聞聲識海豚

文 / 薩拉·普拉托（意大利） 譯 / 楊云舟

我從小就十分喜愛小動物，身邊一直有小動物陪伴。長大之后，這份對動物的親昵之情自然而然地讓我萌生了從事獸醫職業的想法。不過，我的父母一開始對此表示反對，他們始終希望我能去攻讀像法學一類的實用學位。但憑借著堅持不懈的努力，我最終說服了父母。也正是因為這份堅持，我最終說服了獸醫學教授允許我前去加納利群島旅行。在研究獸醫學的日子里，海豚這種動物引起了我極大的興趣，而加納利群島廣闊的海岸能為我帶來與海豚親密接觸的豐富機會。

在海島上，我花了很多時間來研究動物們的行為，時不時還會向它們提供一些幫助。不過我知道，自己想要的不僅是這些。我希望能夠了解動物之間的交流方式。當還只有5歲的時候，我就有了第一次與動物交流的經驗。通過模仿母貓的聲音，我成功地把小貓從藏身處哄出來一起玩耍。于是，在一位德國教授的幫助下，當時還是學生的我從加納利群島搬到了以色列，繼續進行著海豚研究。海豚和海豚之間——以及海豚與人類之間——究竟是如何互動的？它們用什么方法來交流？它們又是如何傳達自己需求的呢？與此同時，我一直沒有忘記自己的另一個追求：為那些需要照料的動物提供幫助。我曾前往美國和加拿大的多家機構，與那里的工作人員一起為海洋動物和其他動物朋友們提供醫療和保護上的援助。

在這之后，2007年，我來到了中國，開始著手進行博士后研究。自2017年開始到現在，我一直在江漢大學任教。

奇妙的海豚和奇妙的聲音

海豚和人類都是社會性哺乳動物，都有著非常相似的社會結構，即“裂變—融合社會”。什么叫裂變—融合社會呢？這其實指的是由不同個體組成的小家庭作為社會單位又組成了社會。一個裂變—融合社會中的家庭成員在各自的日常生活中都會有很多事情要分頭處理。例如，人類要上班，海豚則要出去捕食。我們每個人都會離開家庭去 做各自的事情，但是到了最后，大家又會聚在一起。但人類和海豚又大有不同。我們生活在不同的環境中，也因此進化出了不同的感官系統來適應環境。生活在堅實的陸地上的我們有著獨特的大腦構成，海豚的大腦則與我們的不同。不過，盡管有這樣那樣的差異，人類和海豚在小社會或大社會中卻都有著共同的交流需求。

薩拉·普拉托（Sara Platto，意大利），江漢大學生命科學學院副教授，中國生物多樣性保護與綠色發展基金會生物與科學倫理秘書長。普拉托博士在動物福利、動物行為、野生動物病理學等方面都有著研究貢獻。

像海豚一樣在海底生活和交流可能會面臨著不少的挑戰。其中一個挑戰就是視覺能力。深海環境中的海水模糊不清，四周一片漆黑，幾乎沒有任何光線能到達這里。而就算在海水尚還清澈的地方，可見光也只能到達海平面以下100米處的深度。更何況，大海里還常常有海浪的干擾和海草等障礙物的阻擋。所以，我們在海面下很有可能只能看到幾米，甚至幾厘米開外的東西。這樣一看，視覺感官似乎對于海洋動物來說并沒有那么大的作用。但是，如果海豚的視力如此之差，它們又是怎么能夠如此自在地游來游去，和其他海豚交朋友，還要躲避其他捕食者的呢？它們要利用什么感官呢？答案就是——聲音！

聲音在海水中的傳播速度受到多種因素的影響。由于水和空氣的密度不同，聲音在海平面以下的傳播速度是在海平面以上時的4.5倍。除此之外，聲音的傳播速度還與海水的溫度和鹽度有關。水溫越高、海水越咸，聲音的傳播速度就越快。還有，海洋深處的水壓明顯高于海面，而此時聲音的傳播速度也會相應加快。

