Transcript Ch. 13 How Populations Evolve

Evolution: How Population
Evolve
PreAP Biology
Lamarck’s Theory of Acquired
Inheritance (early 1800s)
• Jean Baptiste Lamarck
• Observed fossil records
and the current diversity
of life
• Suggested that
organisms evolved by the
process of adaptation
• Traits gained during a
lifetime could then be
passed on to the next
generation
Lamarck’s Theory of Acquired
Inheritance
• Suggested giraffes
acquired long necks
because ancestors
stretched higher and
higher into the trees
to reach leaves at a
time when there was
drought in the African
prairies
– Lengthened neck was
passed to offspring
Charles Darwin
• Observed organisms and
their distributions on
Galápagos Islands
• Saw similarities b/w
Galápagos organisms
and those in South
America.
Figure 13.5
Darwin’s Theory of Natural
Selection
• Observations:
– Overproduction of offspring leads to competition of
limited resources (food, space, breeding partners)
– Individuals of a population vary in characteristics,
and many such traits are passed on to offspring
• Conclusions:
– Individuals with inherited characteristics make
them best adapted to survive in their environment
and reproduce and leave more offspring than less
fit individuals
The theory of natural selection is comprised of
several logical steps, based on observation and
inference:
1.
2.
3.
4.
5.
There is competition among
individuals in a population.
There is variation among
individuals in a population.
This variation is, at least in
part, heritable.
This variation contributes to
fitness; fitter individuals will
leave a larger contribution of
offspring in the next
generation.
The succeeding generation will
have an increased proportion
of the traits that confer the
higher fitness.
Natural Selection
• Prominent force in nature
• Support in the results of artificial
selection—selective breeding of
domesticated plants/animals
• Populations tend to
evolve in response
to environmental
conditions
Hundreds to thousands
of years of breeding
(artificial selection)
Ancestral dog (wolf)
Figure 13.2B
Evidence of Evolution
•
•
•
•
•
Fossil Record
Biogeography
Comparative anatomy
Comparative embryology
Molecular Biology
Evidence: Fossil Record
• Fossils
– Are preserved
remnants or
impressions left by
organisms that lived in
the past.
– Are often found in
sedimentary rocks.
http://www.buzzle.com/img/articleImages/191116-18med.jpg
Fossil Formation
1.
Dead animal sinks. Tissue
begins to decay
2.
Carcass covered with sediment.
Lower layers turn to rock.
3.
Rock is folded.
4.
Fossil is exposed at the surface.
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The fossil record
• Is the ordered sequence of fossils as they
appear in rock layers.
• Reveals the appearance of organisms in a
historical sequence.
• Fits with other evidence of evolution.
http://cache.eb.com/eb/image?id=398&rendTypeId=4
Fossil Record reveals that
organisms have evolved in a
historical sequence
Figure 13.3H
http://www.biblicalcreation.org.uk/images/Matthew_Fig.jpg
Evidence: Biogeography
• Biogeography, the geographic distribution
of species
– Suggested to Darwin that organisms evolve
from common ancestors
• Darwin noted that Galápagos animals
– Resembled species of the South American
mainland more than animals on similar but
distant islands
Evidence: Comparative Anatomy
• Comparison of body structures between
different species
– Similarities give signs of common descent
• Homologous structures—features that
have similar structure but have different
functions
Evidence: Comparative Anatomy
•
Vestigial structures—Small body
structures that may have been functional
in the ancestors of a species, but has no
real function at the present time
(appendix, tail bone)
Evidence: Comparative embryology
• Different organisms go through similar embryonic stages
• All vertebrates have an embryonic stage in which gill
pouches appear in the throat region—evidence of a
common ancestor
http://www.utm.edu/staff/nlillega/phil120_files/image010.gif
Molecular Biology
• Study of molecular basis of genes and
gene expression
• Universality of genetic code
• Conservation of amino acid sequences in
proteins such as hemoglobin
Figure 13.13
Populations are the Units of
Evolution
• A population
– Is a group of individuals of the same species
living in the same place at the same time
• A species is a group of populations
– Whose individuals can interbreed and
produce fertile offspring
Populations are the Units of
Evolution
• Population genetics
– Focuses on populations as the evolutionary
units.
