Evolution Biol 4802 - Lecture 7

Topics for today

History of life on earth

    1. Archaean
    2. Proterozoic
    3. Paleozoic – Cambrian explosion

EvoBeaker: HIV

 

Why is there little evidence of early life?

  • Earth still volatile
  • Erosion, volcanoes, plate tectonics obliterated evidence
  • Ongoing bombardment by meteors
  • Complex aggregations of molecules that left no fossil record

 

Early organisms left chemical traces

  • 13C:12C ratio in atmosphere is ~1:99
  • Living organisms prefer 12C because its more reactive
  • Graphite deposits in 3.7 byo Greenland rock have isotopic signature of life

 

Experimental conditions of early earth produced basic building blocks of life

  • Purines, pyrimidines, and amino acids

 

Other experiments have synthesized

  • Artificial cells
  • Artificial cell membranes
  • Chemical reactions that could have built cellular material from nonliving sources

 

The chicken or the egg? Protein or DNA?

  • Proteins can do all kinds of complicated tasks except replicate themselves
  • DNA can storing and transmitting genetic information but cannot do any biological work
  • 1980’s small enzymes made of RNA, ribozymes, were discovered that could break nucleic acid bonds

 

RNA can do it all! (It’s not just the poor cousin of DNA!)

“RNA world” hypothesis

  • Ribozymes evolved into:

Ribosomes

mRNA

 

  • short sequence of RNA
  • Timeline from Big Bang to DNA based life

 

For >1/2 of life’s history only prokaryotes were present

  • Concept single ancestor too simple

 

Deep roots of the tree are difficult to discern

  • Different genes tell a different story of relationship
  • Early prokaryotes swapped genes (horizontal gene transfer)

 

Prokaryotes continue to swap genes today

  • Pathogenic - 1,387 different genes
  • Benign - 528 different genes

 

Early life

  • 3.5 byo stromatolite fossils have same structure as those formed today by cyanobacteria

ARCHEAN

•         Origin of life

•         Diversification of bacteria

•         Increased oxygen in atmosphere

•         Aerobic respiration

PROTEROZOIC

•         Earliest Eukaryotes

•         Origin of Eukaryotic kingdoms

•         Multicellularity

 

Origin of the Eukaryotes

 

Advantages of endosymbiosis:

  • Mitochonridia provided aerobic metabolism
  • Choloroplasts provided autotrophy

 

Establishment of Eukaryotic Kingdoms

PALEOZOIC

•         Cambrian explosion

•         First large morphologically complex animals

•         Prior to the invasion of land

•         10-25 my period (geological blink of an eye)

•         Almost all modern phyla and classes of marine animals and many now-extinct lineages appear

 

How do we know about the Cambrian explosion?

  • 505 mya an enormous mud slide off the coast of Canada smothered teeming marine life below
  • Successive mudslides created Burgess Shale
  • Uplifted 2 miles into the Canadian Rockies
  • Discovered in 1909 but not understood until 1970s

 

Fossils of the Burgess Shale

  • Fundamental body plans
  • Some internal organs are preserved

 

Present during the Cambrian

  • Earlier fossils in Chengjiang, China
  • Later fossils in Burgess shale, British Columbia, Canada

 

Causes?

  • Higher oxygen concentration allowed

·        Higher metabolic rates

·        Larger size possible

·        Made tissue development possible

·        Efficient metabolism powered movement

 

How could we tell whether it was really explosive or just had a long fuse?

  • Molecular clock
  • Estimated rate of hemoglobin evolution among vertebrate groups with known fossil ages
  • Compared hemoglobin of vertebrates and invertebrates and back calculated the time when they must have diverged
  • Earliest branching occurred 1000 my prior to fossil record evidence
  • Progenitors probably small and/or lacked skeletons

 

 

Evolution Biol 4802 - Lecture 7

Topics for today

History of life on earth

    1. Archaean
    2. Proterozoic
    3. Paleozoic – Cambrian explosion

EvoBeaker: HIV

 

The problem

  • Recognized 1981
  • Infected 60 million people
  • Virtually 100% fatal
  • 2020 AIDs will kill 90 million
  • 5% of all deaths worldwide
  • 70 % in Sub-Saharan Africa
  • Thought to be most infectious disease to affect humankind

 

 

 

 

 

 

 

 

AIDs epidemic

  • Infection rates 15-45yr
  • 2/3 in sub-Sarahan Africa
  • % adults infected

·        39 Botswana

·        34 Zimbabwe

·        33 Swaziland

·        31 Lesothos

  • Reduced life expectancy from 62 to 47 years
  • 90 % in poor countries of Southern hemisphere
  • Rapid increase

 

What is HIV?

  • Intracellular parasite
  • Enters host through body fluids
  • Parasitizes cells of human immune system – macrophages and T cells
  • Simple structure
  • Co-opts cell’s machinery for replication

 

How does your body react?

  • Body kills virions in blood stream and infected cells
  • T cells and macrophages essential for immune response
  • Eventually HIV depletes infected helper CD4 T cells and immune system collapses
  • Opportunistic infections by bacteria and fungus that do not normally cause disease

 

With-host evolution

  • 9 patients taking AZT
  • Viral DNA sampled overtime
  • What should the phylogeny look like?
  • Continual immune drive selection
  • Selective replacement of strains overtime