Most steer well clear of it - and
merely talk about their expectations.
--
__________
|im |yler http://timtyler.org/ t...@tt1.org
Tim Tyler
: why is it that we ended up with two sexes that can't breed with other
: members of the same sex?
: Surely it wouldn't be too difficult for an organism to evolve a
: mechanism whereby either sex can produce offspring (having the sperm
: and egg combined, being produced by any member of the species). The
: advantages for this, not least in terms of preventing inbreeding,
: would be great. I'm sure it goes on in some organisms (in a way), but
: why is there any survival advantage of making sure that an organism
: can only breed with half of its own species?
Why are we not hermaphrodites?
Two popular books that examine this question are:
"The Red Queen" - Matt Ridley
"Mendel's Demon" - Mark Ridley [authors not closely related]
While the answer they provide is facinating, I also think it is not
entirely correct.
Their theory fails to explain why many plants are hermaphrodites - while
few animals are.
It also apparently predicts that aliens/far-future lifeforms will
/probably/ be hermaphrodites.
I think the explanation misses an important element of the advantages
of dividing the sexes in mobile creatures.
That is that the adaptions that work best for distributing seed to many
places are different from those that work best for giving
birth. Combining these both in a single organism would mean that it is
not optimally adapted to either role.
That may not be the explanation for the /origin/ of the sexes being
dimorphic - but it contributes to its /maintenance/ - and it seems likely
to persist when the other advantages of divided sexes vanish.
Robert Reichenberger
question to you would be "Wouldn't females be more female evolving
threw female?" I would have to move step aside and let the first
people on earth give you the answer to this because they probably know
why there is a limit to people being born like them on the first day
of life.
John Wendt
> Two popular books that examine this question are:
>
> "The Red Queen" - Matt Ridley
> "Mendel's Demon" - Mark Ridley [authors not closely related]
Mark Ridley's book is published in the U.S as "The Cooperative Gene".
He argues that (1) sexuality, i.e. the exchange of genes (which occurs
in bacteria as well as multi-celled forms), provides greater genetic
variety, hence phenotypic variety, hence adaptability, than mutation
alone, and (2) if mitochondria from the two parents joined in the
daughter cell they would fight (not hypothetical, there are examples
from other types of cells), hence it is to the advantage of the
species that the mitochondria from one of the parents be excluded from
the match. The gender that loses its mitochondria (hence contributes
only genes) we call male, the gender that keeps its mitochondria
(hence provides the basis of the new organism) we call female. So
gender (not sex) arises, in this hypothesis, from the Margolisian
symbiosis in which eukaryotes became aerobic.
> Their theory fails to explain why many plants are hermaphrodites - while
> few animals are.
But hermaphrodites are still bisexual; if I understand correctly,
self-fertilization is rare in the plant kingdom as well as the animal.
---
John Wendt
John Wendt
> But hermaphrodites are still bisexual; if I understand correctly,
> self-fertilization is rare in the plant kingdom as well as the animal.
>
Forget I said that; it's irrelevant.
There are human hermaphrodites; see for instance
http://www.devbio.com/chap17/link1711b.shtml. Development of primary
sexual characteristics seems to be a consequence of timing in
development, so that is where the answer might have to be found.
Separate sexes might not be an adaptation at all.
---
John Wendt
Tim Tyler
: j_w...@acm.org (John Wendt) wrote in message news:<36ab6b9c.02063...@posting.google.com>...
:> But hermaphrodites are still bisexual; if I understand correctly,
:> self-fertilization is rare in the plant kingdom as well as the animal.
: Forget I said that; it's irrelevant.
Drat - "with my reply poised on my lips" ;-)
: There are human hermaphrodites; see for instance
: http://www.devbio.com/chap17/link1711b.shtml.
Interesting - both fertile, I wonder?
If so, we could have had parthenogenesis a while ago ;-)
Boikat
found out it was fun.
Boikat
Richard S. Norman
Sorry. The first sexual critters were almost certainly pretty much
the same as each other. Male and female came along much later!
That doesn't meanit wasn't fun!
Earle Jones
"Boikat" <boi...@bellsloth.net> wrote:
*
Boikat: Your answer is probably a better answer than you realize.
Have you ever read Jared Diamond's book, "Why Sex is Fun"?
You might be surprised.
To most species, sex is not fun. Sex occurs only at specific times of
the season when the females become receptive and put out signals
(chemical, behavioral) to that effect.
Only in homo sapiens, do participants have sex around the clock, around
the year, independent of seasons of fertility.
Why?
Read Diamond's book.
He also wrote "The Third Chimpanzee, and won the Pulitzer prize for,
"Guns, Germs, and Steel." -- another great book.
Regards,
earle
*
John Wilkins
> In article <3d1fae2f$1...@news5.nntpserver.com>,
> "Boikat" <boi...@bellsloth.net> wrote:
>
> > As to the question posed in the thread: Because the first sexual critters
> > found out it was fun.
