Having thus sketched an outline of the monkey tribe as regards their
more prominent external characters and habits, we must say a few words
on their general relations as a distinct order of mammalia. No other
group so extensive and so varied as this, is so exclusively tropical in
its distribution, a circumstance no doubt due to the fact that monkeys
depend so largely on fruit and insects for their subsistence. A very
few species extend into the warmer parts of the temperate zones, their
extreme limits in the northern hemisphere being Gibraltar, the Western
Himalayas at 11,000 feet elevation, East Thibet, and Japan. In America
they are found in Mexico, but do not appear to pass beyond the tropic.
In the Southern hemisphere they are limited by the extent of the forests
in South Brazil, which reach about 30° south latitude. In the East,
owing to their entire absence from Australia, they do not reach the
tropic; but in Africa, some baboons range to the southern extremity of
the continent.
But this extreme restriction of the order to almost tropical lands is
only recent. Directly we go back to the Pliocene period of geology,
we find the remains of monkeys in France, and even in England. In the
earlier Miocene, several kinds, some of large size, lived in France,
Germany, and Greece, all more or less closely allied to living forms of
Asia and Africa. About the same period monkeys of the South American
type inhabited the United States. In the remote Eocene period the same
temperate lands were inhabited by lemurs in the East, and by curious
animals believed to be intermediate between lemurs and marmosets in the
West. We know from a variety of other evidence that throughout these
vast periods a mild and almost sub-tropical climate extended over all
Central Europe and parts of North America, while one of a temperate
character prevailed as far north as the Arctic circle. The monkey tribe
then enjoyed a far greater range over the earth, and perhaps filled a
more important place in nature than it does now. Its restriction to the
comparatively narrow limits of the tropics is no doubt mainly due to the
great alteration of climate which occurred at the close of the Tertiary
period, but it may have been aided by the continuous development of
varied forms of mammalian life better fitted for the contrasted seasons
and deciduous vegetation of the north temperate regions. The more
extensive area formerly inhabited by the monkey tribe, would have
favored their development into a number of divergent forms, in distant
regions, and adapted to distinct modes of life. As these retreated
southward and became concentrated in a more limited area, such as were
able to maintain themselves became mingled together as we now find them,
the ancient and lowly marmosets and lemurs subsisting side by side with
the more recent and more highly developed howlers and anthropoid apes.
Throughout the long ages of the Tertiary period monkeys must have been
very abundant and very varied, yet it is but rarely that their fossil
remains are found. This, however, is not difficult to explain. The
deposits in which mammalian remains most abound are those formed in
lakes or in caverns. In the former the bodies of large numbers of
terrestrial animals were annually deposited, owing to their having been
caught by floods in the tributary streams, swallowed up in marginal bogs
or quicksands, or drowned by the giving way of ice. Caverns were the
haunts of hyenas, tigers, bears, and other beasts of prey, which dragged
into them the bodies of their victims, and left many of their bones to
become embedded in stalagmite or in the muddy deposit left by floods,
while herbivorous animals were often carried into them by these floods,
or by falling down the swallow-holes which often open into caverns from
above. But, owing to their arboreal habits, monkeys were to a great
extent freed from all these dangers. Whether devoured by beasts or birds
of prey, or dying a natural death, their bones would usually be left on
dry land, where they would slowly decay under atmospheric influences.
Only under very exceptional circumstances would they become embedded
in aqueous deposits; and instead of being surprised at their rarity
we should rather wonder that so many have been discovered in a fossil
state.
Monkeys, as a whole, form a very isolated group, having no near
relations to any other mammalia. This is undoubtedly an indication of
great antiquity. The peculiar type which has since reached so high a
development must have branched off the great mammalian stock at a very
remote epoch, certainly far back in the Secondary period, since in the
Eocene we find lemurs and lemurine monkeys already specialized. At this
remoter period they were probably not separable from the insectivora,
or (perhaps) from the ancestral marsupials. Even now we have one living
form, the curious Galeopithecus or flying lemur, which has only recently
been separated from the lemurs, with which it was formerly united, to be
classed as one of the insectivora; and it is only among the Opossums and
some other marsupials that we again find hand-like feet with opposable
thumbs, which are such a curious and constant feature of the monkey
tribe.
This relationship to the lowest of the mammalian tribes seems
inconsistent with the place usually accorded to these animals at the
head of the entire mammalian series, and opens up the question whether
this is a real superiority or whether it depends merely on the obvious
relationship to ourselves. If we could suppose a being gifted with
high intelligence, but with a form totally unlike that of man, to have
visited the earth before man existed in order to study the various forms
of animal life that were found there, we can hardly think he would have
placed the monkey tribe so high as we do. He would observe that their
whole organization was specially adapted to an arboreal life, and this
specialization would be rather against their claiming the first rank
among terrestrial creatures. Neither in size, nor strength, nor beauty,
would they compare with many other forms, while in intelligence they
would not surpass, even if they equaled, the horse or the beaver. The
carnivora, as a whole, would certainly be held to surpass them in the
exquisite perfection of their physical structure, while the flexible
trunk of the elephant, combined with his vast strength and admirable
sagacity, would probably gain for him the first rank in the animal
creation.
But if this would have been a true estimate, the mere fact that the ape
is our nearest relation does not necessarily oblige us to come to any
other conclusion. Man is undoubtedly the most perfect of all animals,
but he is so solely in respect of characters in which he differs from
all the monkey tribe--the easily erect posture, the perfect freedom
of the hands from all part in locomotion, the large size and complete
opposability of the thumb, and the well developed brain, which enables
him fully to utilize these combined physical advantages. The monkeys
have none of these; and without them the amount of resemblance they have
to us is no advantage, and confers no rank. We are biased by the too
exclusive consideration of the man-like apes. If these did not exist
the remaining monkeys could not be thereby deteriorated as to their
organization or lowered in their zoological position, but it is doubtful
if we should then class them so high as we now do. We might then dwell
more on their resemblances to lower types--to rodents, to insectivora,
and to marsupials, and should hardly rank the hideous baboon above the
graceful leopard or stately stag. The true conclusion appears to be,
that the combination of external characters and internal structure which
exists in the monkeys, is that which, when greatly improved, refined,
and beautified, was best calculated to become the perfect instrument
of the human intellect and to aid in the development of man's higher
nature; while, on the other hand, in the rude, inharmonious, and
undeveloped state which it has reached in the quadrumana, it is by no
means worthy of the highest place, or can be held to exhibit the most
perfect development of existing animal life.--_Contemporary Review_.
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[JOURNAL OF THE SOCIETY OF ARTS.]