CPSP118G Spring Semester: Earth, Life & Time Colloquium
Charles Darwin and the Discovery of Evolution
Thomas R. Holtz, Jr.
Charles Robert Darwin (1809-1882)
Childhood and Education:
- Born same day as Abraham Lincoln (Feb. 12, 1809)
- Wealthy family of doctors
- Only a mediocre school kid, more interested in chasing rats, shooting birds, and
playing with dogs
- In 1825 went off to University of Edinburgh to study medicine (like dad and granddad).
- Did not like the sight of blood, and found medicine boring
- Took a geology class, found it boring too
- Did learn taxidermy on the side, from a freed Guyana slave
- Over summer vacation, would learn about local wildlife
- 1827, quit med school
- In 1827, went to Christ's College at Cambridge University to study for the clergy
- Did not take to studying very much
- Was VERY impressed by Botany classes with John Henslow,
and began to take more interest in Natural History
- By Feb. 1829, was already doubting he could be a clergyman, and was more interested
in studying Nature
- Began to dream about traveling to South America (or anyplace in the tropics)
- Graduated in 1831, plans to travel to the Canary's with a friend fell apart with the
- Around graduation time, saw a lecture by geologist Adam Sedgwick,
and was hooked on geology! Studied field geology with Sedgwick, and learned of Charles Lyell's
Principles of Geology
- Coming back from Wales with Sedgwick, found out position of "Captain's Companion"
available on the HMS Beagle
for its five year mapping mission
- Captain Robert FitzRoy,
as a member of the upper class, would not be allowed to fraternize with the crew
- The person would be expected to serve as naturalist (at least in part) for this
- Henslow recommend that Darwin read the Principles of Geology, with the warning
that he "on no account accept the views therein advocated"
- Beagle left Plymouth on Dec. 27, 1831
- Darwin immediately fell seasick...
- At Cape Verde Islands, noted a shell bed 45 feet above sealevel, not quite parallel
with sea level. Supported Lyellian view of uplift.
- Beagle mapped South America
- After 3 crewmen died, the ship's surgeon left. (This may also be because HE was
supposed to have been the naturalist).
- Darwin collected many living plants and animals, but also rocks and fossils
- Noted that the fossil forms were more similar to modern South American animals, though often of much larger size, than to comparably-aged fossils from Europe
- Found evidence of terrestrial-marine-terrestrial transitions in the rock record, even for relatively recent rocks
- Witnessed an earthquake, noting the rise of land in the region and seeing it as supporting Lyell's uniformitarian views
- Sept. 15, 1835: first sighting of Galápagos
- Sept. 16-Oct. 20, 1835: Exploration of Galápagos
- Main aspects that interested Darwin
- Islands were all volcanic, so very new
- All living things on it had their closest relations in South America
- The South American forms might be more commonly associated with very different
(more humid environments)
- Why not animal and plant species from similar arid environments, but from other parts
of the world?
- Each island had slightly different variations of same species or closely related
- Yet these species were not found elsewhere, even if some (e.g., marine iguanas) might
do very well in other parts of the world
- Some closely related species on the islands had anatomies or behaviors more like many
distantly related forms in other parts of the world (esp. the finches)
- Animals on these islands were essentially without fear of humans, and records show
them being more fearless in the past
- Similar records show similar traits in other islands (Falklands), although they were more cautious by the time that Darwin arrived
- Traveled on to Tahiti, New Zealand, Australia, the Cocos Islands, Mauritius, Cape Town
Colony, St. Helena and Ascension Islands, back to eastern South America for a few
corrections in measurements, then the Azores and finally home to England (Oct. 2, 1836)
Darwin's Professional Life
- Brought information and data to colleagues, and was introduced to other
naturalists (including Sir Richard Owen
and Charles Lyell, both on October 29, 1836)
- Put forth as a Fellow of the Royal Geological Society on Nov. 1
- Gave his first talk on Jan. 4: about slow geological change in South America, and
how its inhabitants adapted to those changes. Differed from Lyellian views on changing faunas,
where old species simply disappeared and new ones appeared to replace them as environments changed.