我們在水里也能聽到聲音。但海豚的聽力和我們一樣嗎？遺憾的是，由于人類耳朵的形狀和結構，我們在水中只能接收到有限的聲音頻率范圍。出于同樣的原因，我們在游泳時雙耳也無法辨別聲音的方向。那海豚呢？它們在水中的聽覺能力要先進得多，因為它們不像人類——人類只能接收20Hz—15kHz的頻率，而海豚可以接收75Hz—150kHz的所有聲音頻率。

那么，海豚是如何發聲的？我們人類用聲帶來發聲，而海豚則采用了另一種方法——它們通過自己鼻腔的器官發聲，這個鼻腔器官位于額隆部位（海豚頭頂的圓形部分）。空氣會通過海豚的呼吸孔進入一個類似口袋狀的結構中，一旦這個口袋狀的結構發生震動，就會產生聲音。但除了這一部分的器官，海豚還有另外的非常重要的發聲裝置——它們體內的兩套唇狀器官。這兩個聲唇使它們能夠同時發出兩種聲音：既可以發出用來交流的哨聲，也可以發出用來掃描環境的定位回聲。

這些聲音在發出來后是怎么被海豚聽到的呢？海豚額隆里的脂肪組織和水的密度是一樣的。這些組織的功能就像一個透鏡，可以通過改變形狀來把聲音傳到各個不同的方向和角度。在海豚的下顎周圍也存在著類似的脂肪組織。當聲音傳來時，頜骨內的脂肪組織就會感知到它們的震動，然后將聲音傳到海豚耳朵的內部，而海豚的耳朵也被同樣的脂肪組織所包圍。雖然它們有耳朵，也有耳道，但由于結構與人類不同，海豚在水面上的聽力不如在水下時的好。

海豚的“聲音百寶箱”

為了能夠更好地了解海豚所發出的聲音，研究人員將幾種不同模式的聲像圖分離了出來。從這些不同的聲音模式中，科學家們能夠辨別出這些聲音發出時的場景，如當時海豚的心情怎樣，或者當時它們是在趕路還是在做其他的事。

在海豚發出的不同聲音里，有一種被稱為“口哨”的聲音，平均頻率范圍在75Hz—24kHz（有時候會超過24kHz）。哨聲是全向的，這意味著很難根據它來辨別聲音的源頭。一聲哨聲由兩個部分組成：基礎頻率，即主哨，以及以基礎頻率的整數倍頻率傳播的諧波，通常都達到了超聲波（>20kHz）范圍。同時含有非指向性和指向性成分的哨音被稱為“混合指向”哨音。研究人員發現，哨聲中的諧波其實可以用來進行方向追蹤。因此，當海豚既要傳達自己的信息，又要表達自己的位置時，就會同時釋放出哨聲和諧波。

人都有自己的名字，每個人都通過對方的名字來認識不同的人。海豚也有名字——這就是每只海豚的標志性哨音。海豚可以用特定的哨音給自己貼上標簽——就像名字一樣——每只海豚都有自己特有的哨音。這種標志性哨音也可以被其他海豚模仿，用來呼喚單獨某一只海豚，就像我們叫一個人的名字一樣。

海豚頭部內聲音發收結構示意（繪圖：Vko Gorter）

除了口哨聲外，海豚還有另一種聲音，是用來回聲定位的“嘀嗒聲”，聽起來就像木棍互相撞擊的聲音。海豚用這種聲音來掃描周圍的環境，尋找食物或障礙物。每一次嘀嗒聲之后都有一個間隔，在這個間隔中，海豚會等待回聲的返回，然后再發出下一次嘀嗒聲。通過測量這個時間間隔，海豚可以計算出自己與某個物體的距離，從而在腦海中繪制出一幅環境地圖。

