Download How do populations change over time?

How do populations change over time?
Evolution and Natural Selection
Last time...
• Classification/organization of life on earth
• Puzzling observations (homologous structures,
biogeography, vestigial traits, etc.)
• Proposed explanation: evolution!
Evolution
• Change over time
• Biologically: Descent with modification
• Small scale: changes in gene frequencies in a
population from one generation to the next
• Large scale: accumulation of changes over
thousands/millions of years leads to the descent
of different species over many generations
Thus...
• All organisms share common ancestors
• Some are more distant than others
• Classification is really study of genealogy
Taxonomy: study of species’ genealogy
Common panthera ancestor
Common felis ancestor
Common carnivora ancestor
Common mammal ancestor
Common vertebrate ancestor
Common animal ancestor
Common ancestor of all living organisms
How?
Charles Darwin & Alfred Wallace
• HMS Beagle (1831) chart the
coast of South America
• Darwin was offered job as
naturalist, collecting specimens
and recording observations
• Naturalist
• 1848 expedition to Amazon
• 1854-1862 travelled through Malay
Archipelago studying island biogeography
• Known as the father of biogeography
Who was Darwin?
1816
1830’s
1842
1881
The Voyage of the Beagle (1831-1836)
(Darwin was 22 when he left.)
Darwin’s observations: fossils
armadillo
?
glyptodont
Darwin’s observations: geographic variation
z
?
Darwin’s observations: life on islands
Darwin’s observations: life on islands
“One might fancy that,
from an original paucity of
birds in this archipelago,
one species has been
taken and modified for
different ends…”
Two of Darwin’s actual
finch specimens
?
Darwin’s finches (finches: Family Fringillidae)
warblers (Emberizidae), woodpeckers (Picidae), parrots (Psittacidae), flycatchers (Tyrannidae)
Influences on Darwin: domestic animals
Influences on Darwin: Charles Lyell
uniformitarianism
Influences on Darwin: Thomas Malthus
Influences on Darwin: Thomas Malthus
# that can be
supported by
natural
Resources
Natural resources are limited and the production of more individuals than the environment can
support leads to a struggle for existence among individuals of a population, with only a fraction
surviving each generation
Darwin puts it all together
• Observations (Voyage of the Beagle)
– Fossils
– Biogeography
– Life on islands
• Influences
– Bird breeders (Artificial Selection)
– Charles Lyell: Uniformitarianism (Small changes
accumulate to produce large changes, also the earth is
much older than assumed)
– Thomas Malthus: The reproductive potential of an
organism surpasses the resources available, so at some
point only a fraction of all individuals in a generation will
survive and reproduce.
Darwin’s big idea:
Evolution by Natural Selection
1. The individuals that make up a population are not all
identical. (variation)
Darwin’s big idea:
Evolution by Natural Selection
1. The individuals that make up a population are not all
identical. (variation)
2. At least some of this variation can be inherited.
(heritability)
Darwin’s big idea:
Evolution by Natural Selection
1. The individuals that make up a population are not all
identical. (variation)
2. At least some of this variation can be inherited.
(heritability)
3. Some of those heritable traits will allow individuals to
reproduce more than others that do not possess those
traits. (reproductive consequences)
Darwin’s big idea:
Evolution by Natural Selection
1.
2.
3.
The individuals that make up a population are not all identical. (variation)
At least some of this variation can be inherited. (heritability)
Some of those heritable traits will allow individuals to reproduce more than
others that do not possess those traits. (reproductive consequences)
In this way the frequency of characteristics carried by individuals in the population
will change over generations. The population evolves!!
Summary
Evolution by Natural Selection involves...
NON-RANDOM
REPRODUCTIVE
SUCCESS
Q. Where does initial variation in a
population come from?
A. Mutations – random changes in DNA that
cause changes in phenotype
“Survival of the fittest”
Which one is more ‘fit’?
A
B
“Sneaky” males
Depends on which has more offspring that survive to reproduce
Types of reproductive consequences
• Survival
• Fertility vs. parental care
• Mating (sexual selection)
Differential Reproduction: individuals differ in the reproductive
success. Some individuals have more offspring than others
Testing Natural Selection!
• John Endler (1970s)
• Guppies (small fish)
• Naturally found in small ponds in
Venezuela
• Males vary in coloration largely due to
genetics
• Endler noticed that males in ponds
with predators present were more
drab while males in ponds without
predators were bright and colorful
Testing Natural Selection
• Question: Why are males in ponds with
predators present more drab while males in
ponds without predators are bright and
colorful?
• Hypotheses?
• How would you design an experiment to test
this?
Male from pond
with predators
Male from pond
without predators
Testing Natural Selection!
No
predators
Few
predators
Many
predators
In less than 15 generations!
Re-summary
Individuals that possess heritable traits
that improve fitness will reproduce
more than others and those traits will
accumulate over time in the
population
How does Darwin’s hypothesis account for
the major patterns of life??
I. Adaptations (giraffe’s necks, for example)
time 1
time 2
(regular old
antelopes)
(next generation)
less short
(aka “long”)
(one antelope is born
with a slightly longer
neck due to genetic
change; it has an
advantage)
time 3
time 4
(next generation)
(next generation)
(increased
frequency of longishnecked animals)
(giraffe-alopes?)
short
1
2
3
Time
4
NOW
Genus
Family
Order
LONG LONG AGO
How does Darwin’s hypothesis account for
the major patterns of life?
I. Adaptations (giraffe’s necks, for example)
II. Hierarchy of Shared Characteristics
Taxonomic patterns
Homologous traits, vestigial traits
Can Darwin’s Idea Explain Homologous Traits?
Text material © 2002 by Steven M. Carr
Vertebrate Forelimb
Way back when….
?
Text material © 2002 by Steven M. Carr
Modern Vertebrate Forelimb Derived from Shared Ancestor
Pederpes finneyae. 348
MYA
(transitional from lobefinned fishes to semiterrestrial amphibian
ancestors)
Nature 418, 72-77 (4 July 2002)
Modern Vertebrate Forelimb Derived from Shared Ancestor
evolution.berkeley.edu/.../similarity_hs_03
How Does Darwin’s Idea Explain Vestigial Traits?
How Does Darwin’s Idea Explain Vestigial Traits?
Basilosaurus sp. (35 MYA)
Ambulocetans natans (50 MYA)
http://www.neoucom.edu/DEPTS/ANAT/Thewissen/whale_origins/
How Does Darwin’s Idea Explain Vestigial Traits?
Physeter macrocephalus
(modern sperm whale)
http://www.neoucom.edu/DEPTS/ANAT/Thewissen/whale_origins/
How does Darwin’s hypothesis account for
the major patterns of life?
I. Adaptations (giraffe’s necks, for example)
II. Hierarchy of Shared Characteristics
Taxonomic patterns
Homologous traits, vestigial traits
III. Biological Diversity?
now
A’
B
C
?
then
A
A
Next time...
• Speciation (the formation of new species)
• Other types of evolution
• Misconceptions about evolution