When it comes to evolution these days, scientists tend to present a uniform front of agreement for political and rhetorical reasons, so you maybe didn’t know that, in private, some theoretical biologists have grawlix-laced thoughts about certain colleagues, whose work on one issue in particular they regard as not only wrong but stubbornly, perversely so, crumbling on clearly termite-eaten logic, and vice versa for the second group against the first—but there you go.
A divisive example: While most female lions are dutiful about guarding the borders of their camps against attacks, there are definitely some Cadillac Queens among them who don’t help out at all. The lionesses lazy in this regard benefit disproportionately because they don’t put themselves in danger when attacks come and can concentrate on breeding in the meantime and yet still get all the benefits of the others’ work, since they cannot help but be warned by all the scrambling around and yelling during any breach of security. Natural selection therefore favors lazy lionesses who defect—and if you want to be reductive, it seems to favor genes that make lions lazy defect.
The catch is that if there are too many lazy lionesses, the entire group will get wiped out in one attack, which isn’t good for anyone’s genes. So for the long-term survival of the species natural selection must favor the genes for self-sacrifice. Except that’s not quite right, either. Day to day, the lazy lions still have an advantage over the dutiful lions, and day to day, the lazy lions’ genes are still more likely to spread. In which case natural selection is selecting both for and against genes that are less fit, which isn’t natural selection in any real sense. It gets even knottier when you look at competition between groups, because when individuals decide to cooperate and coalesce into groups, complicated properties emerge. It’s no different than collections of limp neurons firing themselves up into a mind with memory, emotion, and volition. Can one neuron think? Can natural selection meaningfully be said to “work” on individuals when it only favors groups of those individuals working together, and not the individuals themselves?
This is what cleaves biologists. No one argues that natural selection is a monolithic force propelling evolution onward without purpose or design (the uniform front), but what does it act on?—genes, individuals, whole groups at once? Until the 1960s, most biologists were too busily focused on squaring Mendel with Darwin, what’s known as the Modern Synthesis, to ponder this problem. Most, as Charles D. did, lazily assumed selection happened on multiple levels. Ever since then, biologists realized they needed to be a lot more explicit about the assumptions undergirding their models.