a国产亚洲欧美精品一区在线观看_看一级黄色毛片_在线观看播放_一级片精品_国产精成人品日日拍夜夜免费_草久在线视频

食品伙伴網服務號
 
 
當前位置: 首頁 » 專業英語 » 英語短文 » 正文

“返祖現象”是怎么回事

放大字體  縮小字體 發布日期:2008-09-09
核心提示:我們都聽說過一些返祖現象,比如某個嬰兒身上的毛發特別多,或是長了尾巴;還有本來沒有腳的動物比如鯨魚,卻多出了兩只像腳一樣的東西。那么,返祖究竟是怎么回事呢?有人認為這是基因的問題。 Four-year-old Jiaxue, of China, was born with hairy black moles cove


我們都聽說過一些“返祖現象”,比如某個嬰兒身上的毛發特別多,或是長了尾巴;還有本來沒有腳的動物比如鯨魚,卻多出了兩只像腳一樣的東西。那么,”返祖“究竟是怎么回事呢?有人認為這是基因的問題。

Four-year-old Jiaxue, of China, was born with hairy black moles covering parts of her back, chest, neck and face. The media reported her condition as an atavism.
 
Perhaps you've heard of the world's hairiest man. The media loves to show his picture. Newspapers call conditions like this and others atavisms(返祖現象). Is the world's hairiest man really a throwback to our simian(猿) ancestors? Not quite. Ape faces are clear of hair, as Michael Le Page notes in his New Scientist article on atavisms. So hypertrichosis(多毛癥), a condition in which excessive amounts of hair cover the body, isn't an atavism -- unless our ancestors were werewolves(狼人). If it is an avatism, it's not from the animals we point to when we talk about evolution, like chimps.

What's the difference between atavisms and vestigial(發育不全的,退化器官的) structures? They're actually pretty close. Vestigial structures are body parts that survive as degenerate, imperfect versions of what they should be. Think of the ostrich: It has wings, but it can't fly. Ostriches use their wings for other purposes, like balance, but their wings can't function as wings. Their wings are vestigial -- they're used for a purpose, but not the purpose for which they were designed.

Atavisms are traits of distant ancestors that reappear in the modern day. In order for the trait to be an atavism, an organism's parents can't have the trait, and neither can recent ancestors. The atavism you've probably heard of most often? The human tail. It's not just a gag to pull in a Farrelly brothers movie -- it really happens. There are two kinds of human tails, however: the pseudo-tail and the much rarer, true human tail. The pseudo-tail doesn't have any bones or cartilage(軟骨) -- it's skin and fat. But the true human tail has nerves and muscles and sometimes even cartilage or vertebrae(椎骨), although there seems to be some scientific debate about this last point. All vertebrates have the ability to make a tail, and guess what? Humans are vertebrates. Way back when, maybe we all had tails, and they provided some important function for us, perhaps to help us balance.

So how do these traits crop up? One idea is that instead of genes being lost during evolution, they're merely silent - they're still there, they're just not doing anything. But maybe these genes can be turned back on. Studies have shown species that lose and regain wings millions of years afterward. Are these species just evolving once again? Or did a silent gene labeled "grow wings" suddenly switch back on?

Scientists aren't sure how atavisms work -- not yet. They point to embryos to help decipher the answer. Embryos develop characteristics in the womb that later disappear. Whale embryos do grow buds where their legs would be, but they lose them as they develop. When you were a fetus, you had a little bud where a tail would be, but it disappeared before you were born. But on rare occasions, they don't disappear, and a baby whale is born with leg-like appendages or a human baby is born with a tail, which is usually amputated.

So why do atavisms happen? What place do they have in evolution? We don't know the answer. Often when people think of genetic information, they think about cloning, designer children and other controversial topics. But as scientists delve more deeply into our genetic information, this could be one of the most exciting areas of research -- finally figuring out where we came from and how we got to where we are.

更多翻譯詳細信息請點擊:http://www.trans1.cn
 
關鍵詞: 返祖 現象
[ 網刊訂閱 ]  [ 專業英語搜索 ]  [ ]  [ 告訴好友 ]  [ 打印本文 ]  [ 關閉窗口 ] [ 返回頂部 ]
分享:

 

 
推薦圖文
推薦專業英語
點擊排行
 
 
Processed in 0.170 second(s), 17 queries, Memory 0.89 M
主站蜘蛛池模板: 日韩专区视频 | 麻豆影视在线播放 | 日韩高清一区 | 成人黄色免费视频网站 | 精品伊人久久97 | 微拍福利88| 日本精品国产 | 91在线精品一区二区 | 国内精自视频品一2区 | 精品欧美一区二区久久久伦 | 亚洲中文字幕AV在天堂 | 一区二区三区国产免费 | 日韩精品无码一区二区 | 极品尤物AV美乳在线观看 | xxxxxx在线 | 国产精品全国免费观看高清 | 91.九色视频 | 97最新国自产拍视频在线完整在线看 | 熟女无套高潮内谢吼叫免费 | 亚洲午夜激情视频 | 国产嫖妓风韵犹存对白 | 欧美激情在线一区二区 | 亚洲资源在线观看 | 精品性影院一区二区三区内射 | 国产精彩视频在线 | 精品成人影院 | 免费av免费观看 | 成人羞羞国产免费图片 | 九九中文| 日本公交车上xxxxhd少妇 | 欧美精品一区二区中文字幕 | 美女久草 | 日本国产忘忧草一区在线 | 潜行者40集在线播放免费观看国语 | 日本成a人片在线播放 | 日本va欧美va国产激情 | 国产首页天堂在线 | 最近日本中文字幕 | 中文精品一卡2卡3卡4卡 | 含着奶头搓揉深深挺进视频 | 国产OO后高中生在线视频 |