Macroevolution

Macroevolution vs. Microevolution

• Macroevolution: Evolutionary change above the species level.
• Microevolution: Evolutionary change within a species or small group of organisms, especially over a short period.

Transitional Stages

• Transitional stages may not persist long due to:
  • Little fossil evidence.
  • Results of relatively rapid change.
  • Creationist claims of no evidence.

Current Macroevolution Winner

• Beetles: Over 1.5 million species.

Evolutionary Faunas

• Cambrian, Paleozoic, Modern.
• Evolutionary Fauna: Groups of organisms that dominate the fauna for extended periods.

Tetrapods

• Vertebrate animals having four feet, legs, or leg-like appendages.
• Humans are considered tetrapods because they are backboned animals with four limbs bearing digits (fingers + toes).

Hox Genes and Tetrapods

• Hox gene mutations have resulted in some tetrapods becoming limbless or two-limbed.

Birds

• May or may not fly, with vertebra, lay eggs, have feathers.
• Classified in the class of Aves.

Darwin's Gradualism

• Involves slow and steady cumulative change.
• Believed by Darwin to lead to new species.
• Also called phyletic gradualism or anagenesis.

Saltation

• Sudden evolutionary changes that happen in a single generation, rather than gradually.
• Also called punctuated equilibrium, abrupt speciation, sudden evolution, abrupt transformation, mutationalism, saltational evolution.

Evolution of Novelty

• Probably not due to a "hopeful monster".
• Often due to change in function.
• Exaptation = preadaptation.

Evolution of Sting Analyzed

• Modified ovipositor.
• Proteins co-opted for poison.
• Includes waste products of metabolism.
• Some sequestered from diet.

Novelty Due to Mutation

• Frameshift in development.
• Change in Hox genes.

Homology and Emergence of Novel Characters

• Some "new" characters come from other structures that have been modified.
• Darwin's "descent with modification".
• Ex. Sesamoid thumb.

From Macroevolution to Microevolution

1. Affected by rates of evolution
2. Changes in natural selection pressures
3. Open niches fuel macroevolution

Rate of Evolution

1. Can be variable within a lineage
2. Often view rates as its average
3. Low rates can produce large changes given enough time

Facts About Punctuated Equilibrium

1. May be the most common method
2. Stasis, rapid change, stasis
3. Time of stasis may vary greatly