What does the term punctuated equilibria describe?

Explain how each of the following makes it difficult to clearly define a species: variation within a species, geographically isolated populations, asexual species, fossil organisms.

A revolution in the study of human evolution is under way thanks to the invention of techniques that enable DNA sequencing of not only modern humans, but also ancient humans.Modern humans (Homo sapiens) and archaic humans called Neanderthals (H. neanderthalensis) shared a common ancestor in Africa but diverged in different geographic areas. When modern humans migrated out of Africa and dispersed around the world starting about 100,000 years ago, they overlapped with Neanderthals in Europe. This scenario is best described asa. species living in sympatry following allopatric speciationb. species living in sympatry following sympatric speciationc. species living in allopatry following allopatric speciationd. species living in allopatry following sympatric speciation

Explain why allopatric speciation would be less likely on an island close to a mainland than on a more isolated island.

Svante Pääbo and colleagues were the first to sequence the Neanderthal genome from fossils and compare the sequences to modern humans. According to the data shown here, did the two species interbreed when they overlapped in Europe? Explain.

If you sequenced the DNA of all your classmates, you would probably observe that the percentage of Neanderthal genes in their genomes varies from 0–4%. How would you know whether there is a significant difference in percentage between students with blue eyes and students with brown eyes?

Can factors that cause sympatric speciation also cause allopatric speciation? Explain.

Neanderthals disappeared about 40,000 years ago when the modern human population increased. This is an example of what outcome(s) of secondary contact (see Table 24.4)? Predict one way this result might have come about.

Cultivated American cotton plants have a total of 52 chromosomes (2n = 52). In each cell, there are 13 pairs of large chromosomes and 13 pairs of smaller chromosomes. Old World cotton plants have 26 chromosomes (2n = 26), all large. Wild American cotton plants have 26 chromosomes, all small. Propose a testable hypothesis to explain how cultivated American cotton probably originated.