Charles Darwin (1809-1882)

The voyage on the Beagle (1831-36):
Reads Lyell’s Principles: uniformitarianism and deep time
Darwin’s finches in the Galapagos with their gradation of beaks, and each island being like a little world, with a high number of endemic species.

In Structure and Distribution of Coral Reefs (1842) he rejects Lyell’s theory that coral reefs are formed by corals on top of extinct volcanic crates submerged by a few feet of water. Instead he proposes that the sea floor level slowly subsided while the corals keeps growing one atop of the older dead corals. Hence, atolls result from fringe ot barrier reefs once the land subsides. The process, of course, must take a very long time.
Upon drilling, we know now that coralline limestone is several thousand feet deep.

Darwin’s The Origin of Species (1859) many editions with enlargements and modifications. The two basic ideas are that of the tree of life and of natural selection.

Tree of life: living organisms are organized as the limbs of a great tree, with more general groups branching into lesss general ones. Moreover:

1. species change over time (transmutation)
2. some species go extinct (extinction)
3. some species keep diverging, splitting eventually into multiple descendent species (common descent).

NOTE:extinction and common descent are not necessary for transmutation. For example, Lamark rejected extinction and common descent (species don't split).

Natural Selection is the principal mechanism for descent with modifications (evolution). Its existence can be established by considering the following:

First Fact: The Struggle for Existence

• intraspecific: two canids struggling for scarce food; several mistletoes parasitizing the same tree and trying to attract birds to disseminate their seeds, etc.
  
• interspecific: the same mistletoes competing with other fruit bearing plants; a plant’s seed germinating in a crowds field, etc.
  
• environmental: a plant at the edge of the desert struggling against drought, etc.
  

NOTES:
In equatorial areas, the struggles is mostly intra and inter-specific, while in hostile environments (e.g., Arctic regions, or high mountains) the competition is mostly environmental.
Intrageneric struggle is very intense because species of the same genus are close in structure and often in habits. This is the basis for the Principle of Divergence, by which the more diversified the descendants from one species become, the more successful they’ll be.

• an annual plant producing only 2 seeds a year will have 2ⁿ descendants in n years. In general, organisms tend to increase in geometric ratios.
  
• domestic animals run wild in new environments often have population explosions.
  

NOTES:
Malthus’ influence.
The complexity of ecological interactions: clover-humble bees-mice-cats.

• How could complex organs be the product of evolution?
  

Answer: They can be result of small modifications, each favorable, through a very long period of time. Example, eye starting with nerves which are light sensitive. This addresses the issue of irreducible complexity (the all or nothing objection) advanced by Paley with respect to the eye.
NOTE: In his study of orchids (1862) D. also notes that their various reproductive contrivances for attracting insects are formed out of pre-existing material (typically petals).
In addition, often organs are not contrivances but contraptions (Gould’s panda’s thumb).

• How can different species descending from on parent have become so geographically separated?
  

Answer: we don’t know of the climatic and geographical changes which may have facilitated migration or brought about the extinction of a species in the intermediate region.

• How come we don’t observe intermediate forms all around us? Why are not all organic being blended together in an inextricable chaos?
  

Answer: Intermediate forms existed not between existing forms, but between each existing form and some extinct one. Moreover, the Principle of Divergence tells us that intermediate forms are tend to become extinct.

• Why doesn’t the geological record show the innumerable intermediate forms between the present ones and other extinct ones?
  

Answer: the geological record is sorely incomplete. In addition, the principle of Divergence tells us that the intermediate species become extinct quickly.

• Thompson (Kelvin) says there has not been enough time.
  

Answer: we don’t know at what rate species change, and we still don’t know enough of nature to exclude a time longer than Kelvin allows.

• Forms of life are arranged in few great classes and in groups subordinate to groups. The theory of species creation is unable to explain this fact. By contrast, the principle of divergence explains the tendency of large groups to increase in size and diverge in character,
  
• The principle of divergence also explains the extinction of older intermediate varieties, and therefore gives an account of the fossil record, incomplete as it is.
  
• Cases of want of perfection involving vestigial or rudimentary organs/features: upland geese which almost never swim have webbed feet; thrushes that dive and feed on sub-aquatic insects; the sting of bees causing their own deaths; occasional horses with stripes on their legs and shoulders etc.; at times organs are badly designed, more contractions than contrivances. Species creation cannot explain this, while evolution can.
  
• Interspecific breeding (e.g. horse/donkey) follows the same inheritance laws as intraspecific breeding (varieties of same species). This is explained by species being not essentially different from varieties. But for creationism, species are independently created while varieties are produced by secondary laws, so that the two are essentially different.
  
• Oceanic islands are occupied by few species, but often with peculiar subspecies. Divergence explains this, while separate creation does not.
  
• Homology: the bone structure is the same in hand of man, fin of porpoise, wing of bat, and leg of horse. Descent with modification explain this, but separate creation does not.
  
• Embryos of a fish, bird, mammal are very much alike even if the adults are not (e.g., embryos of mammals deveop a 2 chamber heart, like fish). Descent with modification explain this, but separate creation does not.
  

• There was no sense of deep time
  
• the geological record has been taken to be complete, and it doesn’t show the insensible variaations from extinct species to present ones.
  
• We are slow in admitting great chneges of which we don’t see the steps. But Lyell has disabused us of this prejudice.
  

• Sexual Selection. Introduced in the second part of Descent, to account for features like the peacok tail (large tails directly favored by females) or deer antlers (competition with other males in order to get females)
  
• Origin of Man: In The Origin, D. had merely stated that his theory might shed some light about the orign of man. In the first part of Descent he tried to make good on his claim. The procedure is predictible: morphologically, we are quite similar to the great apes; as Huxley noted, the foot of the gorilla is closer to ours thatn to that of the orongutan’s. the real problem has to do with higher functions (e.g. intelligence) and their manifestations, e.g., moral behavior, religious beliefs, etc. His explanation was that religious beliefs favor the sense of remorse, which in turn supprts morality, which in turn favors the group, and indirectly the individual (groups w/t any moral sense cannot survive for long).
  

NOTE: Wallace’s rejection of D’s thesis about man’s higher powers.

• problem of evil
  
• collapse of the argument from design
  
• being an evolutionary product, our intelligence cannot deal with transcendent issues.
  

• Some Christians (e.g., the Catholic st. George Mivart and the Calvinist McCosh) argued that the element of chance involved in the production of variations is not enough to produce the variety we observe, and appealed insted to God as the source of evolution. In this wasy, God was a constant participant on the history of life. Evolution, then has a predetermined providential direction for the good.
  
• Many religious tenets could be reinterpreted in evolutionay terms. So, the struggle between spirit and flesh could be understood as that between recent and earlier evolutionary aspects of man (e.g., Lyman Abbott-1897). The presence of suffering could be explained away as the inevitable byprodut of the evolutionary process (Asa Grey).
  

• What happens to the Bible story? was there an Adam; and if not, what of the original sin? what of Christ’s redemptive mission?
  
• Various attempts at repression of Darwinian teachers and religious thinkers (e.g., Mivart)
  
• Catholic condemnation of evolution as applied to man, including the body) (1893)
  
• Overt anti-clerical and irreligious position of many Darwinists (e.g.,Haeckel), or at least agnostic position (Huxley).