The Darwinian Revolution II Charles Darwin

The Darwinian Revolution II
Charles Darwin

Charles Darwin (1809-1882)
1. Son of a prominent family (father and grandfather were physicians, mother was a Wedgwood)
2. Abandoned medical studies; studied to become an Anglican minister
3. Lacking direction, signs on to be the naturalist and gentleman companion of the skipper of the Beagle for a five year mapping project
  1. Social conventions of the time did not allow upper class captains to socialize with lower class crew; such arrangements were common
  2. Journey, originally meant for two years, becomes five - 1831-1836
4. Beset by illness and independently wealthy, devoted the rest of his life to study and writing on nature
5. His scientific output was enormous, and he was recognized as a leading naturalist long before publishing on evolution
The Voyage of the Beagle
1. Darwin proved to be an able observer and collector, and over the journey became a frequent and important correspondent with leading British naturalists
2. Important observations that influenced his thinking
  1. Noted changes across space as related bird varieties gave way to others in different environments
  2. Surprised to find that the environments of the Galapagos and the Cabo Verdes had not the same species, but rather variants of the species of nearby continents
  3. Noted the wide variety of finches on the Galapagos, but only in discussion with naturalists in Britain did he realize these were distinct species
3. His Beagle notebooks hint only once at the possibility that species might change across time, and not be immutable
Malthus and Natural Selection
1. After returning from the Beagle, Darwin becomes convinced of the reality of evolution, but lacked a mechanism to explain it
2. Finds and answer in the work of Robert Malthus's Essay on the Principle of Population (1798)
  1. Written to explain social change, not biological change
  2. Malthus argued that while population increases geometrically (2x2x2x2=16), food supply increases arithmetically (2+2+2+2=8)
  3. The resulting mismatch means that people must compete for food, and only swifter, stronger, hardier will get it
  4. This then, for Malthus, explains how societies develop over time
  5. It will also serve as an argument against "welfare" in the 19th century, as helping the poor only delays the inevitable
3. Darwin applies this to biology
  1. Burgeoning populations are kept in check by high mortality in a competition for resources
  2. Only the best adapted members of a population will get those resources and survive to produce offspring
Reluctance to publish
1. Insight came in 1838 - first sketched out an essay in 1842; prepared a longer manuscript by 1844
2. Initially reluctant because he felt his proactive idea needed more sustaining evidence, and he needed also to build his own reputation
3. Was also concerned about the reception to Robert Chamber's 1844 book, Vestiges of Creation
  1. Chambers argued that changes in species across time was part of God's original plan, and was built into their design
  2. Strongly criticized on religious, philosophical, and scientific grounds
  3. No serious discussion of evolution in the scientific community in the two decades after Beagle
4. Only a letter from Alfred Wallace (1823-1913), who had independently reached the same conclusion, forced him to publish
The Origin of Species (1859 - several revisions followed)
1. Full title: On the Origin of Species by Means of Natural Selection, or the Preservation of Favored Races in the Struggle for Life
2. Organized in three sections
  1. Lays out the basic idea
    1. lacking a lot of hard evidence, depended heavily on analogies from livestock breeding
    2. relied heavily on Malthus, using an analogy of a a tightly packed sphere of wedges, constantly being hammered down
  2. Laid out possible critiques to his idea, with his responses
    1. Examined a number of complex behaviors and structures and worked to show they could have developed through incremental change
    2. On the lack of fossils (fossil discoveries being very poor at the time), argued that fossils naturally were few in number and very random
  3. Examined a number of elements he believed were better explained by his ideas than by special creation
    1. Evidence for species extinction over time
    2. Distribution of different species across the Earth - widely differing species in similar environments
    3. Numerous collections of apparently related but distinct species
    4. Striking similarities of embryos of extremely different species
    5. Existence of vestigial or non-functioning organs and structures
  4. Only hints at the question of humans, which he takes up in The Descent of Man (1871)
  5. Notable that Origins appears before:
    1. Genetics
    2. Biochemistry
    3. Any evidence that the Earth was more than a few hundred thousand years old
    4. Before any human or humanoid fossils had been found
    5. Before anything close to a well developed fossil record had been unearthed
Became a quick sensation, and produced a number of objections upon publication
1. Wouldn't a new trait be diluted across several generations?
  1. This happens with livestock if they are allowed to breed freely
  2. Darwin did not know the work of Gregor Mendel (1822-1888)
    1. Gregor worked out the concept of dominant and recessive traits in 1865
    2. But he published in an obscure journal, and his work was not known until decades later
2. Physicists argued that neither the Earth nor the Sun could be old enough
  1. Working from laws of thermodynamics, physicists argued that the Earth and the Sun both would have cooled much to soon
  2. No one knew that the Earth's mantle was kept warm by radioactive isotopes or that the Sun was heated by hydrogen fusion
3. Conservative Victorian society objected, largely on religious grounds, though to a great degree this becomes more important later
4. Darwin himself becomes something of a Neo-Lamarkian has he responded to his critics, though he never abandoned natural selection