海豚還有第3種聲音，叫作“脈沖聲”。脈沖聲包含了情感成分。當海豚感到不高興或相互爭吵時，它們就會發出這種聲音。科學家們根據脈沖聲的細微不同把這種聲音分成好幾類，如喊聲、哭聲、啜泣聲。不同種類的海豚能夠發出的聲音其實不盡相同。例如，無鰭江豚就只能發出脈沖聲，而發不出口哨聲。

海豚感知的世界

人類主要通過視覺和語言來創造自己的現實。每當看到新的事物，我們就會忙不迭地給它命名，從而也就認識了它。一般來說，“自我”概念建立的根基是大腦對如以自我為中心的空間和時間軸等外部信息的處理，以及頭部、身體的位置和方向等內部信息的定位。這些都是構建自我的要素。除此之外，記憶、期望、計劃等只不過是一些附加要素。對于海豚來說，所有關于外部世界的信息都來自回聲定位。

人類在交談時會問：“你看到我所看到的了嗎？”或者“你看到我剛剛說的了嗎？”海豚則不同，它們會問：“你看到我剛剛聽到的了嗎？”每當海豚通過嘀嗒聲來回聲定位、掃描周圍的環境時，它們就能在大腦中構建出一種“全息圖像”。令人驚奇的是，這些回聲可以被附近的另一只海豚接收到，而它們則會收到完全相同的“全息圖像”！當不同的人從不同的角度看同一個物體時，他們看到的畫面也自然不一樣。這取決于他們每個人如何感知他們的現實。回聲定位有一個與人類語言截然不同的特征，即在此處，海豚大腦對現實的構建基于的其實是個體所產生的信號。在從回聲定位構建現實的過程中，海豚可以彼此分享“原始”的感官信息。與我們用語言分享信息相比，這真是不同尋常。這些信息存在于聽覺領域，它們所產生的“物體”圖像就如同人類看到的畫面一樣真實。這是我們難以想象的。盡管這只是一種推測，但科學家認為，海豚之間存在一種社會性或者共同感知的可能性是存在的。事實上，一個由共享的原始數據構建的感知世界將賦予一個群體以不同尋常的凝聚力和個體概念。更有趣的是，海豚的感官共享有可能是一個主動的過程，而非純粹被動地接收。這就像每個人都能夠同樣感知到某一個人所看到的世界的畫面一樣。感官共享的能力將大大改變“自我”的界限，“個體”的概念也將得到重新定義。

當一兩只海豚生病擱淺時，族群中其他的個體都會紛紛相隨

海豚大腦的特殊結構為這一假說提供了有力支持。人類的大腦可以劃分出3重主要復合區：爬蟲腦復合區、邊緣系統和新皮層。然而，在鯨類身上，我們看到了一個徹底的進化跳躍——大腦結構中加入了第4段。這個部分被稱為副邊緣，位于邊緣系統和新皮層之間，并突入新皮層之中。這種結構只存在于鯨類動物的大腦中。鯨類大腦的整個邊緣系統是用于處理情緒和形成記憶的多個結構的組合，而副邊緣額葉這一獨特的進化則表明鯨類或許有能力處理更復雜的思想和情緒。由于鯨類的這一系統非常大，而且獨特的副額葉又與新皮層雙雙合并，人們認為，它們的大腦中可能會產生出情緒和認知思維的混合。副邊緣額葉也被認為是感覺區和運動區的延續。人類大腦中每個投射區之間的距離都很遠，意味著我們從視覺、聲音和本能中接收到的所有信息都必須沿著纖維道一點點傳播到位。這一過程的時間和信息損失都非常大。鯨類的副邊緣額葉則將所有感官反射集于一身，以我們無法理解的豐富性和迅速性處理著所有信息。副邊緣系統的獨特進化表明，在共同處理情緒和聲音信息的背后，海豚之間有一些非常精密、復雜的交流機制。它們的大腦可能已經掌握了一種在動物王國中前所未有的社會共性。這將把所謂“社會性”的概念提升到一個完全不同的層次。而事實上，海豚在群體層面有著很強的凝聚力，當一兩只海豚生病擱淺時，族群中所有其他的個體都會紛紛相隨。這在很大程度上可能是情感依戀的產物，這些動物可能有一種強烈的集體意識。一些科學家將海豚的這種凝聚力稱為“集體靈魂”。

