Is there room for punctuated equilibrium and species selection in macroevolution?

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!

 

Is there room for punctuated equilibrium in macroevolution?

• Matthew W. Pennell ,
• Luke J. Harmon,
• Josef C. Uyeda

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Highlights

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The theory of punctuated equilibrium is a mix of conceptually distinct parts.

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We identify and disentangle four questions that are often associated with the theory.

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We review recent progress towards each of these four questions.

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Lumping these four questions together as ‘punctuated equilibrium’ is problematic.

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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.

Extant mammal body masses suggest

punctuated equilibrium

Tiina M. Mattila and Folmer Bokma

Is gradual microevolutionary change within species simultaneously the source of 

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

only a small part of body size variation between mammal species.

Reinventing species selection with molecular phylogenies

When I was a PhD-student in Sweden in the nineties, one of the most ugly words you could say was "group selection", and the so-called "selfish-gene paradigm" of Richard Dawkins was taken as almost a religious truth. These were the days when behavioural ecology ruled much of of the scentific activities in biology in Scandinavia and Britain. Lower-level selection of selfish genes was assumed to be either the only or at least the major evolutionary force that would explain all adaptation and biological diversity. Higher-level selection, on goups, demes, populations or species, was either deemed impossible or dismissed as unimportant.

This remarkable dogmatic reductionism in Scandinavian behavioural ecology seems, in the aftermath, as both dogmatic and not very well supported by either theory or empirical evidence. Even the great population geneticist R. A. Fisher did actually believe in group selection, and for him it was mainly an empirical issue how strong it was, compared to lower-level selection of individuals and genes.

However, one thing is certain: scientific paradigms change, and clearly group-selection (or rather multi-level selection) is on the rise again. This week's lab-meeting (Wednesday May 4), we will discuss a relatively recent TREE-paper on how molecular phylogenies might be used to study the process of species selection in a statistically rigorous and empirical way. Increasing evidence suggest that macroevolutionary trends, such as increases or decreases in diversity, speciation and extinction can simply not be extrapolated from lower-level selection processes, challenging the selfish-gene paradigm. Below, you will find an abstract and a link to the paper.

Time as usual: 13.30 on Wednesday (May 4) afternoon. Place: Probably "Argumentet".

Rabovsky, M. L. & MacCune, A. R.


Trends Ecol. Evol. 25: 68-74


Abstract: Species selection as a potential driver of macroevolutionary trends has been relegated to a largely philosophical position in modern evolutionary biology. Fundamentally, species selection is the outcome of heritable differences in speciation and extinction rates among lineages when the causal basis of those rate differences can be decoupled from genotypic (within-population) fitnesses. Here, we discuss the rapidly growing literature on variation in species diversification rates as inferred from molecular phylogenies. We argue that modern studies of diversification rates demonstrate that speciesselection is an important process influencing both the evolution of biological diversity and distributions of phenotypic traits within higher taxa. Explicit recognition of multi-level selection refocuses our attention on the mechanisms by which traits influence speciation and extinction rates.