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Why do I exist? This isn't a philosophical cri de coeur; it's an evolutionary conundrum. At 58, I'm well past menopause, and yet I'll soldier, on, with luck, for many years more. The conundrum is more vivid when you realize that human beings (and killer whales) are the only species where females outlive their fertility. Our closest primate relatives--chimpanzees, for example--usually die before their 50s, when they are still fertile. 我为什么存在？这不是一句哲学的呐喊，而是一个进化方面的谜题。58岁的我早已过了更年期，但如果幸运的话，我还会再活很多年。当你认识到人类（以及虎鲸）是雌性在生育期过后继续存活的唯一物种之后，这个谜题就显得更加突出了。与我们血缘最近的灵长类亲戚――比如黑猩猩――一般在还有生育能力的50多岁之前就死去了。 This isn't just a miracle of modern medicine. Our human life expectancy is much longer than it used to be--but that's because far fewer children die in infancy. Anthropologists have looked at life spans in hunter-gatherer and forager societies, which are like the societies we evolved in. If you make it past childhood, you have a good chance of making it into your 60s or 70s. 这不只是现代医学创造的奇迹。我们人类的平均寿命比过去长了很多――但这是因为早夭的儿童大大减少。人类学家考察过狩猎采集社会的人类寿命。这些社会跟我们最终进化形成的各种社会有相似之处。如果活到童年过后，那么你就很有可能能够活到60多岁或70多岁。 | 
