The schoolhouse is a place in which messages for student consumption are typically found with classroom lectures, text, and activities. As with any social setting, however, the communication is not confined to one space but extends, in this case, to hallways, common spaces, and exterior of the building. One of the most common practices for the delivery of messages to students within the schoolhouse is through visual signage. Visual signage can traverse disciplines encompassing concepts from the fields of communication, semiotics, language, literacy, and even interior design. In an effort to understand the impact these signs have on student populations this dissertation asks the question: How are signs within public high schools produced, consumed, and influential to persons in contact with intended messages that are presented in public school spaces? The study utilizes ethnography to describe the production, consumption, and influence of fixed signs in the interior hallways and common spaces at three public high schools in Texas. At each campus, student volunteers, one from each grade level, provided their individual course schedule to follow their daily route from class to class at their particular high school. Post these observations these students engaged in focus groups to discuss the various signs displayed on their campus. In addition, faculty/staff members from each high school volunteered to participate in a separate faculty/staff focus group to discuss the use of signage in schools and the observations made by both the students and myself during the observations. The data suggest that district directives and social happenings guide the production of messages for each campus. The consumption and influence of these messages though is far more complex as a variety of factors contributed to the student and faculty/staff consumption, or lack thereof, and influence to action. As ethnography, this dissertation sheds light onto these complexities revealing that a host of external and internal issues dictate the messages displayed through school signage within the individual schoolhouse.

The purpose of the study was to improve the understanding of the present situation and the key problems regarding the conservation of designed landscapes of the recent past. Another aim was to investigate roles and initiatives undertaken by key stakeholders and recommend key areas for measures and action to enhance the conservation and protection of designed landscapes of the recent past. The emphasis of the research was on the United Kingdom but relevant findings and actions from an international context were included. A qualitative method was applied using the between-method triangulation research methodology, which combined two methods of investigation, namely data triangulation and theory triangulation. Theory triangulation allowed for an investigation of the wider context or ‘the general’ and a comparison of findings from published sources and records, including an examination of the existing inventories and the roles and initiatives of key stakeholders. The data triangulation used a case study survey, with questionnaires and interviews, to enable the collection and analysis of data from different categories of stakeholders from a site-specific perspective or ‘the particular’ context. The case study survey investigated eleven case study sites using questionnaires and interviews. A total of 146 respondents were contacted and 103 completed responses were received. The results revealed that several recommendations for actions to improve the conservation and protection of heritage of the recent past exist, and that general conservation principles and methodologies exist for the conservation of designed landscapes, but that a lack of recognition and awareness for the significance of designed landscapes of the recent past results in poor implementation of such principles, and the continuing destruction and disfigurement of significant sites. The findings of the study led in the conclusions to the preparation of recommendations for measures and actions by stakeholders, to improve the protection and conservation of landscapes of the recent past.

Thesis (MA)--Stellenbosch University, 2003. / ENGLISH ABSTRACT: This thesis explores the role played by drawings in the creation of knowledge. The study specifically focuses on drawings of the South African landscape and how it led to knowledge of our country. The Western perception of the concept of nature in relation to culture or civilisation is investigated by brief reference to a few periods in Western history. It is argued that man and nature was separated in Western thought by the establishment of rational thinking. This concept led to man's exploitation of nature to his own advantage. The division between man and nature was broadened in the quest for technological advancement. The first European travellers came to South Africa with a Western mind set, hoping for better economical conditions. The illustrated traveller's report reflects the verbal and visual capturing and exploitation of the South African landscape. It is further argued that European travellers tried to structure the landscape according to Western aesthetical traditions. Drawings appear to be picturesque but have radical political, economical and social implications. Colonial depictions created knowledge, but in fact symbolically legitimise the expansion of power. Until the middle of the twentieth century Western aesthetic traditions were applied to visual depictions of the South African landscape. During this period, artists were uncritical of the oppressive political system and in doing so gave their tacit consent. Ever since the middle of the twentieth century, several artists voiced their opinions against the unfair policy of the ruling political party. Visual images asked subtle questions and gave radical judgements; thus knowledge was created and a contribution made to the freedom of all South Africans. My drawings of South African landscapes are to be understood against this theoretical background. I use drawings to ask questions about the relationship between the visual image and the establishment of knowledge. I also refer to the relationship between the original and the copy, reality, the photo and the drawing. I conclude the following: drawings lead to the creation of knowledge and landscape depictions have implications of power. The solution to this problem lies, in the end, once more III drawings.My depictions of South African landscapes are given as an answer. / AFRIKAANSE OPSOMMING: Hierdie tesis is 'n ondersoek na die rol wat visuele beelde kan speel in die oordrag van idees. Daar word spesifiek gekyk na hoe tekeninge van die Suid-Afrikaanse landskap gelei het tot die totstandkoming van kennis oor ons land. Die Westerse verstaan van die begrip natuur in verhouding tot kultuur of beskawing word ondersoek deur kortliks te verwys na 'n paar periodes gedurende die Westerse geskiedenis. Daar word aangevoer dat Westerse denke die mens en die natuur van mekaar geskei het deur die instelling van rasionele denke. So het daar 'n geloof in menslike rede ontstaan. Dié beskouing het daartoe gelei dat die mens die natuur begin uitbuit het tot eie voordeel. Die kloof tussen mens en natuur het al hoe dieper geword in 'n strewe na tegnologiese vooruitgang. Die eerste Europese reisigers het vanuit 'n Westerse verwysingsraamwerk na Suid-Afrika gekom met die hoop op beter ekonomiese vooruitsigte. Die geïllustreerde reisverslag weerspieël die inneming en uitbuiting van die Suid-Afrikaanse landskap visueel en verbaal. Daar word aangevoer dat Europese reisigers die landskap deur middel van tekeninge, uitgevoer volgens Westerse estetiese tradisies, probeer struktureer het. Tekeninge kom skilderagtig voor, maar het radikale politiese, ekonomiese en sosiale implikasies. Koloniale tekeninge het kennis geskep en in werklikheid magsuitbreiding simbolies gelegitimeer. Westerse estetiese tradisies is tot die middel van die twintigste eeu toegepas op visuele uitbeeldings van die Suid-Afrikaanse landskap. Gedurende dié tydperk het kunstenaars die onderdrukkende, heersende politieke stelsel in werklikheid ondersteun deur totaalonkrities daarteenoor te staan. Teen die middel van die twintigste eeu het verskillende kunstenaars in opstand gekom teen die onregverdige beleid van die regerende party. Visuele beelde is gebruik om subtiele vrae te stel sowel as radikale uitsprake te lewer en het so kennis geskep en bygedra tot die bevryding van alle Suid- Afrikaners. My tekeninge van Suid-Afrikaanse landskappe moet teen dié teoretiese agtergrond gelees word. Ek gebruik teken om vrae steloor die verhouding tussen die visuele beeld en kennis wat so tot stand kom. Daar word verwys na die verhouding tussen oorspronklike en kopie, werklikheid, foto en tekening. Die gevolgtrekking is dat tekeninge kan lei tot die totstandkoming van kennis en dat uitbeeldings van landskappe magsimplikasies kan hê. Die oplossing vir hierdie probleem lê uiteindelik weer in tekeninge. My uitbeeldings van Suid-Afrikaanse landskappe word as antwoord gebied.