> >
> > Boikat
>
> *
> Boikat: Your answer is probably a better answer than you realize.
>
> Have you ever read Jared Diamond's book, "Why Sex is Fun"?
>
> You might be surprised.
>
> To most species, sex is not fun. Sex occurs only at specific times of
> the season when the females become receptive and put out signals
> (chemical, behavioral) to that effect.
>
> Only in homo sapiens, do participants have sex around the clock, around
> the year, independent of seasons of fertility.
Diamond's ironic comment is that if dogs were anthropologists, they'd
really wonder about these extremely atypical mammals, who have sex in
private, at all times of the year.
I wonder what they'd make of advertising - a dog might find selling a
car by placingit next to a really juicy bone more appealing than some
bitch being draped over it.
>
> Why?
>
> Read Diamond's book.
>
> He also wrote "The Third Chimpanzee, and won the Pulitzer prize for,
> "Guns, Germs, and Steel." -- another great book.
>
> Regards,
>
> earle
> *
--
John Wilkins
Sweet Analytics, 'tis thou hast ravished me [Marlowe's Faust]
Boikat
"Richard S. Norman" <rno...@umich.edu> wrote in message
news:tvcvhu0p36undf5ap...@4ax.com...
True, that would have started the slippery slope, so to speak.
Boikat
>
>
Cyde Weys
"Tim Tyler" <t...@tt1.org> wrote in message news:GyGKK...@bath.ac.uk...
> Richard S. Norman <rno...@umich.edu> wrote:
There are males and females so the two can get together and have a lot of
fun. There is fun when males and females get together (if you know what I
mean). Hmmm, a perverted tautology, what fun ...
Floyd
> In article <3d1fae2f$1...@news5.nntpserver.com>,
> "Boikat" <boi...@bellsloth.net> wrote:
>
> > As to the question posed in the thread: Because the first sexual critters
> > found out it was fun.
> >
> > Boikat
>
> *
> Boikat: Your answer is probably a better answer than you realize.
>
> Have you ever read Jared Diamond's book, "Why Sex is Fun"?
>
> You might be surprised.
>
> To most species, sex is not fun. Sex occurs only at specific times of
> the season when the females become receptive and put out signals
> (chemical, behavioral) to that effect.
>
> Only in homo sapiens, do participants have sex around the clock, around
> the year, independent of seasons of fertility.
Not "only" H. sapiens. Bonobos (_Pan paniscus_) are even more
amourous than we are, and use sex in much the same way as _P.
troglodytes_ uses grooming. That doesn't change the validity of your
point at all, since _P. paniscus_ is one of the two most closely
related species to humans (along with _P. troglodytes_), so this
"talent" may predate our split from them, with the common chimps
having secondarily lost it (or it may have arisen independently in
both Homo and P. paniscus, take your pick). HTH
>
> Why?
>
> Read Diamond's book.
>
> He also wrote "The Third Chimpanzee, and won the Pulitzer prize for,
> "Guns, Germs, and Steel." -- another great book.
>
> Regards,
>
> earle
> *
I second these suggestions, whole heartedly!
-Floyd
pz
far...@u.washington.edu (Floyd) wrote:
> Earle Jones <earle...@attbi.com> wrote in message
> news:<earle.jones-17F1...@netnews.attbi.com>...
> > In article <3d1fae2f$1...@news5.nntpserver.com>,
> > "Boikat" <boi...@bellsloth.net> wrote:
> >
> > > As to the question posed in the thread: Because the first sexual
> > > critters
> > > found out it was fun.
> > >
> > > Boikat
> >
> > *
> > Boikat: Your answer is probably a better answer than you realize.
> >
> > Have you ever read Jared Diamond's book, "Why Sex is Fun"?
> >
> > You might be surprised.
> >
> > To most species, sex is not fun. Sex occurs only at specific times of
> > the season when the females become receptive and put out signals
> > (chemical, behavioral) to that effect.
> >
> > Only in homo sapiens, do participants have sex around the clock,
Don't they ever get tired?
> > around
> > the year, independent of seasons of fertility.
>
> Not "only" H. sapiens. Bonobos (_Pan paniscus_) are even more
> amourous than we are, and use sex in much the same way as _P.
> troglodytes_ uses grooming. That doesn't change the validity of your
> point at all, since _P. paniscus_ is one of the two most closely
> related species to humans (along with _P. troglodytes_), so this
> "talent" may predate our split from them, with the common chimps
> having secondarily lost it (or it may have arisen independently in
> both Homo and P. paniscus, take your pick). HTH
Danio rerio will have sex every morning of every day, as long as they
are well fed and healthy. Every sexual encounter is also successful,
producing 50 or more fertilized eggs.
It's just human chauvinism to think that people are unusually sexy.
--
pz