The smelly mystery of the human pheromone

"Pheromone" is a very powerful word. It conjures up sex, abandon, loss of control, and you can see, it's very important as a word. But it's only 50 years old. It was invented in 1959. Now, if you put that word into the web, as you may have done, you'll come up with millions of hits, and almost all of those sites are trying to sell you something to make you irresistible for 10 dollars or more. Now, this is a very attractive idea, and the molecules they mention sound really science-y. They've got lots of syllables. It's things like androstenol, androstenone or androstadienone. It gets better and better, and when you combine that with white lab coats, you must imagine that there is fantastic science behind this. But sadly, these are fraudulent claims supported by dodgy science.

The problem is that, although there are many good scientists working on what they think are human pheromones, and they're publishing in respectable journals, at the basis of this, despite very sophisticated experiments, there really is no good science behind it, because it's based on a problem, which is nobody has systematically gone through all the odors that humans produce -- and there are thousands of molecules that we give off. We're mammals. We produce a lot of smell. Nobody has gone through systematically to work out which molecules really are pheromones. They've just plucked a few, and all these experiments are based on those, but there's no good evidence at all.

Now, that's not to say that smell is not important to people. It is, and some people are real enthusiasts, and one of these was Napoleon. And famously, you may remember that out on the campaign trail for war, he wrote to his lover, Empress Josephine, saying, "Don't wash. I'm coming home." (Laughter) So he didn't want to lose any of her richness in the days before he'd get home, and it is still, you'll find websites that offer this as a major quirk. At the same time, though, we spend about as much money taking the smells off us as putting them back on in perfumes, and perfumes are a multi-billion-dollar business.

So what I want to do in the rest of this talk is tell you about what pheromones really are, tell you why I think we would expect humans to have pheromones, tell you about some of the confusions in pheromones, and then finally, I want to end with a promising avenue which shows us the way we ought to be going.

So the ancient Greeks knew that dogs sent invisible signals between each other. A female dog in heat sent an invisible signal to male dogs for miles around, and it wasn't a sound, it was a smell. You could take the smell from the female dog, and the dogs would chase the cloth. But the problem for everybody who could see this effect was that you couldn't identify the molecules. You couldn't demonstrate it was chemical. The reason for that, of course, is that each of these animals produces tiny quantities, and in the case of the dog, males dogs can smell it, but we can't smell it. And it was only in 1959 that a German team, after spending 20 years in search of these molecules, discovered, identified, the first pheromone, and this was the sex pheromone of a silk moth. Now, this was an inspired choice by Adolf Butenandt and his team, because he needed half a million moths to get enough material to do the chemical analysis. But he created the model for how you should go about pheromone analysis. He basically went through systematically, showing that only the molecule in question was the one that stimulated the males, not all the others. He analyzed it very carefully. He synthesized the molecule, and then tried the synthesized molecule on the males and got them to respond and showed it was, indeed, that molecule. That's closing the circle. That's the thing which has never been done with humans: nothing systematic, no real demonstration.

With that new concept, we needed a new word, and that was the word "pheromone," and it's basically transferred excitement, transferred between individuals, and since 1959, pheromones have been found right the way across the animal kingdom, in male animals, in female animals. It works just as well underwater for goldfish and lobsters. And almost every mammal you can think of has had a pheromone identified, and of course, an enormous number of insects.

So we know that pheromones exist right the way across the animal kingdom. What about humans? Well, the first thing, of course, is that we're mammals, and mammals are smelly. As any dog owner can tell you, we smell, they smell.

But the real reason we might think that humans have pheromones is the change that occurs as we grow up. The smell of a room of teenagers is quite different from the smell of a room of small children. What's changed? And of course, it's puberty. Along with the pubic hair and the hair in the armpits, new glands start to secrete in those places, and that's what's making the change in smell. If we were any other kind of mammal, or any other kind of animal, we would say, "That must be something to do with pheromones," and we'd start looking properly.

But there are some problems, and this is why, I think, people have not looked for pheromones so effectively in humans. There are, indeed, problems. And the first of these is perhaps surprising. It's all about culture. Now moths don't learn a lot about what is good to smell, but humans do, and up to the age of about four, any smell, no matter how rancid, is simply interesting. And I understand that the major role of parents is to stop kids putting their fingers in poo, because it's always something nice to smell. But gradually we learn what's not good, and one of the things we learn at the same time as what is not good is what is good.

