The puzzle of why animals have sex and the evolutionary purpose of seemingly ''useless'' males has been answered by a pair of University of Otago researchers. David Green, from the anatomy department, said the prevalence of sex in the animal and plant kingdom had puzzled scientists for the past 40 years.
This was because sex, when compared with clonal reproduction, was inefficient due to the need for males, which were seemingly ''fairly useless'' from an evolutionary standpoint.
''The cost [of sexual reproduction] is the cost of males, because males fundamentally are fairly useless. They provide 50% of the genetic material, and only sometimes help with the upbringing,'' Prof Green said.
The inefficiency of sex gave rise to the question of why more organisms did not reproduce by cloning themselves, like some species of stick insects or dandelions, and why organisms reliant on clonal reproduction typically became extinct sooner.
Using computer software developed by co-author Chris Mason, it was found that species solely reliant on clonal reproduction did not respond as quickly to pathogens, which themselves evolve rapidly, to outwit immune systems. This was because in periods of rapid environmental change, clonal species produced a multitude of ''lines'' with different mutations which competed with each other, slowing down the process of natural selection.
''If you have lots of independent [lines] that are very similar, it's difficult for natural selection to act on them and produce a winner quickly, because they are all interfering with each other.''
This phenomenon, called clonal interference, meant that sexual reproduction, despite its inefficiencies, provided a faster and more effective defence against disease. The findings were part of a paper published in the journal BMC Evolutionary Biology and Prof Green said it was exciting to answer a question which had been puzzling scientists for so long.
''People have been unable to come up with a fully fledged answer for 40 years,'' he said.
