Darwin and the Theory of Evolution,
and Artificial Selection
· Variation in Nature
· 1.3 billion species
· 750,000 insects, 250,000 plants, 4000 mammals, 5000 sponges
· Why is there such enormous variety in
· Lamarck (1744-1829) -
- inheritance of
acquired characteristics gave rise to evolution
· Darwin (1809-1882) - The Origin of
- Malthusian theory
of population growth - more offspring than can survive.
selection - breeders select more desirable individuals and allow them
selection - natural analog of artificial selection - better adapted individuals
leave more offspring.
"monstrosities" in animals or "sports" in plants
arise (now called mutations). Darwin's estimate of mutation rate was 1 in
106, which is close to modern estimates.
- "The laws
governing inheritance are for the most part unknown..." (from
Chapter 1 of the Origin of Species - Mendel's work was not known to him).
· Alfred Russell Wallace (1823-1913) -
- Co-discoverer of
natural selection as primary mechanism of evolution.
· Gregor Mendel (1822-1884)
· Artificial Selection
- Darwin built his theory of
Natural Selection from what he knew of Artificial Selection
- Domestic Dogs - argued that
not all breeds have wild prototypes - "who could believe that greyhounds, bloodhounds, pug dog, Blenheim spaniel,
so unlike all wild
Canidae - ever existed in a state of nature?"
- Domestic Pigeons - ( Photos of breeds
) - Studied intensively by Darwin
- "I am fully
convinced that all [hundreds of breeds] are descended from the rock
- "Hybrids or
mongrels from between all breeds of pigeons are perfectly fertile, as I
can state from my own observation.
- Within a breed,
characters are variable
- Pigeons have been bred
for 5000 years
- Pairs mate for life so
multiple breeds can be kept together
- Adaptation in domesticated
animals is "not indeed to the animal's or plant's own good, but
rather to man's use or fancy."
- "We cannot suppose that
all breeds were suddenly produced as perfect and a useful as we now see
them, in many cases we know that this has not been their history. The key
is man's power of cumulative selection: nature gives successive
variations; man adds them up in certain directions useful to him"