evolution bio exam 1 study set

Earth age (Darwin)

Darwin recognized evolution required an old Earth

Lord Kelvin’s estimate

Kelvin argued Earth was ≤20 million years old (later shown flawed)

Radiometric dating age of Earth

~4.56 billion years old

Why early Earth age estimates were wrong

They were based on flawed assumptions

Stable isotope

An isotope that does not decay

Unstable isotope

An isotope with a fixed probability of decay

Fast-decaying isotopes

Isotopes with high decay probabilities decay rapidly

Slow-decaying isotopes

Isotopes with low decay probabilities decay slowly

What fossils teach us

Fossils help us learn about extinct species (morphology, behavior, development)

Why most organisms don’t fossilize

The fossil record can never be complete because most organisms don’t fossilize

How fossil ages are estimated

Age can be estimated using geological context and dating methods

Evidence fossils can provide about behavior

Fossils can give clues about behavior

Evidence fossils can provide about development

Fossils can give clues about development

Scanning electron microscopy (SEM)

Can provide evidence of cellular structure

Melanosomes and plumage

Melanosome structure suggests striking plumage in extinct organisms

CT scans in paleontology

CT scans help determine function of structures like hadrosaur crests

Hadrosaur crest function hypothesis

Crest connected to nasal cavity and may have generated sound by blowing air

Hadrosaur hearing adaptation

Ears may have been tuned to crest sound frequency

Soft tissue fossilization

Occasionally soft tissues fossilize

Burgess Shale age

~505 million years old

Burgess Shale fossils found

~65,000 specimens and ~93 species

Key concept (technology + fossils)

Technology helps reveal natural history, behavior, and appearance of extinct organisms

Biomarker

A distinctive molecule produced only through biological activity

Okenane significance

Okenane indicates purple sulfur bacteria existed ~1.64 billion years ago

Carbon isotopic signatures use

Used to infer diet of early hominins

C4 plants vs C3 plants (C13 levels)

C4 plants have lower C13 than C3 plants

C13/C14 ratio purpose

Used to infer types of plants eaten

Key concept (isotopes/biomarkers)

Isotopes and biomarkers carry information about the history of life

Why search old rocks for life

Scientists search for evidence of life in old rocks because earliest life unlikely preserved as fossils

Carbon in early rocks

Presence of carbon may suggest life; isotopic signatures can distinguish biological vs lifeless sources

Oldest potential evidence of life

~3.7 billion years ago (controversial claim)

Oldest accepted bacterial fossils

Stromatolite fossils ~3.45 billion years ago

Stromatolites

Layered bacterial structures that can fossilize

Key concept (early life timing)

Signs of life may date to 3.7 bya but are controversial; earliest accepted bacterial fossils date to 3.45 bya

Key concept (microbial life)

Earliest life is microbial, and microbes remain most of Earth’s biomass/genetic diversity

Multicellularity importance

Origin of multicellularity was a major evolutionary transition

Multicellularity evolution pattern

Evolved independently in multiple lineages

Oldest multicellular fossils

~2.1 billion years old

Placement of oldest multicellular fossils

Unclear where they fit on the tree of life

Earliest algae fossils

~1.6 billion years ago

Earliest red algae fossils

~1.2 billion years ago

Earliest green algae fossils

~750 million years ago

Key concept (multicellularity timeline)

Multicellularity began at least 2.1 bya and evolved independently in many lineages

Early animals resembled sponges

Oldest animal fossils (~650 mya) resemble sponges

Biomarkers for sponges

Biomarkers also support sponge existence around ~650 mya

Earliest animal tracks

~585 million years old

Ediacaran fauna time range

Dominated oceans ~575–535 million years ago

Ediacaran fauna classification issue

Many are hard to place taxonomically

Early Cambrian range

~542–511 million years ago

Chordates first appear

~515 million years ago

Key concept (Ediacaran → Cambrian)

Few Ediacaran forms relate to modern lineages; most extinct within ~40 million years; most modern lineages appear in Cambrian

Ocean-to-land transition significance

Transition from ocean to land was a major evolutionary event

First terrestrial colonizers

Prokaryotes colonized land first (fossils ~2.6 bya)

Oldest terrestrial plant fossils

~475 million years old

Forest ecosystems timing

Large forests formed within ~100 million years after first land plants

Fungi on land

Fungi appear ~400 mya and are associated with plants

Invertebrate trackways on land

~480 mya (likely insect/spider relatives; unclear if fully terrestrial)

Oldest fully terrestrial animal fossil

~428 million years old

Oldest tetrapod trackways

~390 million years old

Oldest tetrapod fossils

~370 million years old

Lineages missing 350 mya

Teleost fish, mammals, birds, flowering plants had not yet evolved

Mammal origins

Mammals evolved from synapsids

Synapsids dominance

Synapsids were dominant vertebrates ~280 mya

First mammals emerged

~150 million years ago

Mammal diversification trigger

Mammals diversified after dinosaur extinction (~65 mya)

Whales, bats, primates emergence

Whales, bats, primates emerged ~50 mya

Oldest human fossils

~200,000 years old

Bird origins

Birds evolved ~150 mya and are descendants of dinosaurs

Flowering plants origin

Flowering plants evolved ~132 mya

Grasses diversification

Grasses diversified ~20 mya

Insect emergence

Insects emerged ~400 mya but many current lineages appeared later

Key concept (recent diversification)

Many of the most diverse plant/animal lineages evolved relatively recently

What is a phylogeny?

A visual representation of the evolutionary history of populations, genes, or species.

How did Darwin view evolution?

As a branching process like a “Tree of Life.”

What is a phylogeny similar to?

A family tree.

What do phylogenetic trees represent?

The branching pattern of evolution over time.

How is life organized according to phylogeny?

In a nested hierarchy.

When are taxonomic units considered legitimate?

Only if they represent a clade.

What are clades?

Monophyletic groups.

What is a monophyletic group?

A group containing an ancestor and all of its descendants, defined by one or more synapomorphies.

What is a paraphyletic group?

A group consisting of an ancestor but not all of its descendants.

What is a polyphyletic group?

A group that does not include the common ancestor of the group.

What is an outgroup?

A group outside the groups in question used to define polarity of character transformations.

What is a sister group?

A monophyletic group more closely related to the group under examination than any other group.

Can taxa be rotated around nodes and still show the same relationships?

Yes, they still depict the same relationships.

Can phylogenies be drawn in different styles?

Yes.

Is any currently existing species ancestral to any other existing species?

No.

Can trees be drawn with fewer species?

Yes.

What identifies clades?

Synapomorphies.

What is a synapomorphy?

A shared derived character state.

What is phylogeny reconstruction based on?

Analysis of characters.

Are all traits similar due to common descent?

No.

What is homoplasy?

Character state similarity not due to common descent.

What is convergent evolution?

Independent evolution of a similar trait.

What is an evolutionary reversal?

Reversion back to an ancestral character state.

What is the principle of maximum parsimony?

The tree requiring the fewest evolutionary steps is usually best.

What do you do if more than one tree is equally parsimonious?

Construct a consensus tree.

What is a polytomy?

Relationships are uncertain.

What are phylogenies considered?

Hypotheses based on the best available evidence.

How do phylogenies help scientists?

They help identify questions that can be tested with additional evidence.