Chapter 15

Tracing Evolutionary History

1. Abiotic Synthesis of Small Organic Molecules (SOM)

2. Polymerization of SOM to form proteins and nucleic acids

3. Packaging of molecules and polymers into « protocells »

4. Self-replication of molecules necessary for « inheritance »

How Did Life Arise?

Early Earth Conditions

2. Early photosynthetic Bacteria forming Stromatoliths

1. Reducing atmosphere including water vapour, CO2, CH4, NH3, H2, H2S2, Nitrogen & its sulfids

The Miller Experiment

Mixture of gases simulating atmospheres of early Earth

Spark simulating lightning storms

Condensation chamber

Cold water cools chamber, causing droplets to form

Water vapor

Liquid containing amino acids and other organic compounds

1

2

3

4

Miller’s Experiment Revisited

Analysis of a 4.5 BY-old meteorite that landed in Australia in 1968 contains 80 types of amino acids, lipids, simple surgars and uracil

Alternate Theory for the Appearance of Amino Acids

Formation of ProtocellsMembrane-enclosed

vesicles form when lipids are mixed with water

Adding clay increase rate of vesicle formation while organic molecules concentrate on the surface of the clay

RNA monomers form short RNA polymersAssembly of complementary RNA chain, may

have been the first step in the replication of the original « gene »?

RNA formed the first genes?

Endosymbiosis

Learn.Genetics –U of Utah

Major Advances in Life History

Tree of Life

Use the ages of rocks to identify the ages of fossils found in them

Use radiometric dating

Carbon-14 for young fossils (½ life of 5730 years)

Potassium-40 for older fossils (½ life of 1.3 BY)

How do we know?

Geological Record

Plate Tectonics which caused continental drift causes allopatric speciation

Mass Extinctions wiped out many species at a time which allowed survivors to thrive with less competition/predation

Adaptive Radiation – usually following mass extinctions

« Evo-devo » – slight genetic changes can cause drastic morphological differences b/w species

Mechanisms of Macroevolution

Earth’s Tectonic Plates

Continental DriftSpecies became

separated as the continents drifted, then evolved separately

Lungfish Distribution

Mass Extinctions

Adaptive Radiation of Mammals after the Cretaceous Mass Extinction

Changes in Rate and Timing

Changes in Spactial Pattern

New Genes and Changes in Genes

Changes in Gene Regulation

EVO-DEVO (interface b/w evolutionary biology and developmental biology)

Paedomorphosis – adults that present some juvenille characteristic of an ancestral species

Example : This sexually mature Axoloti is a salamander that retained external gills instead of developing lungs in adulthood

Changes in Rate and Timing

Genes for prognathism are turned off early in humans, while the brain continues to develop at a faster rate after birth

Changes in Rate and Timing cont...

Changes in homeotic genes (HOX genes) or in how or where they are expressed changes body form

Changes in Spatial Pattern

Duplications of HOX genes and subsequent mutations allow for novel characteristics

Two duplications of the hox gene clusters seem to have occured in during the evolution of invertebrates to vertebrates allowing for backbones, jaws and limbs.

New Genes and Changes in Genes

Changes in Gene Regulation

Thought to be only one origin of light-sensitive cells shared among all animals with the capacity to detect light

Evolution of the Eye

A particular structure can become adapted for alternative functions

Feathers were probably used for mating rituals or thermoregulation in dinosaurs, but eventually became adapted for flight

Exaptation

Evolutionary trends depend on the interaction of the organism and their current environment

If the environment changes, the trend can change or even reverse

For example, without grasslands, there would not be a strong selection for grazers in horse ancestors

Evolution may not be GOAL-directed

Taxonomy

Phylogenic Trees (Cladograms)

Reading Phylogenic Trees

Creating Phylogenic Trees

Phylogentic Tree of LIFE!

Based on:

Shared characteristics

Molecular similarities (DNA or A.A. sequences)

Parsimony (simplest explanation is ususally the best)

Phylogenic Trees are Hypotheses

Genes that seem to have reliable rate of change over time can be used as molecular clocks

Molecular clocks help track evolutionary time

Commonly Used Molecular Clocks