We think that it is normal to have ice at both poles of our planet. After all, there has been ice there for longer than there has been human civilization. But in the long history of the Earth, polar ice caps are rare, and having two polar ice caps at the same time may be unique. Indeed, it may be the presence of those polar ice caps which has made

This meant that by breeding the animals for tameness, Belyaev had actually created a different animal.

“It would have been as easy to count or to estimate the number of leaves in a forest as to calculate the number of buffaloes living at any given time during the history of the species previous to 1870,” William Hornaday, who served as the chief taxidermist at the Smithsonian and later as director of the Bronx Zoo, wrote. By 1889, Hornaday reckoned,