Transcript The Origin of Species - Dr. Spence

Darwin’s Theory of Evolution
Science’s Answer to the Question:
“Where Did Life on Earth Come
From?”
Charles Darwin
(12 Feb. 1809 – 14 April 1882)
• Robert Darwin, father, and Erasmus Darwin, grandfather - both
physicians and Unitarian free thinkers.
• Quit physician training to become a minister. Most naturalists in
1800’s were ministers who studied “natural theology,” which
sought to discover the Creator’s plan and purpose for all
creatures.
• Voyage of the HSM Beagle (1831-1836).
• Charles enlisted specialists (ornithologists, botanists, geologists
to help him wade through his data
• On the Origin of Species (1859)
Voyage of the HMS Beagle 1831 - 1836
England
EUROPE
NORTH
AMERICA
ATLANTIC
OCEAN
PACIFIC
OCEAN
Galápagos
Islands
Darwin in 1840,
after his return
AFRICA
HMS Beagle in port
SOUTH
AMERICA
Andes
AUSTRALIA
Cape of
Good Hope
Tasmania
Cape Horn
Tierra del Fuego
In 1839 he published his “Journey on the Beagle”
New
Zealand
Alfred Russel Wallace
(8 Jan. 1823 – 7 Nov 1913)
Wallace was a British naturalist, explorer, geographer, anthropologist, and biologist.
He is best known for independently conceiving the theory of evolution through
natural selection; his paper on the subject was jointly published with some of
Charles Darwin's writings in 1858. This prompted Darwin to publish his own ideas
in On the Origin of Species. Wallace did extensive fieldwork, first in the Amazon
River basin and then in the Malay Archipelago, where he identified the faunal
divide now termed the Wallace Line, which separates the Indonesian archipelago
into two distinct parts: a western portion in which the animals are largely of Asian
origin, and an eastern portion where the fauna reflect Australasia.
He was considered the 19th century's leading expert on the geographical distribution
of animal species and is sometimes called the "father of biogeography". Wallace
was one of the leading evolutionary thinkers of the 19th century and made many
other contributions to the development of evolutionary theory besides being codiscoverer of natural selection. These included the concept of warning colouration
in animals, and the Wallace effect, a hypothesis on how natural selection could
contribute to speciation by encouraging the development of barriers against
hybridisation.
http://en.wikipedia.org/wiki/Alfred_Russel_Wallace
In 1844, Darwin wrote a long essay on the origin of species and
natural selection…
- But he was reluctant to introduce his theory publicly, anticipating
the uproar it would cause.
-At the time, most people believed that the Earth was 6,000 years
old and that all species had been created by the Creator all at once.
His theory of evolution is incompatible with this view.
- In June 1858 Darwin received a manuscript from Alfred Russell
Wallace (in Indonesia) who had developed the theory of natural
selection independently of Darwin.
Darwin quickly finished The Origin of Species and published it the
next year, 16 years after he had written it.
- Darwin collected many plant and animal specimens from the
Galapagos Islands off South America.
- He studied his finch
collections, especially
the differences in their
beaks, when he got
home and began to
make connections
between adaptations
and how new species
originated (speciation).
(which is why The
Origin of Species
became his book title…)
Natural selection works on individuals, but
populations/species evolve
•
Geospiza fortis (Galapagos
ground finch of Daphne Major)
•
In 1977, 180 of 1200 individuals
survived a drought.
•
Larger harder-shelled seeds
survived the drought and so did
the bird with the deepest and
larger beaks.
•
Evolution occurred - allele
frequencies change in a
population
How do Populations and Species change?
2 Primary Sources of Genetic Variation
• Mutations – creates variation
• Sex - shuffles the deck and spreads
mutations around…..
Three basic mechanisms of
evolutionary change
• 1. Natural Selection
• 2. Genetic Drift
• 3. Migration
(Gene Flow or Gene
Migration)
Linnaeus (classification)
Hutton (gradual geologic change)
Lamarck (species can change)
Malthus (population limits)
Cuvier (fossils, extinction)
Darwin (evolution, nutural selection)
Mendel (inheritance)
• The historical context of
Darwin’s life and ideas
Lyell (modern geology – Earth is old
Wallace (evolution, natural selection)
American Revolution
1750
French Revolution
1800
U.S. Civil War
1850
1900
1795 Hutton proposes his theory of gradualism.
1798 Malthus publishes “Essay on the Principle of Population.”
1809 Lamarck publishes his theory of evolution.
1830 Lyell publishes Principles of Geology.
1831–1836
Darwin travels around the world on HMS Beagle.
