Michael Le Page tells us at New Scientist that the common Eurasian lizard, Zootoca vivipara, gives birth to its young.
But there are exceptions. Two small populations on the edge of the common lizard’s range lay eggs. One of these subspecies is found around the border between Spain and France, and the other in the southern Alps. More.
This is identified as “a rare example of a species re-evolving a complex trait that had been lost.” (paywall)
It’s odd the way terms around evolution are used. Why should we assume that the trait was “lost”?
Anyway, Josh Davis at IFL Science notes,
To test this, researchers carried out genetic analysis of over 70 lizards collected throughout their range in Europe, in order to flesh out a detailed evolutionary tree. Their results are published on bioRxiv.
It turns out that the tree is a little more complicated than they originally thought. The population of egg-laying lizards still knocking about in the Alps did indeed turn out to be a remnant group of the original egg-laying reptiles. But the lizards laying eggs in Spain were found to have re-evolved this ability, meaning that evolution basically went backwards.
This is interesting since in 1893, Belgian palaeontologist Louis Dollo presented a principle that in effect said that evolution is unidirectional, and so once an organism looses a complex trait (such as egg laying), it is not able to re-evolve it, even if it was to once again find itself living in the same environment. This is known as Dollo’s law, however the new analysis of the common lizard adds to mounting evidence that this is not strictly true.
As a matter of fact, Dollo’s “Law” has been known to be nonsense for decades but it still walks abroad as one of the ghosts of Darwinian Zombie Science.
A more likely explanation than convoluted Darwinian evolution claims is that egg-laying and live birth are simply innate alternatives for adaptation in reptiles and that successful types do not readily lose the alternative.
But to suspect that would, of course, eliminate Dollo’s Law. Science wouldn’t survive.
See also: Remember Dollo’s Law?: Once a trait was lost through evolution, it could not be regained. (2011)
And about a frog: Apparently, G. guentheri has acted in violation of Dollo’s law, according to which traits lost through evolution cannot be regained.
Devolution, the skinny: Getting back to the simple life