Fitness

ByDr. Girish Chandra

Darwinian Fitness

(By Dr. Girish Chandra)

 

            Darwinian fitness is the reproductive advantage that an individual obtains from its genotype. It is also known as Selective Value or Adaptive Value and is a composite of many advantageous as well as disadvantageous characteristics of the animal. Fittest is not the individual that can survive but the one that can leave the largest number of offspring reaching reproductive age. Reproductive success is therefore the key element of fitness.

            Relative fitness is symbolised by the letter w, and is inversely related to selection coefficient, s.

            w = 1- s   or it can be w = 1+ s 

                       The frequency of the recessive gene a will decrease in the next generation owing to lower fitness and that of dominant gene A will increase because of higher fitness. As the frequency of recessive gene goes down, selection against the recessive gene a becomes progressively slower. For instance, if q = 0.5 in the beginning, it will take 8 generations to reduce the frequency of gene a to 0.1, 100 generations to reduce it to 0.01 and 1000 generations to reduce the value of q to 0.001.


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The Evidence for Evolution


Features: University of Chicago Press
By (author): Alan Rogers

According to polling data, most Americans doubt that evolution is a real phenomenon. And it’s no wonder that so many are skeptical: many of today’s biology courses and textbooks dwell on the mechanisms of evolution – natural selection, genetic drift, and gene flow – but say little about the evidence that evolution happens at all. How do we know that species change? Has there really been enough time for evolution to operate? With “The Evidence for Evolution”, Alan R. Rogers provides an elegant, straightforward text that details the evidence for evolution. Rogers covers different levels of evolution, from within-species changes, which are much less challenging to see and believe, to much larger ones, say, from fish to amphibian, or from land mammal to whale. For each case, he supplies numerous lines of evidence to illustrate the changes, including fossils, DNA, and radioactive isotopes. His comprehensive treatment stresses recent advances in knowledge but also recounts the give and take between skeptical scientists who first asked ‘how can we be sure’ and then marshaled scientific evidence to attain certainty. “The Evidence for Evolution” is a valuable addition to the literature on evolution and will be essential to introductory courses in the life sciences.
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