60秒科学:1 Million Years B.C.: Humans Rare

1 Million Years B.C.: Humans Rare
A study in the Proceedings¹ of the National Academy of Sciences used genomic analysis of modern humans to reveal that the population of our ancestors a million years back was below 20,000. Karen Hopkin reports

At one time or another, you’ve probably said, “It’s a small world.” Well, it used to be much, much smaller. Because according to scientists from the University of Utah, about a million years ago our ancestors numbered fewer than 20,000. The estimate appears in the Proceedings of the National Academy of Sciences.

The scientists based this ancestral census² on a reading of modern human genomes. In particular, they tracked the positions of transposable elements. These small pieces of DNA³ are basically genomic parasites⁴. Over time, they’ve spread through our genomes and though they’re still capable of hopping⁵ from one place to another, they do so quite rarely. One particular transposon first appeared about a million years ago. And by seeing where these sequences now sit, scientists can get a sense of the size of the breeding population back then.

Their estimate of 18,500 individuals is pretty sparse⁶ considering that these early humans were spread across the Old World. By comparison, some 25,000 gorillas⁷ and 21,000 chimps⁸ were concentrated in Africa alone. So a million years ago, we were essentially⁹ an endangered species. Here’s hoping our recovery is permanent.
 

1 proceedings   

n.进程，过程，议程；诉讼(程序)；公报

参考例句：

• He was released on bail pending committal proceedings. 他交保获释正在候审。
• to initiate legal proceedings against sb 对某人提起诉讼

2 census   

n.(官方的)人口调查，人口普查

参考例句：

• A census of population is taken every ten years.人口普查每10年进行一次。
• The census is taken one time every four years in our country.我国每四年一次人口普查。

3 DNA   

(缩)deoxyribonucleic acid 脱氧核糖核酸

参考例句：

• DNA is stored in the nucleus of a cell.脱氧核糖核酸储存于细胞的细胞核里。
• Gene mutations are alterations in the DNA code.基因突变是指DNA密码的改变。

4 parasites   

寄生物( parasite的名词复数 )； 靠他人为生的人； 诸虫

参考例句：

• These symptoms may be referable to virus infection rather than parasites. 这些症状也许是由病毒感染引起的，而与寄生虫无关。
• Kangaroos harbor a vast range of parasites. 袋鼠身上有各种各样的寄生虫。

5 hopping   

n. 跳跃 动词hop的现在分词形式

参考例句：

• The clubs in town are really hopping. 城里的俱乐部真够热闹的。
• I'm hopping over to Paris for the weekend. 我要去巴黎度周末。

6 sparse   

adj.稀疏的，稀稀落落的，薄的

参考例句：

• The teacher's house is in the suburb where the houses are sparse.老师的家在郊区，那里稀稀拉拉有几处房子。
• The sparse vegetation will only feed a small population of animals.稀疏的植物只够喂养少量的动物。

7 gorillas   

n.大猩猩( gorilla的名词复数 )；暴徒，打手

参考例句：

• the similitude between humans and gorillas 人类和大猩猩的相像
• Each family of gorillas is led by a great silverbacked patriarch. 每个大星星家族都由一个魁梧的、长着银色被毛的族长带领着。 来自《简明英汉词典》

8 chimps   

（非洲）黑猩猩( chimp的名词复数 )

参考例句：

• Chimps are too scarce, and too nearly human, to be routinely slaughtered for spare parts. 黑猩猩又太少，也太接近于人类，不可以作为人器官备用件说杀就杀。 来自英汉非文学 - 生命科学 - 医学的第四次革命
• And as nonprimates, they provoke fewer ethical and safety-related concerns than chimps or baboons. 而且作为非灵长类，就不会产生像用黑猩猩或狒狒那样的伦理和安全方面的顾虑。 来自英汉非文学 - 生命科学 - 医学的第四次革命

9 essentially   

adv.本质上，实质上，基本上

参考例句：

• Really great men are essentially modest.真正的伟人大都很谦虚。
• She is an essentially selfish person.她本质上是个自私自利的人。