Religious beliefs about human origins have served as both a guide and justification for human actions.
Humans were considered separate from the natural world but evolution connected humans to the
Mid 18th Century: Linnaeus - classification of plants and animals places humans in the order Primates.
At first “Progressionism” and “Natural Theology” attempted to fit biology into a religious framework.
Progressionism is the stair theory – everything is working towards God’s image and is on a different
step. This was racistly used to rank people in the western world
FIRST systematic evolutionary theory - JEAN LAMARCK. Based theory on the inheritance of acquired
Acquired characteristics means that your children will inherit things that you have acquired – can be
proven wrong because if you cut off your hand your children will still have two.
Evolution had little impact until genetics was explained
Big problem for early evolutionists was the 6,000 year biblical time-span, which did not allow time for
evolution to occur. The emerging science of geology challenged this short chronology.
Charles LYELL- publishes “Principles of Geology”
This promoted “uniformitarianism”, the idea that the earth’s form was derived from SLOW and
GRADUAL processes of uplift, erosion and deposition. This contradicted “catastrophism” = earth forms
all created by cataclysmic floods, volcanic eruptions, etc.
Charles Darwin became a biologist and was appointed ship’s naturalist on the Beagle for a survey of the
coast of South America. Darwin went ashore and collected at every opportunity. This gave him a North
to South, then South to North transect where he could observe geographical variation in related
species, AND the link of that variation to environmental differences. This refined his concept of
Darwin strongly influenced by “Essay on Population” by Thomas Malthus
“Struggle for existence” in which more offspring are born than can survive to reproduce.
5 MAJOR POINTS OF DARWINIAN EVOLUTIONARY THEORY
• 1. Organisms produce more offspring than can survive to reproduce.
• 2. Because numbers of individuals in a species are usually constant, there must be a high
• 3. Individuals in each species vary in their characteristics.
• 4. Variants that fit their environment better will be favored over those less fit. Fitness is
defined by DIFFERENTIAL REPRODUCTIVE SUCCESS. By inheritance, better fit individuals pass
on their beneficial characteristics in greater numbers because they have more offspring that
survive and reproduce. This process is “natural selection”.
• 5. Following generations will continue to exhibit and refine adaptations realized by their
This left 2 major unanswered questions.
• A: What is the source of individual variation?
• B: How are characteristics inherited?
Alfred R. Wallace develops the same theory from his work in Southeast Asia.
Darwin publishes “Origin of Species” in 1859, causing great controversy!
Scientific challenges to Darwinian Theory stressed his inability to explain inheritance, and his reliance
on a long age for the earth.
Darwin believed in “blending inheritance”, where characteristics from each parent mixed like liquids so
if you had one parent with light eyes and one with dark, your eyes would be somewhere in the middle.
This was a crucial flaw!
The major scientific challenges were:
• 1. Fleeming Jenkin - 1867 - showed statistically that with blending inheritance, single favorable
mutations would be diluted out of existence over time, making Darwin’s natural selection
impossible. Realizing Jenkin was right, Darwin reverted to Lamarkian explanations of
inheritance, undermining his own theory
• 2. Lord Kelvin - Argued that the universe was governed by chemical reactions and had a short
history. His paper claimed that the time that the earth took to cool to its present state was as
short as 20 million years. His prestige caused geologists to reduce their estimated age of the
earth, leaving no time for gradual evolutionary processes.
Evolutionary theory rehabilitated by 2 discoveries:
• 1. In 1900, biologists discover the work of Mendel - foundation of modern genetics - This
reestablished natural selection as a viable process.
• 2. Pierre Curie and Albert Laborde discover atomic energy in 1903, making Kelvin’s age
estimates for the earth meaningless.
