What is a Species, and What is Not? by Ernst Mayr
Originally Published in Philosophy of Science, Vol. 63 (June 1996) pp. 262-277.
Highlights: Green My Comments: Gray
Mayr: I analyze a number of widespread misconceptions concerning species. The species category, defined by a concept, denotes the rank of a species taxon in the Linnaean hierarchy. Biological species are reproducing isolated from each other, which protects the integrity of their genotypes. Degree of morphological difference is not an appropriate species definition. Me: And yet, anthropologists obsess over very small differences between individual hominid specimens to declare “new” species. Most often this is done using fragmentary bone evidence; tiny pieces of skulls and parts are pieced together out of whatever fragments are available, even using mixed genders to created “Dr. Frankenstein” creatures.
Mayr: What is a species and what is not? “…the reading of some recent papers on species has been a rather troubling experience. There is only one term that fits some of these authors: armchair taxonomists. Since many authors have never personally analyzed any species populations or studied species in nature, they lack any feeling for what species actually are. Me: So it’s not my imagination?
These authors make a number of mistakes that have been pointed out again and again in the recent literature. Admittedly, the relevant literature is quite scattered, and some of it is perhaps rather inaccessible to a non-taxonomist. Yet, because the species concept is an important concept in the philosophy of science, every effort should be made to clarify it. Me: But will “armchair taxonomists” pay attention? They obviously prefer pursuing personal agendas that don’t include rigorous application of scientific thinking.
Mayr: The species is the principal unit of evolution and it is impossible to write about evolution, and indeed about almost any aspect of the philosophy of biology, without having a sound understanding of the meaning of biological species. Me: Are universities teaching “philosophy” of science or just grinding out generations of “whatever is in my head” students who have no basis for doing science other than “politically correct” (whatever your prof wants to hear) guidelines and conclusions?
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. Me: Yes! This has been the source of my frequent complaints: if researchers are going to chop up hominid “finds” into myriad species (the “every anthropologists gets his or her own species” phenomenon) then analysis of species is a social activity that serves to locate the “finder and namer” higher on the academic (and pop-science) social pyramid. The ambitious and attention-seeking researcher makes sure to get media exposure and tends to degrade or pollute the value of science to the public. “Science trivia of the day” is the result.
Mayr: 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.
Why are there species of organisms? Why is the total genetic variability of nature organized in the form of discrete packages, called species? Why are there species in nature? What is their significance? The Darwinian always asks why questions because he knows that everything in living nature is the product of evolution and must have had some selective significance in order to have evolved. Me: Again; these questions and answers come from NATURE and not from “word magic” – essentially social ideas that do not qualify as hypotheses and cannot be tested; ideas that lie outside of physical reality and are not testable or provable. Such as; the conclusion that a set of scratches on one individual stone, supposedly made by a Homo sapiens (but nowhere to be found) at such and such a date, in x location “proves” that not only the individual who made the scratches, but the entire existing Homo sapiens species at that point in time miraculously achieved “modern social cognition.”
Mayr: He therefore asks: What selection forces in nature favor the origin and maintenance of species? The answer to this question becomes evident when one makes a certain thought experiment. “It is quite possible to think of a world in which species do not exist but are replaced by a single reproductive community of individuals, each one different from every other one, and each one capable of reproducing with those other individuals that are most similar to it. Each individual would then be the center of a concentric series of circles of genetically more and more unlike individuals. What would be the consequence of the continuous uninterrupted gene flow through such a large system? In each generation certain individuals would have a selective advantage because they have a gene complex that is specially adapted to a particular ecological situation. However, most of these favorable combinations would be broken up by pairing with individuals with a gene complex adapted to a slightly different environment. In such a system there is no defense against the destruction of superior gene combinations except the abandonment of sexual reproduction. It is obvious that any system that prevents such unrestricted outcrossing is superior” Me: When there is but one species – us – Homo sapiens, isn’t that effectively what exists, an “uninterrupted gene flow through a large system” Boundaries to reproduction have been demolished due to migration and travel technologies. Humans may have evolved as several species by natural geographic isolation, but that has been done away with; few humans are reproductively isolated at this point. Indeed this process of “doing away with separate populations” can be observed in the collection of humans into agricultural – urban centers.
Can HS be one vast reproductive population? Are we abandoning “random” sexual reproduction for genetic products that design “better humanoid” creatures or replacement robots?
Mayr: The biological species is such a system. The biological meaning of species is thus quite apparent: “The segregation of the total genetic variability of nature into discrete packages, so called species, which are separated from each other by reproductive barriers, prevents the production of too great a number of disharmonious incompatible gene combinations. This is the basic biological meaning of species and this is the reason why there are discontinuities between sympatric species.
We do know that genotypes are extremely complex epigenetic systems. There are severe limits to the amount of genetic variability that can be accommodated in a single gene pool without producing too many incompatible gene combinations” (Mayr 1969, 316). The validity of this argument is substantiated by the fact that hybrids between species, particularly in animals, are almost always of inferior viability and more extreme hybrids are usually even sterile. “Almost always” means that there are species interpreted to be the result of hybridization, particularly among plants, but except for the special case of allopolyploidy, such cases are rare.