Figure 1.

Contagious Cancer Cells May Have Contributed to the Evolution of Sex

(A) Asexual reproduction results in low genetic diversity and high inter-individual similarity within a population that can lead to increased risk of vertical and horizontal transmission of contagious cells.

(B) Sexual reproduction results in greater genetic and inter-individual diversity in a population that limits the transmission probability of contagious cancer across individuals. Recognition of invading non-self cells is facilitated by higher inter-individual diversity. Selfish malignant cells regularly emerge in an organism, but unless the rare confluence of environmental and genetic factors occur (“perfect storm”), transmission of contagious cells will not occur (modified from Thomas et al., 2019).