Religious opposition to Darwin
• Many early evolutionists thought evolutionary theory should replace religion as a guide to
• Religious progressives like William Jennings Bryan strongly opposed evolution because they
thought it would replace morality and ethics with a “Law of Hate”
These concerns were legitimate! Many supporters of evolution had adopted two VERY problematic
ideas that mirrored their own class and racial biases:
• 1. “Unilinear Evolutionism” Thought evolution was directed toward the production of Western
civilization. Considered 3rd World peoples to be “living fossils”, inferior to Europeans, who were
“naturally” more intelligent and moral. Justified colonialism to “uplift” native peoples.
“Atavisms” (i.e. throwback “primitive” traits) used to explain European crime, etc.
• 2. “Social Darwinism” & the Eugenics movement Social Darwinism = concept of “survival of
the fittest” justifies exploitation of the weak by the strong. Eugenics movement = attempts to
prevent “inferior” peoples from breeding. Ultimate expression of these ideas was Nazism.
So, UNLIKE today, many 19th Century opponents of evolution were humanists and progressives, who
believed that evolution was simply a “scientific cover” for vicious social ideas. BUT, these ideas distort
the real meaning of evolutionary theory. Darwin and others realized that fitness could result from
cooperation as well as competition. Evolution describes biological processes, and does NOT provide a
guide for moral or ethical behavior, which are cultural constructs.
Neanderthal fossil discovered in 1854 by quarry workers. Dismissed because scientists expected early
humans to have a human-like head on an ape-like body (they thought large brains evolved first).
Eugene Dubois - deliberately looked for early humans in Java (he thought humans were descended from
orang-utans). Found skullcap & femur near Trinil. Named Pithecanthropus erectus (now Homo
erectus). Dismissed for the same reason as Neanderthal.
Charles Dawson finds modern-like cranium with ape-like jaw near Piltdown, England, in 1912. Because it
corresponded to expectations, this fake was not exposed until the 1950's.
Canadian Davidson Black finds “Peking Man” near Beijing, China, in 1927. Similar to Dubois’
Raymond Dart finds the “Taung Baby” in South Africa in 1924. Named Australopithecus africanus.
Claimed humans originated in Africa, not Eurasia. Skeptics argued it was a baby chimp.
Louis and Mary Leakey find Australopithecine fossil in Olduvai Gorge, Tanzania, in 1959. Crude stone
tools directly associated with the fossil. Date of 1.92 million years BP (MYBP) doubles the estimated
age of the human line and validates Dart’s claim of an African origin for humans.
Gregor MENDEL - Publishes “Experiments in Plant Hybridization” describing his particulate theory of
inheritance. Was ignored for 35 years because most biologists couldn’t understand probability
Trait = any physical characteristic of an organism.
Genes = The physical structure that transmits hereditary potential. Now defined as a “segment of a
chromosome that produces a recognizable effect and separates as a unit during the formation of sex
Genes can have alternate forms that produce different effects = alleles
Phenotype is the product of the genotype and influences of the environment.
Mendel’s Law of Segregation = Alleles separate during the production of sex cells. This contributes to
Independent assortment of genes = each gene at a single location on a pair of chromosomes (one
chromosome from the father, the other from the mother) is equally likely to be transmitted when sex
cells are formed.
SOURCES OF VARIATION
1. Mutation - random changes in the DNA molecule. This is the only source of truly NEW genetic
variation. Mutation can occur in individual genes, or in entire chromosomes through either numerical
(i.e. adding or deleting an entire chromosome) or structural changes (i.e. addition of a segment, loss of a
segment, reversal of a segment, etc.) most mutations are neutral and don’t affect the phenotype
2. Recombination - the creation of new genotypes resulting from segregation and the exchange of
genetic material between paired chromosomes during sex-cell formation (meiosis).
SPECIES = Any group of organisms which can interbreed to produce fertile offspring. This corresponds to
the “biological species concept”. Species may be one contiguous population or be separated by barriers
Mendelian Population = a population in which genetic material is actually being exchanged. Often
equivalent to sub-populations.
Gene pool = All of the genes in a Mendelian population.