[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 lit