This is something of a quibble, but you really shouldn’t think of species-level selection as a kind of group selection. In both group and individual selection, it is the species that evolves. But in species-level selection, the species does not evolve. It is selected—it either lives or dies.
Just because we are dealing with one individual, that doesn’t mean it doesn’t evolve. Check with the definitions of the term “evolution”—they (mostly) refer to genetic change over time. You could argue that they also (mostly) talk about a “population”—and one individual doesn’t qualify as a “population”—but if you think through that objection, it too is essentially wrong.
Perplexed: In both group and individual selection, it is the species that evolves. But in species-level selection, the species does not evolve. It is selected—it either lives or dies.
Tim: Just because we are dealing with one individual, that doesn’t mean it doesn’t evolve.
Uh, I’m pretty sure I just stated that an individual—the species—does evolve. It evolves by way of organism-level or group-level selection. It just doesn’t evolve by going extinct or not.
As for whether one individual qualifies as a population, I’ve thought about that and completely failed to imagine a population of one individual evolving by way of the standard mechanisms of evolutionary population genetics. That kind of population cannot evolve by differential birth, death, or migration. (I suppose it can change by mutation).
The thing you have forgotten in trying to extrapolate the meaning of ‘population’ in this way is that the essential feature of a biological evolving population is that its size is not fixed and its membership changes in time, whereas a population of exactly one entity by definition does not change its membership count in time.
Now, I will agree that a population of entities (say, the population of biological species within a genus) can evolve by selection even though its membership count occasionally fluctuates through having only a single individual. The genus does evolve. But the evolution of the genus as a population of individual species and the evolution of the component species as (possibly structured into groups) populations of
individual organisms are conceptually distinct processes.
But here is not the place to continue this discussion. If you wish, please bring it up on sbe, and Dr. Hoeltzer can join in. I think he is getting probably lonely over there since we left, and the newsgroup is dominated by John, Tom, and Peter.
Perplexed: In both group and individual selection, it is the species that evolves. But in species-level selection, the species does not evolve. It is selected—it either lives or dies.
Tim: Just because we are dealing with one individual, that doesn’t mean it doesn’t evolve.
Uh, I’m pretty sure I just stated that an individual—the species—does evolve. It evolves by way of organism-level or group-level selection. It just doesn’t evolve by going extinct or not.
“Does NOT evolve” was the term you used. However, with your clarification, it now looks as though this was mostly just a misunderstanding.
IMO, it is mostly OK to think of species level selection as a type of group selection—where the “groups” are species. Maybe there are some meanings of “group selection” for which this is bad—but I would say: mostly OK.
Yes, a population of 1 changes by mutation. Self-directed evolution is an example of that.
If you A) insist on a population having more than 1 member and B) define evolution in terms of genetic change in populations, then the conclusion is that one big organism would no longer be “evolving” when it changed—which I think would be a totally absurd conclusion—a sign that you had got into a terminology muddle.
That may not be a big deal for today’s organic evolution—but it makes a big difference for the study of cultural evolution. There, populations with only 1 member are much more common.
Just because we are dealing with one individual, that doesn’t mean it doesn’t evolve. Check with the definitions of the term “evolution”—they (mostly) refer to genetic change over time. You could argue that they also (mostly) talk about a “population”—and one individual doesn’t qualify as a “population”—but if you think through that objection, it too is essentially wrong.
Uh, I’m pretty sure I just stated that an individual—the species—does evolve. It evolves by way of organism-level or group-level selection. It just doesn’t evolve by going extinct or not.
As for whether one individual qualifies as a population, I’ve thought about that and completely failed to imagine a population of one individual evolving by way of the standard mechanisms of evolutionary population genetics. That kind of population cannot evolve by differential birth, death, or migration. (I suppose it can change by mutation).
The thing you have forgotten in trying to extrapolate the meaning of ‘population’ in this way is that the essential feature of a biological evolving population is that its size is not fixed and its membership changes in time, whereas a population of exactly one entity by definition does not change its membership count in time.
Now, I will agree that a population of entities (say, the population of biological species within a genus) can evolve by selection even though its membership count occasionally fluctuates through having only a single individual. The genus does evolve. But the evolution of the genus as a population of individual species and the evolution of the component species as (possibly structured into groups) populations of individual organisms are conceptually distinct processes.
But here is not the place to continue this discussion. If you wish, please bring it up on sbe, and Dr. Hoeltzer can join in. I think he is getting probably lonely over there since we left, and the newsgroup is dominated by John, Tom, and Peter.
“Does NOT evolve” was the term you used. However, with your clarification, it now looks as though this was mostly just a misunderstanding.
IMO, it is mostly OK to think of species level selection as a type of group selection—where the “groups” are species. Maybe there are some meanings of “group selection” for which this is bad—but I would say: mostly OK.
Yes, a population of 1 changes by mutation. Self-directed evolution is an example of that.
If you A) insist on a population having more than 1 member and B) define evolution in terms of genetic change in populations, then the conclusion is that one big organism would no longer be “evolving” when it changed—which I think would be a totally absurd conclusion—a sign that you had got into a terminology muddle.
That may not be a big deal for today’s organic evolution—but it makes a big difference for the study of cultural evolution. There, populations with only 1 member are much more common.