August 22, 2009. I am at the annual meeting of the European Society for Evolutionary Biology (ESEB) in Turin, Italy. Twelve hundred evolutionists have gathered to strut their stuff and party over a five-day period. I'm here to speak at a symposium on levels of selection that is being held on the first day.

The symposium is one of six held concurrently and all of them are preceded by a plenary talk in a room large enough to accommodate everyone.

The plenary speaker is Hanna Kokko, a theoretical biologist from Finland who has risen to the top of her field. I just turned 60 and Hanna seems awfully young to be giving plenary talks, but anyone who worries about women in science should see her lead a huge audience through her theoretical models on diverse ecological and evolutionary topics.

Hanna's first two examples illustrate the fact that evolution at a local scale can be maladaptive at a larger scale and can even lead to extinction. In the first example, a species of fish in which the females are asexual but still need to mate with males of a sexual species for their eggs to develop outcompetes the sexual species and therefore drives itself locally extinct. In the second example, an endangered bird species on a small island evolves large territory sizes, reducing its population size and increasing its chances of extinction. If local evolution favors traits that are so detrimental over the long term, how can more sustainable traits evolve? When Hanna mentions group selection as a possibility, she shows this image of a man so panicked that he's about to jump out the window (thanks to Hanna for providing me the image).

No one laughed harder than me at Hanna's humor slide, which speaks volumes about the current status of group selection among professional evolutionists and evolutionists-in-training. Group selection is still a taboo subject that seems shocking when seriously invoked. Most people in that vast audience had been taught only one thing about group selection: Don't do it. Can you imagine this image making sense, even as a humor slide, for any other subject in evolutionary theory?

Hanna's plenary talk is the perfect advertisement for the levels of selection symposium. The room is filled to capacity. The first speaker is Samir Okasha, an excellent philosopher of biology and author of the highly regarded Evolution and Levels of Selection (2006). I can follow Samir's presentation but sense that most other people in the audience are mystified. They need a basic tutorial explaining why group selection is no longer taboo. Samir is discussing highly derived issues, such as the merits of different covariance formulas and types of group selection.

I'm up next and try to provide the tutorial that I think the audience needs, starting with the all-important original problem that I have stressed throughout this series. I assure you that it was new material for most people in the audience. That is the degree to which the stigmatization of group selection has led to basic ignorance within the profession. The remaining speakers give a whirlwind tour of current topics in multilevel selection theory, including species-level and ecosystem-level selection. Daniel Rankin and Kevin Foster, the symposium organizers, are pleased with the result of their labors and feel that they have provided an important service to their scientific community.

But the anti-group selectionists aren't going quietly into the night. Andy Gardner, a young theorist who won last year's prestigious John Maynard Smith award, is scheduled to speak at a symposium on cooperation the next day. He actually changes the title of his talk to "Why I Am Not A Group Selectionist" in response to the levels of selection symposium. Whatever he means by this title, he has no quarrel with the fact that between-group selection is often a significant evolutionary force, as measured for example by the Price equation. His talk and the other talks in the cooperation symposium are filled with slides showing traits that evolve on the strength of their group-level benefits, despite being selectively disadvantageous within groups. Even though Andy acknowledges that multilevel selection theory and inclusive fitness theory are equivalent and even calls the distinction "empirically empty", he regards inclusive fitness theory as superior in some important sense. He also makes a distinction between group selection and group adaptation, based on a new article that he has co-authored with Alan Grafen.

Most of the action at a conference such as this takes place in the halls, at meals, and at drinking sessions that go far into the night. The multilevel selectionists are as angry as a disturbed hornet's nest. We're sick of seeing example after example that anyone would have called group selection in the 1960s presented without using the G-word. Where does Andy get off saying that his formalism leads to greater insights when we also publish in the best and most rigorously peer-reviewed journals? Does Andy and the other anti-group selectionists even read the literature framed in terms of multilevel selection? Not very much, judging by what they cite. We're especially irritated by an article that appeared in the journal Nature several months earlier by Geoffrey Wild, Andy Gardner, and Stuart West, claiming to explain the evolution of decreased virulence in parasites without invoking group selection. In truth, the avirulent strain is selectively disadvantageous within local groups and evolves only on the strength of their differential contribution to the total gene pool--in other words, classic group selection. All the model does is state the result in the lingo of inclusive fitness theory. Another demonstration of equivalence isn't new, but not only is the article published in Nature, but it's featured in Nature's News section with the title "The Nail in the Coffin for Group Selection?" No wonder the whole world remains confused! We're so mad that Mike Wade has coordinated a multi-authored letter to submit to Nature in protest.

The ESEB conference richly illustrates how the group selection controversy remains both settled and unsettled at the same time. The original problem has been settled: Contrary to the consensus that emerged in the 1960s, between-group selection is often a significant and sometimes even a dominating evolutionary force. That's why Andy and the other anti-group selectionists are willing to say--in this context--"We're all group selectionists."

Then there are a number of derived issues that cause Andy and his colleagues to proclaim that they're not group selectionists. I will provide a brief guide to these derived issues in the final installment of the T&R series. Whatever we decide about them, they should not be confused with the original problem. I'm reminded of a scene in an old western movie where a cowboy is riding furiously on his horse. His horse is shot and the cowboy jumps onto an adjacent horse to continue riding furiously without skipping a beat. Whatever horses the anti-group selectionists are riding now, everyone needs to be aware that the first horse is dead.

You might think that we're all so pissed off at each other that we refuse to talk or get into ugly shouting matches. Not so! George Williams and I are old friends, as I have already mentioned. On one of my visits to his house, he taped a hand-lettered sign on his lawn mower at the driveway entrance that read "superorganisms welcome here," which has graced the door of my laboratory ever since. At the ESEB conference in Turin, the jousting was intense but cordial and leavened with humor. If there must be controversy, let it be over Italian food and wine in an open-air restaurant in August. Ciao!