Now, the cheese behind me is a British, if not an English, delicacy. It's ripe blue Stilton. Liking it is incomprehensible to people from other countries. Every culture has its own special food and national delicacy. If you were to come from Iceland, your national dish is deep rotted shark. Now, all of these things are acquired tastes, but they form almost a badge of identity. You're part of the in-group.

The second thing is the sense of smell. Each of us has a unique odor world, in the sense that what we smell, we each smell a completely different world. Now, smell was the hardest of the senses to crack, and the Nobel Prize awarded to Richard Axel and Linda Buck was only awarded in 2004 for their discovery of how smell works. It's really hard, but in essence, nerves from the brain go up into the nose and on these nerves exposed in the nose to the outside air are receptors, and odor molecules coming in on a sniff interact with these receptors, and if they bond, they send the nerve a signal which goes back into the brain. We don't just have one kind of receptor. If you're a human, you have about 400 different kinds of receptors, and the brain knows what you're smelling because of the combination of receptors and nerve cells that they trigger, sending messages up to the brain in a combinatorial fashion. But it's a bit more complicated, because each of those 400 comes in various variants, and depending which variant you have, you might smell coriander, or cilantro, that herb, either as something delicious and savory or something like soap. So we each have an individual world of smell, and that complicates anything when we're studying smell.

Well, we really ought to talk about armpits, and I have to say that I do have particularly good ones. Now, I'm not going to share them with you, but this is the place that most people have looked for pheromones. There is one good reason, which is, the great apes have armpits as their unique characteristic. The other primates have scent glands in other parts of the body. The great apes have these armpits full of secretory glands producing smells all the time, enormous numbers of molecules. When they're secreted from the glands, the molecules are odorless. They have no smell at all, and it's only the wonderful bacteria growing on the rainforest of hair that actually produces the smells that we know and love. And so incidentally, if you want to reduce the amount of smell, clear-cutting your armpits is a very effective way of reducing the habitat for bacteria, and you'll find they remain less smelly for much longer. But although we've focused on armpits, I think it's partly because they're the least embarrassing place to go and ask people for samples. There is actually another reason why we might not be looking for a universal sex pheromone there, and that's because 20 percent of the world's population doesn't have smelly armpits like me. And these are people from China, Japan, Korea, and other parts of northeast Asia. They simply don't secrete those odorless precursors that the bacteria love to use to produce the smells that in an ethnocentric way we always thought of as characteristic of armpits. So it doesn't apply to 20 percent of the world.

So what should we be doing in our search for human pheromones? I'm fairly convinced that we do have them. We're mammals, like everybody else who's a mammal, and we probably do have them. But what I think we should do is go right back to the beginning, and basically look all over the body. No matter how embarrassing, we need to search and go for the first time where no one else has dared tread. It's going to be difficult, it's going to be embarrassing, but we need to look. We also need to go back to the ideas that Butenandt used when he was studying the silk moth. We need to go back and look systematically at all the molecules that are being produced, and work out which ones are really involved. It isn't good enough simply to pluck a couple and say, "They'll do." We have to actually demonstrate that they really have the effects we claim.

There is one team that I'm actually very impressed by. They're in France, and their previous success was identifying the rabbit mammary pheromone. They've turned their attention now to human babies and mothers.

So this is a baby having a drink of milk from its mother's breast. Her nipple is completely hidden by the baby's head, but what you'll notice is a white droplet with an arrow pointing to it, and that's the secretion from the areolar glands. Now, we all have them, men and women, and these are the little bumps around the nipple, and if you're a lactating woman, these start to secrete. It's a very interesting secretion. What Benoist Schaal and his team developed was a simple test to investigate what the effect of this secretion might be, in effect, a simple bioassay. So this is a sleeping baby, and under its nose, we've put a clean glass rod. The baby remains sleeping, showing no interest at all. But if we go to any mother who is secreting from the areolar glands, so it's not about recognition, it can be from any mother, if we take the secretion and now put it under the baby's nose, we get a very different reaction. It's a connoisseur's reaction of delight, and it opens its mouth and sticks out its tongue and starts to suck. Now, since this is from any mother, it could really be a pheromone. It's not about individual recognition. Any mother will do.

