Download Descent With Modification

Descent With Modification
Darwin’s theory of evolution
Before Darwin…
• Aristotle’s scala naturae
– scale of complexity
• He basically just rated
everything on a scale of
rock to God.
• He believed species
were fixed.
Influences on Darwin
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Paleontology
Geology
Lamarck
Malthus
Paleontology/ Geology
• Paleontology= Study of fossils (in
case you didn’t know)
• Could roughly date by strata
(rock layers)
• Older fossils were less similar to
today’s life
Take-aways for Darwin:
- The Earth is super old (closer
to 4.5 billion than 6000 years)
- Slow processes over great
time can also act on life.
Thomas Malthus
• Economist
• Hypothesized that much of human suffering was
due to the population increasing faster than food
supply or resources.
• More people are born than can survive
Lamarck
• Gets made fun of by
evolutionary biologists
(and not just because of the
haircut)
• Compared fossil and
modern species and
noticed lines of
descent.
• Older species changed
to become modern
species.
Lamarck’s Theory
• Use and disuse– Body parts that are used become bigger and
stronger.
– This can be passed on to offspring
So we know he wasn’t right…
Or was he?
- First reasonable
explanation of fossil
record.
- Maybe science can shed
light on the forms of
modern species.
- Also epigenetics
validates him to some
extent.
Well, mostly he was wrong, but
he opened the door for new
ideas.
Charles Darwin
• At age 16, Darwin was
sent by his father to
study medicine.
• He left and enrolled at
Cambridge to become a
clergyman. (A career that
interestingly allowed him
to pursue his interest in
becoming a naturalist)
• At the age of 22, Darwin
set out on a voyage on
the HMS Beagle.
I’m on a boat!
The Voyage
• The goal was to chart the
South American coast.
• Darwin’s job was to
collect and document the
species he encountered.
The Galapagos
• Young volcanic islands west
of South America
• Although geologically close,
the islands each offered
unique conditions and
ecosystems.
• Darwin hypothesized that
the organisms of the islands
were descendants of
colonizing species from the
mainland that had changed
over time.
Adaptation
• Characteristics of organisms that increase
fitness.
• These can be inherited!
• Classic example  Finches
Natural Selection
• Observation 1: Members of a population have
variation in their traits.
• Observation 2: Offspring inherit traits from
their parents.
• Observation 3: All species are capable of
producing more offspring than the
environment can support. (Malthus)
• Observation 4: Many of these offspring are
unable to survive
Therefore we can infer…
1. Individuals with traits that allow them to
better survive and reproduce tend to leave
more offspring than other individuals.
2. Traits that help organisms survive will
become more frequent over generations.
The Origin of Species
Wallace: the first hipster???
• Darwin first wrote about
natural selection in 1844,
but put off publisihing
• In 1858 Alfred Russel
Wallace sent Darwin a
copy of his theory of
natural selection- Darwin
finally stopped
procrastinating and
published his theory. He
got the credit because he
wrote it first and because
Wallace was cool about it.
The Origin of Species
• Over the years,
Darwin had collected
overwhelming
evidence and support
for his theory:
– Fossil record, artificial
selection and so many
examples!
Darwin’s theory was
accepted by most
scientists within a decade.
Important Points
1. Although natural selection relies on the
interactions of individuals with their
environments, individuals do NOT evolve.
Populations evolve.
2. Natural selection can only work on traits
that are inherited (sorry Lamarck)
3. The environment varies over space and time.
A trait that is favorable in one environment
may not be helpful in another.