Birds Do It, Bees Do It…But Why?

A mating pair of albatrosses; photo by William Allen


As any biologist will tell you, sex doesn’t seem to make sense. It requires males, which waste resources but don’t directly produce offspring. Why bother with males at all when asexual reproduction–where offspring arise from a single parent through self-fertilization–is so much more efficient?

According to a team at Indiana University, it all comes down to parasites. Some parasites co-evolve with their host organisms so that they can continue to infect new generations. Self-fertilizing organisms essentially produce copies of themselves, making them easy targets for infection. Meanwhile, with sexual reproduction, the DNA of two parents is combined, making it more difficult for parasites to adapt. The IU team demonstrated this by comparing round worms that mate sexually to those that self-fertilize. When faced with the threat of co-evolving pathogenic bacteria, the asexual worms were rapidly driven to extinction, while those that mated sexually were able to adapt and survive.  In a sense, we may have parasites to thank for sex.

The results of this study were published in the journal Science.

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Meet the Author
Since 2005, Michael has been a librarian at National Geographic.