from Cuvier onwards, have acknowledged its many points of likeness to a
well-known genus of extinct Eocene mammals, _Palaeotherium_. Indeed, as
we have seen, Cuvier regarded his remains of _Anchitherium_ as those of
a species of _Palaeotherium_. Hence, in attempting to trace the pedigree
of the horse beyond the Miocene epoch and the Anchitheroid form, I
naturally sought among the various species of Palaeotheroid animals for
its nearest ally, and I was led to the conclusion that the _Palaeotherium
minus_ (_Plagiolophus_) represented the next step more nearly than any
form then known.
I think that this opinion was fully justifiable; but the progress of
investigation has thrown an unexpected light on the question, and has
brought us much nearer than could have been anticipated to a knowledge
of the true series of the progenitors of the horse.
You are all aware that, when your country was first discovered by
Europeans, there were no traces of the existence of the horse on any
part of the American Continent. The accounts of the conquest of Mexico
dwell upon the astonishment of the natives of that country when they
first became acquainted with that astounding phenomenon--a man seated
upon a horse. Nevertheless, the investigations of American geologists
have proved that the remains of horses occur in the most superficial
deposits of both North and South America, just as they do in Europe.
Therefore, for some reason or other--no feasible suggestion on that
subject, so far as I know, has been made--the horse must have died out
on this continent at some period preceding the discovery of America. Of
late years there has been discovered in your Western Territories that
marvellous accumulation of deposits, admirably adapted for the
preservation of organic remains, to which I referred the other evening,
and which furnishes us with a consecutive series of records of the fauna
of the older half of the Tertiary epoch, for which we have no parallel
in Europe. They have yielded fossils in an excellent state of
conservation and in unexampled numbers and variety. The researches of
Leidy and others have shown that forms allied to the _Hipparion_ and the
_Anchitherium_ are to be found among these remains. But it is only
recently that the admirably conceived and most thoroughly and patiently
worked-out investigations of Professor Marsh have given us a just idea
of the vast fossil wealth, and of the scientific importance, of these
deposits. I have had the advantage of glancing over the collections in
Yale Museum; and I can truly say, that so far as my knowledge extends,
there is no collection from any one region and series of strata
comparable, for extent, or for the care with which the remains have been
got together, or for their scientific importance, to the series of
fossils which he has deposited there. This vast collection has yielded
evidence bearing upon the question of the pedigree of the horse of the
most striking character. It tends to show that we must look to America,
rather than to Europe, for the original seat of the equine series; and
that the archaic forms and successive modifications of the horse's
ancestry are far better preserved here than in Europe.
Professor Marsh's kindness has enabled me to put before you a diagram,
every figure of which is an actual representation of some specimen which
is to be seen at Yale at this present time (Fig. 9).
The succession of forms which he has brought together carries us from
the top to the bottom of the Tertiaries. Firstly, there is the true
horse. Next we have the American Pliocene form of the horse
(_Pliohippus_); in the conformation of its limbs it presents some very
slight deviations from the ordinary horse, and the crowns of the
grinding teeth are shorter. Then comes the _Protohippus_, which
represents the European _Hipparion_, having one large digit and two
small ones on each foot, and the general characters of the fore-arm and
leg to which I have referred. But it is more valuable than the European
_Hipparion_ for the reason that it is devoid of some of the
peculiarities of that form--peculiarities which tend to show that the
European _Hipparion_ is rather a member of a collateral branch, than a
form in the direct line of succession. Next, in the backward order in
time, is the _Miohippus_, which corresponds pretty nearly with the
_Anchitherium_ of Europe. It presents three complete toes--one large
median and two smaller lateral ones; and there is a rudiment of that
digit, which answers to the little finger of the human hand.
The European record of the pedigree of the horse stops here; in the
American Tertiaries, on the contrary, the series of ancestral equine
forms is continued into the Eocene formations. An older Miocene form,
termed _Mesohippus_, has three toes in front, with a large splint-like
rudiment representing the little finger; and three toes behind. The
radius and ulna, the tibia and the fibula, are distinct, and the short
crowned molar teeth are anchitheroid in pattern.