那么，海豚算得上聰明嗎？它們必須要“像我們一樣”才能稱得上是智慧生物嗎？雖然鯨類動物擁有包括人類在內的動物中最大的大腦，但這并不一定意味著它們比我們智力更高。不過，智力的定義其實是一個相當模糊的問題。到目前為止，我們還沒有完全了解人類大腦的全部功能，也沒有找到定義智力的準確標準。我們通常只會用我們的現實來定義其他動物的智力：因為我們會說話、會寫字、做很多了不起的事情……所以我們把所有做不到我們能做的事的動物都歸類為不太聰明的物種。但是，在海豚的世界里，我們會表現得相當愚蠢：我們無法在水下聽到聲音，無法把自己的腦袋變成聲吶發生器，也無法發出像海豚那樣多種多樣的聲音。但即便如此，我們就不“聰明”了嗎？不，我們和海豚只是不一樣罷了。那么，海豚必須要“像人類一樣”才能被人類視作平等的生物來對待嗎？我們是否需要其他動物做到“像我們一樣”，才能給予它們平等的待遇？

問題在于，人類不可能完全平等地對待任何與他們不同的生物。

Growing up with pets around my house, I’ve found my fondness towards animals early in my life. I would tend to these lovely creatures with love and care that has naturally led myself to aspire after becoming a veterinarian in my future life. Yet, hoping me to get a “decent” degree in subjects like law, my parents were initially opposed to this idea. It was for my persistence that mom and dad finally let me have my way, and it was the same persistence that, when I was studying veterinarian, persuaded my professor to allow me on a travel to Canary Islands, where the sea presented profusion of intimacy with dolphins, my newly found passion.

Spending lots of time there studying animal behaviour and taking care of them, I knew that I wanted more than this. My ambition was to understand how animals communicate with each other. When I was only five, I have already had my first experience in animal communication. By mimicking the sound of the mother cat, I successfully coaxed the kittens out of their hiding place and played with them. With the help of a German professor, I moved to Israel to continue my study on dolphins. How they interact among themselves and with human beings? What methods they deploy to communicate? How do they convey their need?

All this time, I haven’t forgot the other seeking of mine: helping animals. I have been to facilities and institutes in the U.S. and Canada, working with staff there to offer medical treatment and protection mainly to marine animals.

After this, in 2007, I came to China, where my post-doctoral research awaited. I have collaborated with several institutes. Since 2017, I have been working here at Jianghan University.

The Wonders of Dolphins and Sounds

Dolphins and humans are both social mammals. In fact, these two types of mammals share a very similar social structure, namely the fission-fusion society. What does this mean? A fission-fusion society is where individuals are grouped into small families. Each individual in one family will have many agendas to attend on a routine basis—for example, humans have to go to work, and dolphins have to go out and hunt—each of us will leave for our separate business, but we all come back togetheragain at the end of the day. Yet, dolphins and humans are no doubt different. We live in different environments, thus we developed different sensory systems to adapt to and master these environments. We, living on firm lands, have our unique brain composition that are different to the brains of dolphins. Yet despite this difference, humans and dolphins share the need to communicate within their little or big societies.

Living and communicating undersea like dolphins may face quite a few challenges. One of the challenges is visual sight, for that a deep water environment can be dark and dense, the place where little light can reach. Even when the water is very clear, visible light can only travel 100 metres beneath the sea level. Actually, the sea water is hardly that clear, not to mention the disruption of waves and obstruction coming from seaweed and other things in the water. So it is far more likely that we can only see things metres, even centimetres away. In this, visual senses are not that useful for marine animals. But how can dolphins swim around, make friends with other dolphins, or hide away from predators with such poor eyesight? What senses are they going to utilize? The answer is sound!

