Transcript Principles of Evolution

Principles of Evolution
“Nothing in biology makes sense without
understanding evolution”
Andrew Goldenkranz--Aptos High School
1. Things We Easily Observe in Nature
• --species are adapted
to their environment
• --populations over
reproduce and are held
in check by limiting
factors
• --genetics provides
variation within
populations
2. Setting the Stage
for a Complete TheoryDiscoveries in the 50 years before Darwin
1--Lyell and Kelvin
proved that the
Earth is much older
than we thought
3--Dinosaurs and other fossils
discovered in early 19th
century
2--Malthus described a
natural world of
overpopulation, limited
by famine, pestilence,and
warfare
4--Darwin observed the process of
artificial selection practiced by
farmers and breeders in the
English countryside
3. A Simple Argument that
took 25 years to publish
• --genetics provides the raw variation in a
population
• natural selection is the filter that
leads to differential survival and
reproduction among individuals within a
species
• --small selection forces drive changes that
add up over time
• --isolated populations radiate into new
species:
– Geographical, behavioral, reproductive,
ecological
• --selection is local, not global
4. Evidence Waiting for a
Theory to Emerge
• Paley--a watch needs a watchmaker
• Lamarck--organisms pass on acquired traits
(giraffes got long necks by stretching to
reach the tall branches)
• Most scientists know that evolution was
happening, but weren’t sure how. Darwin
provided the connection as evolution by
natural selection
5. Why did he wait so long?
• --Darwin knew this would shake up the
church and was afraid to publish until he
had lots of evidence
• --He found out that Alfred Wallace was
about to publish the same idea, so they went
public together in 1859
• --First edition sold out on the first day!
5. Patterns in Evolution
Radiation:
Convergence:
Isolation
causes
speciation
from two or
more
populations
Different origins
meet at the same
niche; placental
and marsupial
mammals
Parallel Plots:
Co-evolution:
Flight evolved
independently in
insects, birds,
and mammals
Flying insects
and flowering
plants, parasites
and hosts,
symbiotic
partners
6. What is a species?
• Darwin was consumed with this question-after all, the title of his book wasn’t
“Evolution”, it was “The Origin of Species”
– Reproductive concept--a species is a population that
naturally interbreeds and makes fertile offspring
– Genetic concept--a population with definably distinct
genetic characteristics
– Niche or ecological concept--a group occupying a
specific place in an ecosystem
7. How New Species Form
• Geographical isolation --”allopatric
speciation”
• Behavioral isolation (feeding, breeding, etc)
--”sympatric speciation”
8a: The Founder’s Principle aka
the Bottleneck principle
• In a small population, or when the majority of a
population is eliminated, only a few survivors are able
to reproduce and thrive.
• In these situations, because of chance variation or
selection the new population will take on the
characteristics of those “founders”
• Founders can:
– Float onto the island on a log
– Hitch a ride on a truck
– Be resistant to a disease
8b: The Founders’ Principle is one of the
most famous themes in science fiction!
Thought question:
• If Mankind and Chyna were the last two
people on earth, in 20 generations what
would the population look like as a result?
How would that compare to the current
demographics of humans?
9. Evolution Since Darwin
• --Mendel discovers principles of genetics
• --Physicists discover radioisotope dating methods for
specimens
• --Fossil record accumulates
• --Hardy and Weinberg apply develop population genetics
to track changes in gene frequency over time
• --Ernst Mayr fuses genetics and natural selection into a
“New Darwinism”
• --discovery of plate tectonics adds to geologic history
• --biochemical and genetic evidence accumulates since the
1950’s
• --Lucy discovered in 1974, basis of current model of
human origins
10. Genetic Evidence for
Evolution
• Protein homologues
• Genetic similarities of
humans and chimps=
98.9%
• Use of mitochondrial
DNA is very accurate for
short term evolutionary
rates
• Cytochrome substitutions
is an important benchmark
for longer term evolution
11. Conservation in Action
• All cells share similar
features
• Non-coding DNA may be
residue of conserved
genome (use
vector.cshl.org/bioservers
for great simulations and
models of this hypothesis)
• Jaw hinges in reptiles
became middle ear in
mammals
• Embryology highlights
conserved design patterns
12. Homologous structures an important example of conservation
All these
have:
Human
--Radius and
ulna
Chimp
--wrists
--5 digits
Lion
Baboon
(X-ray images available from www.cipe.com)
13. Current Issues in
Evolution
• Rate of change
- Gradual or punctuated?
• What is the unit of selection:
– Individual?
– Species?
– Gene?
• Individuals don’t evolve,
populations do!
– Hardy Weinberg defines evolution as
the change in gene frequency in a
population over time.
Current Issues in Evolution, #2
• Growth of biodiversity is
interrupted by periodic
extinctions
• Causes of Mass Extinction
– Earth is a dynamic, changing
planet
– Large geological events open up
new opportunities for speciation
• Origins of Cells
• Evolution of Viruses
5 mass extinctions in
history
• Permian extinction
--225 mya
--cleared the way for giant
reptiles
• Dinosaurs wiped out
--62-65 mya
--cleared the way for
mammals to speciate
• Are humans causing the 6th
extinction?
Evolution and Creation
.
1. All major religions, except some protestant and evangelical
denominations, have accepted evolution in some form.
2. Pope’s statement in 1996 declared “overwhelming evidence
from a number of fields” to support the natural origin of
humans; reserved “origin of the soul” as a religious, not a
scientific, event.
3. “Scientific Creation” or “creation science” interprets nature
within a religious context, and has been ruled a religion rather
than a scientific concept. Because this model is not falsifiable
or experimental in nature, it has not been accepted as a
scientific theory.
14. What does evolution
predict about human origins?
• Selective force may have
been greater range of
migration, better vision,
ability to throw
• Humans and other modern
primates share a common
ancestor approximately 5
million years ago
• Upright stance freed up
hands and placed selective
force on hand/eye
coordination and brain
development
Books you want to read to find
out more about this subject
• The Beak of the Finch, J. Weiner
• At The Water’s Edge, C. Zimmer
• Evolution and the Diversity of Life, E.
Mayr
• The Blind Watchmaker, R. Dawkins
• Anything by S.J. Gould
“There is grandeur in this view of
life”
Charles Darwin, closing line
in The Origin of Species