SRY has been lost in at least two groups of rodents. The mole voles of eastern Europe, and the country rats of Japan have no Y chromosome, and no SRY, Professor Graves said. Somewhere else in their genome, a new sex determining gene must have taken over the function of SRY. Which gene or genes took over this task, and how they work, are questions we will be investigating in future.

Professor Graves predicts that as the human Y-chromosome deteriorates, one or more sex-determining genes will develop, possibly within different human populations.

What would happen if different new sex determining genes arose in different human populations? Could mole vole man breed with country rat woman? Probably not, so the two populations would ultimately become different hominid species.

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