Cosmos by Carl Sagan Read Free Book Online

animal is exquisitely made; should not a supremely competent Designer have been able to make the intended variety from the start? The fossil record implies trial and error, an inability to anticipate the future, features inconsistent with an efficient Great Designer (although not with a Designer of a more remote and indirect temperament).
    When I was a college undergraduate in the early 1950’s, I was fortunate enough to work in the laboratory of H. J. Muller, a great geneticist and the man who discovered that radiation produces mutations. Muller was the person who first called my attention to the Heike crab as an example of artificial selection. To learn the practical side of genetics, I spent many months working with fruit flies,
Drosophila melanogaster
(which means the black-bodied dew-lover)—tiny benign beings with two wings and big eyes. We kept them in pint milk bottles. We would cross two varieties to see what new forms emerged from the rearrangement of the parental genes, and from natural and induced mutations. The females would deposit their eggs on a kind of molasses the technicians placed inside the bottles; the bottles were stoppered; and we would wait two weeks for the fertilized eggs to become larvae, the larvae pupae, and the pupae to emerge as new adult fruit flies.
    One day I was looking through a low-power binocular microscope at a newly arrived batch of adult
Drosophila
immobilized with a little ether, and was busily separating the different varieties with a camel’s-hair brush. To my astonishment, I came upon something very different: not a small variation such as red eyes instead of white, or neck bristles instead of no neck bristles. This was another, and very well-functioning, kind of creature with much more prominent wings and long feathery antennae. Fate had arranged, I concluded, that an example of a major evolutionary change in a single generation, the very thing Muller had said could never happen, should take place in his own laboratory. It was my unhappy task to explain it to him.
    With heavy heart I knocked on his office door. “Come in,” came the muffled cry. I entered to discover the room darkened except for a single small lamp illuminating the stage of the microscopeat which he was working. In these gloomy surroundings I stumbled through my explanation. I had found a very different kind of fly. I was sure it had emerged from one of the pupae in the molasses. I didn’t mean to disturb Muller but … “Does it look more like Lepidoptera than Diptera?” he asked, his face illuminated from below. I didn’t know what this meant, so he had to explain: “Does it have big wings? Does it have feathery antennae?” I glumly nodded assent.
    Muller switched on the overhead light and smiled benignly. It was an old story. There was a kind of moth that had adapted to
Drosophila
genetics laboratories. It was nothing like a fruit fly and wanted nothing to do with fruit flies. What it wanted was the fruit flies’ molasses. In the brief time that the laboratory technician took to unstopper and stopper the milk bottle—for example, to add fruit flies—the mother moth made a dive-bombing pass, dropping her eggs on the run into the tasty molasses. I had not discovered a macro-mutation. I had merely stumbled upon another lovely adaptation in nature, itself the product of micromutation and natural selection.
    The secrets of evolution are death and time—the deaths of enormous numbers of lifeforms that were imperfectly adapted to the environment; and time for a long succession of small mutations that were
by accident
adaptive, time for the slow accumulation of patterns of favorable mutations. Part of the resistance to Darwin and Wallace derives from our difficulty in imagining the passage of the millennia, much less the aeons. What does seventy million years mean to beings who live only one-millionth as long? We are like butterflies who flutter for a day and think it is forever.
    What happened here on