Unit 3 - Lecture 7 - Macroevolution

Why did Darwin think complex adaptations were difficult to explain?

Because evolution occurs through many small steps, and each step must improve fitness.

What are the three mechanisms for evolving complex adaptations?

1. Functioning intermediates

2. Modification of existing structures (exaptation)

3. Larger developmental or genetic steps (e.g., gene duplication)

What evidence supports stepwise evolution of complex structures?

Existing species show functional organs of different complexity (e.g., mollusc eyes).

What is exaptation?

A structure evolved for one function is co-opted for another function.

Example of exaptation in birds?

Feathers—originally for thermoregulation or display, later for flight.

What are homeotic genes?

Genes controlling segment identity during development. Mutations can cause large phenotypic changes. (e.g., Ubx in fruit flies)

How can small genetic changes create large evolutionary steps?

By altering developmental regulation.

What is gene duplication?

The creation of an extra gene copy that can evolve new functions. Duplicated genes = paralogs

Example of gene families formed by duplication?

Globin genes — α-globin, β-globin, and myoglobin trace back to duplication events.

When did microbial life arise?

Over 3.5 billion years ago.

When do fossils of animals and plants become common?

In the last ~550 million years (Phanerozoic Eon).

What are the three domains of life?

Bacteria, Archaea, Eukarya

What characterizes Gram-negative bacteria?

Two membranes (outer + plasma) and a peptidoglycan cell wall in between

What characterizes Gram-positive bacteria?

Thick peptidoglycan wall, no outer membrane.

Name four major bacterial groups from the lecture.

Spirochetes, Gram-positives, Cyanobacteria, Proteobacteria.

Which bacterial group includes almost all known pathogens?

Proteobacteria

What environments do many Archaea live in?

Extreme environments (extremophiles)

What do methanogens produce?

Methane as a metabolic byproduct.

What is unique about archaeal membranes?

Lipids with branched hydrocarbons, chemically distinct from bacteria & eukaryotes.

Are Archaea more closely related to Bacteria or Eukaryotes?

Eukaryotes.

What is the endosymbiotic origin of mitochondria?

They evolved from an engulfed proteobacterium.

Plastids (chloroplasts) originated from what?

An endosymbiotic cyanobacterium.

Did the endomembrane system (nucleus) evolve by symbiosis?

No — it evolved conventionally before endosymbiosis.

Are most eukaryotes animals, plants, or fungi?

No — most eukaryotic diversity is protists.

What are protists?

All eukaryotes except animals, plants, and fungi (paraphyletic group).

What is the major predator of prokaryotes in ecosystems?

Protists

What group did land plants evolve from?

Photosynthetic green algal protists.

What is the relationship between animals and fungi?

They are closely related; their common ancestor was unicellular.

What are the three eras of the Phanerozoic Eon?

Paleozoic → Mesozoic → Cenozoic (oldest to newest).

When did the Paleozoic, Mesozoic, and Cenozoic begin?

• Palezonic: 541 mya

• Mesozoic: 252 mya

• Cenozoic: 66 mya

Why is it important to learn the Eras and Periods?

They help organize fossil history and major evolutionary events.

What causes mass extinctions?

Sudden environmental change (volcanoes, asteroid impacts).

What was the largest mass extinction?

End-Permian (~250 mya) — wiped out ~90% of species.

What was the most recent major mass extinction?

End-Cretaceous (~65 mya) — killed non-bird dinosaurs & many marine species.

What is adaptive radiation?

Rapid evolution and speciation when ecological niches become available.

When do worldwide adaptive radiations occur?

After mass extinctions—surviving lineages diversify to fill vacant niches.

What major adaptive radiation followed the End-Cretaceous extinction?

Mammals diversified into large land animals after dinosaurs disappeared.

Four key lessons about complex adaptations?

• Functional intermediates exist

• Exaptation is common

• Developmental mutations cause big changes

• New genes often arise by duplication

Key domain differences?

• Bacteria: peptidoglycan walls

• Archaea: branched membranes & extremophiles

• Eukarya: nucleus + endosymbiosis origins

Biggest vs. most recent mass extinction?

• Biggest = End-Permian

• Most recent = End-Cretaceous