BIOL 106 Lecture Topic # 13 Macroevolution

I. Definition: evolutionary changes over long time spans involving many traits and large genetic changes. The derivation of a new group above the species level (e.g., genera, family)

II. Evidence

A. Biogeography = patterns of species distributions

1. 1st suggested common descent to Darwin

2. organisms on islands most closely resemble forms on nearest continent, ex. Galapagos finches

3. Continental Drift - time of separation linked to similarities among organisms on different continents.

B. Taxonomy: Linneaus (fixity of spp)

C. Fossil Record

1. Fossils represent the transformed remains of organisms.

2. A lot more fossil evidence since Darwin's time.

3. The dating of rock reflects the age of the fossil, may provide structure to the information.

D. Homologous Structures = structures developed from common ancestor

1. Envir * genotype interaction thus their function may be different.

ex. mammalian forelimbs

E. Development

1. Observation by von Baer:

related species most resemble each other in juvenile stage

2. Hackel "Ontogeny recapitulate phylogeny":

e.g. -gill like stage in early gestation of humans repeats our evolutionary history as fish

****Timing of development is more important

a. Heterochrony = change in timing of trait development

i. Peramorphosis = adult trait expressed in juvenile

(ontogeny does recapitulate)

a. acceleration of devel.

b. increased duration of devel.

ii. Paedomorphosis = juvenile traits expressed in mature reproducing adult

a. retardation of devel.

b. decreased duration of devel.

***Large changes in morphology can occur through relatively simple changes in rates or timing of development

F. Vestigial Structures = structures with no apparent function, resembling those of presumed ancestors.

ex. human ear muscles, whale pelvic bone

G. Molecular Record -Natural Selection should result in the accumulation of genetic changes, reflected in DNA -Compare DNA sequences among organisms

->er time since divergence will result in more nucleotide changes

ex. Beta chain of hemoglobin

H. Convergent Evolution = independent evolution of similar structures among unrelated organisms, due to similar selective pressures.

1. Analogous Structures = structures with different origins, but similar functions, Given similar environmental demands or selective pressures, ex. -wings of insects and birds

I. Parallel Evolution = Related species evolve same way over time period.

I. Tempo and Mode of Evolution

A. Variable 1. species of mammals relatively young, last 100,000 years

2. horseshoe crab -little change over much longer time period

B. Fossil record indicates that groups of organisms exhibit fast & slow periods of change.

Gradualism vs. Punctuated Equilibrium

Gradualism = gradual evolutionary change, where sel. pressures are relatively constant

PE = evolution proceeds in spurts because of rapid adaptation to novel ecological circumstances followed by periods of stasis.

BUT these observations could also be due to an incomplete fossil record.