Today geologist Charles Darwin is not remembered as great monster hunter, despite some Victorian paleontologists and geologists were interested in the topic, but after discussing how geologists tried to capture "Nessie", it´s time to hunt for "Bigfoot":
Since ancient time people were fascinated by monsters - a term adopted for mythical creatures, but also real animals or humans with grotesque anatomical deformations. In the 18th and 19th century such "freaks of nature" were an essential part of every respectable collection of natural curiosities and naturalists had no problem to mix serious observations with careful descriptions of these monstrosities.
English naturalist Robert Plot (1640-1696) summarizes in his "Natural History of Oxfordshire" (1792) this philosophy as follows:
"I shall consider, first, Natural Things, such as either she hath retained the same from the beginning, or freely produces in her ordinary course; as Animals, Plants, and the universal furniture of the world. Secondly, her extravagancies and defects occasioned either by the Exuberancy of Matter, or Obstinacy of Impediments, as in Monsters. And then lastly, as she is restrained, forced, fashioned, or determined by Artificial Operations."
As therefore even monsters were part of nature, naturalists tried to understand their exact place in the natural order.
Zoologist Étienne Geoffroy Saint-Hilaire (1772-1844), influenced by Lamarck's idea of mutable species, studied the anatomy of "freaks" (a science today known as "teratology") and recognized that even such abnormalities follow certain rules in their biological development.
"Monsters are not sports of nature; their organization is subject to rules, to rigorously determined laws, and these rules, these laws, are identical with those that regulate the animal series; in a word, monsters are also normal beings; or rather, there are no monsters, and nature is one whole."
For Saint-Hilaire animals and humans with birth-defects, like missing body parts, were simply resurfacing stages of a more primitive (possibly fish-like) phase of animal evolution.
Fig.1. A classic freak of nature - a two-headed calf, from the taxidermy collection of the Ferdinandeum, Innsbruck.
In Victorian England public exhibitions of monsters were a big business. The most popular monsters of every freak-show were the classic mermaid and other half human - half animal creatures. However Darwin's model of gradual evolution exposed these specimens as what they really are - scientifically impossible chimeras.
Fig.2. "The deformito-mania", a cartoon published in Punch 1847, mocking the general interest in London´s freak shows (image in publid domain).
Darwin himself considered at first a discontinuous formation of species possible and recognized how individuals with birth-defects can significantly differ from a common archetype. However the deformed variations of a species as displayed in the freak-shows are, as Darwin notes in "The Variation of Animals and Plants under Domestication", also those who are most unsuited to survive. So in the end he favored small changes in the anatomy to provide the necessary variations on which natural selection and evolution acts.
Even if Darwin killed some monsters, in the same time he created new ones. As Darwin's theory of common descent states that humans and other apes share a common ancestor, the idea of and ape-man-creature as a "missing link", a term popularized by geologist Charles Lyell and based on a distorted view of evolution as "scala naturae", became very popular. Soon no freak-show was considered complete if there was not a great ape, monkey or real "savage" (as people of the colonies were regarded) on display.
Fig.3. "What is It?", advertisement for a natural history exposition at the American Museum, March 1860, note the annotation "Is it a lower order of Man? or is it a higher development of the monkey? or is it both in combination?" (image in public domain).
Still today the incorrect "ape-man" idea survives. For the serious researcher Bigfoot sightings are in fact rare encounters with surviving specimens of Gigantopithecus - an orang-utan relative known only from fossil fragments. For the layman Sasquatch and Orang-Pendek are descendants of an early stage of human evolution, the classic chimera made up by parts of modern humans and modern apes - and despite already Darwin stated that transitional forms do not necessary resemble modern animals.
ASMA, S.T. (2001): Stuffed Animals and Pickled Heads. The Culture and Evolution of Natural History Museums. Oxford University Press: 319
BLUMBERG, M.S. (2009): Freaks of Nature. What anomalies tell us about development and evolution. Oxford University Press: 341
BONDESON, J. (1999): The Feejee Mermaid and other Essays in Natural and Unnatural History. Cornell University Press: 315
DA COSTA, P.F. (2000): The understanding of monsters at the Royal Society in the first half of the eighteenth century. Endeavour Vol. 24(1): 34-39
DELISLE, R. G. (2012): Welcome to the twilight Zone: a forgotten early phase of human evolutionary studies. Endeavour Vol. 36(2): 55-64
GOODALL, (2005): Performance and Evolution in the Age of Darwin. Out of the Natural Order. Routledge edition: 288
REGAL, B. (2009): Entering dubious realms: Grover Krantz, science, and Sasquatch. Ann. Sci. Vol.66(1): 83-102
REGAL, B. (2011): Searching for Sasquatch - Crackpots, Eggheads, and Cryptozoology. Palgrave Macmillian Publisher: 249