Introduction to Evolutionary Biology: History of Evolutionary Thought & Mr. Darwin
Introduction to Evolutionary Biology: Lecture 3
Historical Views on Creation
Historically, the predominant belief held that life was created through the will of a supernatural power. This view entailed several core tenets:
A supreme being placed organisms on Earth.
Organisms' appearance and function were according to this supreme being's design.
Species were considered immutable; they did not change over time.
Precursors to Evolutionary Thought
Anaximander (6th Century B.C.E.)
An early Greek philosopher who proposed concepts of common descent and the transmutation of species.
Carolus Linnaeus (1707-1778)
Attempted to understand the divine plan by seeking similarities among organisms.
Developed binomial nomenclature, a two-part naming system for species (e.g., Homo sapiens).
Established a hierarchical classification system for organisms (Kingdom, Phylum, Class, Order, Family, Genus, Species).
James Hutton (1726-1797)
Considered the founder of modern geology.
Proposed that natural processes, such as weathering and erosion, shape rock formations.
Introduced the concept of gradualism: profound geological change is the cumulative product of slow but continuous processes.
Postulated the Great Geological Cycle:
Sedimentation: Sediments deposited by water are compressed to form stone.
Erosion: Rock exposed to elements breaks down into sediment.
Was the first major Western thinker to contradict the young Earth hypothesis, arguing that Earth must be very old.
Famously stated in 1788, concerning geological time: "We find no vestige of a beginning, no prospect of an end."
Example: The Grand Canyon is a testament to gradual geological processes over vast stretches of time.
Adam Smith (1723-1790)
Known as the "Father of Economics," particularly for his work on laissez-faire economics.
Suggested that apparent chaos in markets is governed by an "invisible hand," representing natural forces or self-regulating mechanisms.
Emphasized the benefits of competition for maintaining a healthy environment (economic, though later applicable to biology).
Stressed the importance of self-interest as a primary motivator.
Quote from his 1776 work, The Wealth of Nations: "It is not from the benevolence of the butcher, the brewer, or the baker that we expect our dinner, but from their regard to their own interest. We address ourselves, not to their humanity but to their self-love, and never talk to them of our own necessities but of their advantages."
Jean-Baptiste Lamarck (1744-1829)
Proposed the first truly complete theory of evolution.
Believed that environmental forces shape adaptation, although he did not address the initial creation of life.
His theory included:
Use and Disuse: Body parts that are used extensively become larger and stronger, while those not used deteriorate.
Inheritance of Acquired Traits: Traits acquired by an organism during its lifetime are passed on to its offspring.
Example: Lamarck incorrectly hypothesized that giraffes developed long necks because ancestral giraffes stretched their necks to reach higher leaves, and this acquired longer neck trait was then passed to their progeny. (This mechanism is now known to be incorrect).
Thomas Malthus (1766-1834)
Published "An Essay on the Principle of Population" in 1798.
Argued that populations grow geometrically (1, 2, 4, 8, ext{etc.}), whereas food supplies grow only linearly (1, 2, 3, 4, ext{etc.}).
This disparity inevitably leads to competition for limited resources.
Proposed that "outside forces" such as "sickly seasons, epidemics, pestilence, and plague" or "gigantic inevitable famine" lead to "premature death" to "rectify" this imbalance and lower population size.
Georges Cuvier (1769-1832)
Established the fields of comparative anatomy and paleontology.
Verified, through fossil evidence (e.g., Megatherium, a giant ground sloth), that extinction occurs.
Was a strong proponent of catastrophism: the idea that geological formations and the distribution of species were shaped by sudden, brief, violent events on Earth, rather than gradual processes.
He did not agree with evolutionary thinking.
Charles Lyell (1797-1875)
Authored Principles of Geology (published 1830-1833), which was influential reading for Darwin.
Championed Uniformitarianism: the principle that the same geological processes operating today also operated in the past, often summarized as "the present is the key to the past."
Emphasized the steady, cumulative effect of minute changes over immensely long periods.
Sidebar: Darwin's later theories on the formation of atolls (coral reefs expanding around sinking volcanic islands) supported Lyell's uniformitarianism, demonstrating how gradual processes lead to massive changes.
Charles Darwin (1809-1882)
Formulated the theory of evolution by natural selection.
Key ideas:
Common descent: Species evolve from common ancestors.
Transmutation of species: Species change over time.
The primary mechanism of evolution is natural selection.
The Voyage of HMS Beagle (1831-1836)
Darwin undertook a five-year circumglobal scientific survey.
His observations significantly shaped his evolutionary theory:
Found fossils of extinct animals (e.g., Glyptodon, a giant armadillo-like creature) that resembled living species, suggesting a connection between present and past life forms.
Observed variations in species across different geographical locations, notably on the Galapagos Islands.
Galapagos mockingbirds exhibited distinct appearances on different islands.
Galapagos tortoises displayed shell variations linked to their island environments.
Galapagos finches showed diverse beak shapes adapted to different food sources available on their respective islands.
By 1837, Darwin began his notebooks on the origin of species, sketching the first evolutionary tree, which showed his belief in common ancestry and the branching of species over time.
Darwin's Realization of Natural Selection
In October 1838, after reading Malthus's Essay on the Principle of Population for amusement, Darwin had a profound insight.
He connected the "struggle for existence" (from Malthus) with his observations of animal and plant habits, realizing that under these conditions, "favourable variations would tend to be preserved, and unfavourable ones to be destroyed."
This process, he concluded, would lead to "the formation of new species." This was his "Aha!" moment, providing him with a powerful mechanism for evolution.
Alfred Russel Wallace (1823-1913)
Independently co-discovered the theory of natural selection.
Conducted extensive travels and research in the Malay Archipelago.
Noted striking faunal differences between closely located islands, separated by narrow straits.
Example: "Crossing over to Lombok, separated from Bali by a straight less than 20 miles wide, I naturally expected to meet with some of these birds again; but during a stay there of three months I never saw one of them."
His observations led to the delineation of Wallace's Line, a biogeographical boundary separating Asian fauna to the west from Australian fauna (and transitional species) to the east.
Like Darwin, he recognized the struggle for existence in wild animals.
In 1858, Wallace sent his theory to Darwin, prompting Darwin to finally publish On the Origin of Species in 1859.
Wallace's thoughts on natural selection, similar to Darwin's, stated: "Perhaps all variations…must have some definite effect…in the habits and capacities of the individuals [and]…a variety having slightly increased powers…must inevitably acquire a superiority in numbers."
Darwin's (and Wallace's) "Big Idea" of Natural Selection
As articulated by Darwin in Origin of Species (1859):
"As many more individuals of each species are born than can possibly survive; and as, consequently, there is a frequently recurring struggle for existence, it follows that any being, if it vary however slightly in any manner profitable to itself, under the complex and sometimes varying conditions of life, will have a better chance of surviving, and thus be naturally selected."
"From the strong principle of inheritance, any selected variety will tend to propagate its new and modified form."
Later Discoveries Supporting Evolution
Gregor Mendel (1822-1884)
Known as the "Father of Genetics."
Discovered that traits are inherited by predictable laws, providing the crucial mechanism for how variations are passed from one generation to the next.
Rosalind Franklin (1920-1958), James Watson (1928-), & Francis Crick (1916-2004)
These scientists elucidated the structure of DNA, discovering the means for heritable information to be stored and passed on from one generation to the next, solidifying the molecular basis of inheritance and, by extension, evolution.