That's an interesting bunch of questions. I'll start with the ones with better-known answers, before moving toward guess-work.
> Evolution is "like" the survival of the fittest, but which "gender" is more "fit" than the
> other? How come the weakest gender is not "kicked out" or "eliminated" by nature?
It's important to understand first a basic idea. Creatures are not born with a fitness rating stamped on their skin. How fit a particular creature is depends very much on what its environment is like too. Sometimes that's obvious- it doesn't pay to be a fish out of water. Other times are more interesting. With sex, the fitness of each sex depends on how many of the two sexes are around. It's pretty obvious that if there were a huge surplus of males, it wouldn't be 'fit' to be a male, because then your odds of being in the minority of males who have offspring would be low. On the other hand, if there were a big surplus of females, it would be very fit to be a male because you have a great chance of having descendants. Remember here, in evolution 'fit' just means 'likely to have lots of descendants'. If we follow that reasoning more carefully, we find that in species like ours, natural selection favors almost exactly equal numbers of male and female offspring. Here's a brief explanation.
Let's assume (correctly) that the probable sex of offspring is partially controlled by parental genes. In typical mammal species, there are some basic rules. Each offspring gets very nearly half of its DNA from each parent- one male and one female. Nobody changes reproductive sex after birth. Male and female offspring are about equally costly to raise. So since the total numbers of offspring of males and females are exactly the same, the payoff in grandchildren per cost is higher if you have the less numerous sex of child. If somehow things got out of whack and more of one sex were being born, selection for different genetic tendencies to have males or females would bring the numbers back toward equal. So evolutionary theory predicts that under normal circumstances similar numbers of males and females are born. (There are special cases where that temporarily doesn't apply, and there is evidence that in those special cases the numbers born are typically not equal.)
Now in other species, some of these basic assumptions don't hold, and so neither do the conclusions. In some fish, there's only one male per school. When it dies, the largest female converts to a male. Insects like bees don't pass on equal fractions of their DNA through male and female lines. In other species the sizes of the sexes can be radically different, so the costs of having males and females aren't the same. All these factors can give very unequal male/female ratios at birth. However, one part of our story doesn't change. If there's a relative shortage of one sex, that sex becomes the one that's more fit, and evolution finds a way to replenish it.
> This will move into the origin of the two "genders"...so...what and how from the eariest
> complex molecules and or life forms made this evolution happen?
The most common life forms, bacteria, do not have distinct sexes. They do, however, trade genetic material some. Now an obvious question is what would make it pay for organisms to have to go through sex in order to reproduce. (Of course sex is fun, but that's an after-effect of its evolution, not the cause.) Sex is costly and uncertain, compared to simple single-cell splitting. So why don't asexual reproducers win out? There is both theory and evidence on this question. One of the big effects of sex is that it makes each generation have a somewhat scrambled set of genes, not like either parent. That makes it much harder for bacteria and viruses to evolve to attack the offspring- they're a moving chemical target. In the few cases where animals (fish in isolated ponds, if I remember right) are known to reproduce asexually, it's been found that exposure to a wider variety of organisms (opening up the ponds) can drive the group to evolve back toward sexual reproduction, at least if I remember right.
There's a book called "Why is sex fun?" which analyzes the special functions of sex in human evolution, and Iíve heard itís a lot more careful than my amateur answers.
> Um...uh...hmm...so...when the earth was "formed", complex molecules were also
> "formed", and the simplest forms of life evolved from them, why, and how?
This happened a long time ago, and didn't leave any ordinary fossils, so we have to guess a lot. I'll just give a few conventional thoughts. In order for some molecules to start evolving, they have to have a tendency to make pretty good copies of themselves, and they have to have some ability to promote chemical reactions helping to promote that copying. Looking at the two most commonly discussed types of complex biomolecules, neither fits the bill. Proteins are great at catalyzing reactions, but they don't have any simple way to guide making copies of themselves. DNA makes a great template for copying, but is lousy at catalyzing reactions.
Thinking about this issue, people long ago figured that RNA was a better bet for an important early molecule, because it is pretty good at guiding self-copying, and can fold up into a variety of shapes that catalyze chemistry. A few years ago, the molecular structure of the ribosomes was finally sorted out. Ribosomes are protein-RNA complexes that guide the formation of proteins. These ribosomes are very similar in all life, so they seem to be remnants of early ancestors. The most 'conserved', unchanging part of the ribosome turns out to be a stretch of pure RNA that directly catalyzes the key reaction. That's just what was expected based on the idea that early self-reproducing chemistry had to bootstrap up to more complex life. So this observation nicely confirms the general idea people had about how the early chemistry of life must have worked.
Now that's only one little piece of the story of the early pre-life chemistry. No one knows how much of that ancient story will ever be known. In comparison, the story of the evolution of life once it got going is better understood and supported by a huge array of evidence.
(republished on 07/18/06)