" The Lutz heck that emerges from his writings and actions drifted like a weather vane: charming when need be, cold-blooded when need be, tigerish or endearing, depending on his goal. Still, it is surprising that Heck the zoologist chose to ignore the accepted theory of hybrid vigor: that interbreeding strengthens a bloodline. He must have known that mongrels enjoy better immune systems and have more tricks up their genetic sleeves, while in a closely knit species, however "perfect," any illness that kills one animal threatens to wipe out all the others, which is why zoos keep careful studbooks of endangered animals such as cheetahs and forest bison and try to mate them advantageously. In any case, in the distant past, long before anyone was recognizably Aryan, our ancestors shared the world with other flavors of hominids, and interbreeding among neighbors often took place, producing hardier, nastier offspring who thrived. All present-day humans descend from that robust, talkative mix, specifically from a genetic bottleneck of only about one hundred individuals. A 2006 study of mitochondrial DNA tracks Ashkenazi Jews (about 92 percent of the world’s Jews in 1931) back to four women, who migrated from the Near East to Italy in the second and third centuries. All of humanity can be traced back to the gene pool of one person, some say to a man, some a woman. It’s hard to imagine our fate being as iffy as that, be we are natural wonders. "
― Diane Ackerman , The Zookeeper's Wife