Steps in Human Evolution

October 27, 2009 | Posted by maneerat

Real men arose, we believe, by variational uplifts of considerable magnitude which led to big and complex brains and to the power of reasoned discourse. In some other lines of mammalian evolution there were from time to time great advances in the size and complexity of the brain, as is clear, for instance, in the case of horses and elephants. The same is true of birds as compared with reptiles, and everyone recognises the high level of excellence that has been attained by their vocal powers. How these great cerebral advances came about we do not know, but it has been one of the main trends of animal evolution to improve the nervous system. Two suggestions may be made. First, the prolongation of the period of ante-natal life, in intimate physiological partnership with the mother, may have made it practicable to start the higher mammal with a much better brain than in the lower orders, like Insectivores and Rodents, and still more Marsupials, where the period before birth (gestation) is short. Second, we know that the individual development of the brain is profoundly influenced by the internal secretions of certain ductless glands notably the thyroid. When this organ is not functioning properly the child’s brain development is arrested. It may be that increased production of certain hormones—itself, of course, to be accounted for—may have stimulated brain development in man’s remote ancestors.

Categories: THE OUTLINE OF SCIENCE | Tags: Alertness, Animal Evolution, Better Brains, Brain Development, Development Of The Brain, Ductless Glands, Gestation, Human Evolution, Individual Development, Insectivores, Internal Secretions, Mammal, Mammalian Evolution, Primitive Peoples, Prolongation, Real Men, Rodents, Sifting, Social Heritage, Uplifts | No Comments »