II

That the hazards of the past, to many forms of life, at least, have

been real and no myth, is evident from the vast number of forms that

have been cut off and become extinct; various causes, now hard to

decipher, have worked together to the end, such as changed

geographical conditions, changes of climate, affecting the

food-supply, extreme specialization, like that of the sabre-toothed

tiger whose petrified remains have been found in various parts of

this continent, and who apparently was finally handicapped by his

huge dental sabre. Probably many more species of animals have become

extinct than have survived, but none of these could have been in the

line of man's descent, else the human race would not have been here.

If the Eocene progenitor of the horse, the little four-toed

eohippus, had been cut off, would not the world have been horseless

to-day? The horse in America became extinct, from some cause only

conjectural, many tens of thousands of years ago. Had the same fate

befallen the horse in Europe and Asia, it seems probable that our

civilization would have been far less advanced to-day than it is.

The fate of every species of mammal in our time seems to have been

in the keeping of a single form in early Tertiary times. The end of

the Cretaceous or chalk period saw the extinction of the giant

reptiles both of sea and of land, at the same time that it saw the

appearance of a great many species of small and inconspicuous

mammals, among which doubtless were our own humble forebears.

Extreme specialization in any direction may narrow an animal's

chances of survival; they have but one chance in the game of life,

whereas an animal with a more generalized organization has many

chances. Man is one of the most generalized of animals; no special

tools, no special weapons--his hand many tools and weapons in one.

Hence he is the most adaptable of animals; all climes, all foods,

all places are his; he is master of the land, of the sea, of the

air.

Animal life is often curiously interdependent. I asked our guide in

the Adirondacks if there were any ravens there. "Not nearly as many

as there used to be," he said, and his explanation of their

disappearance seems thoroughly scientific; it was that the wolves

and the panthers kept them in meat, and now that these animals had

disappeared, the ravens had little to feed upon. If the moose were

compelled to graze from off the ground, like a sheep or a cow, the

species would probably soon become extinct. Osborn thinks it

probable that the huge beast called titanothere finally became

extinct early in Tertiary times owing to the form of its teeth,

which were of such a type that they could not change to meet a

change in the flora upon which the creature fed. Of course we shall

never know what narrow escapes our race had from extinction in the

remote past; some forms have ended in a blind alley, like the

sea-urchin and the oyster. Arthropoda have continued to evolve and

have reached their high-water mark of intelligence in bees and

ants. The vertebrates went forward and have culminated in man.

Bergson thinks that in the vertebrates intelligence has been

developed at the expense of instinct, and that in the invertebrates

instinct has been perfected at the expense of intelligence.

Are we not compelled to adopt what is called the monophyletic

hypothesis, that is, that our line of descent started from one pair,

male and female, somewhere in the vast stretch of geologic or

biologic time, and to reason that, had that pair been out of the

race, we should not have appeared?

Can we narrow life to a single point, a single cell, in the past?

Was there one and only one first bit of protoplasm? If we were to

say that life first appeared on the globe in Cambrian times, just

what should we mean? That it began as a single point, or as many

points? When we say that the primates first appeared in Eocene

times, do we mean that one single primate appeared then? If so, what

form went immediately before him? This is all a vain speculation.

Does man presuppose all the vertebrate sub-kingdom? Was he safe as

long as one vertebrate form remained? Are his forebears many, and

not one pair? Can we think of his ancestry under the image of a

tree, and of him as one of the many branches? If so, nothing but the

destruction of the tree would have imperiled his appearance, or the

lopping off of his particular branch. Probably all such images are

misleading. We simply cannot figure to ourselves the tangled course

of our biological descent. If thwartings and accidents arid delays

could have cut man off, how could he have escaped? We cannot think

of man as one; we are compelled to think of him as many; and yet in

all our experience the many come from the one, or the one pair.

How thick the field of animal life in the past is strewn with

extinct forms!--as thick as the sidereal spaces are strewn with the

fragments of wrecked worlds! But other worlds and suns are spun out

of the wrecked worlds and suns through the process of cosmic

evolution. The world-stuff is worked over and over. Extinct animal

forms must have given rise to other, allied forms before they

perished, and these to still others, and so on down to our time.