But the most important discovery of all is the _Orohippus_, which comes
from the Eocene formation, and which is the oldest member of the equine
series, as yet known. Here we find four complete toes on the front-limb,
three toes on the hind-limb, a well-developed ulna, a well-developed
fibula, and short-crowned grinders of simple pattern.
Thus, thanks to these important researches, it has become evident that,
so far as our present knowledge extends, the history of the horse-type
is exactly and precisely that which could have been predicted from a
knowledge of the principles of evolution. And the knowledge we now
possess justifies us completely in the anticipation, that when the still
lower Eocene deposits, and those which belong to the Cretaceous epoch,
have yielded up their remains of ancestral equine animals, we shall
find, first, a form with four complete toes and a rudiment of the
innermost or first digit in front, with probably, a rudiment of the
fifth digit in the hind foot;[6] while, in still older forms, the series
of the digits will be more and more complete, until we come to the
five-toed animals, in which, if the doctrine of evolution is well
founded, the whole series must have taken its origin.
That is what I mean by demonstrative evidence of evolution. An inductive
hypothesis is said to be demonstrated when the facts are shown to be in
entire accordance with it. If that is not scientific proof, there are no
merely inductive conclusions which can be said to be proved. And the
doctrine of evolution, at the present time, rests upon exactly as secure
a foundation as the Copernican theory of the motions of the heavenly
bodies did at the time of its promulgation. Its logical basis is
precisely of the same character--the coincidence of the observed facts
with theoretical requirements.
The only way of escape, if it be a way of escape, from the conclusions
which I have just indicated, is the supposition that all these different
equine forms have been created separately at separate epochs of time;
and, I repeat, that of such an hypothesis as this there neither is, nor
can be, any scientific evidence; and, assuredly, so far as I know, there
is none which is supported, or pretends to be supported, by evidence or
authority of any other kind. I can but think that the time will come
when such suggestions as these, such obvious attempts to escape the
force of demonstration, will be put upon the same footing as the
supposition made by some writers, who are, I believe, not completely
extinct at present, that fossils are mere simulacra [images], are no
indications of the former existence of the animals to which they seem to
belong; but that they are either sports of Nature, or special creations,
intended--as I heard suggested the other day--to test our faith.
In fact, the whole evidence is in favour of evolution, and there is none
against it. And I say this, although perfectly well aware of the seeming
difficulties which have been built up upon what appears to the
uninformed to be a solid foundation. I meet constantly with the argument
that the doctrine of evolution cannot be well founded because it
requires the lapse of a very vast period of time; while the duration of
life upon the earth, thus implied, is inconsistent with the conclusions
arrived at by the astronomer and the physicist. I may venture to say
that I am familiar with those conclusions, inasmuch as some years ago,
when president of the Geological Society of London, I took the liberty
of criticising them, and of showing in what respects, as it appeared to
me, they lacked complete and thorough demonstration. But, putting that
point aside, suppose that, as the astronomers, or some of them, and some
physical philosophers tell us, it is impossible that life could have
endured upon the earth for so long a period as is required by the
doctrine of evolution--supposing that to be proved--I desire to be
informed, what is the foundation for the statement that evolution does
require so great a time? The biologist knows nothing whatever of the
amount of time which may be required for the process of evolution. It is
a matter of fact that the equine forms, which I have described to you,
occur, in the order stated, in the Tertiary formations. But I have not
the slightest means of guessing whether it took a million of years, or
ten millions, or a hundred millions, or a thousand millions of years, to
give rise to that series of changes. A biologist has no means of
arriving at any conclusions as to the amount of time which may be needed
