25/26 - Primate + Human Evolutionary History

What are the main topics of primate and human evolution?

Origin, differences with primates, fossil record, migration, population origins.

Where did humans originate?

Africa.

When did Homo sapiens originate?

~200,000 years ago.

What is wrong with the “march of progress” image?

Evolution is not linear or goal-directed.

Why did Darwin delay publishing human evolution ideas?

Fear of backlash.

What is a synapomorphy?

A shared derived trait.

What are primate synapomorphies?

Large brain, no tail, flexible joints.

What are human-specific traits?

Erect posture, large brain, reduced hair.

What are reproductive traits in humans?

Delayed maturity, visible sex traits.

What did Sarich & Wilson show?

Humans and chimps diverged ~5 million years ago.

Concept: Why was this shocking?

Previously thought to be ~30 million years.

What does molecular clock estimate?

Divergence timing using mutation rates.

What is approximate human-chimp divergence?

~5–6 million years ago.

How many chromosome pairs do humans have?

23 pairs.

How many do chimps/gorillas have?

24 pairs.

What is special about human chromosome 2?

Fusion of two ancestral chromosomes.

Concept: What does chromosome fusion indicate?

Evolutionary relationship.

What percent of DNA differs between humans and chimps?

~1%.

How many nucleotide differences exist?

~35 million substitutions.

What are indels?

Insertions and deletions in DNA.

How many indels separate humans and chimps?

~5 million.

What is segmental duplication?

Large DNA segments duplicated.

Concept: Why are duplications important?

They alter gene expression.

What contributes most to human-chimp differences?

Structural genome changes.

What percent identity do humans and chimps share?

~95–96%.

What is CHON?

Elements in proteins (carbon, hydrogen, oxygen, nitrogen).

Concept: Why are protein differences important?

Affect phenotype.

What is gene expression?

How genes are turned on/off.

Concept: Why is gene regulation important?

Small changes cause big effects.

What are microRNAs?

Regulators that suppress translation.

Concept: Where are major gene expression differences?

Brain and testis.

Concept: What is key takeaway about human evolution genetics?

Regulation matters more than sequence.

Why do humans have low genetic variation?

Recent origin and bottlenecks.

What is mtDNA used for?

Tracing maternal lineage.

Concept: Why use mtDNA?

High mutation rate and no recombination.

What is cultural behavior in chimps?

Learned, socially transmitted behaviors.

Concept: Do chimps have culture?

Yes.

What similarities exist in chimp communication?

Follows linguistic patterns.

Concept: What does this imply?

Common evolutionary roots of language.

What behaviors do chimps share with humans?

Empathy, violence, tool use.

Concept: Do chimps have better memory?

Yes, short-term memory.

What is sexual dimorphism?

Difference between males and females.

Concept: How does dimorphism compare in humans?

Reduced compared to apes.

What was the common ancestor like?

Knuckle-walking, omnivorous, social.

What is Sahelanthropus tchadensis?

Early possible hominin (~6–7 mya).

Concept: Why is it controversial?

Unclear lineage placement.

What are major trends in hominin evolution?

Larger brain, upright posture, smaller teeth.

What is Australopithecus afarensis?

Early hominin (“Lucy”).

When did Lucy live?

~3.2 million years ago.

What was Lucy’s brain size?

~400–500 cc.

Concept: What key trait did Lucy have?

Bipedalism.

What is bipedalism?

Walking on two legs.

When did bipedalism evolve?

~4 million years ago.

What are robust australopithecines?

Paranthropus species.

What was their diet?

Tough plant material.

Concept: Why large jaws/teeth?

For heavy chewing.

What is Homo habilis?

Early Homo species.

What is H. habilis known for?

Tool use.

What is brain size of early Homo?

~510–775 cc.

Concept: What changes occurred in early Homo?

Smaller teeth, flatter faces.

What is Homo erectus/ergaster?

Early human species with larger brain.

Brain size of H. erectus?

~850 cc.

What was unique about H. erectus?

First to leave Africa.

Concept: What traits improved efficiency?

Long legs, upright posture.

What tools did H. erectus use?

Hand axes.

Concept: What hypothesis explains smaller teeth?

Cooking hypothesis.

What is Homo heidelbergensis?

Pre-modern human ancestor.

What behaviors did they show?

Shelter building.

What is Homo neanderthalensis?

Archaic human species.

What behaviors did Neanderthals show?

Burial, culture.

What is Homo sapiens?

Modern humans.

Brain size of Homo sapiens?

~1200–2000 cc.

Key skull traits of Homo sapiens?

High forehead, flat face.

When did Homo sapiens appear?

~100,000–200,000 years ago.

What is Cro-Magnon?

Early modern humans in Europe.

Concept: What behaviors did early humans show?

Art, burial rituals.

Did multiple Homo species coexist?

Yes.

Concept: What does overlap imply?

Competition and interaction.

What is Out-of-Africa theory?

Humans originated in Africa and spread globally.

When did H. erectus leave Africa?

~1.8 million years ago.

When did Homo sapiens leave Africa?

~100,000–50,000 years ago.

What caused migration waves?

Climate change.

What was population bottleneck?

What is African Replacement Model?

Humans replaced archaic populations.

What is Hybridization/Assimilation model?

Humans interbred with archaic species.

Concept: Which model is supported today?

Hybridization.

What percent of Neanderthal DNA is in humans?

~20–30% segments overall.

What did Denisovans contribute?

High-altitude adaptations.

Concept: What does introgression mean?

Gene flow between species.

What is serial founder effect?

Successive population bottlenecks during migration.

Concept: What happens to diversity with migration?

Decreases farther from origin.

What molecular data is used for migration?

SNPs across genome.

Concept: What causes reduced genetic diversity?

Bottlenecks and drift.

Which region was colonized last?

Remote Oceania.

Concept: Why is Madagascar unique?

Late human colonization.

Concept: Are human populations very different genetically?

No, differences are small.

Concept: Where do most differences exist?

Between sexes, not populations.

Concept: Why are racial differences small?

Recent divergence (~100k years).

What is genetic drift?

Random changes in allele frequency.

Concept: How does drift affect small populations?

Greater effect.