The image of a tree is misleading from the fact that all the

different branches of the animal kingdom, from the protozoa up to

man, have come along with what we call the higher branches, the

mammals; the suckers have kept pace with the main stalk, so that we

have the image of a sheaf of branches starting from a common origin

and all of equal length. Man has brought on his relations along with

him.

There is no glamour of romance over that past. It was all hard,

prosy, terrible fact. The earth's crust was less stable than now,

the upheavals and subsidences and earthquakes more frequent, the

warring of the elements more fierce and incessant, deluge and

inundation in more rapid succession, and the riot and excesses of

animal life far beyond anything we know of. And our line of descent

was taking its chances amid it all. The widespread blotting out of

life at the end of Palaeozoic time, and again at the end of Mesozoic

times, when myriads of forms were cut off, probably from some

convulsion of nature or some cosmic catastrophe; and again during

the ice age, when the camel, the llama, the horse, the tapir, the

mastodon, the elephant, the giant sloth, became extinct in North

America--how fared it with our ancestor during these terrible ages?

There is no sure trace of him till late Tertiary times, and it is

probably not more than two hundred thousand years ago that he

assumed the upright attitude and began to use tools. Probably in

Europe fifty thousand years ago he was living in caves, clothed in

skins, contending with the cave bear and cave lion, using rude stone

implements, and hunting the hairy mastodon, etc. In Asia the

probabilities are that he was farther on the road toward the dawn of

history.

We may think of our descent in the historic period under the image

of the stream, though of a stream many times delayed and diverted,

even many times diminished by wars and plagues and famine, but a

stream with some sort of unity and continuity, since man became man.

The stream of life is like any other stream in this respect. Divert

or use up part of the water of a stream, yet what is left flows on

and keeps up the continuity and identity of the stream; dip your cup

into it here, and you will not get precisely the same water you

would have got had none of it been diverted or used far back in its

course--you get the water that was allowed to flow by.

Had there been no loss of life by war and pestilence and accidents

of various kinds, the different countries would have been occupied

by quite other men and women than those that fill them to-day. The

course of life in every neighborhood is changed by what seem like

accidental causes, as when a family is practically wiped out by some

accident or dread disease. This brings new people on the scene. The

farm or the business falls into other hands, and new social

relations spring up, new men and women are brought together or the

old ones driven apart, marriage is hastened or retarded,

opportunities for family life are made or unmade, and fewer

children, or more children, as the case may be, are the result. The

issue of some battle hundreds or thousands of years ago may have

played a part in your life and mine to-day--other races, other

individuals of the race, would have been thrown together had the

issue been different, and other families started, so that some one

else would have been here in our stead.

