Many experts advise common sense. "We don't want to say to children, 'OK, play by the dirty river bank and catch whatever you can, but we can say there's nothing wrong with kids playing in the dirt. They don't have to live in total sanitation, and they won't die from eating something off the floor. It's probably more healthy than not."

　　许多专家建议人们凭常识办事。“我们不会对孩子们说：‘好，去肮脏的河边玩吧，想抓什么就抓什么。但可以这样讲，小孩子玩泥巴没什么大不了的，他们不必生活在完全干净的环境中，也不会因为吃掉到地上的　东西就死掉。这样说不定会使他们更健康。”

　　On a small family farm in Mongolia, a rooster struts around little Bayar's bed, a goat drinks from his bathwater and livestock serve as babysitters.

　　在蒙古国一个家庭小农场里，一只大公鸡在小小的巴亚尔的床边来回踱步，一只山羊过来喝他的洗澡水，周围的家畜就是照料他的保姆。

　　By contrast, Mari, growing up in high-rise, high-tech Tokyo, and Hattie, whose doting parents live a "green" lifestyle in San Francisco, both have modern conveniences and sanitation.

　　与此形成鲜明对比的是，玛丽出生在高楼林立的科技之城东京，海蒂的父母将其视为掌上明珠，在旧金山过着“绿色”的生活方式，两个孩子都享受着便捷的现代生活和干净的卫生环境。

　　Statistically, Mari and Hattie are healthier. Some 42 out of 1,000 children in Namibia, and 41 out of 1,000 in Mongolia die before their 5th birthday; compared with only 8 in 1,000 in the U.S. and only 4 in Japan.

　　数据显示，玛丽和海蒂的身体更健康。在纳米比亚，每1000个孩子中约有42个在过五岁生日前夭折，蒙古为41个;而在美国和日本，这一数字仅为8个和4个。

　　Yet the upscale urban infants are at higher risk for some health problems -- including allergies, asthma and autoimmune diseases like Type 1 diabetes, multiple sclerosis and inflammatory bowel disease -- than the babies in the rural developing world.

　　不过，城市里的宝宝虽然生活条件优越，但与欠发达国家农村地区的宝宝相比，患上某些疾病的风险更高，包括过敏症、哮喘，以及1型糖尿病、多发性硬化和炎症性肠病等自身免疫性疾病。

　　Now, there's research that suggests there may be a way to get the best of both worlds.

　　现在，有一项研究认为，也许有一种方法可以拉近两个世界的距离，让彼此取长补短。

　　According to the "hygiene hypothesis," first proposed in 1989, exposure to a variety of bacteria, viruses and parasitic worms early in life helps prime a child's immune system, much like sensory experiences program his brain. Without such early instruction, the immune system may go haywire and overreact with allergies to foods, pollen and pet dander or turn on the body's own tissue, setting off autoimmune disorders.

　　根据1989年首次提出的“卫生假说” (hygiene hypothesis)理论，孩子在成长早期如果接触多种病毒、细菌和寄生虫，将有利于其免疫系统的发展，似乎这样能促进大脑对其做出更好的防御准备。反之，如果缺乏这类早期接触，免疫系统就可能出现紊乱，做出过激反应，如对食物、花粉和宠物毛屑过敏等，或者引发人体机理问题，出现自身免疫失调。

　　Many of these microorganisms evolved symbiotically with humans over millions of years--the so-called "old friends" theory. But where they've been eradicated, a key part of human development has been thrown off.