目前日期文章:201708 (2)

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AA new way to use DNA to peer into the history of humanity is rewriting what experts know about our long-extinct cousins, the Neanderthals, US researchers said on Monday.

Previous research has suggested that near the end of their existence about 40,000 years ago, only about 1,000 Neanderthals were left on Earth.

The new study, reported in the Proceedings of the National Academy of Sciences, shows their population was far larger — likely numbering in the tens of thousands — though they existed in isolated groups across Europe.

The genetic clues include Neanderthal DNA that contains mutations that usually occur in small populations with little genetic diversity. Also, Neanderthal remains — found in various locations — are genetically different from each other.

“The idea is that there are these small, geographically isolated populations, like islands, that sometimes interact, but it’s a pain to move from island to island,” said co-author Ryan Bohlender, a post-doctoral fellow at the MD Anderson Cancer Center at the University of Texas. “So, they tend to stay with their own populations.”

Using a new method to analyze DNA sequence data, researchers also found that Neanderthals split from another mysterious lineage, known as the Denisovans, about 744,000 years ago, much earlier than any other estimation of the split.

After that, the global Neanderthal population grew to tens of thousands.

“This hypothesis is against conventional wisdom, but it makes more sense than the conventional wisdom,” said lead author Alan Rogers, a professor in the department of anthropology at the University of Utah.

“There’s a rich Neanderthal fossil record. There are lots of Neanderthal sites,” he said. “It’s hard to imagine that there would be so many of them if there were only 1,000 individuals in the whole world.”

Very little is known about the Denisovans, sometimes described as the Eastern cousins of Neanderthals. Only a few pieces of their remains — including some teeth and a pinkie bone — have ever been found.

Denisovans and Neanderthals mated with the ancestors of modern humans, who emerged from Africa about 60,000 years ago.

Researchers are not sure exactly why Neanderthals or Denisovans eventually died out, but it could have been due to harsh climate, or competition for scarce resources with modern humans.

The study was based on comparing the genomes of four human populations: Modern Eurasians, modern Africans, Neanderthals and Denisovans. This improved statistical method, called legofit, helped researchers estimate the percentage of Neanderthal genes flowing into modern Eurasian populations — which they confirmed was about 2 percent.

Its method revealed the date at which these ancestral populations diverged from each other, and their population sizes.

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苏格拉底是单身汉的时候,和几个朋友一起住在一间只有七八平方米的小屋里。尽管生活非常不便,但是,他一天到晚总是乐呵呵的。

有人问他:“那么多人挤在一起,连转个身都困难,有什么可乐的?”

苏格拉底说:“朋友们在一块儿,随时都可以交换思想,交流感情,这难道不是很值得高兴的事吗?”

过了一段时间,朋友们一个个相继成家了,先后搬了出去。屋子里只剩下苏格拉底一个人,但是他每天仍然很快活。

那人又问:“你一个人孤孤单单的,有什么好高兴的?”

“我有很多书啊!一本书就是一个老师。和这么多老师在一起,时时刻刻都可以向它们请教,这怎能不令人高兴呢?”

几年后,苏格拉底也成了家,搬进了一座大楼里。这座大楼有七层,他的家在最底层。底层在这座楼里环境是最差的,上面老是往下面泼污水,丢死老鼠、破鞋子、臭袜子和杂七杂八的脏东西,那人见他还是一副自得其乐的样子,好奇地问:“你住这样的房间,也感到高兴吗?”

“是呀!你不知道住一楼有多少妙处啊!比如,进门不用爬很高的楼梯;搬东西方便,不必花很大的劲;朋友来访容易,用不着一层楼一层楼地去叩门询问……特别让我满意的是,可以在空地上养一丛一丛的花,种一畦一畦的菜,这些乐趣呀,数之不尽啊!”苏格拉底情不自禁地说。

过了一年,苏格拉底把一层的房间让给了一位朋友,这位朋友家有一个偏瘫的老人,上下楼很不方便。他搬到了楼房的最高层——第七层,可是他每天仍是快快乐乐的。

那人揶揄地问:“先生,住七层楼是不是也有许多好处呀?”

苏格拉底说:“是啊,好处可真不少呢!仅举几例吧:每天上下楼,这是很好的锻炼机会,有利于身体健康;光线好,看书写文章不伤眼睛;没有人在头顶干扰,白天黑夜都非常安静。”

后来,那人遇到苏格拉底的学生柏拉图,问道:“你的老师总是那么快快乐乐,可我却感到,他每次所处的环境并不那么好呀。”

柏拉图说:“决定一个人心情的,不是在于环境,而在于心境。”

在工作和生活中,平和、乐观的心态是最重要的。任何对客观环境的不满和怨天尤人都是无济于事的,只有以积极向上的精神去面对工作和生活,才是解决问题的最佳方法。

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