New-York tribune., 1910-06-08

whereas all the tndiyidual tllhioe"0ieS
finally died out. leaving no descendants
number of the three-toed horses did leave
descendants. and these descendants, con-
stantly changing as the ages went oy'
finally developed into the highly special
lied one-toed horses asses and zebras of
to-day.
The analogy between the facts thus indf-
Gated and certain facts in the development
of human societies is striking. A further
analogy is supplied by very curious ten
dency often visible In cases of intense and
extreme specialization. When an animal
form becomes highly specialized, the type
at first because of its specialization, tri-
umphs over its allied rivals and it's enc
mics, and attains a great development;
until in many cases the specialization be-
comes so extreme that, from some cause
unknown to us, or at which we merely
guess, it disappears. The new species which
mark new era commonly come from the
less specialized types. the less distinctive,
dominant and striking types, of the preced-
ing era.
Local Causes of Destruction.
When dealing with the changes. cata-
clysmic otherwise. which divide one
period of archaeological history from an
other. we can sometimes assign causes.
and again cannot even guess at them.
In the case of single species or of faunas
Of very restricted localities the explanation
| is often self-evident. A comparatively slight
change in the amount of moisture in the
climate. with the attendant change in
vegetation. might readily mean the de-
structiOn of a group of huge herbivores
with a bodily size such that they needed a
vast quantity Of food and with teeth so
weak or so peculiar that only one or two
kinds of plants could furnish this food.
Again, we now know that the most deadly
foes of the higher forms of life are various
lower forms Of life, such as insects or
microscopic creatures conveyed into the
blood by insects. There districts In
South America where many large animals,
wild and domestic, cannot live because or
| the presence either of certain ticks or OF
certain baleful flies. In Africa there is
terrible genus OF poison fly, each species
acting as the host of microscopic creatures
| which are deadly to certain of the higher
! vertebrates. One of these species, though
| harmless to man, is fatal TO all domestic
animals, and this although harmless to the
| closely related wild kInsfolk of these AMI
| mails Another is fatal to man himself
| being the cause OF the sleeping Sickness,
| which In many large districts has killed
| off the entire population. OF course, the
! development or the extension of the range
| of any such Insects. and any one of many
| other causes which we see actually AT
| work around US. would readily account for
the destruction of some given species or
| even for the destruction of several species
| in a limited area of country.
Results of the Glacial Period.
When whole faunal groups die out, over
| large areas the question is different, and
! may or may not be susceptible OF explana-
! ton with the knowledge we actually pos
! sess In the old arctogeal continent, for
instance, in what is now Europe. Asia and
North America, the glacial period made a
! complete but of course explicable change
in the faunaI life of the region. At one
/ time the continent held a rich and varied
| fauna Then a period of great cold super
| vened, and a different fauna succeeded the
first. The explanation of the change is
! obvious
| But in many other cases we cannot so
much as hazard a guess as TO why given
! change occurred. One of the most striking
instances of these inexpncable changes is
| that afforded by the history Of South
America toward the close of the tertiary
period. For ages South America had been
America at the very time that the latter
was at least occasionally in land communi-
! cation with Asia During this time very
peculiar fauna grew up in South America,
some of the types resembling nothing now
existing, while others are recognizable as
ancestral forms of the ant-eaters, sloths and
armadilIos of to-day. 1t was a peculiar
and diversified mammalian fauna of, on
the whole rather small species, and with
out any representatives of the animals with
which man has been most familiar during
his career on this earth
The Invasion Through Panama.
Toward the end of the tertiary period there
was an upheaval of land between this old
South American island and North America,
near what is now the Isthmus of Panama,
thereby making bridge across which the
teeming animal life Of the northern conti-
nent had access to this queer southern
continent There followed an inrush OF
huge or swift or formidable creatures,
which had attained their development in
the fierce competition of the arctogeal
realm Elephants, camels, horses, tapirs,
swine sabre-toothed tigers, big cats,
wolves, bears and deer crowded into South
America, warning each against the other
incomers and against the old long existing
forms. A riot of life followed. Not only
was the character of the South American
fauna totally changed by the invasion of
these creatures from the north, which soon
swarmed over the continent, but it was
also changed through the development
wrought in the old inhabitants by the
severe competition to which they were ex-
posed Many of the smaller or less capable
types died out Others developed enormous
bulk or complete armor protection, and
thereby saved themselves from the new
beasts. In consequence. South America
soon became populated with various new
species of mastodons, sabre-toothed tigers,
camels. horses, deer, cats, wolves, hooved !
creatures of strange shapes and some of
them of giant size all of these being de-
scended from the immigrant types. ana
side by side with them there grew up large
autochthonous ungulates. giant ground
sloths, wellnigh as large as elephants,
and armored creatures as bulky OK,
but structurally of the armadilo or ant
eater type; and some of these latter not
only held their own but actually in their
invaded North America. A fauna as varied
as that of Africa sto-day. abundant in
species and individuals, even more note
worthy because of its huge size or odd type
and because of the terrific prowess of the
more formidable flesh eaters was thus de-
deloped in South America, and hOurished
for a period which human history would
Loot