单选题：根据下面资料，回答题： Being a man has always been dangerous. There are

根据下面资料，回答题：
Being a man has always been dangerous. There are about 105 males born for every 100 females, but this ratio drops to near balance at the age of maturity, and among 70-year-olds there aretwice as many women as men. But the great universal of male mortality is being changed. Now,boy babies survive almost as well as girls do. This means that, for the first time, there will be anexcess of boys in those crucial years when they are searching for a mate. More important, another chance for natural selection has been removed. Fifty years ago, the chance of a baby (particularly a boy baby) surviving depended on its weight. A kilogram too light or too heavy meant almost certain death. Today it makes almost no difference. Since much of the variation is due to genes, one more agent of evolution has gone.
There is another way to commit evolutionary suicide: stay alive, but have fewer children. Few people are as fertile as in the past. Except in some religious communities, very few women have 15 children. Nowadays the number of births, like the age of death, has become average. Most of us have roughly the same number of offspring. Again, differences between people and the opportunity for natural selection to take advantage of it have diminished. India shows what is happening. The country offers wealth for a few in the great cities and poverty for the remaining tribalpeoples. The grand mediocrity of today--everyone being the same in survival and number of off-spring--means that natural selection has lost 80% of its power in upper-middle-class India compared to the tribes.
For us, this means that evolution is over; the biological Utopia has arrived. Strangely, it hasinvolved little physical change. No other species fills so many places in nature. But in the past100,000 years--even the past 100 years--our lives have been transformed but our bodies have not.We did not evolve, because machines and society did it for us. Darwin had a phrase to describethose ignorant of evolution: they "look at an organic being as a savage looks at a ship, as at something wholly beyond his comprehension". No doubt we will remember a 20th century way of life
beyond comprehension for its ugliness. But however amazed our descendants may be at how farfrom Utopia we were, they will look just like us.
What used to be the danger in being a man according to the first paragraph? A．A lack of mates.
B．A fierce competition.
C．A lower survival rate.
D．A defective gene.