The full meaning of these statements will be better understood if a concrete example is studied, and perhaps the case of man and his ancestry is most instructive for this purpose. The fact that man has a vertebral column, a brain and nervous system, a heart and blood-vessels, digestive and other systems of organs, built up in accordance with the arbitrary plan which is shared also by all mammals, birds, reptiles, amphibians, and fishes, proclaims that man belongs to the vertebrate group of animals, and that all such vertebrata must originally have sprung from the same common ancestors. The possession of four limbs with five fingers or toes on each, and a host of identical arrangements of bones, muscles, nerves, &c., in these limbs, reveals the fact that all the four-limbed creatures or Tetrapoda represent one group which developed from some fish-like ancestor to become an amphibian. The discovery of fossilized remains of extinct animals reveals that the fishes are much older than the amphibians, and that a number of intermediate stages demonstrate the process of gradual transformation which converted one group of fishes into four-limbed, semi-terrestrial amphibians. Geological evidence also proves that the reptiles came definitely later than the amphibians, and that only one small group of very primitive amphibians shared in the progressive modifications of brain, limbs, and organs of circulation, &c., to become reptiles—creatures able to live wholly on the dry land, and capable of a wider range of activities than the Amphibia. From the primitive reptiles were derived not only the highly specialized forms that have survived to the present day as lizards, tortoises, snakes, &c., creatures that differ profoundly from their earliest reptilian ancestors, but also the ancestors of birds and the ancestors of mammals. One particular group of primitive reptiles is known, from fossilized remains found in South Africa, that reveals many of the distinctive peculiarities of mammals not shared by other reptiles; and it is now certain that these cynodonts—so called from their dog-like teeth—include the parents of the mammals. The fact that all the Mammalia are provided with glands which in the female supply milk for the nutrition of their young, that they have a hairy coat, that they have a highly developed brain more fully adapted for learning by experience than is the case in other vertebrates, that they have limbs capable of a much more varied and active range of skilled movements, and a host of identical transformations of viscera, muscles, nerves, and vessels prove the common ancestry of mammals from some very primitive cynodont reptile. Different mammals have been specialized in structure for amazingly varied modes of life, on land, under the ground, in trees, in the air, or in rivers or the sea. Of the terrestrial animals some have been modified for fleetness, like the horse and the antelope; others for strength, like the elephant; others again, like the lion and the tiger, to prey upon their weaker relatives. At the dawn of the age of mammals one particular group was able to survive without any of the profound alterations of the structure of the limbs which such creatures as the horse and the ox, the elephant and the whale, the tiger and the bat had to adopt to avoid extinction, and retained the primitive type of limbs with their fingers and toes which became the most useful and plastic instruments for performing skilled movements and acquiring experience and knowledge as soon as the brain was sufficiently advanced in structure and capability to put these instruments to their full use. The group of mammals which delayed the time of specialization until it was able to profit by its greater adaptability was the Prosimiæ, the ancestors of the apes and man. These small creatures for a long time lived a life of obscurity in trees without submitting to those extreme adaptations of structure which are found in most arboreal and flying mammals. But the cultivation of their powers of vision, and the acquisition of skill in the use of their primitive but plastic hands, guided by vision, eventually conferred upon some of these Prosimiæ vastly enhanced powers of skilled action and of learning by experience and of acquiring knowledge, which culminated in the attainment of the supreme power of discrimination distinctive of human intelligence.
The fact that man belongs to the same order (Primates) as the apes is proved not merely by the possession of a body which in most respects is identical in structure with such of them as the gorilla and the chimpanzee, of a similar process of development characterized by identical stages up to a certain stage, but also by the fact that the blood of man and the apes react towards one another as those of relatives, and in a way not shared by the blood-reactions of other mammals. The apes, also, are subject to certain human diseases from which other mammals are immune. Man shares with the anthropoid apes (gorillas, chimpanzees, orangs, and gibbons) so many peculiarities which differentiate all of them from the tailed monkeys that there can
be no doubt that the human family was derived from a primitive anthropoid ape, possibly a species that lived in the foothills of the Himalayas in Miocene times, as is suggested by fossils recently discovered by Dr. Pilgrim, director of the Geological Survey of India.
