Evolutionary questions ants’ered

Ian Kaufman
News Writer

Dr. Ehad Abouheif, presented his research on natural selection in ants, last Wednesday, at the ATAC. Photo by Patel Lab.

One hundred and fifty years ago, in his seminal On the Origin of Species, Charles Darwin wrote of “one special difficulty, which at first appeared to me insuperable, and actually fatal to the whole theory.”
This was not an advance warning about creationists; the real challenge to his theory of evolution comes from a much larger and better-organized group: ants.
Most of us, understandably, don’t think too much about ants, except perhaps when we are warding off one of their perennial springtime home invasions. A presentation last Wednesday by evolutionary biologist Dr. Ehab Abouheif gives us reason to rethink this nonchalance.
Abouheif, who studied at Duke and Berkeley and is now a Canada Research Chair in Evolutionary Developmental Biology at McGill, points out that not only do ants outnumber humans worldwide, but collectively, they even exceed total human biomass. Their level of social organization, he says, is second only to humans.
Abouheif’s interest in them coincides with the above-mentioned “special difficulty,” what he calls “Darwin’s greatest dilemma.”
In short, the problem was this: many ant species have developed “sterile castes” – worker ants incapable of reproduction. These species rely instead on a queen ant to produce offspring.
This phenomenon baffled Darwin, who struggled with the seeming contradiction of naturally-selected sterility. As Science Daily now puts it, “if adaptive evolution unfolds by differential survival of individuals, how can individuals incapable of passing on their genes possibly evolve and persist?”
At the time, Darwin hypothesized that perhaps natural selection was working on a broader level: that of the group or “family” rather than the individual.
Abouheif’s recent research has now confirmed that idea.
“Evolution has tinkered with the molecular signals that are used [by the workers’ eggs] to determine what’s going to be the head and what’s going to be the tail, to stop the worker ants from producing viable offspring,” he explains. He calls this “reproductive constraint.”
As for why sterility would be a trait selected for in evolution, it apparently leads to higher cohesion, as there is no competition with the queen to reproduce, and allows worker females to instead lay “trophic eggs,” which serve as a food source.
As Abouheif commented, after learning about the complexity of ant society, you’ll probably think twice the next time you consider bringing your shoe down on one.