Now, why is this important, apart from being simply very interesting? It's because women vary in the number of areolar glands that they have, and there is a correlation between the ease with which babies start to suckle and the number of areolar glands she has. It appears that the more secretions she's got, the more likely the baby is to suckle quickly. If you're a mammal, the most dangerous time in life is the first few hours after birth. You have to get that first drink of milk, and if you don't get it, you won't survive. You'll be dead. Since many babies actually find it difficult to take that first meal, because they're not getting the right stimulus, if we could identify what that molecule was, and the French team are being very cautious, but if we could identify the molecule, synthesize it, it would then mean premature babies would be more likely to suckle, and every baby would have a better chance of survival. So what I want to argue is this is one example of where a systematic, really scientific approach can actually bring you a real understanding of pheromones. There could be all sorts of medical interventions. There could be all sorts of things that humans are doing with pheromones that we simply don't know at the moment. What we need to remember is pheromones are not just about sex. They're about all sorts of things to do with a mammal's life. So do go forward and do search for more. There's lots to find.

Thank you very much.

(Applause) 

Translated by Li Li

Reviewed by Jing Peng

“费洛蒙”是一种非常强大的物质。 它激起性欲，使人放纵或失去控制， 因此它是一种非常强大的物质。 但它只有50岁，在1959年被发明。 如果你在网络中搜索， 也许你已经搜索过了， 你会得到百万的搜索结果。 而且几乎所有的那些网站都试图 卖给你些 10 美元左右的 让人不能抗拒的东西。 这些广告格外吸引人， 并且他们所提到的分子们 听起来很有科学原理。 那些单词都有很多音节。 就像雄甾烯醇，雄烯酮（androstenol, androstenone）。 或雄烯二酮（androstenedione）的单词一样。 接着那些广告越来越吸引人， 当你看到穿着白大褂的科学家时， 你一定会想 这东西蕴含深奥的科学。 不幸的是，那些只是欺诈性的宣传 有伪科学撑腰罢了。

问题出在于，即使有很多 优秀的科学家在进行研究 他们所认为的人类费洛蒙， 并将其发表于值得信赖的杂志中， 但归根到底， 除去那些非常复杂的实验， 还没有真正的科学得以证实， 因为费洛蒙是基于一个问题所猜想出的物质， 人类产生数以千计的气味分子， 但还没有人系统地 研究过人类产生的所有气味。 我们是哺乳类动物。我们产生许多气味。 没有人通过系统研究 找出过真正的费洛蒙。 他们摘取了一些样品， 但所有的实验也只是基于那些而已， 并没有什么确凿的证据。

那并不是说 那气味对人类不重要。 有些人对此非常痴迷。 其中之一便是拿破仑。 你也许会记得， 拿破仑在战争后 写给他的情人Empress Josephine 说道 “别洗。我很快回家。” （笑） 所以他不想在他回家之前 让她失去她的体味。 你可以在网上找到 销售这种怪癖的链接。 但是，与此同时 我们花费同样多的金钱， 先是除去我们的体味， 接着又重新擦上香水。 香水可是创造了数十亿美元的产业。

所以我想在接下来的时间里 告诉你们什么是费洛蒙， 告诉你们为什么 人类会有费洛蒙， 告诉你们关于费洛蒙的误解。 最后 告诉你们一条我们应当走下去的 研究道路。

古希腊人知道 狗给彼此发送隐形的信号。 发情期的母狗 发送隐形的信号 给数英里内的公狗。 这个信号不是声音，而是气味。 如果你沾上了母狗的这种气味 公狗便会尾随你。 但是 人们可以看到这种现象， 却不能确认这种分子， 你不能展示这是一种化学物质。 当然，这其中原因是 这些动物 只有一点点这种气味产生。 拿狗的情况来说， 公狗可以闻到，我们人类却不行。 一个德国的团队花了20年时间寻找这种分子， 终于首次在1959年 发现并且确定了第一个费洛蒙。 这是蚕蛾的性费洛蒙。 Adolf Butenandt团队选择蚕蛾 是因为他们需要数近五十万的蚕蛾 来提取足够的化学物质以进行分析。 但是他建立了一个模型 来启示以后的研究者应当怎样进行费洛蒙的研究。 他系统地 展示了那个唯一存在问题的分子 就是刺激雄性的分子， 排除了无关的分子， 他仔细地分析了 并且合成了这些分子， 他将这些合成分子用于雄性 并且获取他们的反馈， 以确定这些分子是费洛蒙。 由此完成了这一难题。 但如此系统，并且如此强展示性的实验 并未应用于人类。

