1. What influenced Darwin's ideas about species?
The Darwinian Revolution
What influenced Darwin's ideas about species?
Darwin's grandfather, Erasmus Darwin, published one of the first formal scientific theories of evolution, Zoonomia, or,The Laws of Organic Life, in the 1790s.
Evolution is the theory that explains how organisms have arisen and diversified from earlier organisms.
One of Erasmus Darwin's contemporaries, Georges Cuvier, wrote on comparative anatomy and physiology and first established the concept of extinction.
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2. The Darwinian Revolution
Figure 1 Charles Darwin (1809–1882).
Darwin’s fervent interest in the natural world began as a young boy and continued unabated throughout his remarkable career.
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3. What influenced Darwin's ideas about species?
The Darwinian Revolution
What influenced Darwin's ideas about species?
During the 5-year surveying mission in which Darwin served aboard the Royal Navy Brig HMS Beagle as a naturalist, he became intrigued by Charles Lyell's Principles of Geology.
In Principles of Geology, Lyell presents arguments in support of uniformitarianism, the theory that observable processes occurring in the present are sufficient to explain the formation of all geological features over great time periods.
Darwin eventually applied the idea that ongoing, observable processes can account for the variety of features in the natural world to living systems.
Departing the coast of South America, the Beagle arrived at the Galapagos Islands, where Darwin would make his most famous observations of species, including the 14 or so closely related species of finches now commonly referred to as Darwin's finches.
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4. The Darwinian Revolution
Figure 2 Darwin’s finches.
Just four of the Galapagos Islands finch species that Darwin observed, described and drew. He pondered the great range in bill type among these species.
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5. The Darwinian Revolution
Darwin's publications came amid academic discussion on the matter of evolution.
In 1844, Darwin wrote an essay covering the main ideas about how species change slowly over time, a process he called descent with modification, and the mechanism that drives these changes, which he called natural selection.
Instead of immediately publishing his scientific explanation of origins-which did not mention a divine creator-he spent years gathering more supporting evidence.
In 1858, English naturalist Alfred Russel Wallace sent Darwin a manuscript, requesting that he review it and pass it along to Lyell.
Darwin was shocked to read Wallace's hypothesis about natural selection, which was nearly identical to his own.
After receiving Wallace's hypothesis about natural selection, Darwin quickly completed work on his book, On the Origin of Species by Means of Natural Selection, and published it in 1859.
Lyell presented Wallace's paper together with excerpts from Darwin's unpublished 1844 essay to a scientific society in London.
Wallace admired Darwin and respected his work. Recognizing that Darwin had more fully developed the hypothesis, Wallace wanted Darwin to receive primary credit.
Wallace went on to devote himself to research in biogeography, the study of the geographical distribution of species.
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6. The Darwinian Revolution
Figure 4 Alfred Russel Wallace.
Although most people credit Darwin with developing the theory of natural selection, Wallace simultaneously produced a similar hypothesis.
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7. The Darwinian Revolution
Darwin's hypothesis described the evolutionary relationships between taxonomic groups.
Darwin's idea of descent with modification explained how species change slowly over time as they adapt to environments.
Darwin proposed that all species descended step by step from a single common ancestor by adapting to changing environments or to new environments arrived at by migration.
Darwin's work explained taxonomic relationships between groups of organisms, which were related by common ancestry and not necessarily by outward form.
Gaps between forms signalled the importance of extinction. Before Darwin's work, most scientists had not appreciated the phenomenon's relevance, in part because it was not supported by theology.
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8. The Darwinian Revolution
Figure 5 Phylogenetic tree showing evolutionary relationships.
Extinct species represent gaps in body forms of extant species. Fossil discoveries help fill in the gaps and reconstruct the evolutionary trajectory of the group.
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9. The Darwinian Revolution
Darwin proposed natural selection as the mechanism of descent with modification.
In Origin of Species, Darwin constructed a logical argument for the mechanism of natural selection based on two observations and inferences: (1) individuals in a species vary to some degree in traits; and (2) a species produces more offspring than actually survives to mature and reproduce.
Individuals with traits better suited to their environments are more likely to survive and reproduce; therefore, their offspring are more likely to inherit these adaptive traits.
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10. The Darwinian Revolution
Figure 6 Darwin’s logical argument for natural selection.
Since the time of Darwin's writing, researchers have been able to observe the diffferential survival of individuals with adaptive traits over multiple generations. They have seen that, in a population over time of multiple generations, those adaptive traits accumulate (Follow the trend in red and green shapes).
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11. Controversy. The Darwinian Revolution Principles of Biology
Darwin's publications were nothing short of revolutionary. Within a decade of Origin's publication, scientists accepted evolutionary theory as mainstream.
Over the past 150 years, Darwin's theory of natural selection has been refined and supported by great volumes of evidence from varied domains, including genetics, geology, anatomy, physiology, and embryology.
In science terminology, a theory is not an idea or an educated guess, but rather an observed, tested, and accepted fact of the natural world, like gravity.
The Church of England and many of its followers reacted with predictable hostility, but eventually the church softened its stance.
In recent years, Reverend Dr. Malcolm Brown, Director of the Mission and Public Affairs of the Church of England, published an essay entitled "Good Religion Needs Good Science," outlining an acceptance of Darwin's scientific ideas while rejecting some of their social misappropriations.
In certain parts of the United States, the controversy shows no sign of abating as battles still rage over the teaching of evolution in schools.
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