What came first, the chicken or the egg? Professor Mohan Matthen of U of T’s Institute for the History and Philosophy of Science and Technology believes it is the egg. In his recent lecture
Chickens, Eggs, and Speciation, Matthen proposed a new way of thinking about species membership that attempts to resolve longstanding issues. “Species ought to explain similarity or [DNA variations] or whatever distribution there happens to be within a number of organisms in the same species,” he said. His explanatory species concept identifies factors that are responsible for the structure of populations. It is not intended to isolate one species from another, but to explain why things happen.
Organisms belong to the same population if their genes are relatively easy to combine. So, although the first “chicken” may be dramatically different from its predecessors (“pre-chickens”), it is reproductively integrated with “prechickens,” meaning it is in evolutionary competition with them. Genetically and ecologically, it is part of the same group and is therefore a member of the “pre-chicken” population.
“Reproductive and ecological integration is a property of populations,” said Matthen. “It is there that organisms exchange genes, and it is there that they have ecological challenges, and natural selection can take place. Individuals can go from one population to another and can integrate into the population that they go to. Species are simply collections of these populations. On this proposal, an organism belongs to a species because it belongs to a population that belongs to the species.”
A new population is formed when, over the span of evolutionary time, “chicken-types” develop an advantage over “pre-chickens” and it becomes profitable for “chicken-types” to mate with other “chicken-types.” Eventually, the two types of organisms may drift so far genetically from each other that they can no longer mate between groups. “That population, because it is cut off from the other ‘pre-chicken’ populations, is the ‘chicken’ population,” explained Matthen.
On this hypothesis, there can be a moment of speciation (M), where “chicken-type pre-chickens” become “chickens.” In this scenario, there are many “first chickens.” However, there are also many eggs around when the two groups become reproductively isolated from each other. If an egg is a chicken egg because there is a chicken in it, then these would be pre-chicken eggs before ‘M’ and chicken eggs after ‘M’, and there would be no real winner in the chicken and egg debate. However, if an egg is a chicken egg because a chicken hatched from that egg, then these eggs would be chicken eggs before ‘M’, because they will hatch chickens after ‘M’. Therefore, the eggs do come first, but the process by which this conclusion is reached is different.
Another surprising conclusion that can be drawn from this controversial species concept is that it is possible for an organism to change species membership over the course of its lifetime.