但这是个新概念， 我们需要一个新名词， 这就是“费洛蒙”。 费洛蒙在个体之间 传递兴奋。 自1959年费洛蒙发现以来， 这个在雄性与雌性间传递的概念 已在动物王国中证实， 同时在水生生物中同样适用， 比如金鱼和龙虾。 几乎所用的哺乳动物 都有确定的费洛蒙， 当然， 还包括数量巨大的昆虫。

所以我们知道费洛蒙 存在于动物王国中。 那么人类世界呢？ 首先，当然 我们是哺乳动物， 哺乳动物都是有体味的。 养狗的人会告诉你， 我们有体味，狗也有。

但是，我们认为 人类有体味的真实原因是 在我们成长中体味的变化。 青少年房间的气味 与小孩的房间气味 是很不一样的。 什么变化了呢？当然，是青春期。 暴露的毛发 和腋下的毛发， 腺体产生新的物质， 这些都是体味改变的原因。 如果我们是其它种类的哺乳动物 或者其它种类的动物， 我们会说， “这一定和费洛蒙有关”， 然后我们开始研究它。

但是这其中有一些问题。 我认为，这就是人们为什么 不愿意如此深入的研究费洛蒙对于人类的作用。 这确实有几个问题。 首先， 这个原因有可能会使人惊讶， 那就是文化。 蚕蛾不知道 什么是好的气味，而人类知道。 在人类四岁以前， 任何气味，不管有多糟糕， 都是有趣的。 我理解父母的一项主要工作 就是阻止小孩将手指放到大便里面， 因为他们想闻那个气味。 但是逐渐的，我们认识到什么气味是糟糕的。 与此同时， 我们认识到 什么气味是好的。

现在，在我身后的 是一块来自大不列颠的（而不是英格兰）精美的奶酪。 这是一块成熟的蓝斯蒂尔顿（以强烈的气味和味道著名）。 就像其它国家的人可能无法接受这种奶酪一样， 每一种文化都有其独特的食物 和闻名全国的美食。 如果你来自冰岛， 最著名的美食是 深发酵鲨鱼肉。 所有这些都需要口味的适应， 但这和成长环境有关， 和所属群体有关。

第二是嗅觉。 我们每个人都有独特的气味世界。 谈到我们闻到了什么， 我们闻到的完全不同。 嗅觉是最难以 破解的感觉， 2004 年的诺贝尔奖 颁给了 Richard Axel 和 Linda Buck， 因为他们发现了嗅觉是怎样工作的。 这确实非常困难， 但在本质上， 大脑的神经延伸至鼻子 以及鼻子上类似传感器的 暴露在空气中的神经。 气味分子通过吸气 与传感器接触。 如果他们键合，他们给神经传递一个信号， 这个信号将到达大脑。 我们不是只有一种传感器， 人类有400种不同类型 的传感器， 并且大脑根据传感器 和刺激的神经的组合 知道你闻到了什么， 然后用一种组合的方式 将这个信息送达大脑。 但它更复杂一点， 因为那400个传感器中的每一个 都有不同的变种， 取决于你所拥有的种类， 你可能会闻到芫荽，香菜或者香草， 这种好吃又开胃的东西， 或者类似香皂的气味。 所以我们有不同的嗅觉世界。 这让嗅觉研究 变得复杂。

