chapter 15: macroevolution

Chapter 15: Macroevolution

Origin of life

Big Bang

Early Earth

molton

atmosphere

1st this with water vapor and volcanic gasses

as earth cooled, H2O condensed, N2 escaped

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First fossils

3.5 billion years ago

stromatolite

can not be first life because they photosynthesized

Life is therefore older than 3.9 billion years

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How did life begin?

Current hypothesis

1. Abiotic synthesis of organic molecules

2. Small molecules join to form macromolecules

3. Macromolecules get packaged in membrane

4. Origin of self replicating molecule

Evidence

Miller-Urey experiment

1923

tested hypothesis of JBS Haldane and AI Oparin

H2O, H2, CH4, NH3, + sparks = aas

The path to life…

Polymers

produced by dehydration reactions and without enzymes

Protobionts

formed spontaneously in lab

RNA World

Chicken vs Egg:

DNA-----RNA-----Protein

How did it evolve?

RNA that could self replicate (w/out ribosomes or proteins)

Ribozymes

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Once self replication exists, natural selection can begin

Significant Events

Origin of single celled organisms

Origin of multi-celled organisms

Colonization of land

Single Celled Organisms

Prokaryotes

Earth’s sole inhabitants from 3.5 to 3 bya

Transformed the atmosphere

O2 causeddecline in anaerobesincrease in aerobic prokaryotes

Single Celled Organisms

Eukaryote

oldest fossil 2.1 bya

photosynthetic and/or respiratory prokaryotes living in larger cell

Multi-Celled Eukaryotes

Oldest fossils 1.2 bya

Molecular clock suggests 1.5 bya

More diverse fossils 600 mya

Cambrian Explosion 535 to 525 mya

Colonization of land by multi-celled eukarotes

500 mya

Plants and fungi colonized together

Arthropods and Tetrapods are the most widespread and diverse

Human lineage diverged 6 to 7 mya

Homo sapiens diverged 195,000 ya

How do we know?

Actual ages of rocks and fossilsradiometric dating

Fossil record documents history of life

Radiometric Dating

Isotopes - use half life to determine age

C12/C14 good for young fossils (<25,000 years)

Other isotopes better for older fossils

Fossil Record

Fossils appear in strata

Earth’s history divided into 3 Eons

Archaeon

Protozeroic

Phanerzoic

Phanerzoic eon divided into 3 eras

Paleozoic

Mesozoic

Cenozoic

Boundaries of eras = mass extinctions

Lesser extinctions often mark boundaries of periods

Cambrian Explosion

Suddenly all modern animal phyla appear

Why the sudden appearance?

1. Lots of empty niches

Or 2. Sudden appearance of hard body parts = good fossils

Mechanisms of Macro Evolution

Continental Drift

Mass Extinctions

Adaptive Radiations

Continental Drift

Proposed in 1916, accepted in 1960s

Since origin of eukaryotes, all continents have come together 3 times

1.1 bya

600 mya

250 mya

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Thin crust on hot mantle

Some places moving apartNorth America and Europe

Others moving together“Ring of Fire”

Pangea

250 million years ago

Brought species together that had evolved separately

Inland seas drained

Interior of continenet probably extreme

Caused big biological shake up

Break-up of Pangea

180 million years ago (mesozoic)

135 mya First split into north and south

65 mya modern continents take shapeend of mesozoic, beginning of cenozoic

55 mya India ran into Eurasia = Himalayas

This pattern of continents merging and breaking up solves a lot of

puzzles

Marsupials vs eutharians

lungfishes

Mass Extinctions

5 over past 500 million years

50% or more of earth’s species went extinct in each event

End of Permian and Cretaceous get most attention

End of Permian took 96% of marine animals

End of Cretaceous took >50% of marine species and dinosaurs

Causes of mass extinctions

Permian

enormous volcanic eruptions in present day Serbia

lava, ash, CO2 increased T

slowed mixing of ocean between pole and equator = decrease in O2 in water

Causes of mass extinctions

Cretaceous

Asteroid

iridium signature

65 my old crater off yucatan, 180 km in diameter

Consequences of mass extinctions

Loss of whole ecosystems

Changes course of evolution

Recovery takes 5 to 10 million years or longer (100 my after permian)

Is the 6th mass extinction underway?

> 1000 species have gone extinct in the last 400 years

100 to 1000 times normal rate

Adaptive Radiations

Evo-devo

Evolutionary changes caused by:

Changes in timing or rate of devolpment

Changes in spatial patterning

New genes/changes in genes

Changes in regulation

How novelties can arrise

Gradual change

e.g. eyes

Exaption

adapted for one purpose,

adopted for another

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Evolution is not goal oriented!

Trends don’t mean there is a goal.

Evolution is the result of existing organisms’ genetic diversity and the CURRENT

environment.

Phylogenies

The evolutionary history of a species or group of species.

Phylogenies

Inferred from

fossil record

morphological homologies

molecular homologies

Analogous vs homologous structures

Convergent evolution can be misleading.

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Ocotillo found in SW US Alluaudia found in Madagascar

Systematics

Focuses on classifying organisms and determines their evolutionary origin

Taxonomists name things

Genus species

Linneaus’s system still used:

SpeciesGenusFamilyOrderClass

PhylumKingdomDomains

africanaLoxodonta

ElephantidaeProboscideaMammaliaChordataAnimalia

Eukaryote

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Problems with the system…

It is all subjective and ultimately, arbitrary.

Phylocode

Since Darwin, systematics

has expanded to reflect

evolutionary relationships in phylogenetic

trees.

Constructing Trees

Cladistics

evolution proceeds when a new heritable trait developes

Shared derived characteristics

Shared ancestral characteristics

Ingroup compared to outgroup

Parsimony

the simplest hypothesis is most likely to be the correct one.

construct trees with fewest changes

Trees as hypotheses

Best tree is only most likely

Always changing with new information

Trees allow us to make and test predictions

The more we know the more accurately we can make and test predictions.

Molecular Systematics

Comparing nucleic acids or other molecules to infer relatedness

Booming field - tons of new data

Molecular Systematics

Can compare recent and ancient divergences

rDNA for ancient

mtDNA for recent

Genome Evolution

Humans have 99% homology to mice

50% homology to yeast

Many shared biochemical and developemental pathways

Overwhelming support for Darwin’s concept of

“decent with modification”

Gene duplication

We can trace evolution of gene families

The number of genes does not increase at the same rate as

organismal complexity.

Molecular Clock

Some genomic regions appear to accumulate change at a constant rate.

Calibrated by graphing nucleotide changes vs date of branch

Molecular systematics is helping link all life.

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A highly resolved Tree Of Life, based on completely sequenced genomes [1].