354 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1926 
Some reader may ask what grounds I have for assuming that 
long lapse of time is involved in this process of racial differentia- 
tion. Why may not the observed differences be induced rather 
quickly, in one or a very few generations of gophers, as conditions 
change locally or as the animals move about, say from one kind of 
soil into another? In reply: For one thing, we find the animals 
“true to type,” in other words, relatively uniform in characters, 
each within its own distribution area—and this despite the great 
local differences in conditions. For example, bottae from the grassy 
tops of the Berkeley Hills is quite like bottae from the campus at 
Stanford University, and quite like bottae from the wooded slopes 
of the Santa Cruz Mountains, and also quite like bottae from the 
sand dunes at Seaside near Del Monte. 
For another thing, we have in the Museum of Vertebrate Zoology 
specimens, skins and skulls, preserved by members of the State 
Geological Survey 60 years and more ago, representative of several 
of our Californian races. Compared with specimens of the same 
races collected to-day I see no appreciable differences. 
And one other line of evidence pointing to the relative perma- 
nence of the species and subspecies with which we are dealing: 
From the Rancho La Brea asphalt deposits near Los Angeles there 
have been exhumed an abundance of excellently preserved skulls of 
Thomomys intimately associated with remains of certain mammals, 
now extinct, of known Pleistocene age. And those gophers show 
cranial characters identical with not only the species bottae, but 
with the subspecies padlescens as it exists in the vicinity of Los 
Angeles to-day. In other words, in upwards of 200,000 years which 
it is thought have passed since those Rancho La Brea gophers lived 
and died, there have been no changes in cranial features such as the 
systematist would recognize in separating geographic races existing 
to-day in different parts of southern California. This adaptive, 
evolutionary process is one which involves very long periods of 
time, therefore, when measured in years. 
To summarize: In this essay I have set forth some of the facts 
in the natural history of the pocket gopher. I have picked out for 
especial comment those features of the animal, as regards both 
habits and structure, which seem significant in a consideration of 
its general distribution. I have also emphasized the fact of the dif- 
ferentiation of the pocket gopher type fgenus Zhomomys) in Cali- 
fornia, into numerous races—species and subspecies. Furthermore, 
I have referred to the seeming correlation of area of occupancy in 
each race with relative uniformity of the conditions of existence for 
that race. The inferior powers of locomotion of this type of rodent, 
as compared, say, with the jack rabbit, has brought upon it a condi- 
tion of extreme provincialism, as it were. That is to say, especially 
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