Hmm—I am not sure I have encountered that. Many definitions of “species” are based on there being little or no gene flow between different species.
Both group selection and species selection face the issue of the fact that reproduction rates are slow—compared to individual reproduction rates—so individual level selection could eliminate much of the variation on which higher-level selection could act.
However, with species selection, we know that species do eventually diverge—so there is some variation left to work on.
With group selection there’s less evidence of divergence between groups—and there’s an additional problem—that occasional gene flow between groups acts to reduce between-group differences. The math[*] suggests around 1 migrant per-generation is enough to make most group selection pretty ineffective—and 1 migrant per-generation is low for most natural groups. These factors are mainly what makes group selection more controversial.
Search for “One-Migrant-per-Generation Rule” for more on this.
Hmm—I am not sure I have encountered that. Many definitions of “species” are based on there being little or no gene flow between different species.
Both group selection and species selection face the issue of the fact that reproduction rates are slow—compared to individual reproduction rates—so individual level selection could eliminate much of the variation on which higher-level selection could act.
However, with species selection, we know that species do eventually diverge—so there is some variation left to work on.
With group selection there’s less evidence of divergence between groups—and there’s an additional problem—that occasional gene flow between groups acts to reduce between-group differences. The math[*] suggests around 1 migrant per-generation is enough to make most group selection pretty ineffective—and 1 migrant per-generation is low for most natural groups. These factors are mainly what makes group selection more controversial.
Search for “One-Migrant-per-Generation Rule” for more on this.