The speed at which the sound travels in sea water is under multiple affecting factors. Because of the difference in density of water and air, sound can travel 4.5 times faster below the sea level than it does above. The transmission speed of sound also has to do with temperature and salinity. The warmer and saltier the water is, the faster the sound travels. More to this, in deeper areas of the ocean, where the water pressure is significantly higher than the surface, sound will accordingly travels at a faster speed .

We can certainly hear sounds in the water, too. But are dolphins hearing the same as we do? Unfortunately, we can only receive a limited range of frequencies of sound in the water owing to the shapes and structures of our human ears. It is for the same reason that we are not able to discern what direction the sound is coming from when swimming. How about dolphins? They are lot more advanced in regard of hearing under the water, unlike human, who can only receive frequencies in the range between 20 Hz to 15 kHz, while dolphins can pick up sound frequencies all the way from 75 Hz to 150 kHz.

How do dolphins make sounds? We human beings use our vocal cords to produce sounds, whereas dolphins have taken up a different method—they make sounds through the nasal organs, which are located in the melon (the round part on top of their head). Air will enter through blowholes into a pocketshaped structures which will vibrate, thus producing sounds. But the core of dolphin’s sound-making are their two sets of liplike organs. This dual-set of lips has allowed them to produce two types of sounds at the same time: whistles to communicate among individuals and echolocation to scan the environment.

Making sounds is just half of the equation. Now, how do dolphins hear these sounds? The fat tissue in the innerest part of the melon, it is of the same density of water. This tissue functions like a lens and can change its shape, transmitting the sound out in different directions. Around the jaws of a dolphin exists similar fat tissues. When the sound comes, fat tissues inside the jaw bones will perceive them, later transmit them to inner parts of dolphin ears that are also surrounded by the same fat tissues. Though they have ears, and also ear canals, but due to different structures from those of a human being, dolphins cannot hear as well out of water as they do under.

Dolphins’ Different Sounds

To understand sounds made by dolphins, researchers have separated out several patterns of sonograms. From these different patterns of sounds, scientists are able to identify the context where these sounds were made, what kind of emotions the dolphins are experiencing, or whether the dolphins are moving or are engaged in other things.

Now we will discuss different types of sounds a dolphin can make. First, there are sounds called “whistles”, of which the average frequency range can be between 75 Hz to 24 kHz (with some whistles going above 24 kHz). Whistles are omnidirectional which means it is difficult to identify which dolphin produces them. Whistles are composed by two parts: the fundamental frequency which is the main whistle, and the harmonics which occur at integer multiples of the fundamental frequency and usually extend into the ultrasonic (>20 kHz) range. Whistles that contain both non-directional and directional components are called “mixed directionality” sounds. In fact, researchers found out that the harmonics could be used for direction-tracking. So when a dolphin is both conveying his or her message and position, he or she will release both whistle sounds and harmonics. People have names, and we know each other by names. Dolphins have names, too - signature whistles. Each individual dolphin can label him or herself with a specific whistle tone - like a name - that is specific to each individual. The signature whistle can be also imitated by other dolphins to call upon the specific individual, just like we call the name of a person.

Besides whistling, dolphins have another type of sounds called echolocation clicks, which sounds like wooden sticks hitting each other. The dolphins use this type of sounds to scan their surroundings and look for food or obstacles. Each click sound is followed by an interval, in which dolphins are waiting for the echo of the click to come back and then to produce another click. Calculating this time lapse, dolphins can figure out how close they are to a certain object, thus mapping out the environment.

There is another type of sound called “burst pulse sound” which contains emotional components. This type of sounds are used by dolphins when they feel upset or argue with each others. Scientists would also describe this type of sounds with different names depending on how the sound goes: yelp, cry, weep. Different kinds of dolphins produce different kinds of sounds. For example, the finless porpoise, can only make pulse sounds but not whistles.

Dolphins’ Perceptual World

Human beings mainly create their reality through visions and speeches. We see something new, we name it, therefore recognize it. In general, the concept of “self” is based on information processed by the brain such as external information about reference axis of space and time with the self at the centre, and internal information about the position and orientation of the head and the body. These are elements of construction of the self. Memories, expectations, plans and so on are just additional elements. For dolphins, all the information about the external world come with the echolocation.

