Thinking About Darwinian Evolution:
What is
evolution?? And
what is this finch
doing?!?
We owe much of our
understanding of
EVOLUTION to
CHARLES DARWIN.
Darwin’s Origin of Species (1859):
1. Descent with Modification (Evolution)
2. Natural Selection as a mode of Evolution
Remember: Mendel publishes in 1866…
Darwin’s Natural Selection:
Observation #1: Individual Variation
Observation #2: Struggle for Existence
Inference: Differential Reproductive Success or
Natural Selection
ADAPTATIONS are the result of natural
selection.
Darwin also proposed that natural selection,
over time, could produce new species from
ancestral species.
This was his
explanation for
the 14 unique
species of finches
he observed on
the Galapagos
Islands.
Darwin’s Historical Context: The
Philosophy of the Time
•Plato (427-347 BC): two worlds: a real (ideal) world,
and an illusory world (imperfect) that we perceive with
our senses.
•Aristotle (384-322 BC): all living forms can be
arranged on a scale or ladder or increasing complexity.
(All rungs taken!)
•Judeo-Christian Context: Biology in Europe and
America dominated by natural theology- classifying
species in order to reveal the steps of the scale of life
God created.
The Historical Context
"Those who which to
succeed must ask the
right preliminary
questions." - Aristotle
Darwin’s Historical Context: The
Philosophy of the Time
FOSSILS: Paleontology (the
study of fossils) is developed
by Cuvier (1769-1832). He
documents the succession of
fossil species in the Paris
Basin. He advocates
catastrophism rather than
evolution.
Darwin’s Historical Context: The
Philosophy of the Time
GEOLOGICAL THEORIES:
Hutton (1726-1797) proposes
gradualism (profound change is
the result of slow continuous
processes). Lyell (1797-1875)
expands to uniformitarianism
(geologic processes have not
changed throughout the Earth’s
long history).
Other Scientists had suggested
EVOLUTION, but none had proposed a
MECHANISM!
First Mechanism: Jean Baptiste Lamarck
Lamarck observes several lines of descent
in fossils. Suggests that use and disuse
results in change in morphology. He
suggests that these acquired
characteristics (adaptations!) could be
inherited.
This is wrong, but visionary!
Darwin is heavily influenced by Thomas
Malthus’ writings on human population (1798)
Malthus contends that
much of human
suffering is the
unavoidable consequence
of the potential for the
human population to
increase faster than food
supplies and other
resources.
Darwin’s MECHANISM = NATURAL
SELECTION
• Natural selection is differential success in
reproduction
• Natural selection occurs through an interaction
between the environment and the variability
inherent among the individual organisms making up
a population
• The product of natural selection is the adaptation
of populations of organisms to their environment.
Darwin’s ideas remain
unpublished until
another scientist, Alfred
Wallace, independently
develops the same
theory of Natural
Selection.
Darwin publishes
second, but in much
more detail.
Darwin illustrates his mechanism with examples
from ARTIFICIAL SELECTION, the
breeding of domesticated plants and animals
If artificial selection can change so much in a relatively short
time, argues Darwin, then natural selection should be capable
of considerable modifications.
Examples of Natural
Selection:
•Insecticide-Resistant
Insects
•Antibiotic-Resistant
Bacteria
•Drug-Resistance in
HIV
Other Evidence of Evolution: Homology
Similarity in characteristics resulting from common
ancestry is known as HOMOLOGY.
Homology can be:
1. Anatomical (Homologous Structures)
2. Molecular (esp. DNA)
3. Embryological- developmental structures
and processes.
Anatomical Homology:
Developmental Homology:
FISH
FISH
REPTILE
CHICKEN
HUMAN
Developmental Homology:
MOLECULAR
HOMOLOGY:
Some HOMOLOGIES are MISLEADING…
as they result from CONVERGENT EVOLUTION.
BIOGEOGRAPHY, or the geographic distribution of
species, provides many clues about their evolution.
Islands are especially good for studying
biogeography as they contain many
isolated, endemic species.
The FOSSIL RECORD provides the last major
line of evidence in support of Darwin’s ideas.
The Darwinian
view of life
predicts the
existence of
evolutionary
transitions.
Bailosaurus
Thus Darwin’s views are supported by multiple,
independent lines of evidence.
Evolutionary patterns of Homology that match
patterns in space (Biogeography) and time (the
Fossil Record).