for a certain quantity of organic change. He takes his time from the
geologist. The geologist, considering the rate at which deposits are
formed and the rate at which denudation goes on upon the surface of the
earth, arrives at more or less justifiable conclusions as to the time
which is required for the deposit of a certain thickness of rocks; and
if he tells me that the Tertiary formations required 500,000,000 years
for their deposit, I suppose he has good ground for what he says, and I
take that as a measure of the duration of the evolution of the horse
from the _Orohippus_ up to its present condition. And, if he is right,
undoubtedly evolution is a very slow process, and requires a great deal
of time. But suppose now, that an astronomer or a physicist--for
instance, my friend Sir William Thomson--tells me that my geological
authority is quite wrong; and that he has weighty evidence to show that
life could not possibly have existed upon the surface of the earth
500,000,000 years ago, because the earth would have then been too hot to
allow of life, my reply is: "That is not my affair; settle that with the
geologist, and when you have come to an agreement among yourselves I
will adopt your conclusions." We take our time from the geologists and
physicists, and it is monstrous that, having taken our time from the
physical philosopher's clock, the physical philosopher should turn round
upon us, and say we are too fast or too slow. What we desire to know is,
is it a fact that evolution took place? As to the amount of time which
evolution may have occupied, we are in the hands of the physicist and
the astronomer, whose business it is to deal with those questions.
[Illustration: Fig. 9]
Fore Foot. Hind Foot. Fore-arm. Leg. Upper Molar. Lower Molar.
RECENT.
EQUUS.
PLIOCENE.
PLIOHIPPUS.
PROTOHIPPUS
(_Hipparion_).
MIOCENE.
MIOHIPPUS
(_Anchitherium_).
MESOHIPPUS.
EOCENE.
OROHIPPUS.
FOOTNOTES:
[5] I use the word "type" because it is highly probable that many of the
forms of _Anchitherium_-like and _Hipparion_-like animals existed in the
Miocene and Pliocene epochs, just as many species of the horse tribe
exist now; and it is highly improbable that the particular species of
_Anchitherium_ or _Hipparion_, which happen to have been discovered,
should be precisely those which have formed part of the direct line of
the horse's pedigree.
[6] Since this lecture was delivered, Professor Marsh has discovered a
new genus of equine mammals (_Eohippus_) from the lowest Eocene
deposits of the West, which corresponds very nearly to this
description.--_American Journal of Science_, November, 1876.
FIGHTING PESTS WITH INSECT ALLIES
LELAND O. HOWARD
[Dr. Howard is Chief of the Division of Entomology in the
United States Department of Agriculture at Washington. He is
a lecturer at Swarthmore College and at Georgetown
University. He has written "The Insect Book," published by
Doubleday, Page & Co., New York; and a work on Mosquitoes,
issued by McClure, Phillips & Co., New York. Both are books
of interest from the hand of a master: they are fully
illustrated. The narrative which follows appeared in
_Everybody's Magazine_, June, 1901.]
Some twenty-five years ago there appeared suddenly upon certain acacia
trees at Menlo Park, California, a very destructive scale bug. It
rapidly increased and spread from tree to tree, attacking apples, figs,
pomegranates, quinces, and roses, and many other trees and plants, but
seeming to prefer to all other food the beautiful orange and lemon trees
which grow so luxuriantly on the Pacific Coast, and from which a large
share of the income of so many fruit-growers is gained. This insect,
which came to be known as the _white scale_ or _fluted scale_ or the
_Icerya_ (from its scientific name), was an insignificant creature in
itself, resembling a small bit of fluted wax a little more than a
quarter of an inch long. But when the scales had once taken possession
of a tree, they swarmed over it until the bark was hidden; they sucked
its sap through their minute beaks until the plant became so feeble that
the leaves and young fruit dropped off, a hideous black smut-fungus
crept over the young twigs, and the weakened tree gradually died.
In this way orchard after orchard of oranges, worth a thousand dollars
or more an acre, was utterly destroyed; the best fruit-growing sections
of the State were invaded, and ruin stared many a fruit-grower in the
face. This spread of the pest was gradual, extending through a series of
years, and not until 1886 did it become so serious a matter as to
attract national attention.
