Ernst Mayr, The Growth of Biological Thought. Cambridge: Harvard University Press, 1982.

Characteristics of | Similar Populations



Creatures separated by:


A. biological characteristics (birds: song, nest, migratory pattern) & range or reproductive isolation (behavioral or geographical)


B. "a reproductively isolated population." (Mayr, 1982, p. 271)


C. populations + distinctiveness due to reproductive gap  +  coexisting


D. both behaviorally (not interbreeding) and ecologically (not fatally competing)

divergent species (Mayr 1982, p. 272)


E. Distinct forms "which are physiologically incapable of interbreeding." (after Dobzhansky in Mayr 1982, p. 273).


F. "A species is a reproductive community of populations (reproductively isolated from others) that occupies a specific niche in nature." (Mayr 1982, p. 273).


"In the course of time, more and more devices that prevent species  from interbreeding were discovered, for instance differences in breeding or flowering season and occupation  of different habitats." (Mayr 1982, pp. 273-74).


Isolating mechanisms: (after Dobzhansky, 1937)


            geographical (Geospiza)


the bill size of Galapagos finches (David Lack, 1940-1949) is an " adaptation to a species specific food niche...." {Mayr 1982, pp. 274-75}.

finches' beaksThese different sized beaks are what Mayr is referring to as an niche adaptation to specific food sources for these different species found on different islands.


"Indeed, the major meaning of reproductive isolation is that it provides protection for a genotype adapted for the utilization of  specific niche."

(Mayr 1982, p. 275).


Population thinking


"all organisms occur in nature as members of populations."


"the biological properties of organisms" include "physiological, biochemical, and behavioral characters as well as morphological ones."

(Mayr 1982, pp. 276-77).

"Local populations had a unity maintained by the interbreeding of the individuals by which the populations were composed."

p. 286.





genes | speciation | diversity | descent

Mayr | Thomas | Wilson | Hardin | Darwin | Margulis | Steingraber | Tattersall | Carr | Keller | Watson

Genetics Index | What makes genetics significant? | History of Genetics | DNA discovery | RNA | Resistance | Visual images