A&O – EVOLUTION

EVOLUTION by means of NATURAL SELECTION – key observations and their inferences

• Overproduction [individuals tend to produce as many offspring as possible]
• Stability [population size seems to remain stable from generation to generation in stable environments]
• Limited resources [there is not enough for everyone]
  • inference: COMPETITION: Struggle for existence inferred
• Variability [offspring manifest varying traits]
• Heritability [traits are to some extent inherited]
  • inference: DIFFERENTIAL SURVIVAL (=Natural selection) inferred [some traits allow their bearers to produce more offspring than other individuals = be more fit]
  • inference:  EVOLUTION: Over many generations, differential survival leads to changes in the frequencies of genes and thus the traits they influence.

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Adaptation is . . .   “The processes by which organisms or groups of organisms maintain homeostasis in and among themselves in the face of both short-term environmental fluctuations and long-term changes in the composition and structure of their environments.”  (Rappaport, 1971)(homeostasis refers to stability of an organism’s inner environment, essential for life, maintained by a dynamic balance of the multiple interacting systems that operate in an organism.)

The ESSENCE of “EVOLUTION” then, is that biologically relevant information is transmitted from one generation to the next.

what constitutes “cooperation” is a matter of common usage — arguably, most complex organisms are amalgams of ancestors (and/or parts of their genomes) … including endosymbionts such as “mitochondria” 

COMPETITION and COOPERATION.   “In a field defined by the cruel logic of natural selection, group selection appears to be the rare hint of virtue. The one biological force pushing back against the obvious advantages of greed and deceit.   ‘I see human nature as hung in the balance between these two extremes,’ Wilson says.  ‘If our behavior was driven entirely by group selection, then we’d be robotic cooperators, like ants.  But, if individual-level selection was the only thing that mattered, then we’d be entirely selfish.  What makes us human is that our history has been shaped by both forces.   We’re stuck in between.’”  (E.O. Wilson quoted by Jonah Lehrer in The New Yorker “Kin and Kind” Mar 5, 2012 pp. 36-42  q on p 42.)

“Social Selection?” According to sexual selection principles, males and females compete to maximize their fitness, and a key way to do this is by minimizing their investment in specific offspring: it is often manifest as “who does the most parenting.”   Joan Roughgarden believes (“The Genial Gene: Deconstructing Darwinian Selfishness” 2009) “sexual selection: should be renamed “social selection” to emphasize the extent to which parents cooperate rather than compete.  For example, in sexual selection, the first direct parental investment in offspring is the relative amount of tissue/nutrients contributed.  Females provide a huge egg, but males “cheat” & provide little more than genes in the head of a sperm. But Roughgarden can show mathematically that this is the best way to meet conflicting needs. (book review of “The Genial Gene”)       

 On the Origin of Cooperation

Elizabeth Pennisi

In the ninth essay in Science‘s series in honor of the Year of Darwin, Elizabeth Pennisi explores why an individual would help another at a cost to itself when natural selection favors the survival of the fittest. Charles Darwin suggested that selection might favor families whose members were cooperative, and researchers today agree that kinship helps explain cooperation. But cheaters—those who benefit without making sacrifices—are likely to evolve because they will have an edge over individuals who spend energy on helping others, thus threatening the stability of any cooperative venture. That puzzle has inspired biologists, mathematicians, even economists to come up with ways to explain how cooperation can arise and thrive. Researchers have spent countless hours observing social organisms from man to microbes, finding that even single-celled organisms have sophisticated means of working together. As genomics has come of age, researchers are getting down to the genetic nuts and bolts of cooperation in a variety of systems for the first time.

Full story at http://www.sciencemag.org/cgi/content/full/325/5945/1196?sa_campaign=Email/sntw/4-September-2009/10.1126/science.325_1196