NATURE’S WORKSHOP

Otago Daily Times, Issue 18877, 1 June 1923, Page 5

NATURE’S WORKSHOP

MYSTERIES OF GROWTH. THE TAIL IN THE MAN. PINEAL EYE OF THE TDATARA. (Feom Ode Own Correspondent.) LONDON, April 18. Yesterday Sir Arthur Keith continued at the Royal Institution his course of lectures on the Machinery of Human F- olution. He discussed the methods em ed by Nature in getting rid of structure., which have become useless in the human body. Nature, he said, was almost absurdly conservative in the way in which she kept on reproducing certain structures which had long since ceased to serve their original purpose. She was like a saving housewife who kept storing away od(J pieces of material with the idea that some day they would be useful. There still remains in every one of us, it seems, a vestige of the “palatial” nose with its nerve leading off to the brain. In animals which have this structure fully formed it is placed near the floor of the nose, just above a passage* in the roof of the mouth. In browsing animals, like the j sheep, it serves a most useful purpose by sampling the odours of food as soon as ft passes the portal of the lips and front teeth. In man this structure is an heirloom dating from a pre-ape stage of evolution, for as soon as hands were developed and food could be lifted and sampled by smelling there was no use for it. The New Zealand Sphenodon or tuatara, one of the oldest of reptiles, still has a i pineal eye with lens complete, althoilgh the power of sight is not there. This the creature has inherited from some far-off ancestor. Possibly a fish found excellent use for an eye on the top of the head But the possession has been continuously handed on until it now takes the form in man of the small pineal body without lens and without nerves embedded deep in the brain. It has persisted because it has been converted to serve a new purpose. In recent times it has been found that it has an important part to play in the regulation of growth. .WHY MAN LOST HIS HAIR. Every member of the great order of animals to which man belongs is clad in a hairy covering. We may safely presume that early man wore the ape’s livery. How has man become, comparatively speaking, a nude animal? We obtain soma light on (his problem by noting' the fact that the young of anthropoid apes, six weeks before birth, aro, as regards a hairy covering, exactly in the same condition as new-born children. The hair on their scalps is long, but that on the rest of their bodies is an almost invisible dotyn. Somehow Nature has succeeded in bringing about the nude condition of the body by arresting ban growth in our bodies at the stage which is reached by anthropoid apes some time before birth. When a useless structure such as a. hairy covering is to be got rid of, Nature does not pursue the extravagant method of allowing it to grow up and then sweeping it away, but nips it in the bud stage. This nudeness of the human body iias become one of the groat factors in making it possible to regulate the temperainro by artificial clothing and thus to be able to find a habitation in almost every part of the globe. HUMAN TAILS NOT UNKNOWN. Surgeons, in examining recruits for war purposes, had been to find that traces of an outward tail were commoner than bad been supposed.?* Every human embryo in the sixth week of development has a free projecting tail, which in point of form and size is similar to that possessed by an embryo monkey. But towards the end of the second month of development, wnile the monkey’s tail continues to form new joints and to grow in length, the human tail shrinks, withers, and disappears below the surface—a dimple on the skin marking the point at which the free end of the tail becomes submerged. Children born with tails are those in which the embryonic submergence fail to occur. The loss of the tail is not a human prerogative; the tail disappears just in the same way in the embryos of gorillas, chimpanzees, orangs and gibbons—indeed, in all the ape-like stock to which man is linked by a great number of structural resemblances. Long before the human form began its evolution the tail had already become a mere matter . of history. The tail was lost long before

man came on the scene. It disappeared when the anthropoid type of man’s ancestry gained a place in the world. In the body of an embryo, as in a city, conduced the lecturer, there was a continual struggle going on between the re formers and the die-hards. In the embryonic body it was necessary to suppose that there was a continuous struggle between the various departments regulating development and growth. In this struggle useless structures like the tail were starved out. The struggle for survival, recognised by Darwin as part of the machinery of evolution, was as true of the living units making up an embryo as it was of human communities. In both cases the struggle was regulated, in one case by legislation; in the other by cnemical messengers or hormones.