The progress of evolution

Understanding a recent study done by researchers on the Eurasian common lizard which exhibits both egg-laying and live-bearing modes within the same species

Recknagel, H., Carruthers, M., Yurchenko, A.A. et al. “The functional genetic architecture of egg-laying and live-bearing reproduction in common lizards.” Nat Ecol Evol 1546–1556 (2021). https://doi.org/10.1038/s41559-021-01555-4

Convergent evolution is a phenomenon where different species evolve similar characteristics though they come from very different lineages. For example, birds, bats and insects have all evolved the power of flight through very different evolutionary pathways. In this context, it is an impressive statistic that live-bearing behaviour or viviparity (as opposed to laying eggs to beget young ones or oviparity) has evolved independently in vertebrates at least 150 times. In reptiles alone, it has evolved independently some 121 times, and to specify further, in squamates (a group including lizards, snakes and worm lizards or amphisbaenians) it has evolved independently 115 times. It is perhaps not surprising then, considering the many routes taken by evolution in forging this difference, that within this group there should be seen this rare incidence of both behaviours (oviparity and viviparity) within the same species: the Eurasian common lizard (Zootoca vivipara).