Column I. contains the names of the successive sedimentary strata.
" II. contains the percentage of the duration of the various epochs,
according to _Williams_, the time from the Cambrian until recent times
being taken as 100.
" III. gives the estimated duration in years of the Palæozoic,
Mesozoic, and Cænozoic periods, according to _Walcott_.
" IV. gives in years the duration of the various smaller epochs, as
computed from Walcott and Williams' statements.
" V. Representatives of stages of the ancestral line of man. The
names stand in the level of the stratum in which they have made their
first appearance.
" VI. contains the number of years which, in the present
calculation, have been assumed necessary for the animal to reach
puberty.
" VII. contains the number of generations which can have elapsed
from stage to stage. For example, 60,000 generations separate the
earliest known anthropoid apes from Pithecanthropus.
Let us follow the descent of man further back. The next stage,
reckoning backwards, is that from Pithecanthropus to _bonâ-fide_
anthropoid apes. They are represented in the Miocene by various
genera--_e.g._, Pliopithecus and Dryopithecus. According to Croll and
Wallace, 850,000 years ago carry us into the Miocene epoch. Assuming
that these apes lived about 600,000 years before Pithecanthropus,
namely, in the later half of the Miocene, and taking puberty at ten
years of age, a high estimate, we get not less than 60,000 generations.
2. From Apes back to lowest Lemurs in the lowest Eocene. The date of
Eocene being fixed at 3,000,000, we have about 2,100,000 years for this
stage; assuming as much as five years for puberty, this results in
420,000 generations.
3. From Lemures to Prototheria. The earliest known mammalian remains
come from the Rhætic, or top formation of the Triassic epoch; allowing
for the Rhætic only 100,000 years, we have to add the whole of the
Jurassic and Cretaceous, in all about 5,500,000 years. Assuming three
years for a generation, we get 1,800,000 generations.
4. From Prototheria to something like the Theromorpha at the bottom of
the Triassic strata. A duration of 1,700,000 years divided by four
gives 425,000 generations.
5. From Theromorpha to Proreptilia, represented by Eryops and Cricotus
from the Lower Permian of Texas. Allowing 1,000,000 years, each
generation at four years, we obtain 250,000 generations.
6. From Proreptilia to Eotetrapoda, the first terrestrial Vertebrata,
represented by something like the Stegocephali, the earliest of which
are known from the Coal-measures. Assuming them to have come into
existence at the bottom of the Coal-measures, for the duration of which
we may guess 2,000,000 years, we get, with four years' allowance for
puberty, 500,000 generations.
7. From Eotetrapoda to a not yet separated or differentiated group
of Crossopterygian and Dipnoan fishes, both of which are known from
Devonian strata. The duration of the latter has been computed at
4,000,000 years, which, with 1,000,000 for the Mountain Limestone
formation, gives us 5,000,000 for this stage. Assuming, for the sake
of round numbers, as much as five years for a generation, we get
1,000,000 generations.
8. Earliest stage, down to the first fish-like creatures. Teeth and
spines indicating the existence of fishes are known from the Upper
Silurian. By carrying the earliest fishes down to the bottom of the
Silurian, with 2,700,000 years' duration, and allowing three years for
attaining puberty, the calculation results in 900,000 generations.
Further back we cannot go. We do not know of any Vertebrate remains
from the Ordovician and Cambrian, which together represent 6,700,000
years, enough for at least half as many generations of Prochordate
creatures. The pre-Cambrian or Laurentian epoch lies quite beyond the
reach of calculation, nor have we any trustworthy fossil remains of
living matter from these strata, to which, however, Haeckel and others
refer the first beginnings of life.
All the above calculations are, of course, only approximate. What we
do know is the existence of representatives of the stages, our proofs
being the fossils; but when we refer the origin of the Eotetrapoda,
for example, to the bottom and not somewhere to the middle of the
Coal-measures, we are guessing merely. Alterations in the levels
assumed for the various stage-representatives will, of course, alter
the result of the number of generations; but the leading idea, as
a whole, is not thereby upset. The fact remains that in the Upper
Silurian we have fishes; from the Coal-measures onwards, fishes and
Amphibia; since the Permian, fishes, Amphibia, and reptiles; since the
end of the Trias these three classes and the Mammalia; and lastly, at
least since the Plistocene, man himself. If Evolution is true at all,
the transformation from early fish-like creatures to man has come about
within these epochs. Being able to assign a time of duration to each
of them, with an approximate total of 21,000,000 years, we are also
able to put the whole ancestral series to a test by expressing each
great stage in generations. The result is very satisfactory. The whole
enormous stretch from the lowest fish-like creatures to man has been
resolved into more than 5,000,000 successive generations, and each of
these means a little step forwards in onward Evolution.
Nothing is to be gained for the understanding of our problem of
Evolution if we multiply this enormous number of generations by ten
or any other multiple. We are not able to conceive changes so small
as those which necessarily have existed between Pithecanthropus and
man if the whole striking difference is analysed into 17,000 steps.
Every one of these stages in the modifications of the muscles, the
skeletal framework, increase of brain, shortening of the trunk,
lengthening of the legs, improvement of the hands, loss of the hairy
coat, etc., is truly microscopical, imperceptible, just as the
Evolutionist imagines the whole process to have been. Again, where is
the difficulty implied by the change from an air-breathing, in many
structural points half-amphibian, fish into a primitive land-crawling
four-footed creature, if we are allowed to resolve the transformation
into 1,000,000 stages? So far from there being any difficulty, rather
does it appear questionable if so many infinitely small changes have
been necessary to bring about this result.
One thousand years make apparently no difference in the evolution of
animals, nor does one second change the aspect of the hands on the
face of a clock, nor did Julius Cæsar's commission of scientific men
appreciate the error of about eleven minutes in the length of the year
beyond its real value; but now the Russians are, owing to this neglect,
nearly two weeks behind the civilized nations.