evolution of reproduction

[theod]

Why / how did organisms evolve reproduction?

[mith]

you could be more specific...

[Danniel]

reproduction was already present even before life started, but many adaptations for reproductions came to evolve later.

First types of reproduction, pre-biotic were like reproduction of peptides, and nearly purely mechanical processess... eventually it evolved to cells which reproduce more like extant unicellulars do, by a history that no one knows yet exactly how could have been. In between there are viral reproduction, which still persists, and perhaps had its role on the evolution of life as it is presently.

Unicellulars reproduce just by cellular reproduction, which is a whole process that perhaps is well described here:

http://en.wikipedia.org/wiki/Mitosis

Primitive multicellulars probably were somewhat like present day Volvox and others, which are basically unicellulars, but sometimes gather forming a colony that is somewhat like a multicellular organism, even with some primitive "tissue" or body organization.

The next step was that the communal form was more well established, and tissue specializations were more evolved, but reproduction was sitll in form of a part of the organism simply tearing apart and a new organism growing from that broken part while the parent would "heal" the lost part.

Some organisms (like some sort of jellyfishes, I guess) have primitive specialized body parts for reproduction that are just a tissue whose cells are fragmented and spread free, eventually growing into an adult form.

It actually does not differ much in essence from more complex reproduction in some senses, the oogenesis and spermatogenesis is just the growth and release of cells by specialized tissues, but the cells achieved a higher degree of specialization, are more environment-dependant, and these specialized tissues are organized more inside organisms within tubes and chambers.

Actually I've omitted totally the part of haploidy of germinal cells, but I do not know how it evolved quite well, but in general lines the recombination were advantageous and then rather than releasing clonal or nearly clonal cells to reproduce, some organisms released random shuffling of the "halves" of their genomes in some cells, and these would then met another half and make a complete genome.