一项令人惊讶的新研究表明，你也能够在草地上跟踪一种气味，但前提是必须要趴在地上，并且将鼻子贴近地面。这一发现不太可能让猎犬和毒品嗅探狗失业，但它却能够为人类“可怜的”嗅觉赢得一点点尊严。
人类普遍认为自己并不善于追踪一种气味，尤其是在与其他哺乳动物，例如狗和啮齿动物相比时，这一弱点更是暴露得一览无余。但是很少有人对此真地进行试验。由美国加利福尼亚大学伯克利分校的Jess Porter和Noam Sobel领导的一个研究小组，用巧克力香精浸泡了10米长的线绳，并将其放置在一片草地上，从而形成了两条夹角为135°的直线。随后，研究人员为32名大学生戴上眼罩，并让他们穿上耳套、厚手套和护膝，目的是防止他们获得嗅觉之外的任何感官暗示。当这些大学生完成了在草地上进行的测试后，2/3的受试者都能够成功追踪气味，他们就像猎狗跟踪野鸡一样，来来回回地呈“之”字形前进。研究人员在12月17日出版的《自然—神经科学》杂志上报告了这一研究成果。
Porter表示，几乎所有的受试者都认为这项试验具有挑战性，然而其中的4名大学生通过实践提高了自己的跟踪技能。经过几天的练习，他们学会了如何更快地跟踪气味以及减少偏差。尽管如此，他们的表现依然不及其他研究人员对狗进行的测试。另一项针对嗅觉进行的实验表明，人类能够利用两种方法确定气味——比较连续呼吸间的气味强度以及比较一次呼吸中两个鼻孔的气味强度。
耶鲁大学的神经学家Gordon Shepherd表示：“这是一项具有创新性的工作，它对人类的实际嗅觉能力进行了梳理。”Shepherd说，我们曾假设，在人类的灵长类祖先开始用两条腿行走后，他们的嗅觉功能便逐渐减弱。与其他动物将鼻子贴近地面相比，灵长类动物的嗅觉受体基因已所剩无几，这似乎支持了上述观点。然而Shepherd指出，这项新的研究表明，“如果能够重新四肢着地、贴近地面，我们或许能够完成一些之前想都不敢想的事情”。
英文原文：
Human Scent Tracking Nothing to Sniff At
A surprising new study suggests that people can track a scent across a grassy field--at least if they're willing to get down on their hands and knees and put their noses to the ground. The findings are unlikely to put hunting hounds and drug sniffing dogs out of work, but they may earn a little respect for the poorly regarded human sense of smell.
Humans are widely believed to be poor at tracking scents, especially when compared to other mammals such as dogs and rodents. But few had ever put that idea to the test. A research team led by Jess Porter and Noam Sobel at the University of California, Berkeley, dipped 10 meters of twine in chocolate essence and laid it in a field to form two straight lines connected at a 135° angle. Then they blindfolded 32 undergraduate students and had them don earmuffs, thick gloves and kneepads to prevent them from using sensory cues other than smell. When set loose in the field, two-thirds of the subjects successfully followed the scent, zigzagging back and forth across the path like a dog tracking a pheasant, the researchers report online 17 December in Nature Neuroscience.
Nearly all the subjects reported that the task was challenging, Porter says, but four of them got a chance to improve with practice. Over the course of several days, they learned to follow the trail faster and deviate less. Even so, their performance remained well below what other researchers have reported in dogs. Additional experiments with noseplugs suggested that people use two strategies to localize smells: comparing the odor intensity between subsequent sniffs and comparing the odor intensity at the two nostrils during single sniffs.
"This is an innovative approach to teasing out what olfactory abilities humans actually have," says Gordon Shepherd, a neuroscientist at Yale University. It's assumed that after our primate ancestors started walking on two legs, their sense of smell became less acute, Shepherd says. The relatively small repertoire of olfactory receptor genes in primates compared to animals that kept their noses closer to the ground seems to support this notion. However, Shepherd says, the new study suggests that "if we go back on our four legs and get down on the ground, we may be able do things we had no idea we could do."
