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

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

Darwin’s Voyage on the Beagle

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 1There 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!