EVOLUTION

Sexual Healing

Sex arose as a means to mix DNA

and thereby boost genetic diversity,

according to standard evolutionary

theory. But it may also exist

to help repair DNA damaged by

environmental stress, such as heat,

for fitter offspring. Work supporting

this idea exists for single-celled

life-forms, so evolutionary biologist

Richard Michod of the University

of Arizona at Tucson and

his associates experimented on a

multicellular species, the green alga

Volvox carteri, which can reproduce

both sexually and asexually.

Volvox colonies heated for 10

minutes to 42.5 degrees Celsius

had twice the number of DNAdamaging

oxidants as unheated

ones. Researchers found that these

high oxidant levels triggered the

microbe’s genetic pathway for sexual

reproduction, leading the algae

to release mating pheromones. The

report appears in the June 9 Proceedings

of the Royal Society of

London B. —Charles Choi

www.sciam.com SCIENTIFIC AMERICAN 29

AUGUST 2004