ancestry will be found to consist of such varied elements that they are indistinguishable from the sample taken at haphazard from the general population. Galton speaks of the tendency of peculiarities to revert to the general type and says that a man?s brother is twice as nearly related to him as his father is and nine times as nearly as his cousin is. The mean stature of any particular class of men will be the same as that of the race. In other words, it will be mediocre. This tells heavily against the full hereditary transmission of any rare and valuable gift, as only a few of the many children would resemble their parents.? We may add to these thoughts of Galton that Christ himself, as respects his merely human ancestry, was not so much son of Mary, as he was Son of man.
Brooks, Foundations of Zoology, 144-167 ? In an investigated case, ?in seven and a half generations the maximum ancestry for one person is 382, or for three persons 1146. The names of 452 of them, or nearly half, are recorded, and these 452 named ancestors are not 452 distinct persons, but only 149, many of them, in the remote generations, being common ancestors of all three in many lines. If the lines of descent from the unrecorded ancestors were inter-related in the same way, as they would surely be in and stable community, the total ancestry of these three persons for seven and a half generations would be 378 persons instead of
1146. The descendants of many died out. All the members of a species descend from a few ancestors in a remote generation and these few are the common ancestors of all. Extinction of family names is very common. We must seek in the modern world and not in the remote past for an explanation of that diversity among individuals which passes under the name of variation. The genealogy of a species is not a tree, but a slender thread of very few strands, a little frayed at the near end, but of immeasurable length. A fringe of loose ends all along the thread may represent the animals which having no descendants are now as if they had never been. Each of the strands at the near end is important as a possible of union between the thread of the past and that of the distant future.?
Weismann, Heredity, 270, 272, 380, 384, denies Brooks?s theory that the male element represents the principle of variation. He finds the cause of variation in the union of elements from the two parents. Each child unites the hereditary tendencies of two parents and so must be different from either. The third generation is a compromise between four different hereditary tendencies. Brooks finds the cause of variation in sexual reproduction, but he bases his theory upon the transmission of acquired characters. Weismann denies this transmission by saying that the male germ cell does not play a different part from that of the female in the construction of the embryo. Children inherit quite as much from the father
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