Transcript Summary of course

Evidence for Evolution
Graduate Seminar
Wrap-up and summary
Ken Sytsma
The three main claims of
Darwinian evolution
• Living species are related by common
ancestry
• Change through time occurs at the
population not the organism level
• The main cause of adaptive evolution is
natural selection (and related mechanisms)
The main cause of adaptive
evolution is natural selection
• Claim 1: Natural selection happens
– vs. Natural selection does not/cannot happen
• Claim 2: Natural selection is sufficient to
explain even the most complex traits of
living organisms
– vs. natural selection is not sufficient
Evidence for common ancestry
(against separate ancestry)
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Fossil record 
Homology 
Vestigial Structures 
Classification 
Hierarchical distribution of traits 
Biogeography 
Agreement between gene trees 
Evolution during domestication 
 = examined in this course at least adequately
Evidence for natural selection
• Less dealt with or only indirectly inferred in course
• Requires evidence usually at or among population level
• Other mechanisms need to be examined?
– Genetic drift
To understand evolution fully, one must examine all of life
from the level of populations and the formation of
species, of relationships of species and higher taxonomic
levels, and of extinction.
Generation 2006
Generation 2005
In outcrossing diploid
organisms such as
shepherd’s purse, each
offspring of the next
generation receives a copy
of genetic material from
two parents, who in turn
had received their copies
of genes from two parents
of the preceding generation
back in time
As you go back in time to earlier
generations, the genetic
connections appear as a network
within the population of
interbreeding individuals
1 Population
back in time
As you go back even further in
time, the genetic connections
appear as a braided rope within a
species
• discernible populations of
interbreeding individuals are
recognized within a species, these
populations may be genetically
isolated to varying degrees depending
on gene flow and geography
• anagenesis can occur within a
species lineage through time
back in time
As you go back even further in
time in this tree or phylogeny, the
formation of species and the
extinction of species (fossils?) are
seen
• cladogenesis or speciation occurs
when there is complete genetic
isolation between groups of once
connected populations
Evolution is often separated into:
anagenesis - evolution within a species lineage — modification
(Darwin’s term)
cladogenesis - evolution to form new species lineages or
speciation — descent
Although some may
argue that “species” are
no more special than
other recognized taxa
the study of processes that
initially give rise to
divergent clades or bring
them back together are
fundamentally important as
evidence for evolution
• variation in species
• reproductive isolation
• hybridization &
introgression
(Modified after O’Hara, 1993, Syst Biol 42)
Geographical Variation within Species
Achillea lanulosa exhibits clinal variation in
natural populations across the elevational
gradient in the Sierra Nevada
Achillea lanulosa
- wooly yarrow
Clausen, Jens; Keck, David D.; Hiesey, William M. 1948. Experimental studies on
the nature of species. III: Environmental responses of climatic races of Achillea.
Publication 581; Washington, D.C.: Carnegie Institution of Washington.
Geographical Variation within Species
Populations exhibit marked lowering of fitness
and adaptation when placed at other sites —
clinal genetic variation
Clausen, Jens; Keck, David D.; Hiesey, William M. 1948. Experimental studies on
the nature of species. III: Environmental responses of climatic races of Achillea.
Publication 581; Washington, D.C.: Carnegie Institution of Washington.
Pre-zygotic Isolating Mechanism
Hybrid/Allopolyploid Speciation
• Three diploid (2n=24) species
were introduced into North
America about 200 years ago.
Tragopogon - goat’s beard
• By early 1900s, these species
had hybridized with each other
and then formed two different
allopolyploid (tetraploid)
species.
• These two new allopolyploid
species have evolved
numerous times (!) in areas
where the diploid species
overlap in geographical range
in North America
(Modified after Pires & al, 2004, AJB 91)
Where do we go from here?
