Lec 8: Darwin Flashcards
What does the Origin of Species argue?
Evolution is actually tacked in three books
- > Origin of Species
- > The Variation of Animals and Plants Under Domestication (1868)
- > Descent of Man (1871)
Central claim of Origin: ALL KINDS OF LIVING THINGS, WHEN BRED, VARY IN CHARACTER
- > like a pigeon breeder, nature has been breeding plants and animals
- > species spread around, and adapt to the conditions
Summary:
- > speciation occurs because organisms respond to changing environments
- > more diversified and specialized = more efficiently exploiting their environment
- > can happen in isolation, but most often its geographically linked members of the same group, but responding to different challenges of different zones
- > intermediaries disappear in this case, because there is less variation to draw on than the main groups (i.e. intermediaries are small in number)
- > sterility between these groups develops because of the differences, not directly as a result of selection
Explains:
- > changes of fossils through long succession of stratified rocks
- > differences of species between Old/New worlds, by gradually spreading to new countries
- > explains bird/mollusk diversity in small islands vs similarity over large continents
- > framework to discuss issues, which couldn’t be discussed within creationism
- > useless vestiges of organs
- > instincts
- > cross breeding
- > hybrid’s sterility
Ch1: Variation under Domestication
- > influenced by breeders (his family bred sheep, pigeons)
- > minute differences are the key to change
- > changes of the group is summation of the change of individuals
- > organisms may have many forms but one common ancestor - the reason for diversity of selection
- > some not moved - e.g. Huxley
- > artificial breeding shows there is a limit to how far you can push animals/plants
Ch3:
- > struggle for existence corresponds to our selection
- > draws on Malthus - food limits create struggle to exist
- > though by 1850’s Matlhus ideas out of date, as everyone had seen improvement in QOL
Ch4:
- > argues by analogy for natural selection
- > struggle for life is like domestic breeding
- > some variations help survive = natural selection
- > SEXUAL SELECTION (cf Descent of Man)
- > we select not only for practical reasons, but also pleasurable ones - bigger horns, beauty pigeon
- > natural = for surival
- > sexual = for pleasure.
- > 2 parts, selection through male combat & female choice
- > geographical isolation may not be essential
- > isolated populations = too small pop to make enough variations for significant change
- > speciation requires subgroups of large pop
- > principle of divergence
Ch5: Laws of Variation
->our knowledge is limited
Ch6-10 Address Problems with his theory
- > why no intermediate forms?
- > transitional forms smaller and wiped out
- > the eye is highly evolved, but can’t trace evolution
- > abrupt changes in fossil record discredits
- > we haven’t found the fossils yet
- > not enough time for natural selection?
- > jokes, there was
He tried to show how nat sel can explain many areas
->anatomy, paleontology, geographical distributions…
Background of the Origin?
Darwin spends 1832-1836 aboard the H.M.S. Beagle
- > expedition to map, fix longitude, help with chronological calculations worldwide
- > scientific expeditions are commonplace
Brings with him books, e.g. Lyell’s Principles of Geology
He isn’t a biologist
->family of physicians, but no stomach
Fan of Baconian inductivism - stating an initial inductive step
- > says the journey is the beginning
- > seeing SA fossils, turtles/finches of Galapagos opened eyes
- > truth is, it probably crept gradually over time
Wallace writes him on his new idea - NATURAL SELECTION
Alfred Russel Wallace (1823-1913)
Sepnds
Alfred Russel Wallace (1823-1913)
Spent 8 years in Indonesia
- > thought geographical distribution key to organic origins
- > organic world gradually in change, causes always in motion
“On the Law Which Has Regulated the Introduction of New Species”
->every species comes into existence in close proximity (space & time) to a similar species
Inspired by keeping populations in check
- > Malthus’ Essay on the Principle of Population
- > connected Malthus to the animal world
- > NATURAL SELECTION - not all organisms survive
- > survival depends on the organism’s characteristics
- > i.e. the best live - strongest, best digestion. etc
Principle of Divergence:
The more diversified descendants are, the better suited they are for diversified places.
->more likely to increase numbers
Darwin’s Sources
Darwin’s grandpa thought all living things came from common ancestor
->descended over millions of years, during which they were modified and transformed
Evolution wasn’t new
- > Chamber’s “Vestiges of Natural History”
- > Spencer said that you start with homogenous beginnings and evolve to hetero ends. English have larger brains, clearly used intellect and moral sense.
