Evidence
for
Evolution
Chapter The 21
Outline of Topics
Review of Natural Selection
Darwins Finches: Evidence of Natural Selection
Fossil Evidence of Evolution
Anatomical Evidence for Evolution
Biogeographical Record
Convergent Evolution
Artificial Selection
Darwins Critics
Review of Natural Selection
Voyage of the HMS Beagle
Review of Natural Selection
Evolutionary Theory:
Natural Selection
Evolution by natural selection (Charles Darwin and Alfred
Russel Wallace in 1858) proposes that evolution occurs,
thus species change through time. They hypothesized that
natural selection is the process to explain the pattern of
evolution.
Evolution by natural selection has become one of the bestsupported and most important theories in the history of
scientific research.
Review of Natural Selection
How Does Natural Selection Work?
Darwin broke down the process of evolution by natural
selection into four steps:
1. Individuals that make up a population vary in their traits.
2. Some of these trait differences are heritable.
3. In each generation, many more offspring are produced than can
survive. Of these, some will produce more offspring than others.
4. Individuals with certain heritable traits are more likely to survive and
reproduce. Natural selection occurs when individuals with certain
traits produce more offspring than do individuals without those traits.
Review of Natural Selection
How Does Natural Selection Work?
Modern biologists condense Darwins four steps into two
statements: Evolution by natural selection occurs when:
(1) heritable variation leads to
(2) differential success in survival and reproduction.
Darwins Finches: Evidence of Natural Selection
Evolution of Galapagos Finches
Darwins Finches: Evidence of Natural Selection
Evolution of Galapagos Finches
Peter and Rosemary Grant have done long-term research on the
population of medium ground finches found on Isle Daphne Major.
They found that beak form and body size are heritable in these
birds.
Darwins Finches: Evidence of Natural Selection
Beak and Body Size in
Galapagos Finches
During their research a major drought led to
84% of the ground finches dying of starvation.
How does natural selection, resulting from this
natural experiment, alter the finch
population?
Darwins Finches: Evidence of Natural Selection
Changes in a Finch Population
Darwins Finches: Evidence of Natural Selection
Changes in a Finch Population
Darwins Finches: Evidence of Natural Selection
Changes in a Finch
Population
Darwins Finches: Evidence of Natural Selection
Variation within species
We show that calmodulin (CaM), a molecule
involved in mediating Ca2+ signalling, is
expressed at higher levels in the long and
pointed beaks of cactus finches than in more
robust beak types of other species. We validated
this observation with in situ hybridizations.
When this upregulation of the CaM-dependent
pathway is artificially replicated in the chick
frontonasal prominence, it causes an elongation
of the upper beak, recapitulating the beak
morphology of the cactus finches.
Abzhanov et al. (2006) Nature 442:563-567
Darwins Finches: Evidence of Natural Selection
Variation within species
Our results indicate that local
upregulation of the CaM-dependent
pathway is likely to have been a
component of the evolution of
Darwin's finch species with
elongated beak morphology and
provide a mechanistic explanation
for the independence of beak
evolution along different axes.
Abzhanov et al. (2006) Nature 442:563-567
Darwins Finches: Evidence of Natural Selection
Darwins Finches: Evidence of Natural Selection
Variation within species
Previous data had
suggested that high
BMP4 levels were
associated with high
beak depth and width.
High CaM was found to
be associated with
elongated beaks.
Expression of both in
different finch species
correlates beak
phenotype.
Abzhanov with et al. (2006) Nature 442:563-567
Evolutionary Progress?
Evolutionary Progress
Evolution by natural selection is NOT progressive, and it
doesnt change the characteristics of the individuals that
are selected, it changes only the characteristics of the
population.
Animals do NOT act for the good of the species and not
all traits are adaptive. All adaptations are constrained by
trade-offs as well as genetic factors.
Review of Natural Selection
Evolutionary Theory:
Descent with Modification
Descent with modification means that change
over time produced modern species from
ancestral species.
This pattern component of the theory of
evolution by natural selection makes two
testable predictions about the nature of
species:
they change through time, and
they are related by common ancestry.
Fossil Evidence of Evolution
Evidence: Change through Time
Fossils are traces of organisms
that lived in the past.
The many fossils that have
been found and described in
the scientific literature make
up the fossil record.
Most fossils are found in
sedimentary rocks, which
form from layers of sand or
mud.
Fossil Evidence of Evolution
Evidence: Change through Time
Layers of sedimentary rock
are associated with different
intervals in the geologic
time scalea relative time
scale based upon fossil
content.
As the fossil record has become more complete, many transitional
forms have been discovered with traits that are intermediate
between earlier and later species.
Fossil Evidence of Evolution
Fossil Evidence of
Evolution
Anatomical Evidence for Evolution
Vestigial Traits
A vestigial trait is a reduced
or incompletely developed
structure that has no or
reduced function, but is
clearly similar to functioning
organs or structures in closely
related species.
.
Anatomical Evidence for Evolution
Vestigial Traits: Reduced Versions of Traits in
Related Species
Anatomical Evidence for Evolution
Structural Homology
Structural homology refers to similarities in adult
morphologies.
Prediction 1: traits are similar in different species
because the species in question are related to each
other by common descent.
Prediction 2: If species were created independently
of one another, these types of similarities would not
occur.
Anatomical Evidence for Evolution
Structural Homology
Anatomical Evidence for Evolution
Comparative Anatomy and Physiology
Comparative embryology
Biogeography
Biogeography
Lung fish of S. America, Africa and Australia share a common ancestor
Biogeography
Biogeography
Convergent Evolution
Convergent Evolution
Artificial Selection
Natural Selection vs. Artificial Selection
Artificial Selection
Natural Selection vs. Artificial Selection
Common Criticisms of Darwins Ideas
Evolution is just a theory
No missing links
Organisms too complex to have been made
at random, must have a designer
What good is half an eye?
Common Criticisms of Darwins Ideas
Evolution violates the 2nd law of
thermodynamics
Natural selection can produce microevolution, but not macro-evolution
Irreducible complexity
The Evidence for Evolution
Review of Natural Selection
Darwins Finches
differences evolved as species adapted to different
food resources
Variation in gene expression levels during beak
development cause differences in beak phenotypes
Evolution is not progressive
Fossil Evidence of Evolution
Fossil record in sedimentary rocks, geologic time scale,
transitional forms
The Evidence for Evolution
Anatomical Evidence for Evolution
Vestigial traits, structural homology, comparative
embryology
Biogeographical Record
Patterns of plants and animal distribution reflect their
natural history
Convergent Evolution
Different species exposed to similar selection pressures
often evolve similar adaptation
Artificial Selection
Darwins Critics