Why did nature cause male and female to evolve, when the best method would have been to continue to asexually reproduce?

Why do you assume that asexual reproduction is “the best method”? I, in fact, would argue that evolution indicates that it’s not the best method to get the gene pool mixing.

How would evolution know it had the goal of gene pool mixing?

If we all just “bud” and split off, my daughter would be just like me. But sexual reproduction allows genes to combine in new and novel combinations each time, sort of like an experiment. Sometimes, the result is better than either parent, and thus the species improves.

In other words, for some species, sexual reproduction is better, and that’s why it’s stayed around. Evolution doesn’t have “goals” – but its better experiments would flourish while failures generally die out.

You’ve answered your own question. Sexual reproduction is better.

Evolution is not a sentient being that “knows” anything. It simply is. Many species survived because of genetic diversity caused by accidental mutation, not some grand puppet master called “evolution”.

Nature does not know or cause anything. Whatever survives, survives. When conditions change, different traits become advantageous or detrimental.

So, regarding the original question – if you mix up genes, you spread successful traits and mutations around, making the offspring more able to survive.

@squirbel ”How would evolution know it had the goal of gene pool mixing?”
A fair question, especially with such teleological phrasing. Our body cells undergo asexual reproduction all the time in the form of mitosis. Sexual reproduction at the cellular level only occurs in germ cells—eggs and sperm.

The evolutionary “invention” (i.e., appearance as a heritable mechanism) of sex is still largely a scientific mystery due to lack of evidence, lost in the mists of time.

We know that all prokaryotes (single cells with a circular strand of DNA & lacking a nucleus) divide by mitosis. Sexual reproduction involving meiosis of germ cells only occurs in eukaryotes (mostly multi-cellular organisms whose cells have nuclei and whose DNA is organized as paired chromosomes.) This made possible a distinct X and Y chromosome (or Z and W in some animals) to allow sexual dimorphism—differences between male and female.

By the usual Darwinian mechanism of random variation with natural selection, meiosis somehow arose, allowing offspring to reshuffle the genes from two different parents. From then on it would have been wildly successful, because variation could proceed by sexual recombination, picking up the pace of evolution compared to relying on spontaneous mutations alone as mitosis does.

Note that both plants and animals are eukaryotes and can reproduce sexually.

Natural Selection – Evolution does not have any goals. What I try to keep in mind when it comes to evolution is: if something exists, there is probably a survival benefit.

With that in mind, asexual creatures are highly succeptible to mass extinction from disease. When you share so much DNA, there is no variation to allow for survival. I’m not saying this is the reason we have male and female, but it could no doubt be a factor.

Evolution would not have known it had the goal of gene pool mixing, it would have had no goals. But when it happened, and worked, it stuck around.

EDIT:

The way I picture it when I speculate further, the first male and female where probably at the single cell level, and probably freaks among their own kind. they where probably then very successful, and eventually speciated from the original cells. There is no reason why one should be doomed if the other was successful, and hence now days we see a mix of methods.

Major changes in the development of a species happen because of random genetic mutations. Some of these are better for survival and so have a higher chances of getting passed on and some of them are worse for survival and so have a lower chances of getting passed on. As people above have stated, gene mixing seems to be a trait that leads to a higher chance of survival and so when a split in genders came about from random changes it got passed on.

A lot of mistakes in thinking about evolution come from the fact that we talk about it as if its a force that “wants” a species to survive. This is not true. Evolution is just the natural result of a world with a) competition for survival and b) random genetic mutations.

Asexual reproduction has its advantages, but sexual reproduction has it beat hands down. The mingling of DNA from two different members of the same species will result in a more viable organism than does simply “cloning” one individual together with all the attendant imperfections of the original.

Many people are of the opinion that we were created that way.

Because sex is essentially great.. :p

@krrazypassions

Well, yah… that too! : D

In simple terms, the “female” creatures more than a billion years ago invented a new type of “health insurance” for their offspring being faced with ever-changing environmental conditions. The insurance came in the form of a male partner.

Instead of relying on a small number of mutations for dealing with change, this innovative step offered a combinatorial explosion of possibilities.

Sex was the greatest invention since the advent of nucleic acid.

People still enjoy it today.

An article published in Science last week addresses this issue. Using nematode hosts and one of their bacterial parasites, scientists found support for the Red Queen hypothesis:

In reference to an evolutionary system, continuing adaptation is needed in order for a species to maintain its relative fitness amongst the systems being co-evolved with.

Sexual reproduction increases the rate of adaptation, thus increasing an organism’s fitness within its ecosystem, which is filled with also evolving predators and parasites.