只有人類才有下巴？揭秘關(guān)于人體的25個驚人事實(shí)
人類的身體堪稱這個世界上最神秘、最完美的杰作?？茖W(xué)家探索了幾千年，也沒能將人體完全搞清楚。你知道人類是唯一有下巴的動物嗎?你知道人類為什么會起雞皮疙瘩嗎?你知道拇指有自己的脈搏嗎?關(guān)于人體的25個驚人事實(shí)，跟我們一起了解一下。
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1. It’s possible to brush your teeth too aggressively. Doing so can wear down enamel and make teeth sensitive to hot and cold foods.
刷牙時有可能會過于劇烈。這么做會磨損牙釉質(zhì)，使得牙齒對冷熱食物敏感。
2. Goose bumps evolved to make our ancestors’ hair stand up, making them appear more threatening to predators.
我們的祖先之所以會進(jìn)化出雞皮疙瘩，是為了令自己的毛發(fā)豎起來，以此對掠食者更具威脅性。
3. Wisdom teeth serve no purpose. They’re left over from hundreds of thousands of years ago. As early humans’ brains grew bigger, it reduced space in the mouth, crowding out this third set of molars.
智齒沒有任何用處。它們只是幾十萬年前的遺留產(chǎn)物。由于早期人類的大腦逐漸增大，進(jìn)而縮減了口腔內(nèi)的空間，從而擠掉了第三大臼齒。
molar['mol?]: n. 臼齒，磨牙
4. Scientists aren't exactly sure why we yawn, but it may help regulate body temperature.
科學(xué)家們并不完全確定我們打哈欠的原因，但打哈欠可能有助于調(diào)節(jié)體溫。
5. Your fingernails don’t actually grow after you’re dead.
你死后你的指甲不會繼續(xù)長。
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6. If they were laid end to end, all of the blood vessels in the human body would encircle the Earth four times.
如果把人體內(nèi)的所有血管都連成一條直線，其長度可環(huán)繞地球四圈。
7. Humans are the only animals with chins.
人類是唯一有下巴的動物。
8. As you breathe, most of the air is going in and out of one nostril. Every few hours, the workload shifts to the other nostril.
當(dāng)你呼吸時，大部分空氣都會只通過一個鼻孔進(jìn)出。每隔幾個小時，會換到另一個鼻孔。
9. Blood makes up about 8 percent of your total body weight.
血液占你總體重的8%左右。
10. The human nose can detect about 1 trillion smells.
人類的鼻子可以檢測到大約1萬億種氣味。
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11. You have two kidneys, but only one is necessary to live.
雖然你有兩個腎臟，但只需要一個腎就能活下來。
12. Belly buttons grow special hairs to catch lint.
你的肚臍會長出特殊毛發(fā)以捕捉衣物中的棉絨纖維。
lint[l?nt]: n. 線頭;棉絨
13. The satisfying sound of cracking your knuckles comes from gas bubbles bursting in your joints.
掰手指時所聽到的讓你暢快的“咔咔”響聲來自于關(guān)節(jié)中的氣泡破裂聲。
14. Skin is the body’s largest organ and can comprise 15 percent of a person’s total weight.
皮膚是人體最大的器官，可占人體總重量的15%。
15. Thumbs have their own pulse.
拇指有自己的脈搏。
16. Your tongue is made up of eight interwoven muscles, similar in structure to an elephant’s trunk or an octopus’s tentacle.
你的舌頭由八塊交織的肌肉組成，其結(jié)構(gòu)與大象的長鼻或章魚的觸手相似。
trunk[tr??k]: n. 象鼻
17. On a genetic level, all human beings are more than 99 percent identical.
所有人類的基因有超過99%是相同的。
18. The foot is one of the most ticklish parts of the body.
腳是身體最怕癢的部位之一。
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19. Extraocular muscles in the eye are the body’s fastest muscles. They allow both of your eyes to flick in the same direction in a single 50-millisecond movement.
眼外肌是人體中移動速度最快的肌肉。它們使得你的雙眼可在50毫秒的運(yùn)動中掃向相同的方向。
extraocular[,?kstr?'ɑkj?l?]: adj. 眼外的
20. A surgical procedure called a selective amygdalohippocampectomy removes half of the brain’s amygdala—and with it, the patient’s sense of fear.
一種被稱為“選擇性杏仁核海馬切除術(shù)”的外科手術(shù)可切除大腦中的一半杏仁核，從而消除掉患者的恐懼感。
21. The pineal gland, which secretes the hormone melatonin, got its name from its shape, which resembles a pine nut.
分泌褪黑激素的松果體之所以叫這個名字，是因?yàn)槠湫螤羁瓷先ヮ愃朴谒晒?/p>
22. Hair grows fast—about 6 inches per year. The only thing in the body that grows faster is bone marrow.
頭發(fā)生長速度很快：每年約6英寸(15厘米)。而身體中唯一比頭發(fā)長得更快的是：骨髓。
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23. No one really knows what fingerprints are for, but they might help wick water away from our hands, prevent blisters, or improve touch.
沒有人真正知道指紋的作用是什么，但它們可能有助于從手上吸走水份、防止水泡或改善觸感。
24. The heart beats more than 3 billion times in the average human lifespan.
以平均壽命來計算，人的一生中心臟可跳動超過30億次。
25. Blushing is caused by a rush of adrenaline.
臉紅是由腎上腺素激增引起的。
