Today's outline
Honors conversion?
Demo of catalytic cycle in chimera.
Slides on ATP binding sites ( An example for the power (or lack of power) of convergent evolution)
Is there a definition of life? NASA's working definition of life: "life is a self-sustaining system capable of Darwinian evolution"
Are viruses alive?
Can the whole biosphere be considered an organisms?
The Gaia hypothesis argues that the whole biosphere should be regarded as a single organism, with its own homeostatic feed back loops.
Can living systems be divided in smaller sub-systems that are themselves alive? Or, is life a property of the larger system? The ecosystem of the Sargasso sea that includes algae, bacteria and phage (viruses that live on bacteria). The cyanophage play an important role in the system as predators of the primary producers. They lyze the cells allowing for recycling of limiting elements. The phage are part of a living system, but usually are not cindered alive themselves.
Problems of the Gaia hypothesis:
- Earth also includes many feed-forward loops (e.g., melting ice caps lower the albedo, which leads to more warming*). Relying on Gaia's regulatory mechanisms can provide a false sense of safety.
- How does a single organism evolve? With only one Gaia, who would natural selection work?
What is needed for evolution by natural selection to occur? Would selection for persistence work as well? (Differential persistence rather than different number of competing offspring. See Ford Doolittle's recent paper)
Does Darwinian evolution depend on a biopolymer that acts as genetic material?
* Lovelock and Watson developed the Daisyworld model (simulation here), in which black and white Daisies stabilize the climate of the model planet. The release of DMS heat stressed algae creates a Daisyworld like feed back loop, because it acts as nucleating agent in cloud formation.
What is life?Traditional criteria:
See essay on definitions of life: The
Seven Pillars of Life by Daniel E. Koshland NASA's working definition of life: "life is a self-sustaining system capable of Darwinian evolution" von Neumann's computers - alive? A-life? Turing machines and universal computers (Turing's biography) Cellular automata: A'life; John Conway's game of life. [rules: a cell survives if it has two or three living neighbors. A new cell is created on a "dead" square if it has exactly three living neighbors.] The game was popularized by Martin Gardner in Scientific American in 1970. Example: https://en.wikipedia.org/wiki/Conway%27s_Game_of_Life More information on digital life is at Digital evolution homepage at MSU.
Genetic Algorithms in engineering: Ingo Rechenberg and others used "natural selection" in the computer to optimize aerodynamic profiles. Biased walk through "sequence" space. Finding optimal solutions. (To avoid local maxima: use demes with limited migration). For more information you can check a comprehensive collection of links on Evolutionary Computation and its application to art and design. It is amazing that GA work fine with rather small populations. |
What is necessary for evolution to occur?
Natural Selection and EvolutionWhen does "evolution" occur? An algorithmic approach."Darwin's Dangerous Idea" by Daniel C. Dennett, Chapter on Evolution as algorithm is a reading assignment for Monday, Sept. 13. [available through WebCT]What is needed for evolution to occur?(Note, this is different from stating that this is all that occurs in evolution)
What processes in biological evolution go beyond inheritance with variation and selection? (We'll discuss many of the following later in the semester.)
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