Species and Speciation

Chapter Summary

1. Evolutionary biologists have long struggled with how to classify organisms. What makes for a species? How different do two groups have to be before they are considered different species?
2. The evolutionary species concept provides an answer to what a species fundamentally is: a set of populations with their own distinct evolutionary history and a shared future evolutionary fate.
3. The phenetic species concept, the biological species concept, and the phylogenetic species concept each provide different diagnostic criteria for how species boundaries can be drawn in practice.
4. Major models of speciation include allopatric, parapatric, and sympatric speciation. Allopatric speciation includes a dumbbell model of speciation and a peripheral isolate model.
5. Ring species live in a series of populations that are connected to one another in a ringlike fashion. In ring species, we expect gene flow across adjacent populations, but gene flow between populations that are not adjacent, should be minimal and decrease as a function of distance.
6. Evolutionary biologists have identified and studied many types of reproductive isolation—that is, mechanisms that restrict or prevent gene flow.
7. Work on the genetics of speciation includes studies of reproductive isolation via changes in chromosome number, reproductive isolation via chromosomal rearrangement, reproductive isolation via Dobzhansky–Muller incompatibility, and reproductive isolation via Haldane’s rule.
8. Evolutionary biology provides an answer to the question of human origins. Genetic and genomic evidence reveals the relation between humans and other primates.
9. Fossil evidence allows the chance to reconstruct the evolutionary events that occurred from the divergence of the Homo lineage from chimpanzees about 5.5 million years ago to the emergence of our species Homo sapiens.
10. Advances in genetic sequencing and phylogenetic inference have enormously refined our ability to reconstruct the history of how current human populations came to span the globe.