In evolution, what are the steps between asexuality and sexuality?

Question

I'm not anti-evolution. I'm just wondering, how can a species evolve from asexuality to sexuality? Would it have to go through a period where it could do both?

And what came first, the ability to have sex to have kids, or the pleasure the comes from having sex? Neither would help much without the other.

Answer 1

The development of two-gender sexual reproduction from complete asexual happened way back in both single-celled and early multi-cellular organisms, and happened in various stages. There wasn't a sudden leap from asexual reproduction to the type of two-gender sexual reproduction that we practice.

The stages are too numerous to list here ... but (1) there are examples of each still in nature that indicate how it works; and (2) each stage has advantages, which explains why it would have propagated due to natural selection.

For example, even bacteria often exchange genetic material in what's known as 'bacterial conjugation'. Some other species (like aphids) practice both asexual and sexual reproduction (sometimes reproducing sexually, but any individual able to clone itself into multiple offpring when partners aren't around). And so on.

Sexual reproduction had *huge* advantages to those organisms that discovered it. Every new individual is not only a complete individual, but also a unique individual ... different from either of its parents.

But later stages produced many versions of sexual reproduction with various forms of gender. As mentioned earlier, in most (but not all) flowering plants, for example all individuals are both male and female. In some organisms (like many insect species) males and females are determined not by the genes of the individual, but what it is fed during early development. In other organisms, each individual can become male in some phases of life, and femal in another. In other organisms, males and females are determined by genetics (the presence or absence of a Y chromosome) ... but this is actually not as different from the insect case as it might appear. Development of males and females structure is not determined completely by the genes, but rather than the hormonal environment during development (which is *usually* triggered by the genetics of the offspring, but can be overridden accidentally by hormones).

Finally, while the differences between males and females in humans seems pretty obvious to us (since it's part of our survival that we are *tuned* to see those differences) ... these differences are not so pronounced in other species. The main difference is that during reproduction, one produces the kind of gamete that is small and mobile and produced in large quantities, while the other produces the kind of gamete that is larger so that it can *receive* DNA, and begin the process of cellular reproduction to become a new organism.

Other than that ... all other differences between males and females are just secondary differences that get more and more pronounced in later vertebrates, in mammals, and eventually in primates like us.

As for the concept of sexual pleasure ... if pleasure was necessary before the ability to reproduce, then life wouldn't have lasted very long in the bacterial stage. In other words, things have been reproducing as long as there has been life ... everything from bacteria to crocodiles reproduce ... whether they find it "pleasurable" as we mammals do is hard to tell.

Answer 2

Now I'm not that knowledgeable on the subject, but I believe it was very early on. Certain one celled organisms would sometimes "combine" with other one celled organisms of the same species while reproducing asexually. This sometimes created a mix of their DNA to be produced.

In evolution, the more variety in a population, the better. This is because the more differences, the more differences can be weeded out or promoted as good differences. So reproducing sexually instead of asexually is a benefit. So the organisms that started mixing DNA, eventually evolved to always reproduce by combining genes. This led to sexual reproduction.

Answer 3

Originally animal reproduction was a sexual. There were only females. Unfortunately having only one source of genes insures defects will be passed on. When the male gender evolved it brought diversity to the genetic chain so that the stronger product had a tendency to survive.

There are still a few species having only female gender.