Animal Extinction Term Paper

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Extinction

Punctuated Equilibrium

Evolutionists for generations after Darwin imagined a slow and steady process of adaptation, in which daily culling and breeding success very gradually adapted a population from one form into another. Such a process would not be dissimilar to unnatural selection, such as that done with domesticated animals, that gradually worked to change a wolf into a little Cairn Terrier or Shih Tzu. However, some have suggested that there might be a more sudden sort of change involved, in which evolution moves suddenly and with great speed. This theorized form of evolution, called punctuated equilibrium, has been widely debated, but seems to be increasingly accepted by scientists. There appears to be evidence for punctuated equilibrium from laboratory experiments, from field and fossil evidence, from theory and even from Darwin's original work.

It is a common misconception that evolution cannot be experimentally studied in laboratories -- actually, a number of studies have been performed which indicate the existence of punctuated equilibrium in laboratory settings. In 1996 Science magazine, which is a weekly peer-reviewed journal, published an article called "Microbes hint at a mechanism behind punctuated evolution." (Mlot, 1996) The article describes an experiment performed by Lenski and Cooper, in which over 10,000 generations of e. coli were cultivated in a low-sugar solution. Over the generations, the bacteria evolved to survive best in that environment. Later generations of bacteria were larger, more fit, and could produce more offspring within the environment. Their research clearly show: "Cells tended to persist at one average size for many generations, then suddenly go through growth spurts... You can very clearly see dynamics that are punctuated, and that it's arising in this extremely simple system.

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... Statistical analysis showed that the data were best represented not with a smooth curve, but with a stepped curve that took several jumps. That is just the sort of pattern -- stasis followed by rapid change -- that punctuated equilibrium theory suggests." (Mlot, 1996) Though many feel that this research shows that punctuated equilibrium could occur, some argue that if one looks at this at a larger scale of every 500 generations rather than every 100 generations, then the change appears to be gradual. "If you look closely enough at anything, you will eventually see the steps..." (Mlot, 1996)

Punctuated equilibrium has also been evidenced in field work and the fossil record. The year before publishing the results of Lenski and Cooper's research, Science published an article wondering "Did Darwin get it all right?" In this article, the author considers a series of field research programs which have provided evidence for punctuated equilibrium. One study of bryozoan fossils showed that "Through 15 million years of the geologic record, these species would persist unchanged for 2 to 6 million years, then, in less than 160,000 years, split off a new species that would continue to coexist with its ancestor species." (Kerr, 1995) The definition of species and the accuracy with which science could identify species was challenged by varying morphological characteristics, double checking the reliability of morphology as a distinguisher of species, and finally whether genetics and morphology were actually linked in these cases. In the end, "Cheetham's fossil species had passed the biological test with flying colors..." (Kerr, 1995) Not only did the research appear particularly strong, but it was duplicated in several further.....

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