(i) By comparing the biology of man with that of other animals and so determining the degree of their relationship (taxonomy); and
(ii) By looking at fossils and so determining their age and development (paleontology).
By comparing man with other living creatures we know that he is a primate (one of the highest order of mammals) having a large brain, a grasping hand with nails instead of claws, and eyesight which has been developed at the expense of his sense of smell. Primates include tree shrews, lemurs, monkeys and apes.
Within this group man shows the greatest resemblance to apes, not only in posture and means of locomotion (ability to move from place to place), but in the development and coordination of his brain and hands, and in the bio-chemistry of his blood.
Man has, however, been distinguished from other primates, both living and fossil, by his ability to make and use tools.
The comparison of living forms enables us to estimate the affinities of fossils, even from their fragmentary remains; and by studying the tools and animal remains found with fossil men, we can discover something of their way of life and the environment in which they lived.
As described above, biologically, man is related to the apes and diverged from a common ancestral species which, not generally specialized, lived both upon the ground and in trees during the Tertiary Era (65 million years to 63 million years.
The Tertiary Era witnessed the Alpine Orogeny and the emergence of mammals). Apes have become, on the whole, arboreal and vegetarian.
By being able to move rapidly through a forest without descending to the ground, they are secured from capture by more powerful carnivorous land animals, such as leopard or tiger, and can pluck shoots or fruits anywhere between the ground and the lofty canopy of tropical forests.
They are essentially quadrupeds, and most species have prehensile tail. Man has become a piped, by forsaking trees for the land, and has no use for a tail. His feet have become fully adapted for walking or running, and the toes cannot grip a branch, as can an ape’s.
The hand, not required either for walking or for grasping branches during leaps from tree to tree, has become a precisely controlled organ, which, having the thumb opposed to the fingers (instead of alongside), can use a variety of tools.
Adoption of an erect posture has been accompanied by enlargement of the brain, especially of the front, which is the seat of the higher intellectual function.
The eye has become elaborated, and human vision is fully stereoscopic, unlike that of any other animal.
A diminution of the jaw and its controlling muscles appear to have accompanied the increasing variety of food, with greater intelligence he could command and, in the later stages of evolution, prepare for convenient eating.
Thereby freer and more delicately controlled movements of the jaw, face and tongue are possible, giving man the faculty of speech.
Compared with apes, the gestatorial period of the human infant is 280 instead of 240 days, and the child is dependent especially upon the mother but also, indirectly, upon the father for many years whilst it’s mental and physical powers slowly develop. Males and females, therefore, tend to specialize.
The former obtain food and protect the family; the latter tend the young and prepare food. Thus, the family finds its origin in the mutual dependence of male, female and the young.
The change of habitat to the ground from trees brought about a change of diet. To fruits, nuts and edible shoots were added animals, when primitive man became a huntsman.
At the same time, hair growth was arrested, for modern man, apart from the head and certain other localized parts of the body, grows only sparse, very fine hairs. The skin too is thinner and less resistant to abrasion than that of the monkey.
The final stage of evolution as a separate species (Homo sapiens) took place mainly during the half million years of the Pleistocene period, during which the world’s climates underwent great oscillations.
For geological research has shown that throughout the preceding Tertiary Era the land areas of the world, particularly in the middle and higher latitudes of the northern hemisphere, were less extensive than today, and the climate generally milder.
Forests of a tropical or sub-tropical character were more widespread, and it may be inferred that the precursors of both modern apes and men were widely dispersed.
But, in the Pliocene period, great uplifts of land, constituting the final phase of recent world-wide mountain building, increased both the extent of land and its mean altitude.
Large areas became remote from the sea and some were shielded from rain bearing winds by the higher mountains.
Forests became savanna or steppes; and herbivorous animals, as well as the greater carnivorous, multiplied. It was in such a world that man’s ape like forebears became wholly terrestrial and more carnivorous.
The immediate ancestors of modern apes, however, keeping to the denser equatorial and tropical forests, preserved for species of living apes the tree-dwelling habit of existence.
Reduction of hair growth in human beings would be improbable in a more severe climate, which would tend to encourage a shaggier growth; and until perhaps the most recent stage in human evolution, during the latest phases of Pleistocene, when cultural equipment had become fairly elaborate, prehominids, or man like apes, were confined to warm climates.
