The Future of Systematics: Tree-Thinking Without the Tree

Phylogenetic trees are meant to represent the genealogical history of life and apparently derive their justification from the existence of the tree of life and the fact that evolutionary processes are tree-like. However, there are a number of problems for these assumptions. Here it is argued that once we understand the important role that phylogenetic trees play as models which contain idealizations, we can accept these criticisms and deny the reality of the tree while justifying the continued use of trees in phylogenetic theory and preserving nearly all of what defenders of trees have called “the importance of tree-thinking.

Axiomatic opportunities and obstacles for inferring a species tree from gene trees

The reconstruction of a central tendency `species tree' from a large number of conflicting gene trees is a central problem in systematic biology. Moreover, it becomes particularly problematic when taxon coverage is patchy, so that not all taxa are present in every gene tree. Here, we list four apparently desirable properties that a method for estimating a species tree from gene trees could have (the strongest property states that building a species tree from input gene trees and then pruning leaves gives a tree that is the same as, or more resolved than, the tree obtained by first removing the taxa from the input trees and then building the species tree). We show that while it is technically possible to simultaneously satisfy these properties when taxon coverage is complete, they cannot all be satisfied in the more general supertree setting. In part two, we discuss a concordance-based consensus method based on Baum's `plurality clusters', and an extension to concordance supertrees.Comment: 19 pages, 2 figure

Class Attendance and Academic Performance among Spanish Economics Students

This paper presents new evidence on the effects of class attendance on academic performance. We analyse survey data collected for an Introductory Econometrics Course at the Facultad de Ciencias Sociales y Jurídicas of Universidad Carlos III de Madrid, matched to administrative data. Using OLS-proxy regressions to control for unobservable student characteristics potentially correlated with attendance, we find a positive and significant effect of attendance on academic performance. However, the fact that instrumental variable regressions may be failing to account for the correlation not captured by the controls calls for further investigation based on panel data

Phylogeny as population history

The construction and use of phylogenetic trees is central to modern systematics. But it is unclear exactly what phylogenies and phylogenetic trees represent. They are sometimes said to represent genealogical relationships between taxa, between species, or simply between “groups of organisms.” But these are incompatible representational claims. This paper focuses on how trees are used to make inferences and then argues that this focus requires that phylogenies represent the histories of populations

Complete intersection singularities of splice type as universal abelian covers

It has long been known that every quasi-homogeneous normal complex surface singularity with Q-homology sphere link has universal abelian cover a Brieskorn complete intersection singularity. We describe a broad generalization: First, one has a class of complete intersection normal complex surface singularities called "splice type singularities", which generalize Brieskorn complete intersections. Second, these arise as universal abelian covers of a class of normal surface singularities with Q-homology sphere links, called "splice-quotient singularities". According to the Main Theorem, splice-quotients realize a large portion of the possible topologies of singularities with Q-homology sphere links. As quotients of complete intersections, they are necessarily Q-Gorenstein, and many Q-Gorenstein singularities with Q-homology sphere links are of this type. We conjecture that rational singularities and minimally elliptic singularities with Q-homology sphere links are splice-quotients. A recent preprint of T Okuma presents confirmation of this conjecture.Comment: Published by Geometry and Topology at http://www.maths.warwick.ac.uk/gt/GTVol9/paper17.abs.htm

Theorizing the Language of Law

Attaching myself, then, to Giambattista Vico's idea of certainty (although not, of course, from his perspective) throughout this study I shall call "the space of certainty" the theoretical and conceptual construction (which is of both a philological and textual character) stipulated by the legislator in an attempt to control the distinct concepts related to the legal word, its institutional statute and its legal, moral, and cultural hermeneutics. I shall thus attempt to understand the meaning of this space of certainty, in what way it has been constructed, and how it affects legal, political, social, and cultural mechanisms

Grammar and Conversion in the Early Iberian Empire

Grammar is art. Not an art. It is the art among all arts. As Martin Irvine demonstrated in his beautiful book of 1994, this claim is not very new -it is perhaps as old as grammar, and as old as the greek concept of τέχνη. But it is useful to delve into it a little bit more, in order to understand the concrete issue of what did grammar and language teaching mean in Late Medieval Castile and Early Modern Iberian Empire -Spain