If humans came out of the primordial ooze why are there two sexes?

Question

Wouldn't it make more sense that we would have emerged hermaphrodites and reproduce asexually?

Answer 1

Producing asexually means that there is much less genetic variation. Gametes fuse to create zygotes (offspring) that are genetically different from their parents. This allows their fitness (ie chances of survival and reproduction) to increase.

For example, imagine if a population in tropic climate was all hairless. If a sudden change in the environment causes temperatures to plummet, all the individuals would die. If there is genetic variation that led to furry individuals, those could continue to reproduce. Genetic variation is like a safety net.

By the way, mutations are another way for variation, but those are random.

Answer 2

Shall we leave out the unnecessary polemic introduction to your question and pretend you asked 'why are there two sexes?' You make it sound as if humans emerged fully formed from a sea of slime, Aphrodite-like, and no scientist in their right mind has ever claimed such a thing.

Yes, it would make more sense and in fact it happened, but if you reproduce asexually, you're not an hermaphrodite.

Asexual reproduction is fast; you don't need to spend time and resources to find a mate; one cell division is all it takes. But it allows for very little variation.

Sexual reproduction evolved by degrees, possibly several times in the course of evolution. It means a waste of resources for the individual, but it makes a population less prone to be wiped out in case of a catastrophe - extreme frost, for example. Because of the larger variation allowed, *some* individuals can survive and spread again in an environment that has been cleared of competition.

It is unlear how sexual reproduction evolved. My (rather uneducated) guess is that it came from a process similar to bacterial conjugation; I wouldn't even rule out that it's the result of some infection or parasitation in which by chance the DNA of the host ended up in the transferred particle instead of the parasite's.

However, first organisms capable of sexual reproduction had no gender; any two gametes could match and rebuild a new individual. Relics of this behaviour are still present in fungi.

'Sexes' evolved later.

Some mutant individuals produced gametes with a larger citoplasm, which were less mobile because of their size but increased their chance of reproduction because of the nutrient surplus. Of course they could only make so many of these large gametes.

Other mutant individuals produced a LOT of mobile smaller gametes, also increasing their chance of reproduction.

Natural selection favoured the result of large+small gamete encounter; large gametes did not meet, small gametes had too low energy reserves to survive but in the most favourable condition... therefore individuals evolving adaptations so that their gametes could reach the 'opposite' gametes were favoured. Another bonus coming with sexual reproduction was diploidy but that's another subject.

Both in plants, animals and seahorses, we call the individual making a limited number of large immobile gametes female; we call the individual making a large number of small mobile gametes male.

Answer 3

s*x is beneficial.  Spreading genes around a population defeats Mueller's Ratchet, amongst other problems.  Virtually every organism has some method of gene transfer.  For complex organisms that can't use plasmids, sexual reproduction is necessary.

The entire benefit is lost if you reproduce with yourself.

It was simply advantageous, so any population that happened to evolve this pattern survived better than those that did not.

Answer 4

Life *did* emerge asexually.  But since sexual reproduction offers an advantage we evolved over time to have two sexes.  After going through many steps including sexual reproduction without defined sexes (simple exchange of genetic material from one individual to another.)

No, moving towards something that offers an advantage does not imply intelligent thought in the least bit.  Ever heard of natural selection?  Traits which offer a higher survival rate get passed on because more individuals survie TO pass them on.