908 THE STRUCTURE OF EVOLUTIONARY THEORY
The situation becomes even more paradoxical, and also entirely general, when
we take an honest look at our iconographic prejudices in the light of speciational
reformulations for macroevolution. Consider the true "success stories" of
mammalian evolution—the luxurious clades of rodents, chiropterans (bats), and,
among large-bodied forms, the antelopes of the artiodactyl clade that expanded so
vigorously as perissodactyls constantly declined within the guild of large-bodied
hoofed herbivores. Has anyone ever seen, either in a textbook or a museum hall, a
chart or a picture of these truly dominating clades among modern mammals? We
don't depict these stories because we don't know how to draw them under our
restrictive anagenetic conventions.
If we define evolution as anagenetic trending to a "better" place, how can we
depict a successful group with copious modern branches extending in all directions
within the cladal morphospace? Instead, and entirely unconsciously of course, for
we would laugh at ourselves if we recognized the fallacy, our conventions lead us
to search out the histories of highly unsuccessful clades—those now reduced to a
single surviving lineage—as exemplars of triumphant evolution. We take this only
extant and labyrinthine path through the phyletic bush, use the steamroller of our
preconceptions to linearize such a tortuous route as a main highway, and then
depict this straggling last gasp as the progressive thrust of a pervasive trend. I refer
to this pattern of "life's little joke" (see Gould, 1996a).
- RETHINKING HUMAN EVOLUTION. Ever since Protagoras proclaimed that
"man [meaning all of us] is the measure of all things," Western intellectual
traditions, bolstering our often unconscious emotional needs, have invariably
applied the general biases of our analytic procedures, with special energy and
focussed intensity, to our own particular history. As a cardinal example, concepts
of human evolution long labored under the restrictive purview (now known to be
empirically false) of the so-called "single species hypothesis" (see Brace, 1977)—
the explicit claim that a maximal niche breadth, implied by the origin of hominid
consciousness, made the coexistence of more than one species impossible, since no
two species can share the same exact habitat under the "competitive exclusion"
principle, and since consciousness must have expanded the effective habitat of
hominid species into the full ecological range of conceivable living space. Human
evolution could therefore be viewed as a single progressive series gradually
trending towards our current pinnacle.
Needless to say, such a scheme precluded any speciational account of human
history because only one taxon could exist at any one time, and trends had to
record the anagenetic transformation of the only existing entity. (I do not think that
such a relentlessly limiting scenario has ever been presented a priori, or so stoutly
defended in principle even by a special name of its own, for any other lineage in
the history of life.) This theoretical stricture enforced several episodes of special
pleading for apparently contrary data. For example, early evidence for two distinct
and contemporaneous australopithecine lineages (the so-called gracile and robust
forms, now universally regarded as