“An Immense World” 這本書的這個段落，講的是“A Rough Sense, Contact and Flow”，「觸覺」。
海獺的爪子，裸鼴鼠的牙齒，星鼻鼴的星狀鼻，鼠類的觸鬚，鴨嘴獸的嘴喙，人類的手、嘴唇和性器官，鳥類的喙，鳥類頭上的纖羽，海牛的觸鬚，海豹的觸鬚，短吻鱷嘴巴外面及裏面的隆起物，虎紋鳯梨蛛腳上的盅毛，毛毛蟲的毛等等，都是神奇的觸覺器官的例子。
我們自詡是萬物之靈，但是當理解到其實有很動物觸覺的敏感度，高到我們無法想像的程度，我們應該自慚形穢才是。
不過，回到「Umwelt」的觀念，我們最好不要從人的角度來揣測其他的生物，而是應該從其他生物自身的角度，也就是生態棲位的角度來看，那麼所有神奇之所在，就是大自然啊！
“…wild sea otters snag fish, seize sea urchins, and dig out buried clams. Their delicate sense of touch allows them to survive as a small, warm mammal in a big, cold ocean.
The sensitivity of their paws is evident in their brains. As in other species, a region called the somatosensory cortex deals with touch. Different sections of the somatosensory cortex receive inputs from different parts of the body, and the relative size of these sections can hint at an animal’s major tactile organs. In humans, the hands, lips, and genitals are most heavily represented. In mice, its the whiskers; in platypuses, the bill; and in naked mole-rats, the teeth. In sea otters, the part of the somatosensory cortex that receives signals from the paws is disproportionally big compared to those of other mustelids, and even compared to those of other otters.”
海獺抓魚、剝食海膽、挖出蛤蜊。它們敏銳的觸覺，是小型衡溫哺乳動物在深冷的大海中賴以生存之道。
它們爪子觸覺的敏銳程度，可以從它們的大腦看出來。和其他種類的動物一樣，大腦中有一個叫做體感皮層的區域，是負責處理觸覺的。體感皮層不同的區段，分別接收來自身體不同部位傳來的訊息，從那個區段的大小，就可以推測出哪些是主要的觸覺器官。在人類主要就是手、嘴唇和性器官。鼠類是它們的觸鬚。鴨嘴獸是嘴喙。裸鼴鼠是牙齒。而海瀨，它接收爪子傳來訊息的體感皮層區段的大小，比同為鼬科之下的其他動物相對上都要大，甚至比其他水瀨的還要大。
“The star-nosed mole is a hamster-sized animal with silky fur, a rat-like tail, and shovel-like paws. It lives throughout the densely populated eastern parts of North America, but since it dwells in bogs and swamps and spends most of its time underground, few people ever see it…”
星鼻鼴的大小有若倉鼠，身上覆有絲毛，有像老鼠般的尾巴，鏟子般的爪子。它的棲息地在人口稠密的北美東岸，住在酸沼和樹沼的地區，而且大部分時間在地底下，所以幾乎沒有人曾看過過它們。
“The mole’s somatosensory cortex the touch center of its brain is disproportionately devoted to the star, much as a human’s touch center is especially devoted to our hands. And just as our somatosensory cortex has clusters of neurons that represent each of our fingers, the mole’s has stripes of neurons that correspond to each ray of the star…
The 11th pair of rays, which are smaller than all the rest, is represented by a massive chunk of neurons, which take up a quarter of the brain region that’s used for the entire star…the zone where the animal’s sense of touch is sharpest. It’s no coincidence that this zone lies just in front of the mole’s mouth. The instant it decides that an object feels like food, it can part the rith pair of rays and seize the morsel with its tweezer-like front teeth.”
