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Click here to sign up. Submission Websites List. For the academic login, please select your organization on the next page. You will be redirected to verify your credentials. Corresponding Author Steven D. The cytoarchitectural organization of vertebrate brains can differ markedly across species, and this divergence is most striking in the telencephalon.

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In mammals, the telencephalon harbors the neocortex, a 6-layered sheet of neurons and other cell types thought to be largely responsible for mammalian cognitive abilities. The nonmammalian telencephala, in contrast, comprise a range of divergent tissue architectures that do not morphologically resemble the neocortex at all.

Many neuroanatomists, including myself [Briscoe and Ragsdale, a], have sought to understand the evolutionary relationships of telencephalic structures in order to explain the evolutionary history of the neocortex and, by extension, the origins of human cognitive faculties [Striedter, ; Aboitiz and Montiel, ; Butler et al.

However, and as a result of the conceptual problems inherent in comparing very different biological characters, the history of comparative telencephalon anatomy has been a veritable circus of conflicting ideas [Striedter, ]. In this short essay, I aim to eliminate one of them.

Homology and ontogeny: pattern and process in comparative developmental biology

Field homology has emerged as a framework for describing the evolution of vertebrate brains, and it is based upon the proposed developmental origins of neuroanatomical characters within the embryo [Nieuwenhuys and Puelles, ]. In this view, the developing nervous system is regionalized into a grid-like series of territories, or developmental fields, along anteroposterior and mediolateral coordinates.

The fate of adult structures is specified within these fields by conserved transcription factor codes, and each developmental field then gives rise to a specific set of derivatives. The potential for homology of two compared brain regions — whether they are the same thing — is therefore determined solely by whether they arise from equivalent positions in a shared developmental Bauplan [Nieuwenhuys and Puelles, ]. This interpretation of homology is deeply problematic, and its continued application represents a conceptual impediment to future progress in comparative neuroscience.

Homology (biology)

In particular, field homology 1 does not describe either the similarity or common ancestry of compared characters, 2 conflates the independent hierarchical levels of homology, and 3 provides no opportunity for insights into the mechanisms of brain structural evolution. It is, in short, meaningless [Northcutt, ]. Homology, as conceived by most comparative biologists, refers to similarity due to common ancestry [Patterson, ; Hall, ].

Homology refers to similarity, and this component of the definition is essential for a meaningful and practical homology concept. The existence of similarities among organisms — the observation that living things resemble each other and are not instead completely different — itself provides the evidence for the common descent of life and the things it is made of.

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When we compare two extant species and seek homologies, we are searching for those shared similarities present in their last common ancestor and preserved in their respective lineages. The dissimilarities, or the species-specific properties acquired only after divergence, cannot be considered homologous because they were not present in the last common ancestor. Field homology differs substantially from this version of homology. Field homology states that neuroanatomical characters are homologous if they arise from equivalent developmental fields, but both similarity and common ancestry are conspicuously absent from the definition.

Even if a particular developmental field is conserved in two species, the adult derivatives of that field may not be, especially in the telencephalon. Field homology can therefore be used erroneously to define evolutionarily unrelated, species-specific characters as homologs by lumping similarities and dissimilarities indiscriminately together.

This idea is a clear expression of essentialism, a doctrine that the identity and homology of two characters depends upon some essence that transcends their actual physical properties. Consequently, field homology cannot be expected to convey any information about a character beyond the relative location of its progenitors.

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Donoghue and M. This fine book brings together a selection of outstanding comparative biologists, all of whom have struggled to formulate a philosophical foundation for homology that has sufficient generality that it can serve all of biology. We are always looking for ways to improve customer experience on Elsevier. We would like to ask you for a moment of your time to fill in a short questionnaire, at the end of your visit.

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Published Date: 22nd October Hubert L, Arabie P: Comparing partitions. J Classif. J Clin Bioinform. Infect Immun.


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CXC and MM conducted the experiments. CXC prepared the manuscript. All authors read and approved the final manuscript. Reprints and Permissions. Search all BMC articles Search.

Functional Homology and Functional Variation in Evolutionary Cognitive Science | SpringerLink

Abstract Background Clustering sequences into groups of putative homologs families is a critical first step in many areas of comparative biology and bioinformatics. Conclusions Our results demonstrate that sequence divergence, rate heterogeneity and content bias can individually and in combination affect the accuracy with which MCL and UCLUST can recover homologous protein families. Background Homology is the basis of comparative biology [ 1 ], and recognising sets of homologous genes or proteins underlies much of modern bioscience including genome annotation, phylogenetic inference and studies of protein structure.

Figure 1. Full size image. Figure 2. Figure 3. Figure 4. Figure 5. Conclusions We assessed the performance accuracy of two clustering approaches designed for different purposes. References 1. Article Google Scholar Additional information Competing interests The authors declared that they have no competing interests. The number of clusters observed in the reference set R is shown at far left at each panel for comparison.

Figure S2. Figure S3. Figure S4. Number of clusters generated across simulated dataset of various divergence levels. Data are shown for different branch lengths on a tree x in Figure 2 at a 0.