New research finds that sexual reproduction and multicellularity drive diversity among different species.

A new University of Arizona-led study, published in the Proceedings of the Royal Society B, tested whether sexual reproduction and multicellularity might help explain this mysterious pattern.

«We wanted to understand the diversity of life,» said paper co-author John Wiens, a professor in the Department of Ecology and Evolutionary Biology. «Why are most living things animals, plants and fungi?»

To address this, Wiens worked with a visiting scientist in his lab, Lian Chen from Nanjing Forestry University in China. They estimated rates of species proliferation in 17 major groups that spanned all living organisms, including bacteria, protists, fungi, plants and animals. The hard part was to estimate how many species in each group were multicellular versus unicellular and how many reproduced sexually versus asexually. For five years, Chen sifted through more than 1,100 scientific papers and characterized the reproductive modes and cellularity of more than 1.5 million species.

They found that both multicellularity and sexual reproduction helped explain the rapid proliferation of animal, plant and fungal species. The rapid proliferation of these three groups explains why they now include more than 90% of Earth’s known species.

The duo also found that the rapid proliferation of sexual species may help explain the «paradox of sex.» The paradox is why so many species reproduce sexually, despite the disadvantages of sexual reproduction.

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Materials provided by University of Arizona. Original written by Mikayla Mace Kelley. Note: Content may be edited for style and length.