Human cell lines regress to become ‘de-sexualized’ by reconfiguring to a 2:3 X/A ratio of high fitness, thus shedding light on the evolution of mammalian sex chromosomes.

Many different human cell lines, including both normal and cancer cells, appear to converge to a state that contains an unusual number of chromosomes when they are grown in culture.

The evolution columbine genus involved frequent mixing between incipient species, and one chromosome appears to have taken its own path.