POPULAR SCIENCE 93 



monkeys in captivity, and some in the wild state/ die of 

 broncho-pneumonia, which is often tuberculous. They seem 

 to have failed to adjust the heart to the increased strain involved 

 by the erect attitude, and the right side of that organ gives 

 way. The same diseases are depopulating some of the South 

 Sea Islands, where the natives, formerly naked, now wear linen, 

 which chills them after it has been drenched by the tropical 

 rains. The primates usually live in hollow trees, and some of 

 them build shelters from the rain. Man lost his hair at a very 

 early period, for the hair varies profoundly in the three great 

 varieties of man. The hairy parts of the body are well supplied 

 with sebaceous glands, and many races believe that the liberal 

 use of grease prevents any further loss of hair. 



A very long period at the seaside, during which our ancestors 

 were slowly changing from protoman to man, is the best ex- 

 planation of the accentuation of the monthly cycle in woman. 

 This cycle probably began with the ancestral primate, but in 

 some monkeys it is obscured by the fact that they have a 

 definite breeding-season, usually twice a year. This longer 

 cycle is a secondary phenomenon related to the annual food 

 variations at the time of the rains. On a tidal shore similar 

 variations occur every fortnight. As the rise and fall of 

 " spring " tides is about three times as great as the difference 

 between high and low water at " neap " tide, a far greater 

 extent of rock and sand can then be searched for food. More- 

 over, the harvest from below the mean level of low water is 

 much richer than that from the shallow depths exposed at 

 neap tide. For instance, oysters are usually found below the 

 two-fathom line, and are therefore more readily obtained at 

 spring tide. The knowledge that they were there may have 

 induced our ancestors to dive like the Tasmanian women. 

 One week there may have been little to eat except plants ; the 

 following week there was a superabundance of food rich in 

 protein. Turtles also lay their eggs by moonlight, and these 

 may have increased the lunar feastings. Hence the new feasting 

 reinforced a tradition which had been growing all through the 

 Eocene. Dr. Marie Stopes believes that most women have a 

 fortnightly rhythm, marked among other things by a special 

 feeling of bien etre. If this is so, the cause can hardly be referred 

 to anything except the ebb and flow of the tides. 



Another possible result of such a life at the seaside is the 

 human shoulder-joint, which, from the point of view of the 

 " fittest," is evolved beyond the proper limits. Movements 

 are extremely free, the capsule is very loose, and consequently 

 dislocation of the shoulder is several times more common than 

 that of all the other joints taken together. After such an 



^ Darwin, Descent of Man, p. 7. 



