168 
JOURNAL OF MAMMALOGY 
All attempts to implant our ruffed grouse in the old world have been 
utter failures; on the other hand the Hungarian partridge and the 
Mongolian pheasants are immediately successful here. 
Not only is a species of Eurasian evolution stronger than one of Ameri- 
can; but an American is stronger than an Australian; an Australian is 
stronger than a New Zealander; and an African is stronger than a Mada- 
gascan species. Indeed, a continental species always is stronger and 
bigger than an insular form; and creatures evolved in small islands wither 
away before the invading Eurasians like pine boughs in a flame. For 
example, note the dodo of the Mauritius, and the ground-pigeon of 
Samoa, and possibly also our own wild pigeon. 
It seems to be nearly self-evident that all of the dominating land 
animals in North America today are of species that have close kin, 
and apparently their parent stock, in Eurasia. They probably invaded 
this area by way of the northwest land-bridge; for example, the coyote, 
gray-wolf, fox, mountain-sheep, moose, white bear, otter, weasel. 
And the species that cannot hold their own, as attested by paleontol- 
ogy, were those evolved in this region. 
It is pretty weU established that as a rule species increase in size as 
they evolve, and are at their maximum when their race disappears, 
i.e., great size is proof that they have gone far along the trail. 
This rule is evidenced by the fact that the recent or living American 
cats, camels, horse, sheep, bison, wild hogs, horned owl, ostrich, 
etc,, are smaller than those of the older, bigger world. 
If however the giant fox of South America is of the genus Vulpes^ 
then it is an exception to the rule I am trying to formulate. If it is 
obviously of another genus, it is not an exception, and further fore- 
shadows with certainty the finding of extinct giant foxes in Eurasia. 
The same remarks and prophecy apply to the condor and the harpy 
eagle. 
If we compare the gerboas of Africa with the nearly parallel kangaroo- 
rats of America, we find that the former, with their wide range, have 
gone much further in evolution than the latter with their limited 
range. I doubt not that a few thousand African gerboas released in 
our southwest would, by mere pressure of better equipment, drive all 
our dipodomyids to extinction, and possess their range. 
Conversely, no American species has ever been able to establish 
itself in Eurasia, no Australian species has ever conquered Eurasia 
or America, no New Zealand species has ever successfully invaded 
