订阅Testing ancient human hearing via fossilized ear bones
利用耳骨化石测量古人听力
作者：Rolf Quam @ 2015-9-26
译者：沈沉（@你在何地-sxy）
校对：Whig Zhou（@whigzhou）
来源：The Conversation，https://theconversation.com/testing-ancient-human-hearing-via-fossilized-ear-bones-47973
How did the world sound to our ancient human relatives two million years ago?
整个世界在我们200万年前的人族亲戚听来是个什么样子？
While we obviously don’t have any sound recordings or written records from anywhere near that long ago, we do have one clue: the fossilized bones from inside their ears. The internal anatomy of the ear influences its hearing abilities.
显然，我们并没有那么久以前留下来的录音资料或书面记录，但我们确实拥有一条线索：古人耳内的骨头化石。耳朵的内部构造能够影响其听觉能力。
Using CT scans and careful virtual reconstructions, my international colleagues and I think we’ve demonstrated how our very ancient ancestors heard the world. And this isn’t just an academic enterprise; hearing abilities are closely tied with verbal communication.
经CT扫描并精心进行虚拟重构之后，我和一些国际同僚认为，我们已经展示出了远古先人是如何听到这个世界的。这可不仅仅是一项学术事业，因为听觉能力与口头交流是密切相关的。
By figuring out when certain hearing capacities emerged during our evolutionary history, we might be able to shed some light on when spoken language started to evolve. That’s one of the most hotly debated questions in paleoanthropology, since many researchers consider the capacity for spoken language a defining human feature.
通过估计特定听觉能力在人类进化史上何时出现，我们就可能对口头语言何时开始进化有所了解。这是古人类学目前争论最为火热的问题之一，因为许多研究者认为口语能力是一项用来定义人类的特征。
Human hearing is unique among primates
人类听觉在灵长类中非常独特
We modern human beings have better hearing across a wider range of frequencies than most other primates, including chimpanzees, our closest living relative. Generally, we’re able to hear sounds very well between 1.0-6.0 kHz, a range that includes many of the sounds emitted during spoken language. Most of the vowels fall below about 2.0 kHz, while the higher frequencies mainly contain consonants.
与绝大多数灵长动物（包括与我们血缘最近的近亲黑猩猩）相比，现代人在一个更大的频率区间内拥有更好的听力。一般来说，我们能够很好地听清1.0-6.0千赫之间的声音，口语交流时发出的许多声音就处于这一区间内。绝大多数元音大概落在2.0千赫以下，更高的频率则主要包含辅音。
Thanks to testing of their hearing in the lab, we know that chimpanzees and most other primates aren’t as sensitive in that same range. Chimpanzee hearing – like most other primates who also live in Africa, including baboons – shows a loss in sensitivity between 1.0-4.0 kHz. In contrast, human beings maintain good hearing throughout this frequency range.
基于实验室的听力测量，我们知道黑猩猩和绝大多数其他灵长动物对于上述频率区间并没有这么敏感。黑猩猩的听力在1.0-4.0千赫区间内丧失了敏感性，其他绝大多数生活于非洲的灵长动物也是如此，包括狒狒。人类与之不同，在这一频率区间内仍然能有很好的听力。
We’re interested in finding out when this human hearing pattern first emerged during our evolutionary history. In particular, if we could find a similar pattern of good hearing between 1.0-6.0 kHz in a fossil human species, then we could make an argument that language was present.
我们的兴趣是想要找出人类的这种听觉模式在进化史上最早出现于何时。特别是，如果我们能从某个人类化石上面找到在1.0-6.0千赫之间拥有良好听力这种类似模式，那么我们就可以论证说语言已经存在。
Testing the hearing of a long-gone individual
测量远古人类的听力
To study hearing using fossils, we measure a large number of dimensions of the ancient ears – including the length of the ear canal, the size of the ear drum and so on – using virtual reconstructions of the fragile skulls on the computer. Then we input all these data into a computer model.
