John Blanton 30 March 2002 27
Evolution Makes Sense ofHomologies
http://www.zoology.ubc.ca/~bio336/Bio336/Lectures/Lecture5/Overheads.html
Richard Owen (1848) introduced the term homology to refer tostructural similarities among organisms.To Owen, these similarities indicated that organisms were createdfollowing a common plan or archetype.That is, although each species is unique, the plans for each mightshare many features, just as the design plans for a Honda Civic anda Honda Prelude might be similar.Nevertheless, if every organism were created independently, it isunclear why there would be so many homologies among certainorganisms, while so few among others.It is also hard to make sense of the fact that homologous structurescan be inefficient or even useless.
John Blanton 30 March 2002 28
Evolution Makes Sense ofHomologies
http://www.zoology.ubc.ca/~bio336/Bio336/Lectures/Lecture5/Overheads.html
Why would certain cave-dwelling fish have degenerate eyes thatcannot see?Darwin made sense of homologous structures by supplying anevolutionary explanation for them:
A structure is similar among related organisms because thoseorganisms have all descended from a common ancestor that hadan equivalent trait.
Ridley uses a specific definition of homology: "A similarity betweenspecies that is not functionally necessary."I interpret this as: "A similarity between species that exists despiteseveral plausible alternative traits that would function equally well."
John Blanton 30 March 2002 29
The "Universal" GeneticCode
5' T C A G 3'
T
T T T Phe (F)
T T C Phe (F)
TTA Leu (L)
T T G Leu (L)
TCT Ser (S)
T CC Ser (S)
T CA Ser (S)
T CG Ser (S)
T AT T yr (Y )
T AC T yr (Y )
TA A Stop
TA G Stop
T G T C ys (C)
T G C C ys (C)
TG A Stop [Trp (W )]
T G G Trp (W )
T
C
A
G
C
CT T Leu (L)
CT C Leu (L)
CT A Leu (L)
CT G Leu (L)
CCT Pro (P)
CCC Pro (P)
CC A Pro (P)
CCG Pro (P)
CAT H is (H )
CA C H is (H )
CA A G ln (Q )
CA G G ln (Q )
CG T Arg (R)
CG C Arg (R)
CG A Arg (R)
CG G Arg (R)
T
C
A
G
A
AT T Ile (I)
AT C Ile (I)
AT A Ile (I) [M et (M )]
AT G M et (M )
ACT T hr (T )
AC C T hr (T )
AC A T hr (T )
AC G T hr (T )
A AT A sn (N )
A A C A sn (N )
A A A L ys (K)
A AG L ys (K)
AG T Ser (S)
AG C Ser (S)
AG A Arg (R) [Stop]
AG G Arg (R) [Stop]
T
C
A
G
G
G T T V al (V )
G T C V al (V )
G T A V al (V )
G T G V al (V )
G CT A la (A)
G CC A la (A)
G C A A la (A)
G CG A la (A)
G AT A sp (D )
G A C A sp (D )
G A A G lu (E )
G AG G lu (E )
G G T G ly (G )
G G C G ly (G )
G G A G ly (G )
G G G G ly (G )
T
C
A
G
http://www.zoology.ubc.ca/~bio336/Bio336/Lectures/Lecture5/Overheads.html
John Blanton 30 March 2002 30
Evolution Makes Sense ofHomologies
The genetic code for protein-coding genes is nearly universal ineukaryotes and prokaryotes.
The exceptions include most mitochondrial genomes and somenuclear ones (e.g. Mycoplasma and Tetrahymena).
Even in these cases, the genetic code is quite similar.
Millions of alternative genetic codes exist, so why do allorganisms have nearly the same one?
Since the anti-codon is at the opposite end from the amino acidbinding site of a tRNA and does not interact with the bindingsite, there is no chemical necessity for a codon to be assignedto a particular amino acid.
http://www.zoology.ubc.ca/~bio336/Bio336/Lectures/Lecture5/Overheads.html
John Blanton 30 March 2002 31
Evolution Makes Sense ofHomologies
The genetic code is homologous among living organisms: it issimilar despite the fact that there exist many equally goodgenetic codes.Under the hypothesis that evolution has occurred, however, thesimilarity among all genetic codes makes sense:
The common ancestor to all known organisms had agenetic code similar to what we see today.Over the ages, the genetic code has passed unchanged (ornearly so) from parents to offspring, because mutations tothe genetic code would have been disastrous (changing theamino acid sequence of all proteins produced).