The vestigial remains of the muscles, blood-vessels, &c., of the tail reveal the fact that man's Primate ancestry began with a tailed form. In fact, the human embryo actually possesses a tail for some weeks of its existence. If India reveals the fossilized remains of a variety of Miocene anthropoid apes closely akin to the ancestors of man, the gorilla, the chimpanzee, and the orang, the Egyptian Fayum has provided the evidence of the origin of the anthropoid apes in Oligocene times as very diminutive creatures distantly akin to the gibbons, but bearing very obvious indications in the form of their teeth of an affinity with the Prosimian sub-order Tarsioidea, a very interesting group of Eocene Primates found in a fossilized condition in North America and France, one of the members of which has survived in the peculiar Spectral Tarsier still found living in the forests of Borneo, Java, and the Philippines. The detailed study of the structure and development of Tarsius, and comparisons with other Primates and mammals of other orders, provide the information necessary to fill in the gaps left in the geological record, and enable us to sketch out the general scheme of man's ancestry, and to appreciate the nature of the factors which determined the evolution of such an intelligent mammal as man.
Within recent years the increasing knowledge of embryology and comparative anatomy, and the recovery of fossilized remains of vast numbers of hitherto unknown animals, has established the truth of evolution and the exact line of ancestry of many animals. Professor Osborn's work on the evolution of the horse, and Dr. C. W. Andrews's revelation of the ancestry of the elephant, are striking recent illustrations of the exactness of the demonstration palæontology can give of the past history of mammals. Dr. Robert Brown and Professor D. M. S. Watson have given conclusive proofs of the origin of mammals and birds from primitive reptiles, and the latter zoologist has pushed back the ancestry of these higher vertebrates still further, and shown how the reptiles were derived from primitive Amphibia, and the changes that occurred in vertebrate anatomy when certain fishes crawled out of the water and developed into four-footed Amphibia. All of these conclusions are matters of fact and not of theory, even if we are still in the dark as to the exact mechanism whereby the variations which the forces of evolution use in effecting transformations were themselves brought about. Within recent years there has been a revival of interest in the problem whether characters acquired by parents as the result of their individual experience can be transmitted to their offspring. For the last thirty years biologists have been influenced by the teaching of Weismann that nothing happening to the parents can affect the morphological capabilities of the germ plasm from which the next generation is derived; but recent research suggests that this negative doctrine is too rigid, and makes it probable that certain influences brought to bear upon the parents may be transmitted also to the offspring. If this is so, it opens one avenue of explanation of how structural modifications are effected and the possibility of evolution is created. But at the present moment the whole question is being actively investigated and discussed.
Just as every complex animal can be shown to be derived during development from a simple microscopic cell or egg, so the study of evolution reveals the fact that all animals were originally derived from microscopic unicellular animals known as protozoa, which are with difficulty distinguishable from unicellular plants, from which all the varied forms of complex vegetable life were derived. It is equally certain that these unicellular plants and animals are themselves only the specialized descendants of common ancestors—unspecialized unicellular organisms which are neither strictly vegetable nor animal. But we are quite in the dark as to the processes whereby these most primitive living organisms were evolved from inorganic matter, and how they acquired these peculiar properties of growth and differentiation and their powers of reproduction, commonly called vital, which are their distinctive characteristics. Bibliographical references to most of the matters mentioned in this article will be found in the Presidential Address to Section H of the British Association for the Advancement of Science, Dundee meeting (see Report of British Association, 1912).
Ev´ora, a town in Portugal, capital of the province of Alemtejo, 75 miles east of Lisbon. It is an ancient place, poorly built, and its walls, citadel, and forts are all in a state of ruin. It has a Roman aqueduct still serviceable, a Gothic cathedral, and an ecclesiastical seminary. Pop. 17,900. The district of Evora has a pop. of 144,300.
Evremond, or Evremont. See St. Evremond.
Evreux (ev-reu), a town of N.W. France, capital of the department of Eure, in a fertile valley on the Iton. It is an ancient town with narrow streets and has many fine buildings, including an ancient Gothic cathedral. The town was frequently occupied by the English in the fifteenth century. Pop. 18,950.