I bumped into these definitions in a Facebook discussion. They arent quite what im used to seeing, but they do impart a kind of clarity im also not used to seeing!:
1] “Microevolution is change from one generation to the next within a single population lineage.”
2] “Speciation is the splitting of population lineages.”
3] “Speciation happens at the population level.”
4] “Macroevolution is simply describing a pattern of biological variation above the species level. Those patterns occur according to 1) change within populations from one generation to the next (microevolution) 2) splitting of population lineages (speciation) and 3) the loss of population lineages (extinction).”
5] “A metapopulation is a population of populations connected by the exchange of genes. Species are essentially metapopulations that are independent of other metapopulations.”
1, is wrong, 2, is right. 3, says nothing. 4, is stupid, 5, seems wrongish.
Whatever the mechanism. All there is IS populations coming into existence out of a parent population which includes those who have new bodyplans(so gene action) . It could be reversed and no one be the wiser.
Everybody agrees there are bodyplan changes from parent pops to new pops. Its just WHAT is the mechanism??
One could quibble, but not much. Macroevolutionary processes include 1) microevolutionary processes, 2) differential extinction, and 3) differential speciation, the last of which Mays didn’t mention. Whether speciation itself counts as macroevolution is arguable.
The definition of speciation works fine for sexually reproducing eukaryotes; other groups are more problematic.
I also like the speciation model for defining macroevolution in sexually reproducing species. It is the divergence between populations that matters, and it requires microevolution and reproductive isolation to achieve that divergence.
As others mentioned, this definition doesn’t work well for populations separated by time. However, defining fossil species is largely arbitrary anyway. If H. sapiens evolved from H. erectus there would not be an objective point where one species became the other in a continuous population (from a scientific point of view).
Asexual species pose their own difficulties, but genetic divergence could also be used. This would rely more heavily on lineage extinction as new mutations emerge.