★英語(yǔ)聽(tīng)力頻道為大家整理的初中英語(yǔ)聽(tīng)力mp3下載：為什么人類(lèi)身上沒(méi)有斑點(diǎn)或條紋，供大家參考。更多閱讀請(qǐng)查看本站英語(yǔ)聽(tīng)力頻道。
Why Don’t Humans Have Spots Or Stripes?
為什么人類(lèi)身上沒(méi)有斑點(diǎn)或條紋？
Have you ever wondered why we humans don’t have spots or stripes? Well, maybe you haven’t, but it is interesting that so many creatures are multicolored but we are not.
你是否曾經(jīng)好奇過(guò)為什么我們?nèi)祟?lèi)身上沒(méi)有斑點(diǎn)或條紋？也許你沒(méi)想過(guò)，可那么多生物五彩斑斕，我們卻不是，這很有意思。
Melanin Pigments
黑色素
Humans and animals get their skin color from melanin pigments, which can be either black or yellow. 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.
人類(lèi)和動(dòng)物的皮膚顏色來(lái)自黑色素，它不是黑色就是黃色。二者混合可呈現(xiàn)你能見(jiàn)到的各種哺乳動(dòng)物的皮膚顏色：白色、黃色、棕色、黑色和他們之間的過(guò)渡色。產(chǎn)生黑色素的皮
The skin cells that produce melanin are known as melanocytes. In the embryos of mammals, the melanocytes originate from the same group of cells that produces the spinal cord and the brain. From there, these cells migrate through the developing skin towards the belly of the animal.
膚細(xì)胞是黑素細(xì)胞，在哺乳動(dòng)物的胚胎中，黑素細(xì)胞源自制造出脊髓和大腦的同組細(xì)胞。這些細(xì)胞從那里出來(lái)通過(guò)皮膚的生長(zhǎng)遷往動(dòng)物的肚子。
Streaks and Stripes
條紋和條痕
If the melanocytes that produce dark pigments and light pigments migrate in streaks, you end up with stripes. The same goes for spots, but in this case, only random patches of certain pigments survive. In either case, the migration pattern is genetically determined.
如果產(chǎn)生深淺色素的黑素細(xì)胞以條紋狀遷移，那么你身上就有條紋。斑點(diǎn)也是這么來(lái)的。但在這種情況下， 只有隨機(jī)的某些色素斑點(diǎn)能夠存活。不論哪種情況，其遷移方式由基因決定。
For certain species, like zebras, stripes provided an evolutionary advantage because they worked as camouflage. Those animals with stripes were more likely to survive, and to pass along the genes that produce stripes to their offspring. For humans, this apparently wasn’t the case. However, it’s likely that our overall skin color probably is a result of adaptation as well.
對(duì)于特定物種 ，比如斑馬， 條紋因可作為偽裝對(duì)進(jìn)化有利。身上有條紋的動(dòng)物更有可能生存下來(lái)，并把能產(chǎn)生條紋的基因傳給后代。對(duì)于人類(lèi)來(lái)說(shuō)，情況顯然不同。但是我們?nèi)砥つw的顏色也可能是適應(yīng)環(huán)境的結(jié)果。
Why Don’t Humans Have Spots Or Stripes?
為什么人類(lèi)身上沒(méi)有斑點(diǎn)或條紋？
Have you ever wondered why we humans don’t have spots or stripes? Well, maybe you haven’t, but it is interesting that so many creatures are multicolored but we are not.
你是否曾經(jīng)好奇過(guò)為什么我們?nèi)祟?lèi)身上沒(méi)有斑點(diǎn)或條紋？也許你沒(méi)想過(guò)，可那么多生物五彩斑斕，我們卻不是，這很有意思。
Melanin Pigments
黑色素
Humans and animals get their skin color from melanin pigments, which can be either black or yellow. 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.
人類(lèi)和動(dòng)物的皮膚顏色來(lái)自黑色素，它不是黑色就是黃色。二者混合可呈現(xiàn)你能見(jiàn)到的各種哺乳動(dòng)物的皮膚顏色：白色、黃色、棕色、黑色和他們之間的過(guò)渡色。產(chǎn)生黑色素的皮
The skin cells that produce melanin are known as melanocytes. In the embryos of mammals, the melanocytes originate from the same group of cells that produces the spinal cord and the brain. From there, these cells migrate through the developing skin towards the belly of the animal.
膚細(xì)胞是黑素細(xì)胞，在哺乳動(dòng)物的胚胎中，黑素細(xì)胞源自制造出脊髓和大腦的同組細(xì)胞。這些細(xì)胞從那里出來(lái)通過(guò)皮膚的生長(zhǎng)遷往動(dòng)物的肚子。
Streaks and Stripes
條紋和條痕
If the melanocytes that produce dark pigments and light pigments migrate in streaks, you end up with stripes. The same goes for spots, but in this case, only random patches of certain pigments survive. In either case, the migration pattern is genetically determined.
如果產(chǎn)生深淺色素的黑素細(xì)胞以條紋狀遷移，那么你身上就有條紋。斑點(diǎn)也是這么來(lái)的。但在這種情況下， 只有隨機(jī)的某些色素斑點(diǎn)能夠存活。不論哪種情況，其遷移方式由基因決定。
For certain species, like zebras, stripes provided an evolutionary advantage because they worked as camouflage. Those animals with stripes were more likely to survive, and to pass along the genes that produce stripes to their offspring. For humans, this apparently wasn’t the case. However, it’s likely that our overall skin color probably is a result of adaptation as well.
對(duì)于特定物種 ，比如斑馬， 條紋因可作為偽裝對(duì)進(jìn)化有利。身上有條紋的動(dòng)物更有可能生存下來(lái)，并把能產(chǎn)生條紋的基因傳給后代。對(duì)于人類(lèi)來(lái)說(shuō)，情況顯然不同。但是我們?nèi)砥つw的顏色也可能是適應(yīng)環(huán)境的結(jié)果。