But the question of hazard to the race of man in geologic time is

quite a different one. Here our fate seems to hang by a single

thread--a golden thread, we may call it, but, in that terrible maze

of clashing forces and devouring forms of the vast geologic periods,

how liable to be broken! It is not now a question of the continuity

of a stream, but of the continuity of a single evolutionary process,

or, as Haeckel says, the continuity of the morphological chain which

stretches from the lemurs up through tailed and tailless anthropoid

apes to man. If the evolutionary impulse had been checked or

extinguished in the lemur--that small apelike animal that went

before the true ape, the fossil remains of which have been found on

this continent and the survivals of which are now found in

Madagascar--would man have appeared? Again, if the race of lemurs

developed from a single pair, how precarious seems our fate! In

fact, if any of the transitional forms between species can be

reduced to a single pair--as the forms that connect the reptiles

with the mammals--our fate would seem to be in the keeping of these

forms. Over this single frail bridge which escaped the floods and

the tornadoes and the earthquakes of those terrible ages we must

have passed. What risky business it all seems! Was it luck or law

that favored us? Doubtless, if we could penetrate the mystery, we

should see that there was no chance or risk in the matter. We cannot

go very far in solving these great fundamental questions by applying

to them the tests of our own experience, Numberless specific forms

become extinct, but the impulse that begat the form does not die

out. Thus, all the giant reptiles died out--the dinosaurs, the

mesosaurs--but the reptilian impulse still survives. How many types

of invertebrates have perished! but the invertebrate impulse still

goes on. How many species of mammals have been cut off! yet the

mammal impulse has steadily gone forward. These things suggest the

wave that moves on but leaves the water behind. The vertebrate

impulse began in wormlike forms, in the old Palaeozoic seas, and

stopped not till it culminated in man. This impulse has left many

forms behind it; but has this impulse itself ever been endangered?

If one looks at the matter thus in an abstract instead of a concrete

way, the problem of our descent becomes easier.

When we look at the evolution of life on a grand scale, nature seems

to feel her way, like a blind man, groping, hesitating, trying this

road and then that. In some cases the line of evolution seems to end

in a cul de sac beyond which no progress is possible. The forms thus

cornered soon become extinct. The mystery, the unaccountable thing,

is the appearance of new characters. The slow modification or

transformation of an existing character may often be traced; natural

selection, or the struggle for existence, takes it in hand and

adapts and perpetuates it, or else eliminates it. But the origin of

certain new parts or characters--that is the secret of the

evolutionary process. Thus there was a time when no animal had

horns; then horns appeared. "In the great quadruped known as

titanothere," says Osborn, "rudiments of horns first arise

independently at certain definite parts of the skull; they arise at

first alike in both sexes, or asexually; then they become sexual, or

chiefly characteristic of males; then they rapidly evolve in the

males while being arrested in development in the females; finally,

they become in some of the animals dominant characteristics to which

all others bend." Nature seems to throw out these new characters and

then lets them take their chances in the clash of forces and

tendencies that go on in the arena of life. If they serve a purpose

or are an advantage, they remain; if not, they drop out. Nature

feels her way. The horns proved of less advantage to the females

than to the males; they seem a part of the plus or overflow of the

male principle, like the beard in man--the badge of masculinity. The

titanothere is traceable back to a hornless animal the size of a

sheep, and it ended in a horned quadruped nearly as large as an

elephant. It flourished in Wyoming in early Tertiary times. Nature

did not seem to know what to do with horns when she first got them.

She played with them like a child with a new toy. Thus she gave two

pairs to several species of mammals, one pair on the nose and one

pair on the top of the skull--certainly an embarrassment of weapons.

The first horns appear to have been crude, heavy, uncouth, but long

before we reach our own geologic era they appear in various species

of quadrupeds, and become graceful and ornamental. How beautiful

they are in many of the African antelope tribe! Nature's workmanship

nearly always improves with time, like that of man's, and sooner or

later takes on an ornamental phase.

The early uncouth, bizarre forms seem to be the result of the excess

or surplus of life. Life in remote biologic times was rank and

riotous, as it is now, in a measure, in tropical lands. One reason

may be that the climate of the globe during the middle period, and

well into the third period, appears to have been of a tropical

character. The climatic and seasonal divisions were not at all

pronounced, and both animal and vegetable life took on gigantic and

grotesque forms. In the ugliness of alligator and rhinoceros and

hippopotamus of our day we get some hint of what early reptilian and

mammalian life was like.

That Nature should have turned out better and better handiwork as

the ages passed; that she either should have improved upon every

model or else discarded it; that she should have progressed from the

bird, half-dragon, to the sweet songsters of our day and to the

superb forms of the air that we know; that evolution should have

entered upon a refining and spiritualizing phase, developing larger

brains and smaller bodies, is a very significant fact, and one quite

beyond the range of the mechanistic conception of life.

Our own immediate line of descent leads down through the minor forms

of Tertiary and Mesozoic times--forms that probably skulked and

dodged about amid the terrible and gigantic creatures of those ages

as the small game of to-day hide and flee from the presence of their

arch-enemy, man; and that the frail line upon which the fate of the

human race hung should not have been severed during the wild turmoil

of those ages is, to me, a source of perpetual wonder.