Macroevolution (Siva-Jothy)

Question 1

Models of evolutionary change

Answer 1

• Gradualism

- Punctuated Equilibrium

Question 2

Gradualism

Answer 2

Gradual change in morphological change, more and more divergent over time

Question 3

Punctuated equilibirum

Answer 3

During speciation events, organism’s phenotype changes rapidly

Question 4

Graduated Equilibrium

Answer 4

The theory stemmed from Gould and Eldredge who noticed inconsistencies in the fossil record:

• Fossils stay the same for millions of years
• When new groups appear, intermediates are often lacking.

This suggests speciation has been rapid.
The proposed that the rates during and between speciation were different because different processes were occurring.
-They claimed speciation took place in small populations (who are susceptible to genetic drift).
-A genetic revolution too place, due to a process other than natural selection.
However, this can be explained due to the gaps in the fossil record.

Question 5

Why do gaps appear in the fossil record?

Answer 5

1. Fossilisation relies on sedimentation, sedimentation is spatially uncommon, so never represents all species, all the time. If sedimentation never occurs, organisms never appear in the fossil record.
2. Even when sedimentation occurs, it is not continuous (only 1-10% of time is represented). The processes that produce sedimentation rarely ever occur.
3. Even when sedimentation occurs, fossilisation doesn’t always happen. A large amount of dead organisms are eaten by scavengers or decomposers. Fossilisation is infrequent and very rare.

Question 6

Fossils in Solnofen Limestone (upper jurassic - 140Mya)

Answer 6

Fossils are very well preserved. This limestone is found in a shallow, very warm lagoon with little circulation so the environment tends to be anoxic meaning very few organisms live in there. The fossils are mostly of flying creatures, no marine life as expected from a lagoon. This is because they would fly over and fall into the lagoons, and sink. They were very perfectly preserved in fossils, as there was very few organisms the scavenge or decompose the organisms before they fossilised.

Question 7

Can selection alone explain the pattern of evolution?

Answer 7

1. Rapid change
   - Home Erectus (920ml brain), homo sapiens (1400ml brain), over a period of 20,000 years. This is rapid for evolution but supports that natural selection can be responsible for rapid change.
2. Periods of stasis
   - Stabilising selection removes individuals moving variation away from the norm. Meaning with a stable environment, this could be responsible for those periods where very little change occurs within species.

Question 8

Patters of evolution

Answer 8

• Divergent Evolution/Adaptive radiation

- Convergent Evolution

Question 9

Divergen Evolution / Adaptive radiation

Answer 9

Occurs when lineages split and separate. A single species undergoes speciation to produce a large number of species adapted to a variety of habitats. One lineage can produce many species in a short time.

Evolution of a character that allows exploitation of a new environment, e.g. amniote egg. When reptiles arose there was a rapid amount of speciation.
Reduction in competition from other groups
-Mass extinctions: mass extinction of dinosaurs, then in mammals.
-Colonisation: colonisation of new habitats, change in climate, continental drift, chance colonisation.
-Honeycreepers from Hawaii; can be traced back to a single coloniser, lead to huge adaptive radiation. 43 species have arisen (16 now extinct).

Question 10

Convergent Evolution

Answer 10

The traits shared aren’t due to a common ancestor.
-Most species who eat ants and termites (Anteater, Aardvark, Echidna, Pangolin); toothless, long extended snout with a sticky tongue, protective covering, spikes/scales etc, small eyes, four limbs, powerful claws. They don’t share a common ancestor but have all adapted to eating ants/termites so all have convergently evolved features to aid this.