Bio 1B: Lec 7: Macroevolution

Microevolution vs Macroevolution

Microevolution: changes populations (allele frequencies in populations, selection, drift, mutation, gene flow, generations to thousands of years, local adaptation and genetic change)

Macroevolution: explains patterns among species, clades, and deep time (speciation, extinction, clade-level patterns/trends, millions to billions of years, radiations, major innovations, biosphere composition)

Does current variation impose a hard cap?

NO, short-term constraints are real, but long-term evolution can do anything!

Preadaptation

A change in function of an old trait

Original function differs from later function (feathers developed as insulation, later used for flight)

NOT if a trait becomes BETTER, that’s just improvement bruh

Species Sorting

Birth and death at the clade level

A group-level property (geographic dispersion of a species) can change the composition of a clade even when individual-level advantages are not the main driver

Selected FOR vs Selected OF

Selected for: what is better fit

Selected of: which species/type is the better fit

Background regime

Extinction is a natural part of life and constantly ongoing

New species arise while others die out, resulting in turnover

The average lifespan of a species is ~1-10 million years

Mass-extinction regime

Global filter changes who survives

Success before the event may not predict survival through it

Macroevolutionary lens: extinction can create patterns that cannot be explained by adaptation within surviving populations alone

Types of ecological opportunities

Empty habitat, new resource, competitor removed, key innovation

Adaptive Radiation

In the face of an ecological opportunity, rapidly increase species number (radiation) + ecological/morphological divergence to take advantage of the new niche (adaptive)