Lecture 2 Life Origins: Background and additional research

Chapter 21 (book notes)

Alfred R. Wallace postulated tropical conditions arose prior to colder environments.

  • he was co-founder of evolution with Darwin.

phylogenetic effects- characteristics shared by a linage irrespective of environmental factors.

Development of life

  • eukaryotic cell- basic building block of all modern complex organisms
  • evidence of developmet of multicellular organisms (first ones anyway) is small cause they lacked skeletons.
  • MYA (540 Million Years Ago) invertebrates appear.

Divisions of Geologic time
(1) Paleozoic Era (old animals) 542-251 MYA
Initial appearance of animals w/ hard skeletons
(2) Mesozoic era (middle animals) 251-65 MYA
Reptiles, Dinosaurs!
(3) Cenozoic era (recent animals) 65 MYA - present

(* for a more comprehensive look at geological time click on FILES on the bottom right of the page)

_Continental Drift influences the geography of evolution_
Continental drift- the movement of landmass across the surface of the earth.

Two important effects for ecological systems.

  • positions of continents dramatically effect climate patterns
  • creates/dissassembles barriers for biotas (mountains, canyons, ect.)

Pangaea (250 MYA) the big grandfather of continents
Laurasia (N) and Gondwana (S) 150 MYA

Continental drift- effects ocean circulation and heating patterns

Biogeographic regions reflect log-term evolutionary isolation.

Vicariance- the splitting of a widely distributed ancestral population by continental drift (or some other disaster). Illustrated in book by birds.

Six major zoogeographic regions identified by Alfred Russel Wallace (still basically true for today)

(1) Nearctic
(2) Palearctic
(3) Afrotropical
(4) Neotropical
(5) Australasian
(6) Indomalayan

Climate change influences the distribution of organisms
2 MYA Ice age started (Pleistocene epoch)

Ecological envelope- combinations of conditions that allow a population to be sustained.

European flora have not returned to equilibrium state.

Convergence- when unrelated species subject to similar ecological environments evolve to resemble each other more closely than their ancestors did. (interesting!)
Closely related species show convergence and divergence in ecological distributions.
Species need to have some difference to coexist or else they would be too competitive towards each other (red/white oaks).

Species richness is strongly related to age and area of zone. (Equator!)

Additional Reading Notes:

“A Shot of Oxygen to Unleash the Evolution of Animals” Science, Dec. 8, 2006

Trace amounts of oxygen appeared in the geological record 2 bya, just before the evolution of eukaryotes. However, animals did not evolve until 575 mya. While lacking physical confirmation, scientists ventured to guess that oxygen levels were too low to support animal life.

However, recent isotopic and geochemical evidence from rock in Newfoundland, Canada and Oman corroborate this theory. Geochemists, Donald Canfield of University of Southern Denmark,and David Fike of MIT, independently determined that oxygen first reached the deep seas circa 580 mya, around the end of the Glaskiers glaciation. Such a discovery supports the oxygen theory regarding the evolutionary delay of animal life on Earth.

A Taste for Comet Water ( http://science.nasa.gov/headlines/y2001/ast18may_1.htm)

Panspermia and Exogenesis (http://en.wikipedia.org/wiki/Panspermia)

Is evolution repeatable?

Prof Allan brought up as an aside the question posed by Stephen Jay Gould: is evolution repeatable? If we "replayed" the tape of life under the same conditions, would life evolve similarly to how it did this first go-around, or would it diverge and look different? Gould said "we cannot possibly perform the experiment" and while he was right about literally re-running the whole of time, the experiment can be done on a smaller scale. In addition to studying evolution via fossil records and chemistry and so forth, it is possible to study evolution experimentally and watch it happening real-time, which has produced some preliminary answers or at least insight into whether evolution is repeatable (the answer is not really either yes or no - it's pretty complicated and there is evidence both of organisms generally evolving in the same directions but also chance playing an important role along the way). See for example these quick and interesting reads about these experiments and their findings: http://www.sciencenews.org/view/feature/id/40006/title/Molecular_Evolution and http://www.jsmf.org/grants/d.php?id=2008019 and http://mmg.msu.edu/362.html

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