- > it’s the MECHANISM, about variations suited for your environment persisting, that’s new
For both Wallace & Darwin, key is “population”
- > group of things that INTERACT with each other
- > extracted from Malthus
Lyell was important to Darwin
- > supportive father figure, Origin is modeled after Principles
- > not big influence on ideas though
- > Lyell blasted Lamarck for transmutation of species
- > Darwin concealed his ideas
Schweber (1980) argues Darwin’s theory comes from wandering through distant fields, not natural history
- > Comte argues proper theory is predictive, quantitative
- > Stewart “Accounts of the life and Writing of Adam Smith”, laissez faire economics = let the people struggle and compete; order rises from the struggle not some higher control
- > searching for quantification, read Quetelet who referenced Malthus. Population geometric, food arithmetic therefore guarantee struggle to survive
Reactions to Origin
Religious people mad.
- > ends up taking Spencer’s term “surival of the fittest” as selection too close to Deism
- natural preservation may be better
Darwin didn’t convince many scientists/biologists
- > evolution wasn’t new, natural selection was
- > random production of variations and elimination of the unfit clashes with idea of “design” to nature
- > i.e. everything is chance, no planning
How does Darwin counter the “design” issue?
Instead of looking at perfect solutions (butterfly copying dead leaf perfectly) look at the hackjob solutions that no God would do.
V.s. Asa Gray:
e. g. self fertilizing plants (orchids)
- >so many devices to attract insects, which are common components of other flowers turbo retrofitted
- >God wouldn’t reuse parts like this
- >orchids are jury-rigged from limited components; they evolved from ordinary flowers
Asa Gray
Accepted evolution & natural selection, but couldn’t abandon design.
“Design on the installment plan”
->i.e. God chooses the variations
Darwin & Lamarck
People tried to bring back Lamarck to counter Darwin.
- > dropped the spontaneous generation
- > acquired characters came to the front
- > Lamarck said evolution is active response by the organism, but neo-Lamarcks said it was environments impressing themselves upon passive organisms
Lamarck:
- > organism gets info from environment, makes a direct response
- > after appropriate reaction, passes to offspring
- > i.e. directed variation; variation directs itself to adaptation without a secondary force (nat. sel.)
- > good design, purpose to world
Darwin:
- > two-step response
- > different forces for variation and the direction
1) Random variation of offspring
2) Take unordered variation, give greater reproductive success to advantageous variants
- > different forces for variation and the direction
- > no purpose in nature
- > orgs adapt by struggling to reproduce
Darwin & Huxley
An evolutionist, he accepted nat sel
->Darwin’s bull-dog
Huxley&Galton saw nat. sel. assumed nothing on uniformity at rate
- > Huxley thought Evo could go so fast that sedimentation too slow to catch it
- > suggests evolution goes in discontinuous leaps
- > gaps in record could be explained if nat sel drew on discontinuous variations - SALTATIONS
Saltations
Idea by Huxley - discontinuous variations explaining gaps in fossil record
- > nat sel acts on saltations, not individual differences
- > Darwin would consider these to be individual differences, “spontaneous variations” or “sports”
How does Darwin defend Gradualism?
Reject the literal record, and common sense.
Geological record is imperfect - a book with 99% words gone. We see one step in thousands.
Two problems in fossil record:
1) Species show no directional change
- >new species appear looking the same as when they disappear; direcitonless changes
2) In local area, species appear at once fully formed not gradually
Haeckel (Darwin’s German defender) constructs hypothetical organisms to fill in.
- > Amoeba can’t be the base, because it jumps to nucleus & cytoplasm, huge advance
- > to close the living/dead gap, creates the MONERA
Haeckel & Darwin
Supports Evolution, but not Nat Sel
- > environment acts directly on organisms (like Lamarckism)
- > survival depends on interactions with enviro, bit like nat sel
Wallace & Darwin
Advances “Pure Darwinism”
- > throws out sexual selection
- > Darwin uses it to explain features harmful for existence - peacock’s tail feathers
Wallace gives 3 reasons against sex sel:
1) Compromises generality of nat sel
- >supposed to be a battle for life, not limited to sex
2) Emphasis on animal’s own will, esp. female choice
3) Allows for important features, which are irrelevant to an organism which is supposedly well design machine
TLDR: It threatens Wallace’s idea - animals are works of craftsmanship by nat sel.
Wallace doesn’t believe in Nat Sel for humans
- > intellect & morality aren’t random, needs God
- > primitive people have the same brain, humans have evolved SOCIALLY!
