[填空题]There are about 105 males born for every 100 females, but this{{U}} (36) {{/U}}drops to near balance at the age of maturity, and among 70-year olds there are twice as many women as men. But the great universal of male{{U}} (37) {{/U}}is being changed. Now, boy babies{{U}} (38) {{/U}}almost as well as girls do. Fifty years ago, the chance of a baby(particularly a boy baby)surviving depended on its weight. A kilogram too light or too heavy{{U}} (39) {{/U}}almost certain death. Today it makes almost no{{U}} (40) {{/U}}. Since much of the variation is due to genes, one more agent of evolution has gone. There is another way to{{U}} (41) {{/U}}evolutionary suicide: stay alive, but have fewer children. Few people are as{{U}} (42) {{/U}}as in the past. Nowadays the number of births, like the age of death, has become{{U}} (43) {{/U}}. Again, {{U}} (44) {{/U}}. For us, this means that evolution is over; the biological Utopia has arrived. Strangely, it has involved little

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