I am almost convinced that species are not immutable. ~ Charles Darwin in 1844
English naturalist Charles Darwin (1809–1882) took an unpaid position on the survey ship HMS Beagle when he was 22 (1831). Near the end of it 5-year voyage, Darwin observed life on the Galápagos Islands, isolated off the coast of Ecuador. Each island had its own variety of tortoise, mockingbird, and finch.
Inspired by Charles Lyell’s theory of a gradually changing Earth, and Thomas Malthus’ theory of food supply limiting population growth, Darwin derivatively developed a similar hypothesis of biological evolution: gradual change in speciation based upon competition for survival.
(Darwin hardly ever used the word evolution, preferring “descent with modification.” Darwin did not coin “survival of the fittest.”)
In the struggle for survival, the fittest win out at the expense of their rivals because they succeed in adapting themselves best to their environment. ~ Charles Darwin
This was the thrust of Darwin’s evolution hypotheses on variation and selection, described in his 1859 book On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life. The photo shown was taken shortly after the book’s publication, when Darwin was 51.
Darwin’s “natural selection” was concocted from the idea of there being a struggle for survival. Darwin pondered in 1858:
Can it be doubted, from the struggle each individual has to obtain subsistence, that any minute variation in structure, habits, or instincts, adapting that individual better to the new conditions, would tell upon its vigour and health? In the struggle it would have a better chance of surviving; and those of its offspring which inherited the variation, be it ever so slight, would also have a better chance. Yearly more are bred than can survive; the smallest grain in the balance, in the long run, must tell on which death shall fall, and which shall survive. Let this work of selection on the one hand, and death on the other, go on for a thousand generations, who will pretend to affirm that it would produce no effect?
Darwin’s initial hypothesis was that random mutations are passed to the next generation, resulting in incremental evolutionary change. In Darwin’s imagination, these variations are winnowed by “natural selection.” Those variations that do not confer an advantage to the breeding success of a species are not passed on: survival of the fittest as a competitive exercise.
English parson Thomas Malthus published an Essay on the Principle of Population (1797), where he argued that public policies designed to help the poor were doomed because they would simply cause unchecked breeding that could lead to famine and misery for all.
From reading Malthus, Darwin conceived of natural selection as constant environmental competitive pressure forcing change to survive. From this, Darwin believed that “natural selection almost inevitably causes much extinction of the less improved forms of life.” Darwin had no evidence upon which to base this ludicrous claim.
Natural selection acts solely by accumulating slight successive variations. It can produce no great or sudden modification. It can act only by very short steps. ~ Charles Darwin
Darwin’s choice of the term natural selection derived from selective breeding of domestic animals. In Origin he opined:
Good domestic breeds are valued by the negroes of the interior of Africa who have not associated with Europeans. Some of these facts do not show actual selection, but they show that the breeding of domestic animals was carefully attended to in ancient times, and is now attended to by the lowest savages. It would, indeed, have been a strange fact, had attention not been paid to breeding, for the inheritance of good and bad qualities is so obvious.
At the present time, eminent breeders try by methodical selection, with a distinct object in view, to make a new strain or sub-breed superior to anything existing in the country.
In contrast to “actual selection” by breeders, Darwin considered “natural selection” to be Nature competitively selecting the species that survive.
Darwin axiomatically assumed a geologic timeframe for natural selection: a slow, incremental progression. Instead, evolution continuously happens, producing visible results in spurts, from both environmental demands and opportunities.
Darwin wrongly surmised that every aspect of an organism was subject to selection. He had not a glimmer of core conservation: that cellular fundamentals were conserved.
Lamarck haunted Darwin. Darwin initially proposed mutation as occurring first, followed by winnowing, but considered this hypothesis incomplete, as it lacked a mechanism for selection.
Darwin increasingly retreated to Lamarck’s more mysterious but purposeful selection: that living can demand change, that the environment can facilitate or induce adaptation, and that incremental changes from life’s experiences are somehow passed on to offspring.
In 1868, Darwin conjectured pangenesis: a complex mishmash of heredity enveloping sexual reproduction, life-experience heredity, and developmental phenomena, such as cellular regeneration. Darwin’s proposed mechanism for pangenesis were tiny organic particles – gemmules – which transmitted heritable information from all parts of the body to the gonads.
Pangenesis was criticized for its Lamarckian roots: that parents could pass on traits acquired during their lives. Nonetheless, Darwin persisted in tinkering with pangenesis. His last word on the topic emphasized that traits could be inherited which were not manifest in a parent organism, that a developing organism could exhibit trait transition, and that certain traits depended upon an organism’s sex.
While some of his individual conjectures panned out (make enough guesses and you might get some right), Darwin’s speculations fell far short of a well-founded hypothesis outlining a biomechanism for evolution, which is what Darwin sought.