英語聽力文摘 神奇的進化

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蠅蛆的進化

You may already know how the evolution of a new species happens. Two or more populations of one species have to be separated from each other, such as is the case with Darwin’s finches in the Galapagos.

Various populations of the same species of bird divided onto different islands, and because of this isolation they eventually evolved apart into different species. What can the problem of maggots teaches me?

These maggots provided evidence that the separate evolution that is the forerunner of new species does not have to be geographical or physical. You see, apple maggots were originally hawthornmaggots.

Apples weren’t introduced into North America until around 250 years ago, and some time after that, some of the hawthornmaggots shifted from feeding on hawthorn to feeding on apples, separating the maggots into two races.

The hawthorn and apple trees occupy the same lands though, so the two kinds of maggots were never physically separated. In fact, they' re still the same species. By looking at them, you can’t tell them apart.

However, the structure of their proteins and the food they prefer makes them quite different, clearly on their way to becoming new species. Their food preferences are so strong that scientists cannot lure them to the wrong fruit

This goes for mating too, which occurs on the fruit. Because the two maggots are still the same species they are capable of mating together, but they don’t. It’s probably only a matter of time before the maggots do evolve into different species.

也許你已經(jīng)知道一個新物種是怎樣進化的了。屬于某個物種的兩個或更多的生物族群之間不得不相互區(qū)分開來，達(dá)爾文研究的大龜群島上的雀科鳴禽就是一個例子。

同屬鳥禽的不同族群分布在不同的島上。因為這種隔離使得它們最終進化成不同的種類。

分離進化是新物種得以產(chǎn)生的先驅(qū)。這些蠅蛆證明了這種分離并不一定得是地理或地域上的。你看，蘋果蠅蛆原先還是山楂蠅蛆呢。

直到250年以前蘋果才被引進北美。不久之后，以山楂為生的蛆轉(zhuǎn)而以吃蘋果為生，使得蠅蛆分離為兩個物種。

然而蘋果蠅蛆和山楂蠅蛆同存于同一片土地，所以這兩種蠅蛆從未在地理上區(qū)分開來。事實上，他們?nèi)詫儆谕粋€物種。光是肉眼看，很難把它們區(qū)分開來。

但是，它們蛋白質(zhì)的結(jié)構(gòu)和它們偏好的食物不同使得它們差異很大，尤其是它們在進化成一個新物種的過程中表現(xiàn)得很明顯。它們對食物的偏好如此強烈以至于科學(xué)家們很難引誘它們?nèi)コ运鼈儾粣鄢缘臇|西上。

在交配上發(fā)生的例子和在水果上發(fā)生的一樣。這兩類蠅蛆都同屬蛆類，是可以進行配對的，但它們卻不會這樣做。也許，它們會進化成不同物種，這只是時間的問題。