现在，我们应该谈到腋窝， 我可以肯定地说我有好腋窝 但我不会和你们分享。 不过许多人从腋窝 寻找费洛蒙。 这是有原因的。 拥有腋窝 是人猿的独特特征。 其它灵长类动物 在身体的其它部位拥有分泌腺。 人猿的腋窝 充满了分泌腺， 这些分泌腺时时刻刻散发着气味， 这里面包含了数量巨大的分子。 当它们从腺体里散发出来时， 这些分子是无臭无味的 绝对没有气味 这些我们熟悉和喜爱的气味的产生 是由于雨林中 附着在毛发上的细菌 导致的。 所以， 如果你想减少气味， 除去腋窝的毛发 是减少细菌温床的 最行之有效的方法， 并且你会发现这样可以 使减少气味的效果保持得更久。 但是虽然我们只着眼于腋窝， 我认为部分原因是 索取样品不是那么的难为情。 实际上我们不能从腋窝 寻找到通用的性费洛蒙的另一个原因是 世界上20%的人 没有像我这样的腋窝分泌。 他们来自中国，日本， 朝鲜，以及东北亚的其它地区。 他们根本不分泌那些 细菌用于产生气味的前导体， 而自认为高大的我们认为 那是腋窝的特征。 但是并不适用于20%的人口。

所以我们在人类费洛蒙的研究中 应该做什么呢？ 我相信人类有费洛蒙。 我们是哺乳动物， 就像其它的哺乳动物一样，我们确实有费洛蒙。 但是我认为我们应该 回到最开始的研究， 从身体的各个部位寻找费洛蒙。 不管这是多么的令人难为情， 我们应该从无人涉足的区域 第一次寻找和研究。 这将会非常困难， 并且令人难为情，但是我们应当这么做。 我们应该回到 Butenandt 对蚕蛾的研究。 我们应该回到系统地研究 所有分泌出来的分子， 寻找出真正有关联的那些来。 仅仅让一些夫妇说“他们有用” 是不够的。 我们需要展示 它们确实有我们宣称的效果。

我对一个团队有非常深刻的印象。 他们来自法国，他们曾经成功地 确定了兔子的乳腺费洛蒙。 现在他们将注意力转移到 人类婴儿和母亲。

这个婴儿正在 吸嚅母亲的乳房。 她的乳房完全被 婴儿的脑袋挡住， 但是你会注意到 箭头指向的白色小点， 那是乳晕腺的分泌。 不管男性还是女性，我们都有这种腺体， 就是乳头周围的小肿块 哺乳期的女性 会产生这种腺体的分泌物。 这是非常有意思的分泌物。 Benoist Schaal和团队 用一个非常简单的实验来研究 这种分泌物可能产生的作用。 实际上，只是一个简单的生物测定。 这是一个熟睡的婴儿， 我们将一个干净的玻璃滴管放在他的鼻子边。 这个婴儿仍然熟睡， 没有显示任何的兴趣。 如果我们提取任何一个母亲 的乳晕腺分泌物， 这不是亲子鉴定， 这可以来自任何一个母亲， 如果我们提取这种分泌物， 将它放到婴儿的鼻子边， 我们看到截然不同的反应。 这是行家喜悦的表现， 他张开嘴 伸出舌头 开始吮吸。 既然这是来自其她的母亲， 很有可能是费洛蒙， 而不是个体识别。 任何一个母亲都可以做到。

为什么这个实验如此重要， 而不仅仅只是有意思？ 女性具有 不同的乳晕腺数目。 哺乳宝宝的容易程度 和母亲具有的乳晕腺数目 是正相关的。 母亲拥有越多的分泌物， 宝宝就越容易哺乳。 对于哺乳动物， 刚出生的几个小时 是最危险的。 你必须有奶喝， 如果没有，就难以存活， 也就是会死亡。 对于大多数婴儿， 第一次哺乳是困难的， 因为他们没有得到适当的刺激。 如果我们知道其分子， 尽管这个法国团队非常谨慎， 如果我们可以确定其分子式 并且合成它，这意味着 早产儿更有可能哺乳， 每一个婴儿更有可能 存活。 我想说的是，这个例子 使用了系统的、科学的方法， 可以让你理解 费洛蒙。 这可以是某种医疗干预， 或者某种 我们尚且不知道 费洛蒙的用法。 我们要记住的是 费洛蒙不只和性有关 它们和哺乳动物 的各个方面都有关系。 所以应当有更多的研究。 还有很多要发现。

非常感谢。

（掌声）