Download Lecture: Darwin and Wallace

Charles Darwin (1809-1882) &
Alfred Wallace (1823-1913)
British Naturalists
Foundations of Darwinism
 Darwin and Wallace independently came up with a
credible MECHANISM that could produce
evolutionary changes
 Both men Stimulated by:
1. Observations of diversity of life in the tropics
2. “An Essay on the Principle of Population as it
Affects the Future Improvement of Society” (1798)
by Thomas Malthus (1766-1834).
 Malthus Argued:
Human populations will always expand until famine,
war, or disease limits growth
Darwin’s Early Years
 Mediocre student during
early education
 Loved animals and the
outdoors
 1825, entered Edinburgh
University to study medicine,
no stomach for surgery
 Developed fondness for
natural science, especially
Marine Zoology
 Went to Cambridge, to enter
the clergy!
Darwin, the Naturalist

Collected beetles!

At Cambridge, befriended
Professor Henslow, interested in
botany, entomology, chemistry,
mineralogy, geology

Henslow persuaded Darwin, after
graduation, to begin a study of
geology

Arranged for young Darwin to
accompany Professor Sedgwick
on a field trip through North
Wales

Captain FitzRoy invited D to
volunteer as naturalist on the
Beagle, survey ship about to leave
on round-the-world mapping and
collecting expedition
Darwin’s Voyage on the Beagle
 Read Lyell's The Principles of
Geology during early weeks
 Investigated geology of
places ship visited,
understood the slow passage
of geologic time
 Collected fossil bones and
faunal specimens
 1831-1836: visited Cape
Verde Islands, Brazil, Tierra
del Fuego, Patagonia, Chile,
Argentina, the Galapagos
Islands, Tahiti, New Zealand,
Australia, Tasmania, Cocos
Islands, Mauritius, St. Helena,
Ascension, and the Azores
Formation of Darwin’s Ideas on
Natural Selection

Darwin's journal, The Voyage of
the Beagle (1839), sold well

Perceived that SELECTION was
key to success in breeding
domestic plants and animals.

Read Malthus & observed that
animals and plants struggled for
existence and developed habits
and variations

“it at once struck me
that…favorable variations would
tend to be preserved, and
unfavorable ones to be
destroyed. The result of this
would be the formation of new
species" (Darwin, 1898, p. 68).
Alfred Wallace
 Family of Modest Means
 Limited education, worked
many jobs: construction,
surveying, assistant to a
watchmaker, teacher...
 Loved natural history and
the outdoors
 With naturalist Henry Bates,
traveled to Brazil, explored
the Amazon, sold collections
of biological specimens,
especially insects
Wallace’s Formative Years

1848: Wallace and Bates sailed
for South America, gathered
large collections

1852: Sailed back to England,
ship caught fire and sank after 3
weeks! Passengers rescued but
collections lost!

1859: Bates gathered more than
14,000 species in Brazil

1854: Wallace collected in the
Malay Archipelago & recognized
the Archipelago as biologically
divided by a narrow strait,
separating Asian fauna from
Australian fauna, still recognized
as Wallace's Line.
Wallace Forms His Ideas on
Natural Selection
 Applied geological idea of
uniformitarianism to biology
 Charts of a species might
look more like a tree than a
straight line
 No species came into
existence unless coexisted
with another similar species
that was its predecessor
 1855: Wrote paper arguing
for evolution of species,
searching for a
MECHANISM. Malthus
inspired him.
Wallace and Darwin
 June 1858: Wallace drafted his
thoughts, sent them in letter
to Darwin, Darwin was
shattered
 July 1858: Joint credit was
given to Darwin & Wallace at
Linnaean Society
 The announcement attracted
no particular scientific or
public attention!
 1859: Darwin worked
intensely for the next year on
his manuscript, On the Origin
of Species by Means of Natural
Selection (1859), sold out on
day of publication!
Natural Selection
Theory of Natural Selection was based on 3 observations and 2
deductions:
Observation 1
Organisms reproduce in a geometric ratio (Actually Malthus
was wrong; reproduction is exponential, not geometric)
Observation 2
The numbers of any given species tend to remain more or less
constant through time
Observation 3
All living things vary
Deduction 1
There is a universal struggle for survival. More organisms of
each kind are born than can possibly obtain food and survive.
Deduction 2
Individuals with some kind of advantage have the best chance
of surviving and reproducing their own kind
Darwin’s Grand Contribution
 NATURAL SELECTION: some
individuals are more
successful at reproducing
than others
 Advantageous characteristics
become numerous, less
favorable characteristics
disappear
 NS explains how one species
transmutes into another
species
 EVOLUTION became a central
organizing concept in
biology: a NATURAL (v.
supernatural) process could
produce a new species!