Dobzhansky's strong definition is, "That stage of evolutionary progress at which the once actually or potentially interbreeding array of forms becomes segregated into two or more arrays which are physiologically incapable of interbreeding."
The weak definition, proposed by Mayr, is, "Groups of actually or potentially interbreeding natural populations which are reproductively isolated from other such groups.'
Smildee failed to mention where he got this bizzarre concept of a "strong definition" vs a "weak definition" of the term species.
So I did so for him.
That website - called Alternative Science (alternativescience.com) promotes such things as Psychokinsesis, cold fusion, remote viewing, lottery ESP, perpetual motion and something called "no brainer" (where - get this - the notion that the human brain is not necessary)
So, as you can see, Alternative Science is not very mainstream. I am not dismissing it all together, I am just saying that this stuff is not widely accepted for a number of reasons.
In Alternative Sicence's section of speciation we find this earth shattering difference in the definitions proposed by two different scientists early in the 20th century. The entire difference hinges on slightly different usage of the english language. Mayr uses the term "reproductively isolated" and Dobzhansky uses the term "physiologically incapable" of reproducing.
Now, Alternative Science, tries to make the point that there is a huge difference between the two terms and reproductive isolation is simply geographical, where as physiologically incapable means that reproduction is impossible.
However, Mayr himself addresses THIS VERY ISSUE in his paper
What is a Species, and What is Not? (by Ernst Mayr Originally Published in Philosophy of Science, Vol. 63 (June 1996) pp. 262-277.)
"Among the attributes members of a species share, the only ones that are of crucial significance for the species definition are those which serve the biological purpose of the species, that is, the protection of a harmonious gene pool. These attributes were named by Dobzhansky (1935) isolating mechanisms. It is immaterial whether or not the term isolating mechanism was well chosen, nor is it important whether one places the stress on the prevention of interbreeding with non-conspecific individuals or the facilitation ("recognition") of breeding with conspecific individuals. The concept I have just developed is articulated in the so-called biological species definition: "Species are groups of interbreeding natural populations that are reproductively isolated from other such groups." The isolating mechanism by which reproductive isolation is effected are properties of individuals. Geographic isolation therefore does not qualify as an isolating mechanism. "
SO you see Dr. Mayr demonstrates that by reproductive isolation, he is not refering to geographical barriers but physiological ones as well when he says "properties of individuals".
Therefore there is NO REAL DIFFERENCE BETWEEN THE TWO DEFINITIONS EXCEPT FOR CHOICE OF WORDING.
In Mayr's paper cited above, he does attempt to claim that "species" is in fact a concrete concept. He also goes on to use the example of "planet" as being a concrete concept. However, this paper was written 10 years ago. As we have seen recently "planet" is not that concrete at all. I contend, contrary to Mayr, that "species" is not that concrete either.
From the above paper:
"
2. Species of organisms are concrete phenomena of nature. Some recent authors have dealt with the concept of species as if it were merely an arbitrary, man-made concept, like the concepts of reduction, demarcation, cause, derivation, prediction, progress, each of which may have almost as many definitions as there are authors who have written about them. However, the concept biological species is not like such concepts. The term 'species' refers to a concrete phenomenon of nature and this fact severely constrains the number and kinds of possible definitions. The word 'species' is, like the words 'planet' or 'moon,' a technical term for a concrete phenomenon. One cannot propose a new definition of a planet as "a satellite of a sun that has its own satellite," because this would exclude Venus, and some other planets without moons. A definition of any class of objects must be applicable to any member of this class and exclude reference to attributes not characteristic of this class. This is why any definition of the term 'species' must be based on careful study of the phenomenon of nature to which this term is applied. Alas, this necessity is not appreciated by all too many of those who have recently discussed the species problem after a mere analysis of the literature. "
I am inclined to agree with the authors who say that species is arbitrary.
Sorry, Smildee, for shredding your whole "stronger vs weaker" definition thing. You really need to not only cite your souces, but be a little more discriminating in selecting them. Oh well, we all learn from our mistakes.
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