While human would say, “do you see what I see” or “do you see what I am telling you?” (if the person is talking about something), dolphins put it in another way, “do you see what I hear”. Every time a dolphin produces echolocation clicks to scan the surrounding environment, the echoes of the clicks will come back to the source, giving a sort of “holographic image” of what has been scanned. Here comes the amazing part: these echoes can be picked up by another dolphin in the vicinity who will receive the exact same type of “holographic image”. When different humans see the same object, they will perceive it differently, that depends on how each of them perceive their reality. Echolocation shares an unusual structural feature with human language, namely, the construction of the reality by the brain, is based on a signal generated by an individual. In the construction of a reality from echolocation, dolphins could share “raw” sensory information with one another, which would be even more unusual than the way we share information with language. Since the information are in the auditory domain, the “objects” that they generate would be as real as human seenobjects rather than heard-objects, that are so difficult for us to imagine. Even though it is just a speculation, the possibility of a social or communal cognition is something can be seriously considered. In fact, a perceptual world constructed from shared raw data would permit unusual group cohesion and a different kind of individuation. The dolphins’ social world could be an active rather than purely passive communal world. It would be as if humans were able to share the exact same image perceived by one individual. Therefore, the concept of an “individual” would be redefined where a communal experience might change the boundaries of the self to include several individuals.

This hypothesis could be supported by the special structure of the dolphins’ brain. The human brain can be differentiated into three main complexes: the reptilian complex, the limbic system and the cortex. However, with cetaceans we see a radical evolutionary jump with the inclusion of a fourth segment. This segment, called the paralimbic, features between the limbic and cortex, and it erupts into the cortex. This structure is present only in cetaceans and not in any other animal on earth. This unique evolution of the cetacean’s entire limbic system, which is a combination of multiple structures in the brain that deal with emotions and the formation of memories, suggests that cetaceans have the ability to process more complex thoughts and emotions. Since the system is so large in cetaceans, and the unique paralimbic lobe merges with the cortex, it is believed that the lobe may create a mixture of both emotional and cognitive thinking. The paralimbic lobe is also believed to be a continuation of the sensory and motor areas. For humans, projection areas are widely separated from one another, meaning anything we perceive from sight, sound and impulses must travel along fibre tracts with a great loss of time and information. The cetacean’s paralimbic lobe brings this all together in one, processing information rapidly with a richness that we cannot understand. The unique evolution of the paralimbic system suggests that the animals are doing something very sophisticated or complex while they’re processing together, emotions and sounds, and their brains may have adapted for a type of social connectivity unprecedented in the animals kingdom, taking the concept of social to a different level. Dolphins have a very strong cohesiveness in term of grouping: in fact, when one or two animals are sick and stranded, all the rest of the herd follows. A lot of this comes down to the “emotional attachment”, with a possible strong sense in these animals that if something happen to an individual, it happens to the entire group. Some scientist identify this type of cohesion among dolphins as a “collective soul”.

So do we need dolphins to be “like us” to be considered intelligent? Cetaceans have the biggest of the brain among animals, including humans, but this does not make them more intelligent than us. Defining intelligence is a tricky issue, and till now we did not yet completely understand the functions of human brain and found out the structure that defines intelligence. We, usually, define intelligence in other animals with the construction of our reality: we talk, we write, we do amazing things...and we classify animal species as less intelligent because they are not able to do things we do. But in a dolphin world we would be pretty stupid beings: we are not able to hear sounds underwater, to produce sonar with our heads, and to make the sounds as dolphins do. Are we less intelligent because of that? No. We are just different. So, do we need dolphins to be “like humans” to be treated as equal? Do we need other animals to be “like us” to have them treated as equal?

The problem lies in the fact that humans are mostly unable to treat as equal any being different from them. (

Yang Yunzhou contributed to this article

)