Defining the human species
Having read “Humans benefited by interbreeding” (SN: 10/8/11, p. 13), I wonder if I have missed what, to me, seems a major change in the definition of “species.” I was taught that the attempted crossbreeding of animals of two different species could result in either no offspring or sterile offspring.

If modern humans carry genetic information from Neandertal and Denisovan ancestors, stemming from successful interbreeding that resulted in fertile offspring, why aren’t the Neandertals and Denisovans considered to be merely of a different race or breed rather than of a different species?
Alice Grover, Southbury, Conn.

Some anthropologists regard Neandertals as a subspecies of Homo sapiens and see the genetic evidence of limited interbreeding as supporting that view, but those anthropologists are in the minority these days. The majority of researchers today argue that Neandertals and Denisovans were separate species that managed to interbreed successfully with H. sapiens a small number of times. Biologists have a difficult time distinguishing between living species of primates and other animals in hybrid zones, where much interbreeding occurs, so debate about ancient hominid interbreedingand about how to define a specieswill probably continue. —Bruce Bower

Chimps aren’t chumps
Regarding “Chimp has an ear for talk” (SN: 8/13/11, p. 16): Humankind has assumed all other living creatures are stupider than us. And yet experiment after experiment finds “higher cognitive skills” in other animals. We know that trees “talk” chemically, crows use tools, ants draw maps with pheromones. What an enormous change it would be if we adopted the far less arrogant presumption that all creatures possess in some manner the abilities H. sapiens does.
Scott Reuman, Nederland, Colo.