为什么人类要演化出忍受牛奶的能力
六义Why humans have evolved to drink milk
为什么人类要演化出忍受牛奶的能力
Dairy milk has competition. Alternative “milks” made from plants like soya or almonds are increasingly popular. The alternatives are often vegan-friendly and can be suitable for people who are allergic to milk, or intolerant of it. The runner-up in the 2018 ries of The Apprentice (UK) ran a flavoured nut milk business.
乳制品有了竞争对手，由大豆、杏仁等植物制成的替代“牛奶”越来越受欢迎。这些替代品通常适合素食主义者，以及对牛奶过敏或者乳糖不耐受的人。2018年，英国版《学徒》（The Apprentice）节目的亚军，就经营着调味坚果奶生意。
But the ri of alternative milks is just the latest twist in the saga of humanity’s relationship with animal milk. This relationship dates back thousands of years, and it has had a lot of ups and downs.
铁的化学性质
但替代奶的兴起，只是人类与动物奶关系的一个最新发展。这种关系可以追溯到几千年前，历经起伏。
When you think about it, milk is a weird thing to drink. It’s a liquid made by a cow or other animal to feed its young; we have to squirt it out of the cow’s udders to obtain it.
想想看，奶水真是一种奇怪的饮品。它是牛或者其他动物喂养幼崽的液体食物，为了获得牛奶，我们还得把它从母牛的乳房里给挤出来。
In many cultures it is almost unheard of. Back in 2000, China launched a nationwide campaign to encourage people to consume more milk and dairy products for health reasons – a campaign that had to overcome the deep suspicions of many older Chine people. Chee, which is esntially milk that has been allowed to go off, can still make many Chine people feel sick.
在许多文化中，这几乎是闻所未闻的事情。2000年时，全中国范围内发起一场运动，鼓励人们为了健康要多消费牛奶和各种奶制品。这项运动主要针对老年人，帮助他们克服对奶制品的极大疑虑。牛奶变质形成的奶酪，仍然让很多中国人感到恶心。
Set against the 300,000-year history of our species, drinking milk is quite a new habit. Before about 10,000 years ago or so, hardly anybody drank milk, and then only on rare occasions. The first people to drink milk regularly were early farmers and pastoralists in western Europe – some of the first humans to live with domesticated animals, including cows. Today, drinking milk is common practice in northern Europe, North America, and a patchwork of other places.
与人类30万年的历史相比，喝牛奶算是相当新的习惯。大约1万年前，人类几乎不喝牛奶，然后是偶尔喝一喝。第一批经常喝牛奶的是西欧早期的农民和牧民，他们是第一批与驯养动物生活在一起的人，其中就包括奶牛。今天，喝牛奶在北欧、北美和其他一些地方，已经很普遍。
Baby food
婴儿食品
There is a biological reason why drinking animal milk is odd.
变形金刚桌面壁纸
喝动物奶为什么奇怪，在生物学上是有原因的。
Milk contains a type of sugar called lacto, which is distinct from the sugars found in fruit and other sweet foods. When we are babies, our bodies make a special enzyme called lacta that allows us to digest the lacto in our mother’s milk. But after we are weaned in early childhood, for many people this stops. Without lacta, we cannot properly digest the lacto in milk. As a result, if an adult drinks a lot of milk they may experience flatulence, painful cramps and even diarrhoea. (It’s worth noting that in other mammals, there aren’t any lacta-persistent adults – adult cows don’t have active lacta, and neither do cats or dogs, for example).
牛奶所含的乳糖，不同于水果和其他甜食中的糖。当我们还是婴儿的时候，我们身体会产生一种特殊的酶，这种叫做乳糖酶的东西能帮助我们消化母乳中的乳糖。但在婴儿期断奶后，许多人身上就没有这种酶了，就不能很好地消化牛奶中的乳糖。因此，一个成年人喝了很多牛奶后，可能会感到肠胃胀气、疼痛痉挛，甚至腹泻。值得注意的是，其他成年哺乳动物体内也没有活跃的乳糖酶，成年奶牛没有，猫狗也没有；但成年动物并不喝奶，所以也没有乳糖不耐受的问题。
So the first Europeans who drank milk probably farted a lot as a result. But then evolution kicked in: some people began to keep their lacta enzymes active into adulthood. This “lacta persistence” allowed them to drink milk without side effects. It is the result of mutations in a ction of DNA that controls the activity of the lacta gene.
最早一批喝牛奶的欧洲人可能因此胀气、多屁。然后演化开始了，一些人身上的乳糖酶开始保持至成年，这种“乳糖耐受能力”使他们喝牛奶不会产生副作用。这是控制乳糖酶基因活性的DNA片段突变的结果。
“The first time that we e the lacta persistence allele in Europe arising is around 5,000 years BP [before prent] in southern Europe, and then it starts to kick in in central Europe around 3,000 years ago,” says assistant professor Laure Ségurel at the Muum of Humankind in Paris, who co-authored a 2017 review of the science of lacta persistence.
“我们所知的欧洲最早的乳糖耐受能力等位基因，出现在大约5000年前的欧洲南部，然后在大约3000年前，出现在中欧，”巴黎人类博物馆（Muum of Humankind）的助理教授赛哈弗家训
格瑞尔（Laure Ségurel）说。2017年，她与人合著了一篇关于乳糖耐受科学的评论文章。
The lacta persistence trait was favoured by evolution and today it is extremely common in some populations. In northern Europe, more than 90% of people are lacta persistent. The same is true in a few populations in Africa and the Middle East.
随着演化，人类的乳糖耐受能力明显提高，今天在一些人群中，乳糖酶极为常见。在北欧，超过90%的人具有乳糖耐受能力。在非洲和中东的部分人口中，也是如此。
But there are also many populations where lacta persistence is much rarer: many Africans do not have the trait and it is uncommon in Asia and South America.
项城二高但在许多地区，乳糖耐受能力要罕见得多：许多非洲人不具备这种特性，在亚洲和南美洲也很少见。
宠物有哪些
医药销售红叶生菜It is hard to make n of this pattern becau we don’t know precily why drinking milk, and therefore lacta persistence, was a good thing, says Ségurel: “Why was it so strongly advantageous in itlf?”
