Now a biologist at Michigan Technological University has found one good reason: sexual reproduction strengthens an organism’s ability to adapt; specifically, it may lead to stronger disease resistance.

Erika Hersch-Green tested the idea on 32 different species of evening primroses. These native North American wildflowers are unusual in that a number of species reproduce asexually, essentially through cloning themselves. That allowed Hersch-Green and her colleagues to compare 16 species that reproduce sexually with an equal number that function asexually.

“We found that the sexual plants have an increased ability for adaptive, positive evolution,” she said. “That’s in line with many of the theories of evolution of sex.”

Scientists believe that sexual reproduction offers two big advantages: It can sweep bad mutations out of the gene pool more quickly. Also, by shuffling parents’ genetic material e