如有一只老鼠和它的后代一直生活在適宜個頭長大的環(huán)境中，那么到進(jìn)化成大象那樣的“大塊頭”需要多久,？研究人員為這個有趣的問題找到了答案——2400萬代,。
2月1日，英國布里斯托爾大學(xué)發(fā)布公告說，該校研究人員參與的一個國際研究小組分析了地球歷史上各種生物的進(jìn)化情況,，計算得出了這一結(jié)論,。由于小型動物和大型動物每一代的年齡不一樣，如老鼠只能活兩三年,，而大象可以活幾十年,，研究人員在描述這個結(jié)果時沒有用具體的時間，而是用了“代”這個遺傳學(xué)上的常用概念,。
研究還顯示,，如果是兔子般的“身材”，那么進(jìn)化到大象那么大,，需要約1000萬代,。
不過，海洋動物朝大型方向進(jìn)化的速度要快一些,，研究人員在分析了鯨魚的進(jìn)化歷史后認(rèn)為,，海洋動物在進(jìn)化中個頭增長的速率約是陸地動物的兩倍。研究人員認(rèn)為,，這可能是因?yàn)樗懈×?，更容易支撐巨大的身體和體重。
與變大相反的是變小,，研究人員發(fā)現(xiàn)這較為容易,。如果是大象一直生活在適宜變小的環(huán)境中，它在進(jìn)化中變小的速率是前述變大速率的10倍以上,。這種差異可能是因?yàn)閺男∽兇笮枰容^復(fù)雜的進(jìn)化,，如骨骼需要變得能承受更大的體重，而從大變小則沒有這么多麻煩,，還會因?yàn)樗枋澄锔俣菀住?/p>
這項(xiàng)研究報告已發(fā)表在新一期美國《國家科學(xué)院院刊》（PNAS）上,。（生物谷 Bioon.com）
doi:10.1073/pnas.1120774109
PMC:
PMID:
The maximum rate of mammal evolution
Alistair R. Evans, David Jones, Alison G. Boyer, James H. Brown, Daniel P. Costa, S. K. Morgan Ernest, Erich M. G. Fitzgerald, Mikael Fortelius, John L. Gittleman, Marcus J. Hamilton, Larisa E. Harding, Kari Lintulaakso, S. Kathleen Lyons, Jordan G. Okie, Juha J. Saarinen, Richard M. Sibly, Felisa A. Smith, Patrick R. Stephens, Jessica M. Theodor, and Mark D. Uhen
How fast can a mammal evolve from the size of a mouse to the size of an elephant? Achieving such a large transformation calls for major biological reorganization. Thus, the speed at which this occurs has important implications for extensive faunal changes, including adaptive radiations and recovery from mass extinctions. To quantify the pace of large-scale evolution we developed a metric, clade maximum rate, which represents the maximum evolutionary rate of a trait within a clade. We applied this metric to body mass evolution in mammals over the last 70 million years, during which multiple large evolutionary transitions occurred in oceans and on continents and islands. Our computations suggest that it took a minimum of 1.6, 5.1, and 10 million generations for terrestrial mammal mass to increase 100-, and 1,000-, and 5,000-fold, respectively. Values for whales were down to half the length (i.e., 1.1, 3, and 5 million generations), perhaps due to the reduced mechanical constraints of living in an aquatic environment. When differences in generation time are considered, we find an exponential increase in maximum mammal body mass during the 35 million years following the Cretaceous–Paleogene (K–Pg) extinction event. Our results also indicate a basic asymmetry in macroevolution: very large decreases (such as extreme insular dwarfism) can happen at more than 10 times the rate of increases. Our findings allow more rigorous comparisons of microevolutionary and macroevolutionary patterns and processes.