星鼻鼴大腦中的觸覺體感皮層，大部分是用來處理鼻子上的星狀器官傳來的訊息，就像人類腦袋中的觸覺中心，主要是處理手指所傳來的訊息一樣。我們的體感皮層，針對每隻手指有相應的叢聚神經元；星鼻鼴的體感皮層，針對星狀器官的每條射線，都有帶狀集中的神經元。
星狀器官中的第11條射線，比起其他所有的星狀射線是一小部分，但是它卻有很大量的神經元，佔據了大腦中星狀器官相關的體感皮層高達四分之一的區域。
星狀器官的第11條射線，是星鼻鼴觸覺最敏銳的位置。位於嘴巴前面並非巧合，而是精心的設計。當感覺出現的東西是食物的那個瞬間，嘴巴就會張開把它用有若鑷子般的牙齒抓住。
“The beaks of birds are made of bone and sheathed in the same hard keratin that constitutes your fingernails. They seem inanimate and insensitive hard, face-mounted tools for grabbing and pecking. But in many species, the tip of the bill contains a smattering of mechanoreceptors, sensitive to vibrations and movements.”
鳥類的喙是骨骼組織，外面包覆著角蛋白，就像指甲一樣。喙看來好像無生命，無感而且堅硬，是長在臉部用來抓取或啄食的工具。但在很多的鳥類，在它們嘴喙的尖端有一些機械感受器，對震動和移動很敏感。
“…In chickens, which rely heavily on vision to forage, those mechanoreceptors are relatively rare, and concentrated in a few small clusters on the lower beak alone. But in some ducks, like mallards and shovelers, they’re spread all over the bill, upper and lower, inside and out. In some places, these mechanoreceptors are as densely packed as they are in our digits. The mallard’s bill may be covered in the stuff of human fingernails, but it’s extremely sensitive. Ducks use this sense to find food in murky water…They can grab fast-swimming tadpoles in the dark, and filter edible morsels from the inedible mud.”
鷄主要靠視覺覓食，它們喙上的機械感受器相對比較少，而且只集中在下喙。但是在有些鴨類，如綠頭鴨和琵嘴鴨，機械感受器則遍佈在喙的上、下，以及啄的內緣及外側。機械感受器密佈的狀況，就有若我們的手指一樣。綠頭鴨的喙，可能不及人指甲大，但是卻極為敏感。鴨類用這種敏銳的觸覺在昏暗的水中覓食……它們可以抓住游得很快的蝌蚪，從泥水中過濾出可以吃的食物。
“…Even the most deserted beaches are full of buried treasure worms, shellfish, and crustaceans, all concealed within the sand. To reach this hidden buffet, shorebirds like curlews, oystercatchers, sandpipers, and knots probe among the grains with their beaks. Under a microscope, the tips of their bills are riddled with pits, like corncobs with all their kernels bitten off. Those pits are full of mechanoreceptors that are similar to those in our hands and allow the birds to detect buried prey.“
再荒涼的海灘下面，都藏著豐富的寶藏。海蟲、貝類、甲殼類等等，都在沙子裏。濱鳥，如鷸、蠣鷸、磯鷸、濱鷸等等，會用它們的喙在沙粒中找食物。在顯微鏡下，它們的喙的尖端分佈了一些小洞，形狀像去掉玉米的玉米棒子一樣。那些小洞裏，佈滿機械感知器，像我們的手指一樣，濱鳥靠它們偵測埋在沙子裏的獵物。
“Many other birds have stuff bristles on their heads and faces…they could have initially evolved to provide tactile information. As the whiskered auklet shows, an animal only needs a few bristles to extend its sense of touch in useful ways. Perhaps feathers first appeared as small clumps on the heads or arms of dinosaurs, helping them first to feel and only later to fly.”
有許多鳥類在頭上、臉上長了短短的剛毛….. 或許在早期，那是演化來提供觸覺的。從小海雀就可以發現，動物只要一點點剛毛就可以大幅促進觸覺。或許在恐龍的時代，羽毛在頭或臂膀上小撮小撮出現的時候，一開始是為了促進觸覺，後來才發展成飛行的羽毛。
“Mammals have been using whiskers for almost as long as mammals have existed. Today, rats and opossums, which share the habits of their small, nocturnal, climbing, scampering ancestors, still whisk. Guinea pigs do it half-heartedly. Cats and dogs don’t do it at all, although their whiskers are still mobile. Humans and other apes have lost our whiskers entirely and invested instead in sensitive hands. Whales and dolphins are born with whiskers, but these quickly fall out except around the lips and blowholes. Whisking, after all, is too difficult to do in the water. Whiskers, however, can still be useful.”
