Species

264 Species

acceptable similarity between specimens.^58 In the rare cases when many specimens

are found, problems due to variation can cause taxonomic complications. If many

locales are involved, that is if the specimens are allopatric, it is unclear whether they

form a single species or allopatrically isolated but closely related sister species. The

problem is critical in the case of Homo erectus, which has a range from southern

Africa to east and southeastern Asia. If all that remains is skeletal information, can

we really be sure if these are the same biospecies, for example, or even whether

H. erectus is one morph of a broader biospecies, possibly including H. sapiens? The

now-amalgamated species Canis lupus includes morphs like the timber wolf, the

Pekinese pug, and the Great Dane, all interfertile or fertile along a series of interme-

diate forms. Any paleontologist would split them into distinct taxa on morphologi-

cal grounds alone. In the case of many birds, on the other hand, skeletal changes

between good species are minimal, and only behavioral and ecological differences

will tell them apart.

Chronospecies (Successional Species)

A problem that used to be common in discussions of paleontology and species con-
cepts was that of chronospecies, where speciation occurs over time such that at the
starting and end points of a time series, the morphs are different species. This was
discussed by Simpson, for example, in his book on evolutionary tempo and mode.^59
However, the notion of chronospeciation is no longer thought by many to be an oper-
ational one—for a start, many specialists think that for animal species, such changes
do not occur without lineage differentiation—in short, anagenesis is accompanied by
cladogenesis—and that in most cases species remain largely unchanged after their
initial period of adaptation until they go extinct.^60
Chronospecies are formed, according to the author, T. N. George, who proposed
the notion,^61 when a lineage changes sufficiently to be given a new name. In this
respect, it is a temporalized version of the taxonomic species concept, or even an
interpretation of the paleospecies concept.^62 A chronospecies is effectively an arbi-
trary division of a gradually evolving lineage,^63 and seems to have been come to
prominence as the “species concept” of “phyletic gradualism,” the target of criticism
by advocates of the theory of punctuated equilibrium, although it is not often used in
the interim, so far as I can tell.^64

(^58) An excellent discussion and a proposed resolution to this problem is Polly 1997. See also Simpson
1943, George 1956.
(^59) Simpson 1943.
(^60) Eldredge and Gould 1972, Gould and Eldredge 1977, Eldredge 1985, Gould 2002.
(^61) George 1956, 129.
(^62) Cain 1954, 106f, Simpson 1961, 166.
(^63) Eldredge 1989, 98.
(^64) Texts such as Mayr’s and Simpson’s [Simpson 1961, Mayr 1963] refer instead to “chronoclines” as the
directional change of characters in the paleontological record, akin to geographical clines.