Thus, we may infer that as savannas, grasslands and steppes became more extensive towards the close of the Pleistocene period, ape-men ranged in the outer regions of the tropics and in sub-tropical latitudes of Asia, Africa and Europe, for fragments of very primitive skulls and other parts of skeletons have been found in China, Central and Western Europe, as well as in Africa. But their developing intelligence enabled them also to survive near the equator, for some of the most significant remains have been discovered in Java.
Thus, constitutionally, men became adapted to a fairly wide range of warmer climates, and towards the polar margins of his habitat must have become accustomed to seasonal change of temperature.
Before they were able to make fire and skin animals—the latter, especially requiring edged tools, including scrapers, appeared only during the Paleolithic period. The Prehominids could hardly have survived a season with night temperatures much below 16°C (60°F).
To withstand lower temperatures at least a seasonal thickening of hair would be a likely adaptation, if ape-men had been free to drift slowly into higher latitudes and to remain in a cold climate.
But, the Great Ice Age prevented such a biological solution, and stimulated man to technical and social invention.
During the inter-glacial periods, four times the climate oscillated between mildness greater than today, when permanent snow and ice were uncommon even in Arctic regions, and severity which caused much of Europe, Northern and Central Asia to be covered by ice-sheets.
Arctic and sub-Arctic climates, such as today, are largely confined to the regions within the Arctic and Antarctic circles, prevailed as far south as latitude 40° in the northern hemisphere.
The zone over which tropical and sub-tropical climates prevailed was correspondingly reduced. During inter-glacial periods, prehominids spread more widely, for fragments of primitive stone tools have been discovered in Europe and Northern China, worn by the action of ice and running water. During the first three glacial periods, the ancestors of humanity were compelled to retreat towards the tropics.
Thus, each glaciation was a crisis not only for evolving prehominids, but for all forms of life, and many species of plants and animals which flourished at the end of the Tertiary Era failed to survive into the Holocene (Recent).
Ape-men, moving to and fro across the world, were confronted with new perils, and new economic crisis, which their greater mental powers overcame.
By the third inter-glacial period, between the Riss and Wurm glaciations, they were sufficiently advanced to be able to fashion a variety of crude tools and weapons, although we can only guess at the range of their equipment, because only stone implements have survived, and we can but presume that they also used wood, bone, and perhaps skin.
Certainly, during the fourth (Wurm) glaciations, which began about 75,000 years ago and ended about 10,000 years ago, men differing but little from ourselves and spread widely in the Old World.
They were able to survive in more rigorous climates, not by retreat into warmer regions, but to caves, where, by the use of fire and skin garments, they could continue to live close to the glaciers and ice-sheets.
Among the best known of these early races was Neanderthal man, having larger bones and more powerful muscles than modern man, and possessing a more primitive skull, with protruding, massive jaw, a receding forehead and a very prominent bony ridge above the eyes.
Neanderthaloids appear to have evolved as a separate race north of the Tertiary Mountain Belt of Europe and Asia. The remains have been found in Northern China as well as in Europe.
Meanwhile, other races had appeared which are ancestral to most living races. Some crossed to Europe from Northern Africa during the milder interlude in the last glaciation, by using land bridge at Gibraltar and the Sicilian straits.
In what are now the deserts of Northern Africa and South-Western Asia, the art of fashioning flints with great deftness had been acquired. Some of these could be used for pointing arrows and spears.
With these weapons, large animals could be hunted, for the lands south and east of the Mediterranean were steppes rather than deserts.
In France and Spain, which resembled the present tundra of Northern Russia respectively, remarkable cave drawings, amongst other evidence of the life of the times, have enabled us to learn much about this early race of modern man.
Mankind thus appears to have evolved on the whole, south of the mountain zone in Eurasia, and to have lived in India, Java, Western and Southern Asia, and Northern Africa entering Europe, for, especially in South-Eastern Asia and Africa, many skull fragments with rather primitive features have been unearthed.
It seems that Neanderthaloids and more modern races lived together in Europe and South-Western Asia during the latter part of the last glaciation, and although the more specialized Neanderthaloids have not survived as a race, some of their physical characteristics have been identified in living Europeans.
Some authorities believe that the Neanderthaloids of Eastern Asia have contributed more to Mongoloid peoples.