5. 4
Evolution Makes Sense of Homologies
New Functions Evolve from Pre-existing Structures
http://www.entomology.umn.edu/museum/links/coursefiles/
JPEG%20images/Hymenoptera%20web%20jpeg/Siricidae.jpg
Stinger
http://www.sphoto.com/photo.php?photo=781&u=12%7C21%7C...
6. Evolution Makes Sense of Homologies
Vestiges
http://www.ups.edu/Images/
SlaterMuseum/WhaleInstall068Large.jpg
5
7. Evolution Makes Sense of Homologies
Vestiges
http://www.ups.edu/Images/
SlaterMuseum/WhaleInstall068Large.jpg
5
8. Evolution Makes Sense of Homologies
Vestiges
http://www.ups.edu/Images/
SlaterMuseum/WhaleInstall068Large.jpg
5
35. Homologies are Nested
Primate phylogeny
mitochondrial
DNA
testis-specific
Human Chimp protein
Orangutan Gibbon ß-globin
36. Homologies are Nested
Primate phylogeny
mitochondrial
DNA
testis-specific
Human Chimp protein
Orangutan Gibbon ß-globin
37. Homologies are Nested
Primate phylogeny
mitochondrial
DNA
testis-specific
Human Chimp protein
Orangutan Gibbon ß-globin
38. Homologies are Nested
Primate phylogeny
mitochondrial
DNA
testis-specific
Human Chimp protein
Orangutan Gibbon ß-globin
39. Homologies are Nested
Multispecies interactions
Currie CR, Wong B, Stuart AE, et al.
Ancient tripartite coevolution in the attine ant-microbe symbiosis
SCIENCE 299 (5605): 386-388 JAN 17 2003
41. Evidence for Evolution: the Fossil Record
Foraminiferan Evolution
http://evolution.berkeley.edu/evosite/evo101/
VIIA1bPunctuated.shtml
Editor's Notes
Homologies: structural similarities among organisms. (Richard Owen, 1848)
Modern definitions:
similarities between species that are shared because of common ancestry.
Or: similarities that exist despite several alternatives that would do the job as well or better.
Owen: similarities indicated that organisms were created following a common plan or archetype (e.g., design plans of a Honda Civic & a Honda Prelude might be similar).
While this idea might explain many individual homologies, it runs into problems when we consider several PATTERNS OF HOMOLOGIES
(e.g., why some organisms share so many similarities, while others share very few;
existence of similarities with no functional basis: why would cave-dwelling fish have eyes that can’t see?
Nearly every prokaryote & eukaryote on the planet shares the identical genetic code
Exceptions include most mitochondria & a few nuclear genomes (Tetrahymena, Mycoplasma)
But why should this be? There’s nothing particularly special about this genetic code – many of equally good alternatives exist.
Example: the tRNAs that do the translation from nucleic acid to protein.
No chemical reason to associate a given codon with a given amino acid – in fact, they’re as far apart as they can possibly be in the molecule.
Evolution, via common descent, offers a simple explanation for the fact that we all share a genetic code:
The common ancestor of all life had a genetic code similar to this one.
Was passed on almost unchanged from generation to generation
What would happen to an organism that had a mutation in the code itself?
(MOSTLY) THRU THIS SLIDE, LECTURE 5 2007
All eukaryotes & prokaryotes have similar structure to their plasma membranes: the phospholipid bilayer.
(Hydrophilic group is glycerol phosphoric acid)
This similarity, with no “design” reason to it, is easily explained if all organisms share a common ancestor who had this structure
Again, once this structure was in place, fundamental changes to any of it would be disastrous
Pentadactyl (five-fingered limb)
All four-limbed (tetrapod) vertebrates have five-digit limbs at some point during development
Birds start with five digits, then lose two during development
If the bird doesn’t need five digits, why would five develop in the embryo, only to be lost?