哺乳動物一向長有觸鬚。老鼠、負鼠和它們小型夜行性蹦蹦跳跳的始祖們一樣，都保有拂動觸鬚的習慣。天竺鼠偶爾也會無心地動一下。貓和狗的觸鬚都還會動，但它們已經不再使用了。人類和猩猩則完全不長觸鬚，完全靠敏感的手產生的觸覺。鯨魚和海豚都長有觸鬚，但是在水中難以產生作用。雖然如此，總結而言，觸鬚對某些動物還是很有用處的。
“Manatees are the only known mammals that only have vibrissae and no other kinds of hair. Aside from the whiskers on their oral disk, they have another 3,000 scattered all over their large bodies….Manatees use these body-wide whiskers for another purpose to sense the water flowing around them.”
海牛是哺乳動物中唯一擁有觸鬚的物種。除了在嘴盤邊的觸鬚之外，海牛在龐大的身軀上疏疏散佈了大約3,000根的觸鬚……海牛透過這些遍佈身軀的觸鬚，去感受身旁海水流動的狀況。
“Sensory hairs are versatile structures. They can be actively pressed against surfaces to produce tactile sensations, as whisking rats and oripulating manatees do. But they can also be passively bent and deflected by flowing air or water. By responding to that pressure, an animal can detect the flows created by distant objects, touching things from afar without needing to make direct contact. Manatees can certainly do this.”
感官的毛髮(觸鬚)的構造，可以產生多式各樣的知覺。它們可以直接壓在各種表面上產生觸覺，舞動觸鬚的鼠類和用嘴盤探索的海牛，都是這種例子。它們也可以被動讓水流壓彎或反折觸鬚，從產生的壓力，就可以偵測到遠處物體擾動的水流，不必直接摸到就可以從遠處就產生觸覺，海牛就絕對有這種本事。
“As a fish swims, it leaves behind a hydrodynamic wake ——a trail of swirling water that continues to whirl long after the animal has passed. Seals, with their sensitive whiskers, can detect and interpret these trails…”
當魚游過，在它的身後會留下水被擾動的痕跡，在魚游走之後細小的旋渦還會留在那裡。海豹，透過它敏銳的觸鬚，可以偵測並且解讀那些水痕的意義。
“Those fish might be camouflaged and lying perfectly still, but a seal can still feel their breaths with its face. A seal’s tactile world is attuned to flow and motion, and their prey cannot help but move. It would seem like an unfair contest, if those prey didn’t have incredible hydrodynamic powers of their own.”
那些魚類或許可以把自己偽裝起來而且靜靜躺下來，但是海豹還是可以用臉(的觸鬚)感覺到它們的鼻息。海豹的觸覺善於偵測水流和動作，而它們的獵物又不得不逃跑。如果那些獵物的水性不夠好的時候，那就似乎是不公平的競爭了。
“Alligators have rows of dark, raised domes along the edges of their jaws, as if they’re wearing beards made of blackheads…The bumps,…, are pressure receptors that can detect vibration at the water’s surface…The animals use the bumps to scan the thin horizontal layer where air and water meet. They sit in ambush in that layer, waiting for something to land in the water or to arrive at its edge for a drink…The bumps are also found around the teeth and inside the mouth, so crocodilians might use them to assess their food or adjust their bites…”
短吻鱷在嘴頰邊上有幾排黑色隆起的圓點，像戴著黑頭粉刺串成的項鍊一樣。那些隆起物，是壓力的受器，可以偵測水面的震動。……這種動物用那些隆起物掃瞄水面。它們埋伏在那裡，等待獵物掉下來或到那個位置喝水……. 在它們的牙齒的周邊和嘴巴𥚃面，也有那些隆起物，分類上屬於鱷目的物種，可能用它們來品嚐食物或是調整雙顎咬合的力度……
“A clue can be found at the base of each peacock crest feather, where there’s a smaller companion feather called a filoplume. It’s just a simple shaft with a tufted tip, and could act as a mechanosensor. When moving air shakes the crest feather, the crest feather could nudge the filoplume, and the filoplume could trigger a nerve. Filoplumes are found in most birds, and are almost always associated with another feather. Birds can use them to monitor the position of their feathers, perhaps to sense when their smooth plumage has become ruffled and needs to be preened. But filoplumes are especially important during flight.”
