Fact: current life forms
both within and among species.
Evolution accounts for variation among living organisms.
[Variation occurs in time and space]
What is the "Theory
The explanation of observed patterns of temporal and spatial variation
in terms of biological and physical processes.
Theory: an organized set of facts, principles, and hypotheses;
not a "guess", not "just a theory"
and interpretation of organismal
Taxonomic patterns have been described in the second-year core.
Laboratory exercises introduce quantitative & statistical methods.
& ecological processes underlying variation within
Short-term, small-scale (microevolution)
Populations genetics models evolution in terms of allele frequencies.
in the fossil record describe
origin of variation among species:
Long-term, large-scale (macroevolution).
Systematics & the Comparative Method as a means of analyzing evolution.
"Nothing in biology makes sense except in the light of evolution."
I summon the supernatural beings
Who first contrived
In the stuff of life.
You did it for your own amusement.
Descend again, be pleased to reanimante
This revival of those marvels.
Reveal, now, exactly
How they were performed
From the beginning
Up to this moment.
Ovid: Metamorphoses (trans. Ted Hughes)
Biology in the 18th century
The Classical Tradition: Plato & Aristotle (4th cent. BCE)
Theory of Forms (essences, eidos)
'real' objects are manifestations of 'ideal' forms
variation is illusory [see Plato "The Republic"]
Dichotomy: the world is composed of paired opposites
"A" versus "not A" classes
good / bad, right / wrong, up / down, light / dark, male / female, etc.
e.g., vertebrates vs. invertebrates
Aristotle - "Father of Biology"
Five books on zoology ("Generation of Animals")
Biological structures have purpose: Efficient versus Final Causes
Theology: "The Wisdom of God,
in His Creation"
'Ideal' forms exist in the Mind of God:
'real' world created by God (Genesis 1:1)
Scala Naturae: the "Great Chain of Being"
Creation is an infinitely graduated progressive series
Time scale is short (ca. 6,000 years)
Species are static: no new forms, no change, no extinction
The study of nature is a pious activity
Taxonomy (Carl von Linne [Carolus
"Systema Naturae" (1735; 10th ed. 1758)
4,162 animals described
binomial nomenclature: genus + species names
"ad majorem Dei gloriam": for the greater glory of God
creates a Scientific Crisis
New forms are discovered that don't fit the Scala
Extinctions have evidently occurred
Variation is real in space: what about over time?
Biology in the early 19th century:
Change has occurred, how do we explain it?
The Enlightenment favors rational explanation.
Baptiste de Lamarck
"Zoological Philosophy" (1809)
New features arise due to persistent "besoin" (need / want)
(teleological: a goal-directed explanation)
Use and disuse alter morphology:
Altered morphology is passed on to offspring
(Lamarckism: inheritance of acquired characteristics)
Ex.: Giraffes stretch their necks to feed on leaves.
Successive generations gradually acquire longer necks.
[or, trees become taller to escape giraffes]
Therefore, organisms change (evolve) over time
Charles Lyell (1797-1875): "Principles of Geology" (1830)
Observable, gradual processes + enormous time = world geology
The Darwinian Revolution [extended lecture on Darwin]
B.Sc. (Cambridge): pre-med
Naturalist on board HMS "Beagle" (1831-36)
"The Voyage of the Beagle" (1839) a best-seller
Read Robert Malthus "On Population" (1838):
population increases exponentially, resources increase arithmetically
Letter from Alfred Wallace (1823-1913) in June 1858
"On the Origin of Species" (1859)
of evolution by natural selection
(after pp. 80-81 of "Origin")
Observation: In any species, more young are born than can possibly survive.
Observation: Yet a species' numbers do not increase without limit.
CONCLUSION: There is a Struggle
and differential survival and reproduction occur within species.
[Darwin: "I use 'struggle' in a large and metaphorical sense..."].
Observation: Individuals within
species show variation
that affects the probability that they will survive this struggle and leave offspring.
CONCLUSION: Those individuals
survive and reproduce do so in consequence
of their "adaptively superior" variation (they are "more fit")
This process of differential survival and reproduction is called Natural Selection.
Observation: Variation is heritabile:
offspring tend to resemble their parents.
[Remember that Mendelian genetics was unknown in 1859).
Adaptively superior variation will be inherited by the offspring generation.
That is, evolution occurs as descent with modification.
Implications of Darwin's Theory
provides a mechanism for Evolution:
Modern evolutionary theory seeks to clarify this mechanism.
in Nature is due to common
from an ancestor:
Organisms resemble each other because they are related.
of relationship provides a basis for "natural
Taxonomy should reflect the phylogeny of organisms.
things are related (the basic fact of biology):
Humans have evolved from other animals (Darwin's "Descent of Man" 1871).
"The main conclusion arrived at in this work,
namely that man is descended from some lowly organised form,
will, I regret to think, be highly distasteful to many."
Loren Eisley (1959).
"Darwin's Century." Doubleday.
William Irvine (1955). "Apes, Angels, and Victorians: Darwin, Huxley, & Evolution." McGraw-Hill.
Ernst Mayr (1994). "One Long Argument". Harvard University Press.
Gordon Ratray Taylor (1963). "The Science of Life." McGraw-Hill.