Distinguishing ecological from evolutionary approaches to transposable elements

Considerable variation exists not only in the kinds of transposable elements (TEs) occurring within the genomes of different species, but also in their abundance and distribution. Noting a similarity to the assortment of organisms among ecosystems, some researchers have called for an ecological approach to the study of transposon dynamics. However, there are several ways to adopt such an approach, and it is sometimes unclear what an ecological perspective will add to the existing co-evolutionary framework for explaining transposon-host interactions. This review aims to clarify the conceptual foundations of transposon ecology in order to evaluate its explanatory prospects. We begin by identifying three unanswered questions regarding the abundance and distribution of TEs that potentially call for an ecological explanation. We then offer an operational distinction between evolutionary and ecological approaches to these questions. By determining the amount of variance in transposon abundance and distribution that is explained by ecological and evolutionary factors, respectively, it is possible empirically to assess the prospects for each of these explanatory frameworks. To illustrate how this methodology applies to a concrete example, we analyzed whole-genome data for one set of distantly related mammals and another more closely related group of arthropods. Our expectation was that ecological factors are most informative for explaining differences among individual TE lineages, rather than TE families, and for explaining their distribution among closely related as opposed to distantly related host genomes. We found that, in these data sets, ecological factors do in fact explain most of the variation in TE abundance and distribution among TE lineages across less distantly related host organisms. Evolutionary factors were not significant at these levels. However, the explanatory roles of evolution and ecology become inverted at the level of TE families or among more distantly related genomes. Not only does this example demonstrate the utility of our distinction between ecological and evolutionary perspectives, it further suggests an appropriate explanatory domain for the burgeoning discipline of transposon ecology. The fact that ecological processes appear to be impacting TE lineages over relatively short time scales further raises the possibility that transposons might serve as useful model systems for testing more general hypotheses in ecology

Two Myths About Somatic Markers

Research on patients with damage to ventromedial frontal cortices suggests a key role for emotions in practical decision making. This field of investigation is often associated with Antonio Damasio’s Somatic Marker Hypothesis–a putative account of the mechanism by which autonomic tags guide decision making in typical individuals. Here we discuss two ‘myths’ surrounding the direction and interpretation of this research. First, it is often assumed that there is a single somatic marker hypothesis. As others have noted, however, Damasio’s ‘hypothesis’ admits of multiple interpretations (Colombetti, [2008]; Dunn et al. [2006]). Our analysis builds upon this point by characterizing decision making as a multi-stage process and identifying the various potential roles for somatic markers. The second myth is that the available evidence suggests a role for somatic markers in the core stages of decision making, i.e. during the generation, deliberation or evaluation of candidate options. To the contrary, we suggest that somatic markers most likely have a peripheral role, in the recognition of decision points, or in the motivation of action. This conclusion is based on an examination of the past 25 years of research conducted by Damasio and colleagues, focusing in particular on some early experiments that have been largely neglected by the critical literature

Which evolutionary model best explains the culture of honour?

The culture of honour hypothesis offers a compelling example of how human psychology differentially adapts to pastoral and horticultural environments. However, there is disagreement over whether this pattern is best explained by a memetic, evolutionary psychological, dual inheritance, or niche construction model. I argue that this disagreement stems from two shortcomings: lack of clarity about the theoretical commitments of these models and inadequate comparative data for testing them. To resolve the first problem, I offer a theoretical framework for deriving competing predictions from each of the four models. In particular, this involves a novel interpretation of the difference between dual inheritance theory and cultural niche construction. I then illustrate a strategy for testing their predictions using data from the Human Relations Area File. Empirical results suggest that the aggressive psychological phenotype typically associated with honour culture is more common among pastoral societies than among horticultural societies. Theoretical considerations suggest that this pattern is best explained as a case of cultural niche construction

Prospects for a dual inheritance model of emotional evolution

Dual inheritance (DI) models of cultural evolution have been criticized for likening cultural transmission to genetic (lateral) transmission. I argue that although these objections might pertain to the cognitively sophisticated traits that DI theorists typically focus on (e.g. tool making and natural history knowledge), they do not undermine DI models of emotional evolution. Cultural traditions influence emotional development primarily during the early stages of life, before the onset of complex cognition and when children are exposed almost exclusively to their parents. Consequently, many emotional dispositions are transmitted laterally as DI models assume