時尚雙語:人類祖先並不聰明

A monkey-like animal seen as an ancestor of monkeys, apes and humans was not as brainy(1) as expected, according to scientists who analyzed its nicely preserved 29-million-year-old skull.

The finding indicated that primate(2) brain enlargement evolved later than once thought, the researchers said on Monday.

They analyzed a remarkably well-preserved fossilized(3) skull of the little primate Aegyptopithecus(4) zeuxis, which lived in the trees and ate fruit and leaves about 29 million years ago in warm forests in what is now an Egyptian desert.

A technique called microcomputerized tomography(5) scanning -- a computerized X-ray method also called micro-CT -- allowed them to determine the dimensions of the animal's brain.

"What was astonishing is how small this brain is," Duke University primatologist Elwyn Simons, who led the study in the Proceedings of the National Academy of Sciences, said in a telephone interview.

"You can also see it's a pretty darn primitive brain. It would be small for a monkey or an ape," Simons added. "So it's telling us that the speed of achievement of brain enlargement in primates was a little slower than perhaps we had thought."

This skull of a small female was uncovered in a quarry(6) southwest of Cairo in 2004. It was better preserved than another skull of a larger male of the species found in the same area in 1966.

Based on earlier finds, scientists had theorized the species had a relatively large brain. Instead, it had a brain that might have been even smaller than that of a modern lemur, a primate with primitive traits.

Simons said that when this primate lived, Africa was an island, limiting the competition for survival. Simons said brain enlargement may have evolved in this lineage after Africa became connected to Asia, bringing in more animals including new and dangerous predators.

"Brain-volume enlargement is favored under conditions of competition because you need to be smarter," Simons said.

科學家對一個保存良好的2900萬年前的頭骨進行研究，發現這種類猴的猴子、猿和人類祖先並沒有預想得那麼聰明。

週一，研究人員們說此發現顯示靈長類大腦進化時間比原來認爲的要晚。

這個小巧的古埃及猿頭骨化石保存十分完好。此種靈長類動物生活在2900萬年前的溫暖埃及叢林，以樹爲家，以果爲食，但是現在這片叢林已經變成沙漠了。

一項被稱爲微型電子計算機X線斷層掃描的技術可以幫助測算動物大腦尺寸，它也可被稱爲微CT。

杜克大學靈長類動物學家Elwyn Simons在電話採訪中說：“我們很驚訝它的大腦竟然如此之小。” 由他負責的本次研究被刊登在美國國家科學院報中。

Simons說：“它雖然是一個靈長類頭骨，但是比猴子或者猿的都要小。也就是說靈長類動物大腦的飛速發展比我們原來推算的要慢一點。”

這個小的女性頭骨在2004年被髮掘於開羅西南部一個採石場中。它的保存狀況好於1966年在同一地點發現的另一個稍大的同類男性頭骨。

根據之前的研究，科學家們推斷這種動物應該擁有相對大的大腦。但是它的大腦卻比具有原始特點的現代狐猴的還小。

Simons說這種動物生活的時候非洲還是一個島嶼，沒有生存競爭。Simons認爲他們的大腦發展發生在亞非大陸相連的時候，因爲很多動物包括新的和危險的食肉動物都來到了這裏。

他說：“競爭促進腦容量的擴展，因爲你如果不變得更聰明就得死。”