Lecture 5: Macroevolutionary Trends

Question 1

Evolutionary Trends Over Time

Answer 1

Evolution often shows directional trends across eras, such as changes in body size, genome complexity, and phenotypic traits.

Question 2

Cope’s Rule

Answer 2

Definition: A general tendency for body size to increase over time within lineages.

Examples:
o Elephants, Horses, and Sauropod Dinosaurs: Show significant increases in body size over evolutionary time.
o Marine Fauna: Exhibit rapid body size expansion, with maximum sizes increasing by ~2% per million years.

Question 3

Body Size and Cell Complexity

Answer 3

1) Cell Types: Increased body size often correlates with a greater variety of cell types, reflecting the needs of larger, more complex bodies.

2) Scaling: Larger organisms tend to have more diverse cell types, but it’s uncertain if this is directly tied to increased fitness.

Question 4

Evolution of Marine and Terrestrial Fauna

Answer 4

Marine Megafauna: Body size range increased across the Phanerozoic, especially from the Devonian period onward.

Terrestrial Vertebrates: Show diverse trends; some lineages evolved smaller, stable, or larger sizes, depending on the unique evolutionary pressures of each clade.

Question 5

Genome Evolution

Answer 5

1) Genome Size and Protein Coding: Genome size generally increases with organismal complexity, but protein-coding gene numbers may be nearing a limit.

2) Genome Size Variation: Highlights evolutionary flexibility, though larger genomes don’t always mean greater complexity.

Question 6

Complexity and Simplification

Answer 6

1) Complexification: Evolution tends toward greater anatomical complexity in some lineages, like the transition from fins to limbs in vertebrates.

2) Simplification: In other cases, evolution simplifies structures, as seen in synapsid skulls where bones have fused or been lost over time.

Question 7

Random Walk Models

Answer 7

Random Walk Models: Suggest some evolutionary changes (e.g., body size increase) could result from random variation rather than adaptation, especially with an effective “zero wall” (minimum size limit).

Question 8

Evolutionary ‘Approaching Limits’

Answer 8

There may be natural constraints on body and genome size, as life approaches structural or functional maximums.

Question 9

Summarize evolutionary trends and what this lecture was about, the main concepts!

Answer 9

1) Body Size: Maximum body size has generally increased throughout the Phanerozoic, but whether this is adaptive or due to random processes is debated.

2) Genome Complexity: Larger organisms tend to have larger genomes, yet protein-coding capacity seems to plateau.

3) Phenotypic Complexity: Evolution sees both increased complexity (anatomical networks) and simplification (skull structure).

4) Perspective: Macroevolutionary trends depend on selected phenotypes, with each lineage having unique evolutionary paths.