1837 Darwin begins his notebooks on the origin of species.
1844 Darwin writes his essay on the origin of species.
1858 Wallace sends his theory to Darwin.
1859
The Origin of Species is published.
1865 Mendel publishes inheritance papers.
Artificial Selection – selective breeding by
farmers changes species over time
Darwin connected and built on
others’ ideas
• If the Earth is very old and has gradually changed
over time…and if plants and animals have also
changed over great periods of time… and if animals
can be artificially bred to change…and if there is
competition for survival…
• He connected the dots between Cuvier, Lamarck,
Hutton, Lyell, Malthus, and what he saw with
selective breeding of plants and animals (artificial
selection) ….
NATURAL SELECTION
• Darwin made the connection that individuals in all
species compete for survival, that successful individuals
survive and pass on their genes, and in this way the
entire species adapts to its environment.
• Over time, these adaptations can accumulate to create
new species.
• He called this process natural selection. He did not coin
the term “survival of the fittest.”
• How do “successful” individuals get their “good” genes?
Darwin’s Observations
1) Variation heritable differences exists among individuals within species.
2) Overproduction, all offspring do not survive to become reproducing
adults, the environment cannot support all progeny.
3) Adaptation, organisms must be able to survive a changing environment
for their offspring to be able to find mates and produce more offspring.
4) Descent with modification, organisms will change to better fit their
environment as time progresses.
Darwin’s Inferences
Inference 1: The organisms whose variations best fit them to the
environment are the ones who are most likely to survive, reproduce,
and pass those desirable variations on to the next generation.
Inference 2: Unequal survival and reproduction will lead to favored
traits that may become inherited by future generations.
•Darwin developed two main ideas
-Natural selection – mechanism by which fit individuals survive
and pass on their genes. Unfit individuals do not.
-Evolution -natural selection causes change over time, or
evolution. This explains life’s unity and diversity – all life on
earth descended from a common ancestor (life’s unity) and then
evolved into all the diversity that has ever existed on Earth (99%
of which is already extinct!)
**Natural selection is the mechanism; evolution is the result*
•He used the phrase descent with modification to capture both ideas.
Descent captured his idea of a common ancestor from which all life
descended
–Modification captured his idea of adaptations leading to diversity.
• Population - same species, same place, same time
• Species - members of the same population that can
interbreed and produce fertile offspring.. Reproductive
compatibility is key.
• Gene pool - the collection of all of the genes within a
population.
• Populations evolve. Individuals do not!
“Fitness”
Darwin called the ability of an
organism to survive and reproduce in
its specific environment “fitness.”
Fitness is NOT just the strongest
or the fastest!
• Can be the sneakiest! Or best
camouflaged….
• And you have to reproduce or its all for
nothing evolutionarily speaking….
Descent with Modification =
Theory of Evolution
The characteristics of new species are not
entirely new, but rather modified versions
of ancestor characteristics.
…..
Evolution is a process of remodeling, not
inventing.
Mother Nature can only work with the
material she has.
…..
Cladograms
Phylogenetic tree
Both phylogenetic trees and cladograms help show
the relationships between different organisms, but
only phylogenetic trees have branches that represent
evolutionary time and amount of change.
Each group has to write up and submit to Dr. Spence
the reasoning for the arrangement of their groups.
•
•
•
•
Common ancestor
Shared derived trait
Homology
Convergent structure (convergent evolution)
Compare your cladogram with the other groups.
As a group, defend your arrangement.
Nurse young
Vertebra
Internal skeleton
Bilateral symmetry
What is the Evidence for
Evolution?
Evidence for Evolution: Outline
• Research Interventions…biotechnology
• Homology – Evidence of Remodeling of body
designs
–
–
–
–
Anatomical Homology
Vestigial Structures (snake pelvis, appendix)
Embryological Homologies
Molecular Homologies
• The Fossil Record Corroborates Evolution
• Transitional Fossils –
• Biogeography - bears, marsupials and placentals
Homologous Structures - structures that have the same
ancestral origin and develop from same embryonic
tissue, but have evolved to fit their environment and
have different mature forms in different species.