在鸚鵡頭上冠羽的底部，有細小的纖羽。它只是單純長在羽桿上的簇毛，可以作為機械感知器。當氣流搖動冠羽的時候，會向下輕觸到纖羽，纖羽觸動下面的神經。纖羽廣泛存在於鳥類的身上，而且連帶上面有其它羽毛。鳥類可以用纖羽來密切注意羽毛的位置，或許因此可以知道什麼時候該整理弄亂的羽毛。但是，纖羽在維持飛行的平衡上，更為重要。
“The tiger wandering spider doesn’t spin a web to catch food; instead, it sits in wait for its prey. Its legs are covered in hundreds of thousands of hairs, which are packed so densely that there can be 400 in a square millimeter. Almost all of them are connected to nerves and are sensitive to touch…”
虎紋鳯梨蛛並不織網，它只靜靜等待獵物上門。它的腳上長滿很多的細毛，密度高達每平方𨤳米有400根。幾乎所有的毛都連接到神經系統上面，因此觸覺非常敏銳。
“Most of these hairs only respond to direct contact, but some are so long and sensitive that they will also be deflected by the wind. These are called trichobothria, from the Greek words for “hair” (trichos and “cup” (bothrium). Like a bird’s filoplumes or a fish’s neuromasts, they’re flow sensors — albeit exceptionally sensitive ones. Even air that’s moving at just an inch per minute — a breeze so gentle it could hardly be called a breeze — will deflect them. Watch them under a microscope, and you’ll see them fluttering away under the influence of imperceptible currents, while everything around them is still. With a hundred trichobothria on every leg, the tiger wandering spider can tune in to the airflow around its body, in every possible direction. It uses this sensitivity for lethal ends.”
虎紋鳯梨蛛大部分的毛對直接的碰觸產生反應，但有些毛實在太長，會被風吹起來。這種毛叫做「盅毛」(trichobothria)，在希臘文中，是結合了「毛髮 hair」(trichos)和「盅cup」(bothrium)。就像鳥類的纖羽或魚類的體側腺，是對流動的感知器，是非常敏感的那種。甚至空氣以每分鐘移動一吋的速度，根本連輕風都算不上，這些感知器都偵測得到。放在顯微鏡下看，它們好像在看不見的氣流下飄動，而附近的其他的東西則都紋風不動。虎紋鳯梨蛛在腳上有一百條盅毛，它可以針對非常細微的風壓調整自己的身體。它善用這種敏感度，對獵物產生致命的結果。
“Most arthropods — the diverse group that includes insects, spiders, and crustaceans — have hairs that detect the flow of either water or air. The implications of this widespread sense are profound, in ways we have barely begun to grapple with. For example, in 1978, Jürgen Tautz showed that caterpillars can use hairs on their midsection to sense the air movements produced by flying parasitic wasps. They react by freezing, throwing up, or falling to the ground. Thirty years later, Tautz showed that flying honeybees can trigger the same effect. Simply by moving the air around the plants that they visit, bees can reduce the amount of damage that very hungry caterpillars might inflict. Few groups of insects matter more to plants than bees and caterpillars. And yet no one appreciated that these groups the pollinators and the despoilers are connected by the slightest gusts of wind and the minuscule deflections of hairs. The air around us is full of signals that we don’t detect. And so is the ground below us.”
節肢動物門下的諸多生物，包括昆蟲、蜘蛛、甲殼類等等，大部分都長有能偵測氣流或水流的毛。有這麼動物涉及，它的影響是深遠的，但我們目前掌握的還是非常有限。1978年有科學家發現毛毛蟲中段的毛可以偵測到掠食性蛾類飛來，然後它們會停住、嘔吐或掉到地上。30年之後，有科學家又發現，當蜜蜂飛過的時候，也會產生一樣的效果。只是因為蜜蜂飛過所產生的氣流，就可以減少飢餓的毛毛蟲對植物造成的損害。沒有人會料到，授粉者和掠奪者之間的關係，居然是極小的氣流及可以偵測這些氣流的細毛所共同建立起來的。我周圍的空氣中和我們的腳下，充滿了我們無法偵測到的訊息。
*：ED Yong, “An Immense World,” 2022, Random House/New York
2023/9/7 A Rough Sense, Contact and Flow Damakey
