SUMMARY Arguments over macroevolution versus micro- discontinuities impose a hierarchical structure to evolution evolution have waxed and waned through most of the twenti- and discredit any smooth extrapolation from allelic substitueth century. Initially, paleontologists and other evolutionary tion to large-scale evolutionary patterns. Recent developbiologists advanced a variety of non-Darwinian evolutionary ments in comparative developmental biology suggest a need processes as explanations for patterns found in the fossil to reconsider the possibility that some macroevolutionary disrecord, emphasizing macroevolution as a source of morpho. continuites may be associated with the origination of evolulogic novelty. Later, paleontologists, from Simpson to Gould, tionary innovation. The attractiveness of macroevolution reflects Staniey, and others, accepted the primacy of natural selec- the exhaustive documentation of large-scale patterns which between micro- and macroevolution. This second phase em. If the goal of evolutionary biology is to understand the history phasizes the sorting of innovations between species. Other of life, rather than simply document experimental analysis of discontinuities appear in the persistence of trends (differen- evolution, studies from paleontology, phylogenetics, develtial success of species within clades), including species sort- opmental biology, and other fields demand the deeper view ing, in the differential success between clades and in the origination and establishment of evolutionary novelties. These Enwin ysis of speciation pattems in the cheilostonse bryozoan gen- rather than through a lengthy process, this necessarily imcra Memarabdotas and Solopoma remains one of the most plies that apecies have a definite birth, persistence, and rigorous, involving quantitative morphometrics and detailed death.
Furthernore, if species are (usually) discrete from resampling of the fossil record, with the mompometrically de- lated species, interact with the environment, and reproduce fined species confirmed by genetic analysis in many cases with high fidelity (i.e., during branching give rise to daughter (see Jackson and Cheetham 1999). A patiem of punctuation species with similar characteristios to the parent species) and morphological stasis is overwhelmingly supported. Crit- they constitute individuals and are thus subject to selection, ically, whether prpalation geneties can account for any of in a fachion analogous to natural selection (see discussions in these trends is nod at issue. Population genetic models can Stanley 1979; Eldredge 1989; Grantham 1995: Gioald and these trends is not at issue. Population genetic models can Stanley 1979; Eldredge 1989; Grantham 1995; Giould and produce virtually any pattem of momhological ewolution Lloyd 1999). If species do not have the characteristics deand thus provides no clear basis for choosing between op- seribed above, they are members of a class, but not individposing models. Perhaps the most telling examples of the dis- uals (atoms of gold are members of a class, but not individjunction between speciation and intraspecific change comes uals). (Phylogenetic systematics likewise views species as from the paucity of evolutionary change associated with the having clear births and deaths, but for reasons independent elimatic upheavals of the Meistocene glaciations. Yet abun- of punctuated equilibrium, but see also Maddison 1997 . species sorting and species selection. Sorting is the differen- adaptive phenotypes, even if beneficial (Strathmann 1978 ). tial success of species from whatever cause, and implies nei- If an adaptive trait is relatively easy to acquire early in the ther species selection nor natural selection (Vrba and Gould evolution of a clade, but more diffieult to acquire thereafter, 1986; see also Grantham 1995). If, as the evidence suggests, elimination of that trait may lead to a loss of adaptive diver1986; see also Grantham 1995). If, as the evidence suggests, elimination of that trait may lead to a loss of adaptive divertrends must result from differential origination and extine- from a large number of invertebrate classes, limiting the fution of species within clades (Stanley 1979). Within-clade ture evolutionary flexibility of these groups. differences in speciation and extinction rates have long been recognized in the fossil record (e.g., McNamara 1990; Wag- ner 1996) and are one form of macroevolutionary sorting. LARGE-SCALE PATTERNS: DIFFERENTLAL Species selection, unlike species sorting, requires that species be units of selection, and thus there must be properties of the species, rather than the sum of the properties of in- Darwin, famously, wondered why beetles were so saccessdividuals, upon which selection can act. Arguments for spe- ful. The fossil record provides many examples of the waxing cies selection have focused on the issue of whether species and waning of ecologically related groups; competition, on a constitute individuals. If speciation occurs as discrete events, geological time-scale, has been invoked as a generator of Enwin these pattems. Paleuntological studies have addressed this whether they eriginated through microevolution or panctuissue through the empirical stratigraphic distributions of ated equilibrium, may be well adapted to the long intervals genera or families within higher taxa, generally assumed to between mass extinctions, but fortuitomsly not possess, or be be either monophyletic (Foote 1996; Sepkoski and Kendrick mernbers of clades that possess, the eharieters that enhance 1993). In their paper, Sepkoski et al.
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