Evolutionary Proof That (eating) The Chicken Came Before The Egg

"Feeding on the eggs of birds or of squamate reptiles (lizards and snakes) tends to occur in lineages that already feed on birds or squamates," explain the authors. Specifically, the researchers examined snakes that have specialized in eating eggs, finding that, in this case, the chicken came before the egg.

The researchers compared the family tree for four snake species that specialize in eating eggs and found that their ancestors originally ate the lizards that lay the eggs. It might just be that the eggs are in the same location, but there is another possibility. Snakes use chemical cues to recognize prey, and the authors suggest that these snakes may recognize eggs as potential food because of the chemical similarities between eggs and the corresponding animals, just as some insects are attracted to novel food plants that share chemicals with the insects' typical food sources.

"The effects of predispositions on the origins of egg-eating and, ultimately, the evolution of highly specialized egg-eating taxa, represent subtle but important historical influences on the present-day attributes of species," conclude the authors.

Alan de Queiroz and Javier A. Rodriguez-Robles. "Historical contingency and animal diets: the origins of egg-eating in snakes," The American Naturalist 167:5.