• We know a little about a lot - we don’t
know a lot about a little
 We need more stories in detail
Endosymbiosis
Fusion evolution - major process for forming the diversity of life
http://tolweb.org/tree/phylogeny.html
Endosymbiosis
Fusion evolution - major process for forming the diversity of life
Eukaryotes contain a
“fossil” history of 2-3 or
even more distinct lineages
- a mosaic
A plant eukaryotic cell
Endosymbiosis
Fusion evolution - major process for forming the diversity of life
“mitochondria” transfer 2000 mya
“chloroplast” transfer 1600 mya
Endosymbiosis
Fusion evolution - major process for forming the diversity of life
Primary plastid endosymbiosis
• green algae
• red algae
• glaucophytes
Secondary plastid endosymbiosis
• cryptomonads
• dinoflagellates
• haptophytes, heterokonts
• ciliates
Hox Genes - EvoDevo
Molecular tinkering - major process for forming the diversity of life
Gene family, spatial
organization, development
Source: C. Zimmer, Evolution, the Triumph of an Idea
Hox Genes - EvoDevo
Molecular tinkering - major process for forming the diversity of life
Halteres into wings
Antennae into legs
Source: C. Zimmer, Evolution, the Triumph of an Idea
Where do we go from here?
• We know a little about a lot - we don’t
know a lot about a little
• We can’t keep up with all aspects of
evolution
 We need a “clearing-house” for
“new” stories as they emerge for
use in teaching and debate
Nature April 6, 2006
“Here we report a fossil snake with a sacrum
supporting a pelvic girdle and robust, functional
legs outside the ribcage . . .”
“. . . the new fossil retains several features associated
with a subterranean or surface dwelling life that are
also present in primitive extant snake lineages,
supporting the hypothesis of a terrestrial rather than
marine origin of snakes.”
PNAS April 17, 2006
Bat evolution - issues
• 50 my stasis in wing form
• no transitional forms
Paper identifies likely developmental
and molecular basis for bat wing
evolution
Fig. 1. The relative length of bat forelimb digits has not changed in 50 million years
Sears, Karen E. et al. (2006) Proc. Natl. Acad. Sci. USA 103, 6581-6586
Copyright ©2006 by the National Academy of Sciences
Fig. 2. Developmental elongation of bat digits occurs after the initial cartilage condensations are formed
Sears, Karen E. et al. (2006) Proc. Natl. Acad. Sci. USA 103, 6581-6586
Copyright ©2006 by the National Academy of Sciences
Fig. 3. Proliferation and Bmp levels are increased in bat forelimb digits relative to mouse forelimb and
bat hind limb digits
Sears, Karen E. et al. (2006) Proc. Natl. Acad. Sci. USA 103, 6581-6586
Copyright ©2006 by the National Academy of Sciences
Where do we go from here?
• We know a little about a lot - we don’t
know a lot about a little
• We can’t keep up with all aspects of
evolution
• We don’t have time to respond to all
attacks on evolution
 Read selectively on both sides
if you are going to teach/debate
Name
your
title
. . . and philosophers and
historians of science, too
Example from Michael Denton
Cytochrome C variation
All eukaryotes
equally distinct
from bacteria
What’s wrong?
What does evolution predict?
a “tree”- not the Greek “ladder of life” pattern. This confusion or misapplication is the basis of a lot of miscommunication in the “evolutioncreationist” debate.
Data makes
sense based on
a tree!
most recent ancestor
Yes, astonishing what evolution predicts and
how this “test” supports “common ancestry”
Molecular “fossil” record — phylogenetic trees
Further evidence for evolution
Where do we go from here?
• We know a little about a lot - we don’t
know a lot about a little
• We can’t keep up with all aspects of
evolution
• We don’t have time to respond to all
attacks on evolution
• Do’s and don’t’s
 . . . according to Randy Olson,
Director of Flocks of Dodos
• Do’s and don’t’s  . . . according to Randy Olson,
Director of Flocks of Dodos
1.
Quality Control
2.
Attitude - “Never rise above”
3.
Concision – it’s a byproduct of the information era
4.
Modernization
5.
Prioritization - Effective communication costs money
6.
Understanding - intellectuals are handicapped as mass communicators
7.
Risk Taking/Innovation
8.
Humor - it’s yet another byproduct of the information era
9.
Unscripted Media and the Mass Audience - this goes with modernization
10. Sincerity