- By 1837 began to keep several different notebooks on aspects of transmutation
- In October of 1838 read Thomas Malthus'
"Essay on the Principle of Population".
- Married well (his first cousin, Emma Wedgewood): their combined wealth and family
stipends meant that they were better off than most lawyers or physicians, if less than a
big-time merchant, banker, or aristocrat
- Allowed Darwin to devote a lot of time to thinking and researching without needing to
get revenue from publishing or teaching
- Darwin began to publish (on the origin of coral reefs and atolls; on the voyage of the
Beagle; on the biology, anatomy, and taxonomy of barnacles)
- Became increasingly sickly during the late 1830s onward; almost never traveled far
from Down House: even missed his own father's funeral
- During 1840s and 1850s, began to broach his transmutationist ideas with colleagues in
private (in person, or by mail), including Lyell, Joseph Dalton Hooker,
and Thomas Henry Huxley
- Late Spring 1856, Charles Lyell receives a letter from young Alfred Russel Wallace,
describing his idea on the origin of species. Lyell shows it to Darwin, who is not overwhelmed
- June 18, 1858, Darwin receives a much longer, better worked out version of Wallace's
argument, which is MUCH closer to his own theory.
On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life published on November 22, 1859
- Nearly all copies sold out on first day, and Darwin immediately start's editing
a new version
- The Origin is just an abstract of the proposed much longer book Natural Selection,
which is never finished (although parts were published separately)
- The Origin had a far bigger audience than the 1858 papers, and soon discussions
of Darwin, Darwinism (term coined by T. H. Huxley in April 1860), and the implications of
evolution throughout the educated world
- Huxley helped bring ideas about evolution to the working classes, too
- Through all this, Darwin was largely a home-body
- Spring 1871: 6th Edition
of The Origin is published: first version with the word "evolution" in it!
- Darwin continued to write throughout his life, although slowly. Focused mainly on
plants and garden-related topics late in life.
- Died in 1888.
So, What Did Darwin & Wallace Discover?
Their model was called Natural Selection, and was analogous to "artificial selection" (e.g., domestication).
Darwin and Wallace's observations:
- Variability: There is variation in all populations.
- No two members of a population are totally identical.
- Some sources of variation include age and sexual differences; the results of factors that happened during the lifetime
(differences of nutrition, disease, accident, etc.); individual difference in inherited traits; etc.
- The idea that individual variation was significant was a blow to previous models of Nature. Most earlier natural
historians believed in perfect types, and thought variation was degeneration from those types. Darwin and Wallace
documented that the variation is the reality, and the "perfect types" were just myths.
- Heritability: Some (but not all) variation is inherited.
- Causal mechanism of inheritance unknown in Darwin's time.
- Discovery by Gregor Mendel of genetics came later, and discovery of DNA came later still
- Heritable traits are coded in DNA and passed on to descendents
- Note that DNA is NOT a "blueprint" as commonly thought: it is a set of instructions for putting bodies together and maintaining
them after they've been built
- Each little instruction is called a gene: a piece of code that helps the cell to build a protein
- Most genes have slightly different versions called alleles that produce different end products
- It is these alleles (one copy for each gene per parent) that is passed on to offspring
- Different combinations of alleles result in different traits being expressed (that is, different phenotypes). Depending on the
particular combination of alleles an offspring gets, they might have the same trait as their mother, their father, or something different
- This was the major source of individual variation that Darwin & Wallace never knew about!
