Evolution, 4th Edition

12 CHAPTER 1

economist Thomas Malthus. Malthus argued that the rate of human population

growth is greater than the rate of increase in the food supply, so that unchecked

growth must lead to famine. This essay was the inspiration for Darwin’s great

idea, one of the most important ideas in the history of thought: natural selection.

Darwin wrote in his autobiography that “being well prepared to appreciate the

struggle for existence which everywhere goes on from long-continued observa-

tion of the habits of animals and plants, it at once struck me that under these

circumstances favourable variations would tend to be preserved and unfavour-

able ones to be destroyed.” In other words, of the many individuals that are born,

not all survive; and if certain individuals with superior features survived and

reproduced more successfully than individuals with inferior features, and if these

differences were inherited, the average character of the species would be altered

over the course of generations.

Mindful of how controversial the subject would be, Darwin then spent 20

years developing his theory, amassing evidence, and pursuing other researches

before publishing his ideas. In 1844 he wrote a private essay outlining his theory,

and in 1856 he finally began a book he intended to call Natural Selection. He never

completed it, for in June 1858 he received a manuscript from a young naturalist,

Futuyma Kirkpatrick Evolution, 4e

Sinauer Associates

Evolution4e_01.07.ai Date 12-06-2016

Nesomimus spp.

San Cristóbal Mockingbird

N. melanotis

Santiago

Santa

Cruz

Santa Fe

San

Cristóbal

Española

Floréana

Baltra

Marchena

Pinta

Genovesa

Isabela

Fernandina

Galápagos Mockingbird

N. parvulus

Pacic

Ocean

Atlantic

Ocean

Española Mockingbird

N. macdonaldi

Floreana Mockingbird

N. trifasciatus

South

America

Equador

Galápagos

Islands

20 km (Equador)

FIGURE 1.7 Four species of mockingbirds (Nesomimus) on different islands in the

Galápagos archipelago were among the observations that led Darwin to suspect that

different species evolve from a common ancestor.

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