听力文摘：为什么人类身上没有斑点或条纹?

Have you ever wondered why we humans don't have spots or stripes?

你是否曾经好奇过为什么我们人类身上没有斑点或条纹？

Let me think,Humans and animals get their skin color from melanin pigments¹, which can be either black or yellow.

让我想想，人类和动物的皮肤颜色来自黑色素，它不是黑色就是黄色。

Together, these two pigments account for just about every color you might see on the skin of mammals: white, red, yellow, brown, and black and every shade in between.

二者混合可呈现你能见到的各种哺乳动物的皮肤颜色：白色、黄色、棕色、黑色和他们之间的过渡色。产生黑色素的皮

The skin cells that produce melanin are known as melanocytes.

肤细胞是黑素细胞，

In the embryos² of mammals, the melanocytes originate from the same group of cells that produces the spinal³ cord and the brain.

哺乳动物的胚胎中，黑素细胞源自制造出脊髓和大脑的同组细胞。

From there, these cells migrate through the developing skin towards the belly⁴ of the animal.

这些细胞从那里出来通过皮肤的生长迁往动物的肚子。

If the melanocytes that produce dark pigments and light pigments migrate in streaks⁵, you end up with stripes.

如果产生深浅色素的黑素细胞以条纹状迁移，那么你身上就有条纹。

The same goes for spots, but in this case, only random⁶ patches of certain pigments survive.

斑点也是这么来的。但在这种情况下，只有随机的某些色素斑点能够存活。

In either case, the migration⁷ pattern is genetically⁸ determined⁹.

不论哪种情况，其迁移方式由基因决定。

For certain species, like zebras, stripes provided an evolutionary¹⁰ advantage because they worked as camouflage¹¹.

对于特定物种 ，比如斑马， 条纹因可作为伪装对进化有利。

Those animals with stripes were more likely to survive, and to pass along the genes¹² that produce stripes to their offspring.

身上有条纹的动物更有可能生存下来，并把能产生条纹的基因传给后代。

For humans, this apparently¹³ wasn't the case.

对于人类来说，情况显然不同。

However, it's likely that our overall skin color probably is a result of adaptation as well.

但是我们全身皮肤的颜色也可能是适应环境的结果。

1 pigments   

n.（粉状）颜料( pigment的名词复数 )；天然色素

参考例句：

• The Romans used natural pigments on their fabrics and walls. 古罗马人在织物和墙壁上使用天然颜料。 来自辞典例句
• The original white lead pigments have oxidized and turned black. 最初的白色铅质颜料氧化后变成了黑色。 来自辞典例句

2 embryos   

n.晶胚；胚，胚胎( embryo的名词复数 )

参考例句：

• Somatic cells of angiosperms enter a regenerative phase and behave like embryos. 被子植物体细胞进入一个生殖阶段，而且其行为象胚。 来自辞典例句
• Evolution can explain why human embryos look like gilled fishes. 进化论能够解释为什么人类的胚胎看起来象除去了内脏的鱼一样。 来自辞典例句

3 spinal   

adj.针的，尖刺的，尖刺状突起的；adj.脊骨的，脊髓的

参考例句：

• After three days in Japan,the spinal column becomes extraordinarily flexible.在日本三天，就已经使脊椎骨变得富有弹性了。
• Your spinal column is made up of 24 movable vertebrae.你的脊柱由24个活动的脊椎骨构成。

4 belly   

n.肚子，腹部；(像肚子一样)鼓起的部分，膛

参考例句：

• The boss has a large belly.老板大腹便便。
• His eyes are bigger than his belly.他眼馋肚饱。

5 streaks   

n.（与周围有所不同的）条纹( streak的名词复数 )；（通常指不好的）特征（倾向）；（不断经历成功或失败的）一段时期v.快速移动( streak的第三人称单数 )；使布满条纹

参考例句：

• streaks of grey in her hair 她头上的绺绺白发
• Bacon has streaks of fat and streaks of lean. 咸肉中有几层肥的和几层瘦的。 来自《现代英汉综合大词典》

6 random   

adj.随机的；任意的；n.偶然的(或随便的)行动

参考例句：

• The list is arranged in a random order.名单排列不分先后。
• On random inspection the meat was found to be bad.经抽查，发现肉变质了。

7 migration   

n.迁移，移居，（鸟类等的）迁徙

参考例句：

• Swallows begin their migration south in autumn.燕子在秋季开始向南方迁移。
• He described the vernal migration of birds in detail.他详细地描述了鸟的春季移居。

8 genetically   

adv.遗传上

参考例句：

• All the bees in the colony are genetically related. 同一群体的蜜蜂都有亲缘关系。
• Genetically modified foods have already arrived on American dinner tables. 经基因改造加工过的食物已端上了美国人的餐桌。 来自英汉非文学 - 生命科学 - 基因与食物

9 determined   

adj.坚定的；有决心的

参考例句：

• I have determined on going to Tibet after graduation.我已决定毕业后去西藏。
• He determined to view the rooms behind the office.他决定查看一下办公室后面的房间。

10 evolutionary   

adj.进化的；演化的，演变的；[生]进化论的

参考例句：

• Life has its own evolutionary process.生命有其自身的进化过程。
• These are fascinating questions to be resolved by the evolutionary studies of plants.这些十分吸引人的问题将在研究植物进化过程中得以解决。

11 camouflage   

n./v.掩饰，伪装

参考例句：

• The white fur of the polar bear is a natural camouflage.北极熊身上的白色的浓密软毛是一种天然的伪装。
• The animal's markings provide effective camouflage.这种动物身上的斑纹是很有效的伪装。

12 genes   

n.基因( gene的名词复数 )

参考例句：

• You have good genes from your parents, so you should live a long time. 你从父母那儿获得优良的基因，所以能够活得很长。 来自《简明英汉词典》
• Differences will help to reveal the functions of the genes. 它们间的差异将会帮助我们揭开基因多种功能。 来自英汉非文学 - 生命科学 - 生物技术的世纪

13 apparently   

adv.显然地；表面上，似乎

参考例句：

• An apparently blind alley leads suddenly into an open space.山穷水尽，豁然开朗。
• He was apparently much surprised at the news.他对那个消息显然感到十分惊异。