Gould and Eldredge, 1993 (punctuated equilibrium comes of age)

Question 1

The punctuated equilibrium model recognises … as a meaningful and predominant pattern within the history of species. It recasts … as the differential … of certain species, and their descendants, within clades.

Answer 1

stasis, macroevolution, success

Question 2

When was the theory first written up?

Answer 2

1972 - as a novel interpretation for the palaeontological observation that fossils appear instantaneously and remain very similar in the fossil record for long periods of time (often millions of years), rather than the gradualism theory that everything constantly and gradually evolves.

Question 3

Darwin believed that this observation was due to the…

Answer 3

imperfection of the fossils record and should therefore be largely ignored (he believed in phyletic gradualism). Although there is great imperfection in the fossil record, Gould and Eldredge proposed that there was value in the observation.

Question 4

Stasis should characterise the long and recoverable history of … … populations

Answer 4

successful central

Question 5

The theory is often misunderstood as a … theory that suggests geological … represents true evolutionary suddenness

Answer 5

saltational, abruptness

Question 6

… and … developed useful extensions of the theory that helped to “grasp its implications”

Answer 6

Stanley, Vrba

Question 7

Stasis, found …, dominates the fossil record yet was often simply read as the absence of … and largely ignored.

Answer 7

ubiquitously, evolution

Question 8

G and E suggested “pronounced stasis is the….

Answer 8

usual fate of most species”

Question 9

Because species often maintain stability through intense … change (such as … …), stasis must be viewed as an … phenomenon, not a … response to unaltered environments

Answer 9

climatic, glacial cycling, active, passive

Question 10

All substantial evolutionary change must be conceived as sorting based on … … of certain kinds of … species, rather than … … within lineages

Answer 10

differential success, stable, progressive transformation

• this is the crux of the theory

Question 11

There is usually little … change in any species following its …

Answer 11

directional, origin

• this still allows for evolution while explaining the stasis shown within the fossil record
• this would largely decouple macro- from microevolution

Question 12

Darwinian … cannot fully explain the large-scale change in the history of life

Answer 12

extrapolation

Question 13

… rates also determine the stability of clades. Living fossils would once be treated as lineages rendered static by … adaption or unusually stable …, should be reconsidered as members of groups with unusual low … rates and therefore little opportunity to accumulate change.

Answer 13

speciation, optimal, environment, speciation

Question 14

Punctuated equilibrium is not suggested to be … how evolution of lineages occurs, but is a claim for its … ….

• Phyletic gradualism has been well-documented across taxa

Answer 14

exclusively, relative frequency

Question 15

What are the 4 suggested classes of evidence from punctuated equilibrium?

Answer 15

Individual cases - examples of stasis and abrupt replacement - conform to theory but are not direct evidence (could be lulls in phyletic gradualism and replacement could be rapid transformation without branching or migration from elsewhere) - many cases have been well-documented though, e.g. in molluscan fossils in isolated African lakes

Relative frequency - found, often exclusively, in entire groups or faunas, e.g. trilobites and graptolites - much more common than observed phyletic gradualism - majority of species exhibit most change near a speciation event

Inductive patterns

Tests from living organisms - e.g. data from reptiles and allonyms have validated a key claim of punctuated equilibrium: positive correlation of evolutionary distance and speciation frequency

Question 16

How can true branching be identified?

Answer 16

Survival of the putative ancestors to affirm event of true branching rather than phyletic transformation

Question 17

It has been suggested (by Futuyma) that … … is usually required for a a morphological change to …. These changes can occur but without …, interdigitation occurs and the traits tend not to persist for long enough to be registered in the fossil record

Answer 17

reproductive isolation, persist, speciation

• thus, it is “plausible to expect many evolutionary changes in the fossil record to be associated with speciation”