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.
我為什么存在？這不是一句哲學(xué)的吶喊，而是一個進化方面的謎題。58歲的我早已過了更年期，但如果幸運的話，我還會再活很多年。當(dāng)你認(rèn)識到人類（以及虎鯨）是雌性在生育期過后繼續(xù)存活的唯一物種之后，這個謎題就顯得更加突出了。與我們血緣最近的靈長類親戚――比如黑猩猩――一般在還有生育能力的50多歲之前就死去了。
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.
這不只是現(xiàn)代醫(yī)學(xué)創(chuàng)造的奇跡。我們?nèi)祟惖钠骄鶋勖冗^去長了很多――但這是因為早夭的兒童大大減少。人類學(xué)家考察過狩獵采集社會的人類壽命。這些社會跟我們最終進化形成的各種社會有相似之處。如果活到童年過后，那么你就很有可能能夠活到60多歲或70多歲。
It turns out that my existence may actually be the key to human nature. This isn't a megalomaniacal boast but a new biological theory: the 'grandmother hypothesis.' Twenty years ago, the anthropologist Kristen Hawkes at the University of Utah went to study the Hadza, a forager group in Africa, thinking that she would uncover the origins of hunting. But then she noticed the many wiry old women who dug roots and cooked dinners and took care of babies (much like me, though my root-digging skills are restricted to dividing the irises). It turned out that these old women played an important role in providing nutrition for the group, as much as the strapping young hunters. What's more, those old women provided an absolutely crucial resource by taking care of their grandchildren.
原來，我的存在實際上可能是人類本性的關(guān)鍵。這不是狂妄自大的吹牛，而是一套新的生物學(xué)理論：“祖母假說”(grandmother hypothesis)。20年前，猶他大學(xué)(University of Utah)的人類學(xué)家克里斯滕・霍克斯(Kristen Hawkes)去非洲研究狩獵采集族群“哈扎”(Hadza)，以為她會揭開狩獵的起源。但去了之后她注意到很多身材精瘦的老婦人負(fù)責(zé)挖植物的根、做飯、照顧孩子（跟我很像，不過我挖植物根的技能僅限于掰鳶尾根）。原來這些老婆婆對于為集體提供營養(yǎng)發(fā)揮著重要的作用，不亞于那些年輕強壯的狩獵者。另外，老婆婆們照管孫輩，提供了一種絕對重要的資源。
There are many controversies about what happened in human evolution. But there's no debate that there were two dramatic changes in what biologists call our 'life-history': Besides living much longer than our primate relatives, our babies depend on adults for much longer.
有關(guān)人類進化史上發(fā)生過哪些事情的爭議有很多，但沒有爭議的是，生物學(xué)家所說的“生命史”上曾經(jīng)有過兩次重大變化：除了壽命在靈長類親戚基礎(chǔ)上大大延長以外，人類嬰兒依賴成年人的時間也大大延長了。
Young chimps gather as much food as they eat by the time they are 7 or so. But even in forager societies, human children pull their weight only when they are teenagers. Why would our babies be helpless for so long? That long immaturity helps make us so smart: It gives us a long protected time to grow large brains and to use those brains to learn about the world we live in. Human beings can learn to adapt to an exceptionally wide variety of environments, and those skills of learning and culture develop in the early years of life.
幼年黑猩猩到七歲左右時采集的食物已經(jīng)足夠自己吃，人類兒童即便是在狩獵采集社會中，也要到十幾歲的時候才能自給自足。我們的孩子為什么這么長的時間無法自立？這一漫長的未成熟期幫助我們變成了如今這般的聰明，因為它給我們很長的受保護的時間來長成碩大的大腦，并用這些大腦去了解周圍的世界。人類可以學(xué)會適應(yīng)各種各樣的環(huán)境，而這些學(xué)習(xí)以及文化技能是在生命的早年形成的。
But that immaturity has a cost. It means that biological mothers can't keep babies going all by themselves: They need help. In forager societies grandmothers provide a substantial amount of child care as well as nutrition. Barry Hewlett at Washington State University and his colleagues found, much to their surprise, that grandmothers even shared breast-feeding with mothers. Some grandmoms just served as big pacifiers, but some, even after menopause, could 'relactate,' actually producing milk. (Though I think I'll stick to the high-tech, 21st-century version of helping to feed my 5-month-old granddaughter with electric pumps, freezers and bottles.)
但這種不成熟有其代價。它意味著生物學(xué)意義上的母親無法完全靠自己帶孩子：她們需要幫手。在狩獵采集社會，祖母不僅提供營養(yǎng)，也做了大量的育兒工作。華盛頓州立大學(xué)(Washington State University)的巴利・休利特(Barry Hewlett)及其同事非常意外地發(fā)現(xiàn)，祖母甚至和母親共同哺乳。一些祖母僅僅是充當(dāng)大奶嘴的作用，但有些祖母甚至在更年期過后都能“重新哺乳”(relactate)，真的會分泌乳汁。（不過我想我自己會堅持采用21世紀(jì)的高科技方法，用電泵、冰箱和奶瓶來幫助喂養(yǎng)五個月大的孫女。）
Dr. Hawkes's 'grandmother hypothesis' proposes that grandmotherhood developed in tandem with our long childhood. In fact, she argues that the evolution of grandmothers was exactly what allowed our long childhood, and the learning and culture that go with it, to emerge. In mathematical models, you can see what happens if, at first, just a few women live past menopause and use that time to support their grandchildren (who, of course, share their genes). The 'grandmother trait' can rapidly take hold and spread. And the more grandmothers contribute, the longer the period of immaturity can be.
霍克斯博士的“祖母假說”提出，祖母現(xiàn)象是跟我們的漫長幼年期是一起形成的。她認(rèn)為，事實上正是祖母的進化使得我們的漫長幼年期以及與之伴隨的學(xué)習(xí)與文化得以出現(xiàn)。在數(shù)學(xué)模型中，你可以看到，如果最開始只有幾個婦女活過更年期，用這些時間來撫養(yǎng)孫輩（孫輩當(dāng)然也帶有她們的基因），那么會出現(xiàn)什么情況。“祖母遺傳特性”可以迅速形成并擴散。祖母貢獻越大，未成熟期可能就越長。
So on Mother's Day this Sunday, as we toast mothers over innumerable Bloody Marys and Eggs Benedicts across the country, we might add an additional toast for the gray-haired grandmoms behind the scenes.
所以在這個周日的母親節(jié)，在全國各地人們用無數(shù)的血腥瑪麗和班尼迪克蛋向母親們表達(dá)祝福之際，我們不妨也向默默奉獻的銀發(fā)祖母們致以敬意。
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