(What would an evolutionist think if an organism were foundtoday with an entirely different genetic code?)
http://www.zoology.ubc.ca/~bio336/Bio336/Lectures/Lecture5/Overheads.html
John Blanton 30 March 2002 32
Trilobite Evolution
http://www.zoology.ubc.ca/~bio336/Bio336/Lectures/Lecture5/Overheads.html
Although the fossil record is often poor and incomplete, there are certaindeposits where sedimentary layers remain in a nearly continuous series.Fossils from these series provide direct evidence of evolutionary change.Sheldon (1987) examined a series of sedimentary layers from theOrdovician period (500 MYA) containing trilobite fossils (extinct marinearthropods). Samples were obtained from
every three million years. Thenumber of ribs of each speciesof trilobite changed over time(=evolution).Some of these changes overtime were so large that theanimals at the end of theseries are assigned to a newgenus!
John Blanton 30 March 2002 33
Foraminiferan Evolution
http://www.zoology.ubc.ca/~bio336/Bio336/Lectures/Lecture5/Overheads.html
An even finer scale analysis was performed by Malmgren et al. (1983) ona species of foraminiferan (shell-bearing protozoans) from 10MYA torecent times.[Three epochs are represented: Miocene (M; 23.8-5.2 MYA), Pliocene (P;5.2-1.8 MYA) and Pleistocene (Q; 1.8 MYA - 10,000 YA)].Over this period, the fossil shells evolved a larger, thicker shell, with amore pronounced ridge.Although the fossil record demonstrates that change occurred in acontinuous manner (=without breaks or jumps), the rate of change wasnot always the same: shape changed most around the Miocene/Plioceneboundary.These changes were large enough that the lineage is assigned to thespecies Globorotalia plesiotumida in the Miocene, but to the speciesGloborotalia tumida afterwards.
John Blanton 30 March 2002 34
Foraminiferan Evolution
http://www.zoology.ubc.ca/~bio336/Bio336/Lectures/Lecture5/Overheads.html
The fossil record demonstrates evolutionary changes do occur.The disadvantage of the fossil record is that it is generally difficult to determinethe selective forces that may have contributed to these changes.The advantage of the fossil record over present-day observations of evolution isthat higher order evolutionary changes may be tracked (e.g. the origin of newspecies,new genera, etc).SOURCES:
Pentadactyl limbs: Ridley (1997) Evolution.Whale, salamander, primate trees: Freeman and Herron (1998) EvolutionaryAnalysis.Membrane photo: Wessells and Hopson (1988) Biology.Dinosaur information: UC Museum of Paleontology.Trilobite and foraminiferan fossil record: Futuyma (1998) EvolutionaryBiology.
John Blanton 30 March 2002 35
Foraminiferan Evolution
http://www.zoology.ubc.ca/~bio336/Bio336/Lectures/Lecture5/Overheads.html
John Blanton 30 March 2002 36
Whale EvolutionThe evidence
http://www.talkorigins.org/features/whales/
Paleontological evidence
•Sinonyx
•Pakicetus
•Ambulocetus
•Rodhocetus
•Basilosaurus
•Dorudon
John Blanton 30 March 2002 37
Whale Evolution
http://www.talkorigins.org/features/whales/
Sinonyx jiashanensi skull reconstruction
John Blanton 30 March 2002 38
Whale Evolution
http://www.talkorigins.org/features/whales/
Pakicetus skull reconstruction
John Blanton 30 March 2002 39
Whale Evolution
http://www.talkorigins.org/features/whales/
Ambulocetans natans
John Blanton 30 March 2002 40
Whale Evolution
Rodhocetus kasrani
Science, Vol. 293, Issue 5538, 2239-2242, September 21, 2001
John Blanton 30 March 2002 41
Whale Evolution
http://www.talkorigins.org/features/whales/
Rodhocetus kasrani reconstruction
John Blanton 30 March 2002 42
Whale Evolution
http://www-dept.usm.edu/~bsclabs/museum_brochure.htm
John Blanton 30 March 2002 43
Whale Evolution
http://www.talkorigins.org/features/whales/
Dorudon atrox
John Blanton 30 March 2002 44
Whale EvolutionThe evidence
http://www.talkorigins.org/features/whales/
Morphological evidenceThe examination of the morphological characteristics shared by thefossil whales and living ungulates makes their common ancestry evenclearer.
For example, the anatomy of the foot of Basilosaurus allies whales withartiodactyls (Gingerich and others 1990). The axis of foot symmetry inthese fossil whales falls between the 3rd and 4th digits. This arrangementis called paraxonic and is characteristic of the artiodactyls, whales, andcondylarths, and is rarely found in other groups (Wyss 1990).
