TF第52篇Beaks of Darwin_ Finches
1835 年，在他提出进化论之前，查尔斯·达尔文从孤立的加拉帕戈斯群岛收集了 13 种以前不为人知的雀类的标本。加拉帕戈斯雀与生活在南美洲大陆的一种雀非常相似，但每种加拉帕戈斯雀都有一个独特的形状不同的喙。群岛[加拉帕戈斯群岛]，为了不同的目的，已经采取和修改了一个物种。“Th这就是达尔文自然选择进化论的精髓：具有特定喙形的鸟类得以幸存和繁殖，因为它们的喙使它们能够很好地适应使用特定的食物来源。就这样，一个从大陆来到加拉帕戈斯的原始物种最终进化成了13个新物种。
13 种雀科物种的喙与其食物来源之间的对应关系立即向达尔文表明进化塑造了它们。如果他关于祖先雀鸟的喙是由进化形成的说法是正确的，那么应该可以看到不同种类的雀鸟发挥它们的进化作用，每一种都使用它们的喙来获得它们特定的食物特性。这四个例如，那些用喙压碎种子的物种应该以不同的种子为食，那些喙较粗的物种专攻难以压碎的种子。
许多生物学家在达尔文之后访问了加拉帕戈斯群岛，但直到 100 年后，当伟大的博物学家大卫·莱克（avid Lack）终于在 1938 年开始着手对这些鸟类进行了整整五个月的密切观察时，他的假设才进行了这一关键测试，他的观察似乎反对达尔文的提议。莱克经常观察到许多不同种类的雀类以同一种子为食。我们现在知道，在雨季研究鸟类是拉克的不幸，当时食物充足。在这样的冲水时期，雀的喙并不重要。小种子是如此丰富，以至于所有物种的鸟类都能获得足够的食物。
成功验证达尔文关于加拉帕戈斯雀的喙适应不同食物来源的建议的关键：证明是耐心。从 1973 年开始，普林斯顿大学的 Peter 和 Rosemary Grant 以及他们的几代学生在加拉帕戈斯群岛中心的一个名为 aphne Major 的小岛上研究了中型地雀 Geospiza fortis。这些雀类优先以潮湿年份植物大量生产的小而嫩的种子为食。只有当小种子在长时间干燥的天气中枯竭并且植物产生很少的种子时，鸟类才会求助于更大、更干燥的种子，这些种子更难压碎。
The Grants quantified beak shape among the medium ground finches of aphne Major by carefully measuring beak depth(width of beak, from top to bottom,at its base) on individual birds. Measuring many birds every year, they were able to assemble a detailed portrait of evolution in action.' The Grants found that beak depth changed from one year to the next in a predictable fashion. uring droughts, plants: produced few seeds and all available small seeds were quickly eaten, leaving large seeds as the remaining source of food. s a result, birds with large beaks survived better, because they were better able to break open these large seeds. onsequently, the average beak depth of birds in the population increased the next year,only to decrease again when wet seasons returned.
ould these changes in beak dimension reflect the action of natural selection? n alternative possibility might be that the changes in beak depth do not reflect changes in gene frequencies, but rather are simply a response to diet- -perhaps during lean times the birds become malnourished and then grow stouter beaks, for example. If this were the case, it would not be genetics but environment alone that influences beak size. To rule out this possibility, the Grants measured the relation of parent bill size to offspring beak size, examining many broods over several years. The depth of the beak was passed down faithfully from one generation to the next, regardless of environmental conditions, suggesting that the differences in beak size indeed reflected genetic differences.
1. 1835 年，在他提出进化论之前，查尔斯·达尔文从孤立的加拉帕戈斯群岛收集了 13 种以前不为人知的雀类的标本。加拉帕戈斯雀与生活在南美洲大陆的一种雀非常相似，但每种加拉帕戈斯雀都有一个独特的形状不同的喙。群岛[加拉帕戈斯群岛]，为了不同的目的，已经采取和修改了一个物种。“Th这就是达尔文自然选择进化论的精髓：具有特定喙形的鸟类得以幸存和繁殖，因为它们的喙使它们能够很好地适应使用特定的食物来源。就这样，一个从大陆来到加拉帕戈斯的原始物种最终进化成了13个新物种。
2.The correspondence between the beaks of the 13 finch species and their food source immediately suggested to arwin that evolution had shaped them. If his suggestion that the beak of an ancestral finch had been shaped by evolution is correct,then it ought to be possible to see the different species of finches acting out their evolutionary roles, each using their beaks to acquire their particular food specialty.The four species that crush seeds within their beaks, for example, should feed on different seeds, those with stouter beaks specializing in harder-to- crush seeds.