In this year an investigation was begun by the late Professor C. V.
Riley, the Government entomologist then connected with the Department of
Agriculture at Washington. He sent two agents to California, both of
whom immediately began to study the problem of remedies. In 1887 he
visited California himself, and during that year published an elaborate
report giving the results of the work up to that point. The complete
life-history of the insect had been worked out, and a number of washes
had been discovered which could be applied to the trees in the form of a
spray, and which would kill a large proportion of the pests at a
comparatively small expense. But it was soon found that the average
fruit-grower would not take the trouble to spray his trees, largely from
the fact that he had experimented for some years with inferior washes
and quack nostrums, and from lack of success had become disgusted with
the whole idea of using liquid compounds. Something easier, something
more radical was necessary in his disheartened condition.
Meantime, after much sifting of evidence and much correspondence with
naturalists in many parts of the world, Professor Riley had decided that
the white scale was a native of Australia, and had been first brought
over to California accidentally upon Australian plants. In the same way
it was found to have reached South Africa and New Zealand, in both of
which colonies it had greatly increased, and had become just such a pest
as it is in California. In Australia, however, its native home, it did
not seem to be abundant, and was not known as a pest--a somewhat
surprising state of affairs, which put the entomologist on the track of
the results which proved of such great value to California. He reasoned
that, in his native home, with the same food plants upon which it
flourished abroad in such great abundance, it would undoubtedly do the
same damage that it does in South Africa, New Zealand, and California,
if there were not in Australia some natural enemy, probable some insect
parasite or predatory beetle, which killed it off. It became therefore
important to send a trained man to Australia to investigate this
promising line.
After many difficulties in arranging preliminaries relating to the
payment of expenses (in which finally the Department of State kindly
assisted), one of Professor Riley's assistants, a young German named
Albert Koebele, who had been with him for a number of years, sailed for
Australia in August, 1888. Koebele was a skilled collector and an
admirable man for the purpose. He at once found that Professor Riley's
supposition was correct: there existed in Australia small flies which
laid their eggs in the white scales, and these eggs hatched into grubs
which devoured the pests. He also found a remarkable little ladybird, a
small, reddish-brown convex beetle, which breeds with marvellous
rapidity and which, with voracious appetite, and at the same time with
discriminating taste, devours scale after scale, but eats fluted scales
only--does not attack other insects. This beneficial creature, now known
as the Australian ladybird, or the Vedalia, Mr. Koebele at once began to
collect in large numbers, together with several other insects found
doing the same work. He packed many hundreds of living specimens of the
ladybird, with plenty of food, in tin boxes, and had them placed on ice
in the ice-box of the steamer at Sydney; they were carried carefully to
California, where they were liberated upon orange trees at Los Angeles.
[Illustration: Vedalia, or Australian Ladybird]
These sendings were repeated for several months, and Mr. Koebele, on his
return in April, 1889, brought with him many more living specimens which
he had collected on his way home in New Zealand, where the same Vedalia
had been accidentally introduced a year or so before.
[Illustration: Larvae of Vedalia eating White Scale]
The result more than justified the most sanguine expectations. The
ladybirds reached Los Angeles alive, and, with appetites sharpened by
their long ocean voyage, immediately fell upon the devoted scales and
devoured them one after another almost without rest. Their hunger
temporarily satisfied, they began to lay eggs. These eggs hatched in a
few days into active grub-like creatures--the larvae of the beetles--and
these grubs proved as voracious as their parents. They devoured the
scales right and left, and in less than a month transformed once more to
beetles.
And so the work of extermination went on. Each female beetle laid on an
average 300 eggs, and each of these eggs hatched into a hungry larva.
Supposing that one-half of these larvae produced female beetles, a simple
calculation will show that in six months a single ladybird became the
ancestor of 75,000,000,000 of other ladybirds, each capable of
destroying very many scale insects.
