Evolution, 4th Edition

EvoluTIonARy BIology 13

Alfred Russel Wallace (1823–1913). Wallace, who was collecting specimens in the

Malay Archipelago, had independently conceived of natural selection. Darwin’s

scientific colleagues presented extracts from his 1844 essay, along with Wal-

lace’s manuscript, at a meeting of the major scientific society in London. Darwin

immediately set about writing an “abstract” of the book he had intended. The

490-page result, titled On the Origin of Species by Means of Natural Selection, or The

Preservation of Favoured Races in the Struggle for Life, was published on November

24, 1859; it instantly made Darwin, by now 50 years old, both a celebrity and a

figure of controversy.

For the rest of his life, Darwin continued to read and correspond on an immense

range of subjects, to revise The Origin of Species (“on” was deleted from the title

of later editions), to perform experiments of all sorts (especially on plants), and to

publish many more articles and books, of which The Descent of Man is the most

renowned. Darwin’s books reveal an irrepressibly inquisitive man, fascinated with

all aspects of nature, creative in devising hypotheses and in bringing evidence to

bear on them, and profoundly aware that every biological fact, no matter how seem-

ingly trivial, must fit into a coherent, unified understanding of the world. Wallace

made significant further contributions to biology, especially about biogeography, the

geographic distribution of species. He always gave credit to Darwin for the concept

of natural selection, referring to it as “Mr. Darwin’s theory.”

Darwin’s evolutionary theory

The Origin of Species contains two major theories. The first is Darwin’s idea of descent

with modification. It holds that all species, living and extinct, have descended, with-

out interruption, from one or a few original forms of life (FIGURE 1.5B). Species that

diverge from a common ancestor are at first very similar but accumulate differences

over great spans of time, so that they may come to differ radically from one another.

Darwin’s conception of the course of evolution is profoundly different from Lamarck’s,

in which the concept of common ancestry plays almost no role.

The second theory in The Origin of Species is natural selection, which Dar-

win proposed is the chief cause of evolutionary change. He summarized it in the

Futuyma Kirkpatrick Evolution, 4e

Sinauer Associates

Evolution4e_01.08.ai Date 12-06-2016

(A) (B)

FIGURE 1.8 Galápagos giant tortoises (Chelonoidis nigra) differ in shell shape among

islands. Some subspecies, especially those that occupy humid highlands with low veg-

etation, have a domed shell (A), whereas those in dry lowland habitats tend to have a

“saddleback” shell (B) that enables the animal to extend its long neck to reach vegeta-

tion higher above the ground.

Alfred Russel Wallace

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