Rates of evolution

Question 1

What is anagenesis?

Answer 1

The gradual morphological change predicted by Darwin where cladogenesis is the formation of new groups of taxa

Question 2

What contrasting model of evolution did Gould, Eldridge and Stanley propose?

Answer 2

Evolution is a history of punctuated equilibrium with abrupt transition following long periods of stasis, claimed support from the fossil record where new species appear with intermediates rarely found

Question 3

What does the punctuated equilibrium model say about the mechanisms of macroevolution?

Answer 3

Occurs via:

• The splitting of lineages
• Rapidly in small populations
• Place/species fringes
• Changes in a few key genes
• Stable lineages between punctuations

Question 4

What evidence do trilobites provide against the punctuated equilibrium model?

Answer 4

Sheldon found a gradual increase in the number of ribs in the trilobite fossil record

Question 5

What other 4 issues are there with the punctuated equilibrium model?

Answer 5

• Measurement timescale - amount of time you look at is related to the amount of change you expect to find
• Fluctuating evolution - results may be confounded depending on what timescale a researcher uses
• Incomplete records - sometimes intermediate fossils are missing, can only relate speciation to morphological change
• Stasis - morphological stasis does not mean evolution has stopped, although horseshoe crabs are very similar they are very genetically diverse