– Tracks the genetic makeup of populations
over time.
• The modern synthesis
– Connects Darwin’s theory with population
genetics
Populations are the Units of
Evolution
• A gene pool
– Is the total collection of genes in a population
at any one time
• Microevolution
– Is a change in the relative frequencies of
alleles in a gene pool
Genetic Variation in Populations
– Individual variation
abounds in populations.
• Not all of this
variation is heritable.
• Only the genetic
component of
variation is relevant
to natural selection.
– A population is said to be
polymorphic for a
characteristic if two or
more morphs, or forms,
are present in noticeable
numbers.
Sources of Genetic Variation
– Mutations and sexual recombination
•
•
Produce genetic variation.
Are changes in the DNA of an organism.
– Sexual recombination
•
Shuffles alleles during meiosis.
Analyzing Gene Pools
– The gene pool
•
Consists of all alleles of all individuals making up
a population.
– Alleles in a gene pool
•
Occur in certain frequencies.
Analyzing Gene Pools
•In a nonevolving population
– The shuffling of alleles that accompanies
sexual reproduction does not alter the
genetic makeup of the population
– Hardy-Weinberg equilibrium
•
States that the shuffling of
genes during sexual
reproduction does
not alter the proportions of
different alleles in a gene
pool
Figure 13.7A
Webbing
No webbing
Hardy-Weinberg Equilibrium
•
•
•
•
•
The population is very large
The population is isolated
Mutations do not alter the gene pool
Mating is random
All individuals are equal in
reproductive success
One or More of these Conditions will
lead to Evolution
1. Population is small
2. Population is not isolated; migration
in/out
3. Mutations (changes in genes) alter
gene pool
4. Mating is non-random
5. Individuals are not equal in
reproductive success; natural
selection does happen
Causes of Microevolution
• Genetic drift—change in gene pool of a small population
due to chance
– Loss/gain of individuals
Genetic Drift
– Bottleneck effect—
results from an
event/disaster that
drastically reduces
population size
(elephant seals after
being hunted in 1890s)
Original
population
Figure 13.9A
Figure 13.9B
Bottlenecking
event
Surviving
population
CONNECTION
•Endangered species often have reduced
variation
– Low genetic variability
•
May reduce the capacity of endangered
species to survive as humans continue to
alter the environment
Figure 13.10
Causes of Microevolution
• Genetic drift
– Founder effect—random change in gene
pool that occurs in a small colony
• A few individuals start a new
population
Causes of Microevolution
• Gene flow—gain/loss of allele from a
population
– Is the movement of individuals or
gametes between populations
– Can alter allele frequencies in a
population
– Tends to reduce genetic differences
between populations
Causes of Microevolution
• Mutation—random change in organism’s
nucleotide sequence
– Can create a new allele
– Rare events
– Ultimate source of the genetic variation
that initiates evolution
Causes of Microevolution
• Nonrandom mating
– males and females with similar
phenotypic traits tend to mate
– In species that stay in one place,
individuals tend to mate with neighbors
rather than more distant members of the
population
Nonrandom Mating
•Sexual selection may produce sexual dimorphism
•Sexual selection leads to the evolution of
secondary sexual characteristics
– Which may give individuals an advantage in
mating
Figure 13.17A
Figure 13.17B
Natural selection can alter variation in a
population in three ways
•Stabilizing selection
– Favors intermediate phenotypes
•Directional selection
– Acts against individuals at one of the
phenotypic extremes
•Disruptive selection
– Favors individuals at both extremes of the
phenotypic range
Modes of Natural Selection
Insecticideresistant
Populations
Acknowledgements
• BIOLOGY: CONCEPTS AND CONNECTIONS 5th Edition, by
Campbell, Reece, Mitchell, and Taylor, ©2006. These images have
been produced from the originals by permission of the publisher.
These illustrations may not be reproduced in any format for any
purpose without express written permission from the publisher.
• Unless otherwise noted, illustrations are credited to Pearson
Education which have been borrowed from BIOLOGY: CONCEPTS
AND CONNECTIONS 3rd Edition, by Campbell, Reece, Mitchell,
and Taylor, ©2000. These images have been produced from the
originals by permission of the publisher. These illustrations may not
be reproduced in any format for any purpose without express written
permission from the publisher.