- Not separately engineered – remodeled by natural
selection…Mother Nature can only work with the
material she has!
Forelimbs Up Close
Can you think of other
homologous structures?
Evolution.berkeley.edu
Vestigial Structures
•Structures that no longer have a use
•Remnants of structures that were once useful….
•Examples in humans: wisdom teeth, coccyx, appendix,
Darwin’s Tubercle
•What was the ancestral purpose of these structures?
•Why do we still have them?
Embryology
• Embryonic stages reveal anatomical homologies
that disappear in adult organisms
• In vertebrates, the same groups of embryonic
cells develop in the same order and in similar
patterns
• The embryo “is the animal in its less modified
state,” which “reveals the structure of its
progenitor”
Embryology
"ontogeny recapitulates phylogeny“ Ernst Haeckel 1892
http://ncse.com/book/export/html/11831
Transitional Fossils:
Evolutionary transitions have left signs
in the fossil record
Figure
22.18
• Fossilized whales have traits that link today’s whales
to their terrestrial ancestors. Fossilized leg bones of
Basilosaurus and Ambulocetus show the hind limbs
of whale ancestors
Human Transitional Fossil:
Australopithecus Afarensis
Molecular Homologies
•Because the genetic code is universal in all living
things, molecular biology can now explore
evolutionary relationships between very different
species (plants, animals, fungus, bacteria…)
•If two species have some gene and protein
sequences that match closely, the sequences have
probably come from a common ancestor
•More on this when we discuss classification
systems…
Biogeography
• The distribution of species
• Gave Darwin his first clue about evolution: Similar
species live near each other because they have
descended from a common ancestor.
• Islands are showcases for biogeopraphic evidence
because they are isolated
Australian Marsupials
are closely related
- all evolved from a
common ancestor
- therefore have common
characteristics
Convergence:
Evolution’s Wild Card
Not all similarity represents common ancestry!
•Species from different evolutionary branches may
resemble each other because they evolved similar
adaptations in similar environments….in other
words, by coincidence
•This is called convergent evolution and the similar
traits are called analogies (not homologies!)
Sugar Gliders and Flying Squirrels
Convergence:
• Dolphins and Sharks
Sharks and Dolphins
•Dolphins are aquatic mammals
•Sharks are cartilaginous fish (along with rays and
skates)
• They separately evolved similar traits as aquatic
predators: Dorsal fins, fusiform body shape,
coloration
•These are analogous traits
Sea Lions and Seals
Convergence
• Sealions and seals have a
very distant common
ancestor. Sealions are
more closely related to
bears and seals are more
closely related to otters.
• They have converged on a
form. It is a co-incidence.
• Their structures are
analogous to each other.
Prehistoric Convergence
Evolution Research Example:
Reznick and Endler, 1982 Paper
Reznick and Endler transplanted guppies from pike-cichlid pools to killifish pools
and measured the average age and size of guppies at maturity over an 11-year
period (30 to 60 generations).
Pools with killifish,
but not guppies prior
to transplant
Experimental
transplant of
guppies
Predator: Killifish; preys
mainly on small guppies
Guppies:
Larger at
sexual maturity
than those in
“pike-cichlid pools”
Predator: Pike-cichlid; preys mainly on large guppies
Guppies: Smaller at sexual maturity than
those in “killifish pools”
Figure 22.12
They watched evolution happen….
RESULTS
After 11 years, the average size and age at maturity of guppies in the transplanted
populations increased compared to those of guppies in control populations.
185.6
161.5
85.7 92.3
48.5
58.2
Control Population: Guppies
from pools with pike-cichlids
as predators
67.5 76.1
Males
Females
Males
Females
Experimental Population:
Guppies transplanted to
pools with killifish as
predators
CONCLUSION Reznick and Endler concluded that the change in predator resulted in different variations
in the population (larger size and faster maturation) being favored. Over a relatively short time, this altered
selection pressure resulted in an observable evolutionary change in the experimental population.