Notes for Lecture #1:
Early views on the origin and diversity of life
Copyrighted 1996. May not be reproduced for commerical purposes
| You are visitor number |
 |
since 23 Feb 1996 |
Some interesting links
Lecture Notes
Bruce Walsh
- Office hours: M 910, W 89 LSS 327
- jbwalsh@ccit.arizona.edu
- WWW page
Upcoming Exams
- 16 Feb: only covers Rob' s material
- 25 March: my material
Origins of the Diversity of Life
- Today' s lecture: Early views on the origin and diversity of life
Zoo / Aquarium diversity:
- The view most have of organismal diversity is based on variation among large animals and plants. These differences are in fact fairly trivial compared to the spectrum of biological diversity.
Some other examples of diversity
- Insects
- Parasites
- Archaebacteria in thermal ponds at Yellowstone (80C, pH 1.9)
- viruses, viroids
Key Point: Not only are life forms diverse, they are much more diverse that most people can imagine.
How can we account for
The apparent adaptability of these life forms to their environments? The diversity of life forms?
"Nothing in biology makes sense except in the light of evolution"
Th. Dobzhansky (1973)
The Early Seeds of Evolutionary Thinking
- The Classical view
- Buffon 1770
- Erasmus Darwin 1770
- Lamarck 1810
The Classical view:
- Living organisms are constant and unchanging. The roots of this notion trace back to the Greeks, but even the great naturalist Aristotle pondered over bizarre life forms that he could not easily classify, e.g., sponges, which look like plants but feed like animals.
This view gets shaken up:
- Global explorations starting in the 1500s turned up extraordinary diversities of life forms, some of which appeared related to European forms, others with no resemblance.
The world distribution of organisms was puzzling:
- Marsupial mammals generally very rare, but all Australian mammals were marsupials
- Cactus plants common in North and South American deserts, absent in Australian and Asian deserts
If all species were created at the same time in the same place, how could so many be restricted to particular parts of the world?
Buffon (1770s)
-
Noted that if there had been only a single center of creation, species spreading out from this center would have eventually been stopped by mountains or seas. He suggested that the creation of species is spread out in space.
- Buffon also noted that species might not have been created in a perfect state (e.g., pigs have lateral toes that are too high to reach the ground). He suggested that perhaps species become modified over time.
Erasmus Darwin (1770s)
- Was impressed by the diversity of domesticated animals generated by selected breeding. Suggested that all organisms had a common ancestor
- Grandson Charles Darwin used these ideas
JeanBaptiste de Lamarck (1809)
- Suggested that life had been created long ago in a simple state, and had been gradually improving. He proposed a specific mechanism for how this change occurs: the inheritance of acquired characteristics.
- Lamarck thus suggested that species change over time and that the environment was a factor in this change.
What is evolution?
Charles Darwin defined it as descent with modification.
Darwin was not the first to suggest that evolution occurs, but he has the first to suggest a plausible mechanism as well as present an overwhelming case that evolution occurs.
What do we mean by descent with modification?
All organisms can be traced back through a series of common ancestors (here, D and E). If true, should find evidence of this.
Descent with modification allows for tests of Evolution.
House example: unless completely torn down, if we look hard enough, we can find vestiges of the old house.