#1 - Posted: 10/08/2008 02:07
I remember reading a Discover Magazine article asking the same question. The author was confused on how sexual reproduction evolved considering the fact (belief of the author's?) that asexually reproducing organisms can reproduce faster and should win out over sexually reproducing organisms. The organisms in the article were divided into sexually and asexually reproducing organisms. I think a large part of the author's confusion was the fact that he/she neglected the large number of organisms that are capable of both sexual and asexual reproduction. It appears that asexually reproducing organisms appeared on earth first then these organisms developed the ability to exchange genes with other organisms while retaining the ability to reproduce asexually ( for example bacteria). Later, the gene exchanging mechanism evolved more and more into what appears to us as sexual reproduction. Look at Volvox and Algae.
The sexually reproducing organisms that can't reproduce asexually may have evolved from the asexual/sexual organisms and lost the ability for asexual reproduction probably because they have a niche and/or developed defenses that allow them to effectively compete with asexually reproducing organisms which are mostly single celled organisms.