breeds. All are dogs; they recognize each other as such, communicate by the mysterious signals particular to their species,and interbreed to give viable offspring. This diversity is human-made. At the start, there was a single variety of wolf or jackal that established some kind of mutually beneficial association with a human group. From then on, breeders created all the existing varieties artificially, using empirically devised methods based on selection of appropriate progenitors. This history, which was repeated with horses, cattle, chickens, cats, and other domestic animals, as well as with a number of plants, goes back to early days of human development prior to any written record.
Today, we know the cause of diversity. It is due to modifications, or mutations, in the DNA, such that a slightly altered blueprint is transmitted from parent to offspring. This, again, was totally unknown to Darwin. But he was keenly aware of the existence of diversity in the living world and of its role in allowing breeders to use artificial selection in an empirically purposeful manner to generate cows that gave more milk, sheep that yielded thicker wool or better meat, horses that ran faster or carried heavier loads, cereals more resistant to cold or drought, and so on.
Malthus introduced the notion of the âstruggle for lifeâ
Another major influence on Darwinâs thinking was a book by the English clergyman and economist Thomas Robert Malthus (1766â1834), titled
Essay on the Principle of Population as It Affects the Future Improvement of Society.
In this book, first published in 1798, but still popular in Darwinâs time, Malthus contrasted the exponential growth of human populations against the linear growth of resources, inevitably leading to a situation where consumers outgrow resources and start competing for them. This situation, embodied in the celebratedphrase âstruggle for life,â could, according to Malthus, only be avoided by limiting the birthrate, a doctrine that has become known as Malthusianism.
Natural selection lets the âstruggle for lifeâ choose passively among the diversity created by the imperfections of heredity
Putting together natural diversity and struggle for life, Darwin arrived at the conclusion, evident for us today but visionary at the time, that, in any natural situation where there is competition for limited resources, those varieties most apt to survive and, especially, produce progeny under the prevailing conditions must automatically become preponderant ( fig. 7.1 ). Hence the subtitle Darwin gave to his book:
The Preservation of Favoured Races in the Struggle for Life.
In this new view, selection, rather than being purposefully directed toward a predefined end, as in its artificial, human-devised form (such as dog breeding and the like), is taken to occur naturally, automatically, without preconceived intention. Here is where Darwinâs ideas encountered the strongest resistance, lasting up to the present day; they implied a lack of purpose in nature.
Darwin conceived his theory during his famous voyage, from 1831 to 1836, on the
Beagle,
which notably led him to visit the Galápagos Islands. It is there that he made one of his most perceptive observations, namely that the finches on each island had, during their long geographical isolation, acquired differently shaped beaks adapted, in each case, to the locally available food, a paradigmatic instance of natural selection ( fig. 7.2 ). Nevertheless, Darwin continually put off the publication of his theory, patiently accumulating more evidence that would either support it or disprove it, in the true spirit of objective science. It is only when Darwin was informed that his colleague Alfred Russel Wallace (1823â1913) had conceived the same theory that he decided to rush into print. Much has been written about the poor place accorded to Wallace by posterity. He certainly deserves credit for having
Today, we know the cause of diversity. It is due to modifications, or mutations, in the DNA, such that a slightly altered blueprint is transmitted from parent to offspring. This, again, was totally unknown to Darwin. But he was keenly aware of the existence of diversity in the living world and of its role in allowing breeders to use artificial selection in an empirically purposeful manner to generate cows that gave more milk, sheep that yielded thicker wool or better meat, horses that ran faster or carried heavier loads, cereals more resistant to cold or drought, and so on.
Malthus introduced the notion of the âstruggle for lifeâ
Another major influence on Darwinâs thinking was a book by the English clergyman and economist Thomas Robert Malthus (1766â1834), titled
Essay on the Principle of Population as It Affects the Future Improvement of Society.
In this book, first published in 1798, but still popular in Darwinâs time, Malthus contrasted the exponential growth of human populations against the linear growth of resources, inevitably leading to a situation where consumers outgrow resources and start competing for them. This situation, embodied in the celebratedphrase âstruggle for life,â could, according to Malthus, only be avoided by limiting the birthrate, a doctrine that has become known as Malthusianism.
Natural selection lets the âstruggle for lifeâ choose passively among the diversity created by the imperfections of heredity
Putting together natural diversity and struggle for life, Darwin arrived at the conclusion, evident for us today but visionary at the time, that, in any natural situation where there is competition for limited resources, those varieties most apt to survive and, especially, produce progeny under the prevailing conditions must automatically become preponderant ( fig. 7.1 ). Hence the subtitle Darwin gave to his book:
The Preservation of Favoured Races in the Struggle for Life.
In this new view, selection, rather than being purposefully directed toward a predefined end, as in its artificial, human-devised form (such as dog breeding and the like), is taken to occur naturally, automatically, without preconceived intention. Here is where Darwinâs ideas encountered the strongest resistance, lasting up to the present day; they implied a lack of purpose in nature.
Darwin conceived his theory during his famous voyage, from 1831 to 1836, on the
Beagle,
which notably led him to visit the Galápagos Islands. It is there that he made one of his most perceptive observations, namely that the finches on each island had, during their long geographical isolation, acquired differently shaped beaks adapted, in each case, to the locally available food, a paradigmatic instance of natural selection ( fig. 7.2 ). Nevertheless, Darwin continually put off the publication of his theory, patiently accumulating more evidence that would either support it or disprove it, in the true spirit of objective science. It is only when Darwin was informed that his colleague Alfred Russel Wallace (1823â1913) had conceived the same theory that he decided to rush into print. Much has been written about the poor place accorded to Wallace by posterity. He certainly deserves credit for having
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