MANY HAVE WONDERED exactly what this whole human sexual reproduction thing is about – but sadly it turns out the truth isn’t that sexy.

In fact, it turns out we have – wait for it – parasites to blame for our need to have sex.

Indiana University biologists discovered that what prevents humans and other species from self-fertilisation is that sex between two individuals keeps them one step ahead of their biological enemies.

The study title – Running with the Red Queen: Host-Parasite Coevolution Selects for Biparental Sex - came from biologist Curtis M Lively’s Red Queen Hypothesis, which itself was inspired by a line in Through the Looking Glass by Lewis Carroll.

The scientists showed that by combining the DNA of two parents, sex allows them to produce offspring that are genetically diverse.

This is different to self-fertilisation, where the offspring inherit the DNA of their single parent and so are open to being infected by parasites.

Luckily the team didn’t turn to human volunteers to prove their hypothesis – instead, they used the microscopic roundworm Caenorhabditis elegans as a host and the pathogenic bacteria Serratia marcescens to conduct the experiments with.

The team behind the study were Levi T Morran, Curtis M lively of the IU Bloomington College of Arts and Science’s Department of Biology along with biology undergraduates Olivia G Schmidt, Ian Gelarden and Raymond C Parish II.

Read more on the Indiana University website and in Science Daily>