- Mutations are new variations in heritable traits, caused by miscopied DNA (duplication of parts of genes; miswritten
- Some mutations may be deleterious (they result in harm to the organism)
- Many mutations may be neutral (they don't benefit the organism in an obvious way, nor hurt it)
- A small number of mutations may wind up being beneficial (the variation they produce allow it to do better somehow
in the world)
- Superfecundity: Organisms produced far more offspring than can possibly survive
- Application of demographer Thomas Malthus' reproductive excess concept to Nature
- Violated another previously-held belief: that Nature was perfect and everything had its place
Thus, IF some variation gives the individual a slight advantage (bigger, stronger,
smaller, smarter, less tasty, whatever) at surviving; and IF that variation is heritable;
THEN there is a somewhat better than average chance that organisms with that variation
will survive to bear the next generation. Over the long expanse of geologic time, the
accumulation of these variations will change the population from one form to another:
the origin of species.
Natural Selection is the differential survival and
reproduction of variants in a population resulting in a net change in phenotype
of the descendants.
(Short form: "Natural selection is the differential survival and reproduction of variants in a population.")
(Even shorter form with a 20th Century slant: MUTATION PROPOSES, SELECTION DISPOSES)
If Evolution can be summarized as "no one is identical to their parents", then Natural Selection can be summarized as
"no one is identical to their siblings, either; plus, life's hard!"
Key points of Natural Selection:
- Does NOT happen to individuals, only to populations (lineages)
- Analogous to "artificial selection" (domestication), but operates:
- On all traits rather than a few (humans can keep alive crops, farm animals, or pets that might otherwise die in the wild;
obviously, wild plants and animals don't have that help!)
- Over vast amounts of geologic time, rather than just a few generations
- Does NOT require simple things evolving into complex: sometimes a simplified mutation of a structure might be advantageous
than the ancestral complex one (hence, vestigial organs)
- Cannot evolve towards something with a goal in mind; only favors variations that are advantageous at the time of selection
"Survival of the Fittest"?: Not as such. Phrase not in the earlier editions of the Origin, nor
was it coined by Darwin. Comes from economist/philosopher Herbert Spencer:
- Unlike popular idea, evolutionary fitness is NOT being the biggest, strongest, fastest, etc.
- Instead, Fitness = Reproductive Success
- So a great grandmother with dozens of children, grandchildren, and great grandchildren is far
more "fit" (in evolutionary terms) than all the childless Nobel prize winners and Olympic athletes
Some things Evolution and Natural Selection are NOT:
- An argument for atheism per se (at least any more than geologic time, the germ theory of disease,
Newtonian/Einsteinian physics, etc., are)
- Although clearly, like geologic time, it required a world that operated on a different time scale than a literal reading of Genesis!
- An account of the origin of Life (that's abiogenesis: a different field of research)
- A prescription for social behavior or policy (after all, Natural Selection only operates by the
mass death of many individuals: hardly a good society!)
Scientific Reactions to Darwin and the Origin
In the late 19th Century, many parts of Darwin's work were accepted:
On the other hand, while some (Thomas Huxley, Joseph Hooker, O.C. Marsh, etc.) accepted Natural
Selection, many others did not. In part they thought it could not create entirely new morphologies, but
mostly because they accepted Lord Kelvin's incredible short (and inaccurate) time scale. With (for example)
only 3 million years for all the Cenozoic Era, it would be hard for Natural Selection to produce
the vast diversity of modern mammals.
- Evolution in general (special creation no longer a serious scientific possibility)
- Common ancestry (separate origins for different lineages no longer considered reasonable)
- Individual Variation
- Sexual Selection
Darwin died without knowing the mechanism by which variation was generated and passed on: genetics.
(Trivia time: he actually had a copy of Mendel's work at his desk, but he had never gotten around to opening it!).
Gregor Mendel's genetic work only became well-known and studied in the 20th Century. By the
mid-20th Century, new discoveries in genetics, paleontology, ecology, and statistics led to the
New Synthesis: a model demonstrating that Natural Selection is indeed a major force
However, there is more to it than that. Stay tuned...
Last modified: 10 January 2008