How does the current, or sixth, mass extinction differ from the past five mass extinction events? a. the sixth mass extinction is believed to be caused by human-related factors. b. the sixth mass extinction is believed to be caused by natural forces. c. the sixth mass extinction is believed to affect relatively fewer species. d. the sixth mass extinction is believed to affect relatively fewer areas.

Which of the following factors would not contribute to allopatric speciation? a) a population becomes geographically isolated from the parent population. b) the separated population is small, and genetic drift occurs. c) the isolated population is exposed to different selection pressures than the ancestral population. d) different mutations begin to distinguish the gene pools of the separated populations. e) gene flow between the two populations is extensive.