使用化石来测量听力，我们需要在电脑上对易碎的头骨进行虚拟重构，然后测量古人耳朵的许许多多指标，包括耳道长度、耳膜大小等等。然后我们将所有这些数据都输入一个电脑模型之中。
Published previously in the bioengineering literature, the model predicts how a person hears based on his ear anatomy. It studies the capacity of the ear as a receiver of a signal, similar to an antenna. The results tell us how efficiently the ear transmits sound energy from the environment to the brain.
这个模型此前已经在生物工程文献中发表，能够根据一个人的耳朵构造预测其听力。它研究了耳朵作为与天线类似的信号接收器的能力，其结果能告诉我们耳朵将周围环境中的声能传输到大脑的效率。
We first tested the model on chimpanzee skulls, and got results similar to those of researchers who tested chimpanzee hearing in the lab. Since we know the model accurately predicts how humans hear and how chimpanzees hear, it should provide reliable results for our fossil human ancestors as well.
我们在黑猩猩头骨上面检验了这个模型，得到的结果与研究人员在实验室得到的黑猩猩听力相似。因此，我们知道这个模型能够准确预测人类听力和黑猩猩听力，所以将它应用于古人化石上面，也应该能够为我们提供可靠的结论。
What do the fossils tell us?
化石告诉了我们什么？
Previously, we studied the hearing abilities in several fossil hominin individuals from the site of the Sima de los Huesos (Pit of the Bones) in northern Spain. These fossils are about 430,000 years old, and anthropologists consider them to represent ancestors of the later Neanderthals. Based on ear bone measurements we took, the computer model calculated that hearing abilities in the Sima hominins were nearly identical to living humans in showing a broad region of good hearing.
此前，我们已经研究过西班牙北部“胡瑟裂谷”（西班牙语意为“骨坑”）遗址的几个古人类化石的听觉能力。这些化石大概是43万年前的，人类学家认为他们代表了晚期尼安德特人的祖先。基于我们所进行的耳骨测量，电脑模型计算出“裂谷”古人类的听觉能力与现存人类的几近相同，都在很大范围内表现出良好听力。
In our current study published in Science Advances, we worked with much earlier hominin individuals, representing the species Australopithecus africanus and Paranthropus robustus. These fossils were excavated at the sites of Sterkfontein and Swartkrans in South Africa, and likely date to around two million years ago.
在发表于《科学进展》上的最新研究中，我们研究了更为远古的古人类，即非洲南猿和傍人粗壮种。这些化石是在南非的斯特克方藤和斯沃特兰斯遗址发掘出来的，很可能存活于约200万年以前。
Auditory sensitivity between 0.5-5.0 kHz for chimpanzees, humans and the early hominins. Points higher on the curve indicate greater auditory sensitivity. (A) Region of maximum sensitivity. The early hominins are shifted toward slightly higher frequencies compared with chimpanzees. (B) Hearing results. The early hominins are more sensitive than either chimpanzees or humans up to around 3 kHz. Above around 3.5 kHz, the early hominins resemble chimpanzees more closely in showing a drop-off in sensitivity.
黑猩猩、人类和早期古人类在0.5-5.0千赫之间的听觉敏感度。曲线中更高的点代表更高的听觉敏感度。（A）代表敏感度最高区间。与黑猩猩相比，早期古人类的对应区间向更高频率略有偏移。（B）代表听力结果。在约3千赫之前，早期古人类的敏感度既高于黑猩猩，也高于人类。在高于3.5千赫的区间，早期古人类更接近黑猩猩，表现出敏感度的下降。
When we measured their ear structures and modeled their hearing, we found they had a hearing pattern that was more similar to a chimpanzee – but slightly modified in the human direction. In fact, these early hominins showed better hearing than either chimpanzees or modern humans from about 1.0-3.0 kHz, and the region of best hearing was shifted toward slightly higher frequencies compared with chimpanzees.
