philosophy of biology

Mansourati 1

Michel Mansourati

Prof : Bonnie Paller

Species and Macroevolution

Natural Selection and Punctuated Equilibrium

The more popular Darwinian concept on gradual species evolution explains the emergence of new floral and faunal taxa due to natural selection . Its temporal reference is the geological timescale , wherein new phenotypes develop in response to unfavorable conditions in relatively long periods of time . It is the general thought of the development of new traits due to slight genetic changes through generations . An alternative theory called Punctuated Equilibrium by Gould suggests otherwise . Its

proponents posit that rapid species changes punctuate long stasis periods , wherein no evolutionary changes occur . Instead of progressive cumulative changes occurring as in phyletic gradualism , a period of revolution due to unfavorable environmental conditions is proposed to interrupt a long period of equilibrium (Gould 76

Gould 's theory accounts for fossil evidences from subsequent geological layers that demonstrate stability for long periods of time . His theory also suggests explanations for the absence of transitional novel forms regarded by Darwin as imperfection of the fossil records , whose changes may have occurred due to factors that cannot be reflected by fossils such as physiological changes and interspecies relationships (Gould 75 . In the punctuated equilibrium model , species are abruptly replaced by an entirely new species as the former becomes extinct (Gould 75 ) when a segment of a population encounters a speciation event . This model claims that when an entire population of species undergoes evolution , novel species do not arise . Under the gradualistic model , the entire ancestral population progressively changes into its descendant species . On the other hand , the punctuational model suggests that a portion of an ancestral population buds ' off into the new population , allowing the ancestral population to remain in existence (Gould 76

Mansourati 2

Species Concepts

The concept of the species has continually developed through time in accordance to emerging scientific discoveries . One of the first concepts of the species accepted is essentialism . This concept has been the most accepted notion of the species during the pre-Darwinian era . From the time of Aristotle until the 1860 's , this has been the dominant idea of the species . Essentialists believed that God has created everything in perfection , and a perfect being does not require change . This is the primary conflict on this concept , this does not acknowledge that organisms morph over time . Therefore this does not support the concept of evolution that is currently the most widely accepted theory . This fixation of the species does not account for the relationships among species populations and individual taxa brought by millions of years of evolution , redering it currently obsolete . This cannot provide explanations for the existence of ancestral populations and divergent species , contradicting evidences gathered from geological strata (Marks 243

Another concept of the species is the conventionalist school of thought wherein its proponents maintain that science is supposed to establish relationships instead to provide explanations on phenomena . This theory views scientific principles as mere conventions and not based on fundamental concepts as these principles are regarded...