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Evolution
Historical Viewpoints
• Earth and all organisms have always
existed in current state.
– Creation by higher authority so NO
CHANGE possible.
• 18th-19th centuries – evidence that earth
may be much older than originally
thought and may have changed
– Fossils!
Hutton and Lyell (geologists)
• James Hutton (1785) - examined
geologic features such as rock layers
and erosion
– concluded earth very old.
• Charles Lyell (1833) - observed current
earth processes: floods, erosion,
earthquakes, etc.,
– concluded same geologic processes
shaped the earth to current form.
Figure 22.4 Strata of sedimentary rock at the Grand Canyon
Early Evolutionist
• Jean-Baptiste Lamarck
(1809)
• Recognized that species
change over time
• Idea: Inheritance of
Acquired Traits
• Think about genes: Can
experience change
genes to fit?
Social Theory
Thomas Malthus (1798)
• Describes role of competition for
limited resources in human societies.
• Not everyone will compete
successfully.
Charles Darwin
• English scientist born in 1809
• Gave up medical studies, went
to seminary.
• 5 years as naturalist on HMS
Beagle
– Mission: Explore and document
South America’s land forms and
animals.
Darwin and Natural Selection
• Force that causes populations to
evolve.
• Relies on variation in traits
(phenotypes) in any population
• Based on 3 main principles
1) Competition
2) Survival of the Fittest
3) Descent with Modification
1. Competition
• Variation in traits; Some traits give
individuals an advantage - make them
better competitors.
• Members of a species compete with
each other for resources like food and
space.
• “Struggle for existence”
2. Survival of the Fittest
• Organism’s ability to survive in it’s
environment called it’s fitness
• Greater fitness means more
reproductive success!
– If trait a greater fitness, call it an adaptation
– If trait is harmful, a less fitness
Peppered Moths
Which variation is more fit?
3. Descent with Modification
• Alleles for adaptations are passed on
through generations and accumulate in a
species’ gene pool over time.
• If enough difference, produces a new
species.
• Ex. Hawaiian Honeycreepers
– All Hawaiian honeycreepers have similarities in
skeletal and muscle structure that indicate they
are closely related.
• Each Hawaiian honeycreeper species has a bill
specialized for eating certain foods.
• all 23 honeycreeper species apparently arose from
a single species – competition for food.
Descent with modification
Principle of Common Descent
• All species (living and extinct) have evolved
from common ancestors for a very long time.
• Overwhelming evidence supports this –
details of how species change not always
clear.
Descent from common ancestors
Kingdoms
Eubacteria
Archaebacteria
Protista
Plantae
Fungi
Animalia
Comparative Anatomy
• Morphologically
similar structures
that perform
different functions
are called
homologous
structures.
• Supports
evolutionary
relationship.
Fossil Record
• Preserved remain of
ancient life in rock, ice,
tar, etc.
• Fossils found in lower
levels of rock older than
ones above. (relative age)
• Extinction!
• Very hard for an organism
to become a fossil.
(see HHMI evolution, lecture
1: 19)
Comparative Embryology
• closely related organisms go through
similar stages during their embryonic
development
Biochemical Similarities
• All living things use DNA, ATP (energy
molecule), similar enzymes, same
codons for protein synthesis, same 20
amino acids etc.
• Remember, at the cell level we are very
close to most other eukaryotic
organisms!
What can we do with Biochemical
Similarities?
How old is it really?
• Absolute dating:
• For rocks, look at ratios of different
isotopes present; these vary over time.
• When there are remains of organic
material (carbon) in a fossil, we can use
carbon dating to approximate age
objectively
Carbon Dating
• Radioactive isotopes decay at a
constant rate
– Half Life  length of time for ½ of an
isotope to decay
• Ex. Carbon-14 decays to Nitrogen-14
• Half-life = 5,730 years
• Carbon 14 can only be used to date fossils less
than 60,000 years old!
Geographic
Distribution/Biogeography
• distribution of plants and animals
throughout the world
• Some fossils found on different
continents are nearly identical
supporting movement of continents.
• major isolated land areas and island
groups develop indigenous species:
independent evolution
Analogous Structures
• Similar function, very
different structure
– Insect wing and bird
wing
– Whale fin and fish fin
• Develop when
organisms face
similar pressure from
environment:
convergent evolution.
Vestigial Organs
• “Degenerated” structures that are of little
or no use to an organism.
• Examples of vestigial structures include:
– parts of pelvic girdle and leg bones of
walking ancestors still in some whales and
snakes.
– blind, cave-dwelling fish that have eyesockets but no eyes.
• Still using same body instructions as
ancestors.
Evolution of
the Horse
•Track the
changes in foot
and leg
structure as well
as teeth.
•Relate to
environment.
Adaptive radiation
AKA
Divergent
Evolution:
one
ancestor
produces
many new
forms
Effects of Natural Selection
Changing Allele Frequencies
without Natural Selection
• Gene flow – individuals join or leave
the population
• Founder Effect – a few individuals start
a new population.
• Genetic Drift – random events mean
only a few individuals reproduce. Big
problem in small populations.
Evolution of Organisms
• All new inheritable physical traits in an
organism represent changes in that
organism’s genetics: mutations
• Darwin did not understand genetics
and so could not explain how traits
were passed down through
generations.
• We can apply genetics to evolutionary
theory.
So how are new species
created?
• Organisms must become
reproductively isolated.
– Will mate only with others of their own
kind.
– If mating with others does occur, offspring
are not fertile.
• Requires isolating gene pools.
New species
from
geographic
separation
and separate
evolution
New species
from a mutation
in individual that
spreads within
existing
population
Geographic Isolation
Reproductive Isolation may also
be…
• Behavioral – sing the right song, dance the
right dance
• Temporal – time of year or day
• Mechanical – the parts don’t fit
• Biochemical – sperm can’t penetrate egg
• Chromosomal – chromosome numbers
don’t match
How fast does evolution work?