490 THE BRIDGE OF LIFE 



blending of semen from different body parts of both parents, inheritance 

 was accounted for. 



It was not until the microscope was discovered during the latter 

 part of the seventeenth century that a truer picture of heredity became 

 apparent. Anton van Leeuwenhoek, a Dutch lens maker, mentioned in 

 Chapter 2 in connection with the discovery of the cell, gets credit for 

 being the first to observe human sperms. He used crude, yet efficient 

 microscopes of his own making. When he saw these tiny, wiggling 

 organisms in human semen, he suggested that each of these "animal- 

 cules," as he called them, was a potential human being and that any 

 one of them could develop into such if introduced into the womb of a 

 woman where it could be nourished. This theory failed to explain how 

 characteristics could be inherited from the mother, but it did represent 

 a great milestone in the discovery of the true physical basis of heredity. 

 Some scientists of the time even imagined that they could see tiny 

 human beings within the head of the sperms and made drawings to 

 show such (see Fig. 31.1). 



Another Dutch scientist, Regnier de Graaf, helped complete the 

 picture when he observed the similarity between the ovaries of women 

 and those of birds. He concluded that women produce eggs similar to 

 those of birds, but much smaller in size, and that these eggs unite with 

 sperms to produce human embryos. The egg with the cells surrounding 

 it has ever since been called the Graafian follicle. 



A Frenchman, Jean Baptiste Lamarck, came forth with an intriguing 

 theory which was widely discussed during the first decade of the nine- 

 teenth century. His theory held that the reproductive cells were in 

 some way influenced by the bodies of the parents so that the cells 

 transmitted these new characteristics which were acquired to their 

 offspring. A giraffe was supposed to have a long neck because it 

 continually stretched it in an effort to reach leaves on high trees, and 

 this stimulated the growth of the bones, muscles, blood vessels and 

 other structures in the neck region. Each generation's stretching was 

 passed on to the offspring, and the necks of giraffes have become longer 

 and longer from one generation to the next. This supposed inheritance 

 of the effects of use or disuse of a body part is called the theory of the 

 inheritance of acquired characters. 



The famous English scientist, Charles Darwin, came into the picture 

 during the middle of the nineteenth century. He proposed a mechanism 

 by means of which such acquired characteristics could be transferred 

 to the offspring. He assumed that tiny bodies, he called them pangenes, 

 were formed in the various body parts and migrated to the reproductive 

 cells. For instance, if a blacksmith used his arms extensively and the 



