EVOLUTION 1039 



direction. Mr. E. W. Nelson also notices that when the gopher is 

 not digging, it folds the long claws of the hands against the palm 

 and walks on the back of them. And so we might continue to 

 demonstrate that Pocket Gophers are bundles of fitnesses, like most 

 other well-equipped animals. They are not remarkably prolific as 

 rodents go; thus Homaday says that the Red Pocket Gopher has 

 only one family in the year, and only two or three young ones in a 

 litter. 



It looks, then, as if there were some additional reason for the 

 success of Pocket Gophers, and that has been discovered and 

 explained by Joseph Grinnell, of the University of California. He 

 deals in particular with the genus Thomomys, to which all the 

 gophers of California belong — a genus that has been very successful 

 within certain geographical limits since the Miocene period, when it 

 seems to have evolved from a squirrel-like ancestry. The genus is 

 represented in every county in California, "from below sea-level to 

 almost the highest altitudes, from the hottest to the coldest portions 

 of the State, and from the driest to the wettest belts". But the 

 significant fact is that the genus has been broken up into no fewer 

 than 33 different races (species and sub-species), no two of them 

 occupying precisely the same territory. The Californian Pocket 

 Gopher genus has been divided into sub-stocks, each of which has 

 found its own particular niche of opportunity. 



Some stocks are at home on mountains, but each stock has its 

 own favourite altitude; others occur in valleys that have springs, 

 and others on river deltas; distinct groups are sequestered in oases 

 in the desert, surrounded by unoccupiable stretches which, with 

 their feeble powers of locomotion, the gophers cannot cross; others 

 live in humid coastal belts and others on sand dunes. 



The setiological point is that different species or sub-species have 

 learned to live in diverse habitats — different in altitude, rainfall, 

 temperature, light, soil, and vegetation; and each well-marked 

 type of habitat is correlated with particular features in its gophers. 

 Although the genus is highly specialised, e.g. for burrowing, it has 

 retained a measure of detailed plasticity which has enabled each 

 stock to make the best of its particular kind of haunt. Somehow 

 or other, "each of the many and diverse 'gopher differentiation 

 areas' found in California has impressed its occupant with its stamp, 

 namely, a peculiar combination of adaptive characters best fitting 

 that gopher to carry on successful existence in that restricted 

 area." 



It has been suggested that gophers are sometimes of service to 

 man inasmuch as they bring sub-soil to the surface and bury the 

 debris of plants. Thus they act, like gigantic earthworms, as soil- 

 makers. Otherwise, from man's point of view, they have no redeem- 

 ing quality. And yet we must recognise another service to man, 