[Illustration: Twig of olive infected with Black Scale]
Is it any wonder, then, that the fluted scales soon began to disappear?
Is it any wonder that orchard after orchard was entirely freed from the
pest, until now over a large section of the State hardly an Icerya is to
be found? And could a more striking illustration of the value of the
study of insects possibly be instanced? In less than a year from the
time when the first of these hungry Australians was liberated from his
box in Los Angeles the orange trees were once more in bloom and were
resuming their old-time verdure--the Icerya had become practically a
thing of the past.
[Illustration: Rhizobius, the imported enemy of the Black Scale of the
Olive.]
This wonderful success encouraged other efforts in the same direction.
The State of California some years later sent the same entomologist,
Koebele, to Australia to search for some insect enemy of the black
scale, an insect which threatened the destruction of the extensive olive
orchards of California. He found and successfully introduced another
ladybird beetle, known as _Rhizobius ventralis_, a little dark-coloured
creature which has thrived in the California climate, especially near
the seacoast, and in the damp air of those regions has successfully held
the black scale in check. It was found, however, that back from the
seacoast this insect did not seem to thrive with the same vigor, and the
black scale held its own. Then a spirited controversy sprung up among
the olive-growers, those near the seacoast contending that the
_Rhizobius_ was a perfect remedy for the scale, while those inland
insisted that it was worthless. A few years later it was discovered that
this olive enemy in South Europe is killed by a little caterpillar,
which burrows through scale after scale eating out their contents, and
an effort was made to introduce the caterpillar into California, but
these efforts failed. Within the past two years it has been found that a
small parasitic fly exists in South Africa which lays its eggs in the
same black scale, and its grub-like larvae eat out the bodies of the
scales and destroy them. The climate of the region in which this
parasite exists is dry through a large part of the year, and therefore
this little parasitic fly, known as _Scutellista_, was thought to be
the needed insect for the dry California regions. With the help of Mr.
C. P. Lounsbury, the Government entomologist of Cape Colony, living
specimens of this fly were brought to this country, and were colonized
in the Santa Clara Valley, near San Jose, California, where they have
perpetuated themselves and destroyed many of the black scales, and
promise to be most successful in their warfare against the injurious
insect.
This same _Scutellista_ parasite had, curiously enough, been previously
introduced in an accidental manner into Italy, probably from India, and
probably in scale-insects living on ornamental plants brought from
India. But in Italy it lives commonly in another scale insect, and with
the assistance of the learned Italian, Professor Antonio Berlese, the
writer made an unsuccessful attempt to introduce and establish it a year
earlier in some of our Southern States, where it was hoped it would
destroy certain injurious insects known as "wax scales."
In the meantime the United States, not content with keeping all the good
things to herself, has spread the first ladybird imported--the
_Vedalia_--to other countries. Four years ago the white scale was
present in enormous numbers in orange groves on the left bank of the
river Tagus, in Portugal, and threatened to wipe out the orange-growing
industry in that country. The California people, in pursuance of a
far-sighted policy, had with great difficulty, owing to lack of food,
kept alive some colonies of the beneficial beetle, and specimens were
sent to Portugal which reached there alive and flourishing. They were
tended for a short time, and then liberated in the orange groves, with
precisely the same result as in California. In a few months the scale
insects were almost entirely destroyed, and the Portuguese
orange-growers saved from enormous loss.
This good result in Portugal was not accomplished without opposition. It
was tried experimentally at the advice of the writer, and in the face of
great incredulity on the part of certain Portuguese newspapers and of
some officials. By many prominent persons the account published of the
work of the insect in the United States was considered as untrustworthy,
and simply another instance of American boasting. But the opposition was
overruled, and the triumphant result silenced all opposition. It is safe
to say that the general opinion among Portuguese orange-growers to-day
is very favourable to American enterprise and practical scientific
acumen.