EVOLUTION, HEREDITY, EUGENICS 



527 



The pedigree of the horse is the best known. Paleontological 

 evidence is complete for the evolution of the horse from a five-toed 

 ancestor.'^ The pedigrees of the camel and the elephant are both 

 worked out quite satisfactorily also. The pedigree of man has been 

 worked back successfully for many centuries with accompanying 

 flint weapons and implements. 



Man 



BONES or HIND LEGS 



MonKey 



Fig. 264. Hind limb bones of man, monkey, dog, sheep and horse. (After LeConte. 



Courtesy of Amer. Mus. of Nat. Hist.) 



Evidence from Comparative Anatomy. — If we accept the Prin- 

 ciple of Evolution it is easy to explain the similarity in make up of 

 the wing of the bird, the foreleg of the seal and the arm of man, all 

 of which are " homologous " structures. Likewise, we can explain 

 the fact that man has 180 vestigial structures which now have no 

 significance to him. The muscles of the human external ear and the 

 subcutaneous muscles in the forehead and scalp persist, although 

 useless. 



The nearest allies of man in the quadrumanous species lack a tail. 

 Man has one at 6 weeks embryonic life, longer than the hinder 

 limbs. Rarely, a human infant is born with a tail. The tail 

 muscles persist as vestiges. The vermiform appendix of the cecum, 



13 Consult W. D. Matthew, The evolution of the horse. Quart. Rev. of Biol., vol. 

 I, April, 1926. 