在测量了他们的耳朵构造并用模型计算了其听力以后，我们发现他们的听觉模式更接近于黑猩猩，但朝人类的方向略有修正。事实上，在1.0-3.0千赫区间，这些早期古人类的听力比黑猩猩或现代人的都要好。而且与黑猩猩相比，他们的最佳听力区间向高频率方向略有偏移。
It turns out this auditory pattern may have been a particular advantage for living on the savanna. We know A. africanus and and P. robustus regularly occupied the savanna, since as much as half of their diet was made up of resources found in open environments, based on measurements of isotopes in their teeth.
原来，对于稀树大草原上的生活而言，这种听力模式可能别有优势。我们知道，非洲南猿和傍人粗壮种经常会生活在稀树大草原上，因为他们的食谱有一半来自于开阔环境中才能找到的资源，而这是对他们牙齿中的同位素进行测量后发现的。
In more open environments, sound waves don’t travel as far as they do in the rain forest canopy. Sound signals tends to fade out sooner, and short-range communication is favored on the savanna. The hearing pattern of these early hominins – greater sensitivity than humans or chimpanzees to frequencies between 1.0-3.0 kHz and maximum sensitivity at slightly higher frequencies than in chimps – that would work well in these conditions.
在更为开阔的环境中，声波传播不到热带雨林密林中那么远。声音信号消逝更快，因此在稀树大草原上短程交流更受喜爱。在这种环境中，这些早期古人类的听觉模式（在1.0-3.0千赫的频率区间中比黑猩猩或现代人更敏感，且敏感度最高区间的对应频率比黑猩猩要稍高一些）相当适用。
From hearing to talking
从听到说
A. africanus and P. robustus had hearing abilities similar to a chimpanzee, but with some slight differences in the direction of humans.
非洲南猿和傍人粗壮种的听觉能力与黑猩猩近似，同时向人类的方向略有偏差。
There is a general consensus among anthropologists that the small brain size and ape-like cranial anatomy and vocal tract in these early hominins indicates they likely did not have the capacity for language.
人类学家中存在一个普遍共识：这些早期古人类的大脑尺寸较小、颅骨构造和声道更像猿，表明他们很可能并不具备语言能力。
My colleagues and I aren’t arguing that these early hominins had language, with its implications of symbolic content. They certainly could communicate vocally, though. All primates do, and many species regularly emit a variety of vocalizations including grunts, screams, howls and so on.
我和同僚并不是争论说这些早期古人类拥有语言，因为语言包含有符号性内容这层意思。但是，他们肯定能够进行口头交流。所有灵长动物都能做到这一点，而且许多物种还能经常性地发出各种不同的声音，包括咕噜、尖叫、咆哮等等。
But these South African fossils have given us another hearing data point as we try to puzzle out the emergence of language. Two million years ago, it looks like they didn’t have language. But 430,000 years ago, it looks like the Sima de los Huesos hominins did. We suspect that sometime between these early South African forms and the later more human-like forms from the Sima, language emerged. Now we just need to narrow that window.
但在我们尝试解答语言起源的难题时，南非的这些化石给我们提供了另外一组听力数据论点。200万年前，他们似乎还没有语言。但43万年前，似乎“胡瑟裂谷”的古人类已经拥有语言了。我们估计，大概在这些早期南非种和更晚的更像人类的“裂谷”种之间的某个时候，语言就出现了。现在，我们只需要把这个窗口期进一步缩短。
We hope to continue this kind of work on hearing patterns in different groups of ancient hominins from various places and time periods. The discovery of a new hominin species, Homo naledi, announced just a couple of weeks ago from a different site in South Africa, underscores how much there is left to uncover.
我们希望把这项工作继续做下去，研究来自不同地区和时期的不同古人类群体的听觉模式。仅在数周之前，南非另外一个遗址又宣布发现了一种新的古人类物种，即纳勒迪人。这一发现凸显了我们还有多少事情需要去发现。
（编辑：辉格@whigzhou）
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