Posted by Erik Svensson
Next week (Tuesday November 5, 2013 at 10.30) I want to discuss a classical question in macroevolution that was originally suggested by paleontologists Niles Eldredge and Stephen Jay Gould in 1973, but which has gained increased interested with the explosion of molecular phylogenetic information and improved comparative methods: punctuated equilbrium and species selection. A recent TREE-article take a critical look at the evidence, and it should hopefully be an interesting read and stimulate discussion.
The first TREE-article seems critical towards the prospects for punctuated equilibrium, so as a complement (optional reading) I also post a link to an empirical study on extant mammalian body size variation by Folmer Bokma, which is suggestive of punctuated equilbrium. Enjoy that too!
The long-controversial theory of punctuated equilibrium (PE) asserts that speciation causes rapid evolution against a backdrop of stasis. PE is currently undergoing a resurgence driven by new developments in statistical methods. However, we argue that PE is actually a tangle of four unnecessarily conflated questions: (i) is evolution gradualistic or pulsed? (ii) does trait evolution occur mainly at speciation or within a lineage? (iii) are changes at speciation adaptive or neutral? and (iv) how important is species selection in shaping patterns of diversity? We discuss progress towards answering these four questions but argue that combining these conceptually distinct ideas under the single framework of PE is distracting and confusing, and more likely to hinder progress than to spur it.
macroevolutionary differentiation between species? Since its first publication, Darwin’s original idea that
phenotypicdifferences between species develop gradually over time, as the accumulation of small selection-induced
changes in successive generations has been challenged by palaeontologists claiming that, instead, new
species quickly acquire their phenotypes to remain virtually unchanged until going extinct again. This
controversy, widely known as the ‘punctuated equilibrium’ debate, remained unresolved, largely owing to
the difficulty of distinguishing biological species from fossil remains. We analysed body masses of 2143
existing mammal species on a phylogeny comprising 4510 (i.e. nearly all) extant species to estimate rates of
gradual (anagenetic) and speciational (cladogenetic) evolution. Our Bayesian estimates from mammals as
well as separate sub-clades such as primates and carnivores suggest that gradual evolution is responsible for