Self-Organized Cultural Cycles and the Uncertainty of Archaeological Thought

Contributing to the issue of complex relationship between social and cultural evolution, this paper aims to analyze repetitive patterns, or cycles, in the development of material culture. Our analysis focuses on culture change associated with sociopolitical and economic stasis. The proposed toy model describes the cyclical character of the quantitative and qualitative composition of archaeological assemblages, which include hierarchically organized cultural traits. Cycles sequentially process the stages of unification, diversity, and return to unification. This complex dynamic behavior is caused by the ratio between cultural traits’ replication rate and the proportion of traits of the higher taxonomic order’s related unit. Our approach identifies a shift from conformist to anti-conformist transmission, corresponding with open and closed phases in cultural evolution in respect to the introduction of innovations. The model also describes the dependence of a probability for horizontal transmission upon orders of taxonomic hierarchy during open phases. The obtained results are indicative for gradual cultural evolution at the low orders of taxonomic hierarchy and punctuated evolution at its high orders. The similarity of the model outcomes to the patters of material culture change reflecting societal transformations enables discussions around the uncertainty of explanation in archaeology and anthropology.

Punctuated evolution in the learned songs of African sunbirds

Learned traits are thought to be subject to different evolutionary dynamics than other phenotypes, but their evolutionary tempo and mode has received little attention. Learned bird song has been thought to be subject to rapid and constant evolution. However, we know little about the evolutionary modes of learned song divergence over long timescales. Here, we provide evidence that aspects of the territorial songs of Eastern Afromontane sky island sunbirds Cinnyris evolve in a punctuated fashion, with periods of stasis of the order of hundreds of thousands of years or more, broken up by evolutionary pulses. Stasis in learned songs is inconsistent with learned traits being subject to constant or frequent change, as would be expected if selection does not constrain song phenotypes over evolutionary timescales. Learned song may instead follow a process resembling peak shifts on adaptive landscapes. While much research has focused on the potential for rapid evolution in bird song, our results suggest that selection can tightly constrain the evolution of learned songs over long timescales. More broadly, these results demonstrate that some aspects of highly variable, plastic traits can exhibit punctuated evolution, with stasis over long time periods.

Reconstructing single-cell karyotype alterations in colorectal cancer identifies punctuated and gradual diversification patterns

Central to tumor evolution is the generation of genetic diversity. However, the extent and patterns by which de novo karyotype alterations emerge and propagate within human tumors are not well understood, especially at single-cell resolution. Here, we present 3D Live-Seq—a protocol that integrates live-cell imaging of tumor organoid outgrowth and whole-genome sequencing of each imaged cell to reconstruct evolving tumor cell karyotypes across consecutive cell generations. Using patient-derived colorectal cancer organoids and fresh tumor biopsies, we demonstrate that karyotype alterations of varying complexity are prevalent and can arise within a few cell generations. Sub-chromosomal acentric fragments were prone to replication and collective missegregation across consecutive cell divisions. In contrast, gross genome-wide karyotype alterations were generated in a single erroneous cell division, providing support that aneuploid tumor genomes can evolve via punctuated evolution. Mapping the temporal dynamics and patterns of karyotype diversification in cancer enables reconstructions of evolutionary paths to malignant fitness.

The tuatara genome: insights into vertebrate evolution from the sole survivor of an ancient reptilian order

The tuatara (Sphenodon punctatus), the only living member of the archaic reptilian order Rhynchocephalia (Sphenodontia) once widespread across Gondwana, is an iconic and enigmatic terrestrial vertebrate endemic to New Zealand. A key link to the now extinct stem reptiles from which dinosaurs, modern reptiles, birds and mammals evolved, the tuatara provides exclusive insights into the ancestral amniotes. The tuatara genome, at ∼5 Gbp, is among the largest vertebrate genomes assembled. Analysis of this genome and comparisons to other vertebrates reinforces the uniqueness of the tuatara. Phylogenetic analyses indicate tuatara diverged from the snakes and lizards ∼250 MYA. This lineage also shows moderate rates of molecular evolution, with instances of punctuated evolution. Genome sequence analysis identifies expansions of protein, non-protein-coding RNA families, and repeat elements, the latter of which show an extraordinary amalgam of reptilian and mammalian features. Sequencing of this genome provides a valuable resource for deep comparative analyses of tetrapods, as well as for tuatara biology and conservation. It also provides important insights into both the technical challenges and the cultural obligations associated with genome sequencing.

Inferring punctuated evolution in the learned songs of African sunbirds

Signals used in animal communication, especially those that are learned, are thought to be prone to rapid and/or regular evolution. It has been hypothesized that the evolution of song learning in birds has resulted in elevated diversification rates, as learned song may be subject to especially rapid evolution, and song is involved in mate choice. However, we know little about the evolutionary modes of learned song divergence over timescales relevant to speciation. Here we provide evidence that aspects of the territorial songs of Eastern Afromontane sky island sunbirds Cinnyris evolve in a punctuated fashion, with periods of stasis, on the order of hundreds of thousands of years or more, broken up by strong evolutionary pulses. Stasis in learned songs is inconsistent with learned traits being subject to constant or frequent change, as would be expected if selection does not constrain song phenotypes, or if novel phenotypes are frequently advantageous. Learned song may instead follow a process resembling peak shifts on adaptive landscapes. While much research has focused on the potential for rapid evolution in bird song, our results suggest that selection can tightly constrain the evolution of learned songs over fairly long timescales. More broadly, these results demonstrate that some aspects of highly variable, plastic traits can exhibit punctuated evolution, with stasis over fairly long time periods.

Is the blunderbuss a misleading visual metaphor for stasis and punctuated evolution?

I discuss the usefulness of the so-called “blunderbuss pattern” of phenotypic evolution as a visual metaphor for stasis and punctuated evolution that was originally put forward in Uyeda et al. (2011) in their highly influential paper “The million-year wait for macroevolutionary bursts”. I argue the blunderbuss pattern is not surprising, and in some cases it is misleading. I review several publications that cite Uyeda et al. (2011) that seem to be confused about the meaning of the pattern and what it implies. I do not critique the original analysis within Uyeda et al (2011), but show the blunderbuss pattern itself would be produced even when assuming a Brownian motion (completely gradual) model of phenotypic divergence. Finally, I discuss how the interesting results of the paper have been overlooked in favor of the surprisingly powerful, but also misleading visual metaphor of the blunderbuss.