Another example involves the incus (the "anvil" of the middle ear). Theincus of Pakicetus, preserved in at least one specimen, ismorphologically intermediate in all characters between the incus ofmodern whales and that of modern artiodactyls (Thewissen and Hussain1993).
John Blanton 30 March 2002 45
Whale EvolutionThe evidence
http://www.talkorigins.org/features/whales/
Additionally, the joint between the malleus (hammer) and incus of mostmammals is oriented at an angle between the middle and the front of theanimal (rostromedially), while in modern whales and in ungulates, it isoriented at an angle between the side and the front (rostrolaterally).
In Pakicetus, the first fossil cetacean, the joint is oriented rostrally(intermediate in position between the ancestral and derived conditions).
Thus the joint has clearly rotated toward the middle from the ancestralcondition in terrestrial mammals (Thewissen and Hussain 1993);Pakicetus provides us with a snapshot of the transition.
Morphological evidence
John Blanton 30 March 2002 46
The hypothesis that whales are descended from terrestrial mammals predictsthat living whales and closely related living terrestrial mammals should showsimilarities in their molecular biology roughly in proportion to the recency of theircommon ancestor.
In contrast, creationism lacks any scientific basis for predicting what thepatterns of similarity should be…
Molecular studies by Goodman and others (1985) show that whales are moreclosely related to the ungulates than they are to all other mammals...
These studies examined myoglobin, lens alpha-crystallin A, and cytochrome c ina study of 46 different species of mammals. Miyamoto and Goodman (1986)later expanded the number of protein sequences by including alpha- and beta-hemoglobins and ribonuclease; they also increased the number of mammalsincluded in the study to 72.
The results were the same: the whales clearly are included among theungulates.
Whale EvolutionThe evidence
http://www.talkorigins.org/features/whales/
Molecular biological evidence
John Blanton 30 March 2002 47
Whale EvolutionThe evidence
http://www.talkorigins.org/features/whales/
•Vestigial evidence
•Embryological evidence
•Geochemical evidence
•Paleoenvironmental evidence
•Paleobiogeographic evidence
•Chronological evidence
John Blanton 30 March 2002 48
Cross bedding
http://agcwww.bio.ns.ca/schools/EarthNet/english/glossary/c/cross_bedding.html
John Blanton 30 M
arch 200249
Geologic Tim
e
http://pubs.usgs.gov/gip/geotime/divisions.html
John Blanton 30 March 2002 50
Whale Evolution
http://www.umich.edu/~urecord/9697/Mar25_97/artcl01.htm
Sinonyx jiashanensi skull reconstructionAfter nearly 200 hours of concentratedeffort, John Klausmeyer just about has the60-piece, 3-D jigsaw puzzle completed.Using a heat gun, leather gloves, drills andbits, oil and acrylic paints, and various sizebrushes, sponges, and rags, the medicalillustrator has just about finished part of thepuzzle that will be featured in "Back to theSea: The Evolution of Whales." Theexhibition is slated for an October openingat the Exhibit Museum.
John Blanton 30 March 2002 51
References
❚ http://agcwww.bio.ns.ca/schools/EarthNet/english/glossary/c/cross_bedding.html❚ http://www.ge-at.iastate.edu/courses/Geol_100/angular.html❚ http://www.hartwick.edu/geology/work/VFT-so-far/glaciers/glacier1.html❚ http://www.glossary.oilfield.slb.com/DisplayImage.cfm?ID=59❚ http://www.seismo.unr.edu/ftp/pub/louie/papers/dome/fig2.pdf❚ http://www.dgi.com/earthvision/sol_diapir.shtml❚ http://agcwww.bio.ns.ca/schools/EarthNet/english/glossary/d/diapir.html❚ http://woodshole.er.usgs.gov/operations/obs/Images/BlakeRidge/Figure7.html❚ Originally published in Science Express as 10.1126/science.1063902 on September
19, 2001 Science, Vol. 293, Issue 5538, 2239-2242, September 21, 2001❚ Originally published in Science Express as 10.1126/science.1065305 on September
19, 2001 Science, Vol. 293, Issue 5538, 2216-2217, September 21, 2001❚ http://www.brookes.ac.uk/geology/8361/1998/kirsty/trilo.html❚ http://www.aloha.net/~smgon/ordersoftrilobites.htm❚ http://www.zoology.ubc.ca/~bio336/Bio336/Lectures/Lecture5/Overheads.html
John Blanton 30 March 2002 52
References
❚ http://faculty.uca.edu/~benw/debate/whale/sld001.htm
❚ http://www.gsa.state.al.us/gsa/Paleoweb/palpage_statefos2.html