18 March 20152108Homology.ppt1 Theory of Evolution by Natural Selection Homology and Biogeography

18 March 2015 2108Homology.ppt 1

Theory of Evolution by Natural Selection

Homology and

Biogeography


Speciation and Homology

• Speciation produces “sister species” descended from a common ancestor

• Descendant species retain characters of common ancestor possibly in modified form.

• “descent with modification”Modified character = HOMOLOGY


Evidence for common ancestry (genealogical relationship)

• Same character in 2 or more species inherited from a common ancestor = HOMOLOGY possibly modified since split from sister species

• The common ancestor no longer exists, so how can we tell what’s a HOMOLOGY and what’s not?


Criteria for HOMOLOGY (Operational definition)

• 1. Position in relation to other body structures.

• 2. Embryonic origin• 3. Continuity -- Characters homologous to

another character are homologous to each other.


Criteria for HOMOLOGY

• 1. Position in relation to other body structures.• tetrapod forelimbs

• humerus

• radius & ulna

• carpals

• metacarpals

• phalanges



• 1. Position in relation to other body structures. insect wings, legs antennae



• 1. Position in relation to other body structures.• flower parts

• sepals

• petals

• stamens

• carpel (s)



• 2. Embryonic origin similar developmental origin.• pharyngeal arches

• limb buds

• tail bud

• lobes of brain

• heart



• 2. Embryonic origin similar developmental origin.• 1st pharyngeal arch

jaw

• limb buds

• lobes of brain

• heart



• 3. Continuity -- Characters homologous to another character are homologous to each other.• hyomandibular stapes

(stirrup)

• quadrate incus (anvil)

• articular malleus (hammer)


Ways HOMOLOGY provides evidence for evolution.

• Comparative Anatomy: • Comparative Fossil Anatomy (“Fossil Record”)

• Comparative Embryology:

• Comparative Physiology & Biochemistry:


Comparative Anatomy

• Modification of existing characters/organs for OTHER FUNCTIONS• Forelimbs wings in

birds,

• Forelimbs whale flippers

• 1st gill arch vertebrate jaw


Comparative Anatomy

• Modification of existing characters/organs for OTHER FUNCTIONS• Teeth fangs in

rattlesnake

• Salivary gland venom gland


Comparative Anatomy

• "Imperfection" of adaptation• Panda's "thumb"

• actually “radial sesamoid” bone

• Human backbone • "Oh, my aching . . ."

• after 2-3 million years, we are still subject to back strain


Comparative Anatomy• Modification for NO function

– “Vestigial” organs = "Senseless signs of History"• Characters that make no sense in present, but were used &

needed in ancestors


Comparative Anatomy

• Modification for NO function– “Vestigial” organs

• Pelvic rudiments of whales


Comparative Anatomy

• Modification for NO function– “Vestigial” organs

• Limb bones & claws of boas, pythons

• Human coccyx


Comparative Embryology

• Some traits seen only in embryos or larvae.

• HOMOLOGY with larval or adult traits in other organisms.• Notochord in vertebrates.

• Notochord & dorsal nerve cord in tunicate larvae.

• Bilateral symmetry in echinoderm larvae


Comparative Fossil Anatomy: The Fossil Record

• HOMOLOGY relates fossils to existing organisms • Change in lineages

• Extinction

• Examples:• Fossil elephants

• fossil horses


Comparative Fossil Anatomy: The Fossil Record

• HOMOLOGY relates fossils to existing organisms • Change in lineages

• Extinction

• Example:• trilobites


COMPARATIVE Physiology & Biochemistry

• HOMOLOGY applies to physiological & metabolic processes• Glycolysis and Krebs cycle• Mechanisms of cell signaling


COMPARATIVE Physiology & Biochemistry

• HOMOLOGY applies to biochemicals• Proteins’ amino acid sequences • DNA as genetic code• RNA to translate code into protein structure• ATP as “energy currency” of cells


Convergence

• Evolution (adaptation) of dissimilar organisms to common function, superficially similar characters.• piercing sucking mouth in bugs,

mosquitoes, fleas, butterflies• "wings" in bird, bat, pterosaur,

insect, (airplane ??)

• Convergent character NOT present in common ancestor!!


Biogeography:

• Geographic distributions of species, genera, families, etc.

• Organisms have evolved independently in different parts of the world.


Biogeography:

• Organisms have evolved independently in different parts of the world.• Endemic species, genera,

etc. on islands.• Hawaiian honeycreepers

• Galapagos finches


Biogeography:

• Organisms have evolved independently in different parts of the world.

• Continents as big islands• "Patagonian hare" in S. America

• Convergence of placental and marsupial mammals

• Australia• marsupial "wolf," “badger” (T. devil), “mole,” “mouse,”

“deer” (kangaroo),

• South America

• marsupial "horse," "saber-tooth” predator


Biogeography:• Used with fossil record to reconstruct evolutionary history.

• Camels in Asia = camel, dromedary • in S. America = llama, alpaca • How can this distribution be explained?


Biogeography:• Used with fossil record to reconstruct evolutionary history.

• Alligator in SE USA and China/SE Asia,• Hellbenders in SE USA and China, • Cyclocosmia in SE USA and Malaysia


Biogeography:

• Used with fossil record to reconstruct evolutionary history.• Isthmus of Panama

divided Caribbean from Pacific about 3 MYA

• species crabs, snails, fish, etc. have nearest relatives on other side of land barrier.

Documents

18 March 20152108Homology.ppt1 Theory of Evolution by Natural Selection Homology and Biogeography