Levelt’s integrated language production model can be adapted tobilingual language production. This integrated production model provides thepossibility to develop a theory of generalized interaction of the two languagesystems in bilinguals, instead of postulating a different organization of thetwo languages at each level. Two observed facts that were taken as evidenceagainst the subsystems hypothesis at the articulator level have been shown tobe, in fact, compatible with the subsystems hypothesis. A bilingual languageproduction model with consistent relations between the two language systemsacross levels is thus developed.
In accordance with the three-store hypothesis (Paradis, 1980) thatrecognizes one common conceptual store external to the linguistic system, theconceptualizer is not part of the linguistic system. Thus, while the twolanguages of a bilingual speaker are assumed to form subsystems in thelinguistic system, a speaker nevertheless has only one conceptualizer.
Extrapolating Lawrence & Ochman’s result back billions of years may not be realistic. But what if horizontal transfer was the default state? This is the idea Woese has developed. His argument is that genes were so free to exchange that there were no distinct lineages — genes moved more through horizontal transfer than by vertical inheritance. As the genetic system becomes more accurate and as the complexity increases, more genes become interdependent, and transfer gives way to vertical inheritance. Woese argues that translation (and therefore the genetic code) was the first thing to be fixed or crystallised, with other cellular functions following later. From this horizontal transfer dominated system, the three domains (archaea, bacteria and eukaryotes) each emerged independently as lineages.
In an equally insightful commentary, William Martin [Martin 1999] has discussed the implications of this work for our ability to reconstruct phylogenetic trees:
David Penny, Bennet McComish and their coworkers have recently tried to address this question by investigating how far back in time the standard models used in evolutionary tree building can go before they start to go wrong. Their overall conclusion is that the models used do seem to do a little better than might be expected from theory, but that the models still do poorly for very early evolutionary events. Penny and colleagues also criticise the recent trend in reporting conflicting trees as evidence for horizontal gene transfer — given how hard it seems to accurately reconstruct the tree of life, it is hard to say whether conflicting answers are evidence for gene transfer, or just reflect the limitations of the methods for building the trees. Their testing of the models suggests that it is just not reasonable to say that there is horizontal gene transfer just because two trees made with two different genes don’t come back with the same relationships between organisms. They make the following comment, which sums up the problem very succinctly:
Koonin has recently published an updated minimal gene set, using 21 complete genomes [Koonin 2000]. Surprisingly, of the 256 genes in the original set, only 81 remain, and this list is clearly insufficient to describe either the minimum number of genes required for a cell to function, or the genetic makeup of LUCA.
The was first proposed by Allport (1954), who suggested that positive effects of intergroup contact occur in contact situations characterized by four key conditions: equal status, intergroup , common goals, and support by social and institutional authorities (See Table 1). According to Allport, it is essential that the contact situation exhibits these factors to some degree. Indeed, these factors do appear to be important in reducing , as exemplified by the unique importance of cross-group friendships in reducing (Pettigrew, 1998). Most friends have equal status, work together to achieve shared goals, and friendship is usually absent from strict societal and institutional limitation that can particularly limit romantic relationships (e.g. laws against intermarriage) and working relationships (e.g. segregation laws, or differential statuses).
With the ongoing debate on how much horizontal gene transfer there is between organisms, the most exciting contribution to this picture looks not at the genes, but at gene networks. Taking a page from the study of complex networks such as the Internet, Eörs Szathmáry and colleagues [Podani et al. 2001] have recently shown that, while eukaryotic operational genes appear bacterial in origin, the structure of the metabolic network that these genes make up is in fact much much more like what is observed in archaea. In keeping with the business merger analogy, this is perhaps equivalent to keeping the management structures of Archaea Inc. in place.
Intriguingly, Perrett et al. found that when a new group of participants were asked to rate the attractiveness of each of the 3 composite faces (the average of all 60 faces, the average of the 15 most attractive faces and the ‘hyper-attractive’ that had exaggerated attractive qualities) the hyper-attractive face was considered the most attractive of the 3. This is noteworthy because the hyper attractive face was mathematically the least average of all 3 composites. Because the hyper-attractive face was the least average of the 3 composites judged, but also the most attractive, this finding is very strong evidence that averageness is not necessarily the critical determinant of facial attractiveness. In other words, Perrett et al's findings are evidence against the Averageness Hypothesis of facial attractiveness (which proposes that ‘attractive faces are only average’) because the findings show that highly attractive faces deviate systematically from an average shape.
So why is it that fusion hypotheses have become so popular? Indeed, this goes against the classical interpretation, most thoroughly espoused by Tom Cavalier-Smith , who identified a disparate group of eukaryotes that appeared to him to be missing links — the so-called Archaezoa, which look like eukaryotes but lack mitochondria. His hypothesis, that the Archaezoa evolved before the introduction of mitochondria into the eukaryote lineage, held sway for many years, though has recently been dropped in favour of fusion:
In a classic study of facial attractiveness, Perrett et al. (1994) tested the Averageness Hypothesis in an effort to establish if averageness really is the critical determinant of the attractiveness of faces. Perrett et al. first collected a full face photographs of 60 young women (these photographs were taken under the same lighting conditions). One group of participants then were shown these images and asked to rate the attractiveness of each face using a 1 (very unattractive) to 7 (very attractive) scale. Next, Perrett et al used computer graphic methods to manufacture a composite face with the average shape of the whole sample (i.e. to construct the average of all 60 female faces) and a second composite face which was the average of the 15 faces that had been judged to be the most attractive by the first group of participants. Perrett et al. then manufactured what they called a ‘hyper-attractive’ composite face (i.e. a version of the composite of the attractive faces in which its attractive qualities were exaggerated or caricatured) by exaggerating (i.e. caricaturing) the physical differences in shape between the composite of all 60 faces and the composite of the most attractive 15 faces using computer graphic methods.