Evolution and Wheels
In the past, evolutionary biologists contemplating the absence of wheels in nature agreed that the explanation was not undesirability: wheels would be good for animals, just as they are for us. Animals were prevented from evolving wheels, the biologists reasoned, by the following dilemma: living cells in an animals body are connected to the heart by blood vessels, and to the brain by nerves. Because a rotating joint is essential to a wheel, a wheel made of living cells would twist its artery vein and nerve connections at the first revolution, making living impracticable.
However, there is a flaw in the argument that the evolution of wheeled animals was thwarted by the insoluble joint problem. The theory fails to explain why animals have not evolved wheels of dead tissue with no need for arteries and nerves. Countless animals, including us, bear external structures without blood supply or nerves - for example, our hair and fingernails, or the scales, claws, and ho rns of other animals. Why have rats not evolved bony wheels, similar to roller skates? Paws might be more useful than wheels in some situations, but cats claws are retractable: why not retractable wheels? We thus arrive at the serious biological paradox flippantly termed the RRR dilemma: natures failure to produce rats with retractable roller skates.
上一篇: 英语四级考试阅读提高训练(9)
下一篇: 12月大学英语四级阅读理解最常见短语三
体坛英语资讯:Manchester United beat Bournemouth in English Premier League
体坛英语资讯:Messi deserves to win a World Cup, says Peru coach
体坛英语资讯:Midfielder Demirbay extends contract with Hoffenheim
体坛英语资讯:Turkeys Erzurum applies to host 2026 Winter Olympics
体坛英语资讯:Olympic champion Li Xuerui returns to international badminton after 600 days
体坛英语资讯:Bayern take vital Champions League win away to Sevilla
体坛英语资讯:Bayern trash Leverkusen 6-2 in German Cup semifinal
体坛英语资讯:SWM shows support for Iniesta joining Chongqing Lifan
体坛英语资讯:US, Latin American fans lead World Cup ticket demand
体坛英语资讯:Leipzigs Laimer sidelined with injury
体坛英语资讯:Angolas 1o de Agosto, Petro handball teams through to semi-finals
体坛英语资讯:Neymar must join Real Madrid to be worlds best: Rivaldo
体坛英语资讯:Chinas Lyu upsets Fu to reach last 16 at snooker worlds
体坛英语资讯:Indonesia sets 2-gold target in wall climbing in Asian Games
体坛英语资讯:Zhejiang Guangsha make history to reach CBA finals
体坛英语资讯:Coutinho, Jesus to shine at World Cup, says Neymar
体坛英语资讯:OSullivan eliminated after making 147 at World Snooker China Open
体坛英语资讯:Polish yacht docks in Tasmania after clinching Antarctic circumnavigation record
体坛英语资讯:2018 AFC Womens Asian Cup kicks off Friday with China up against Thailand
体坛英语资讯:Ten-man Fluminense beat Cruzeiro in Brazils Serie A
体坛英语资讯:Defending champions Japan held 0-0 by S. Korea in AFC Womens Asian Cup 2018
体坛英语资讯:Bremens head coach Kohfeldt pens extension
体坛英语资讯:Kenyans hail Gor CAF Confed Cup group stage progress
体坛英语资讯:Aguero unlikely to be fit for start of World Cup, says doctor
体坛英语资讯:China beat Jordan 8-1 in AFC Womens Asian Cup 2018
体坛英语资讯:Feature: China, Japan players celebrate ping-pong friendship in Nagoya
体坛英语资讯:Commentary: Bale absence highlights future problems for Real Madrid
体坛英语资讯:Argentina, Uruguay, Paraguay reach venue agreement for 2030 World Cup
体坛英语资讯:Real Madrid beat Panathinaikos 89-82 in Game 2
体坛英语资讯:Hannover overcome Bremen 2-1 in German Bundesliga