Thesis (MScConsEcol (Conservation Ecology and Entomology))--University of Stellenbosch, 2009. / Habitat loss and fragmentation are two of the most pressing threats to biodiversity. Avifaunal diversity and integrity is under immense pressure from these two processes. We have made major advances in our understanding of avifaunal responses to habitat fragmentation, but mostly focus on either fragment scale and/or landscape scale influences of fragmentation on birds. A more comprehensive approach to assessing the impacts of fragmentation was used in this study. The avifaunas of two different geographical regions and bioregions were surveyed and a multiscale analysis of avifaunal responses to fragmentation was attempted. The study sites include the West Coast and East Coast Renosterveld Bioregions in the Cape Floristic Region, South Africa. Assemblage shifts, feeding guild compositional changes, species abundance variation and species persistence were examined at the three spatial scales. Time- and distance-restricted point counts were used to document birds that were directly dependent on the habitat fragments. Forty fragments were selected in each bioregion and a once-off snapshot of the avifaunal richness and diversity was obtained. Results indicate that the avifauna of the two bioregions responded differently to habitat fragmentation. In the East Coast Renosterveld Bioregion, the assemblages, guild composition and species abundances were most accurately predicted by landscape configuration. An assemblage shift occurred at 20 ha fragment area, compared to the 50 ha fragment area threshold of the West Coast Renosterveld Bioregion’s avifauna composition. In the West Coast Renosterveld Bioregion, fragment area was the better predictor of assemblage, guild composition and species abundances. However in both bioregions, the persistence of common species was equally sensitive to area and landscape scale effects.

This thesis examines the shifting relationship between the state and its subjects with regard to responsibility for and entitlement to care. Using Malaysia as a case study the research engages with international medical travel (IMT) as an outcome of the neoliberal retrenchment of the welfare state. I offer a critical reading of postcolonial development strategies that negotiate the benefits and challenges of extending care to non-national subjects. The research draws from relevant media, private-sector and governmental documents and 49 semi-structured, in-depth interviews with IMT proponents and critics representing federal, state and urban governmental authorities, professional associations, civil society, private medical facilities and medical travel agencies in Malaysia’s principal IMT regions (Klang Valley, Penang and Malacca). Across four empirical chapters, the thesis demonstrates how ‘Malaysia’ gets positioned as a destination within a range of imagined geographies of care through a strategic-relational logic of care and hospitality. I argue that this positioning places ‘Malaysian’ subjects and spaces into lucrative global networks in ways that underscore particular narratives of postcolonial hybridity that draw from Malaysia’s ‘developing country’, ‘progressive, moderate Islamic’ and ‘multiethnic’ credentials. In considering the political logics of care-giving, I explore how the extension of care can serve as a place-making technology to re-imagine the state as a provider and protector within a globalising marketplace in which care, increasingly commodified, is tied to the production of new political, social, cultural and economic geographies.

This study investigated bird distributions in relation to local habitat and landscape pattern and the implications which habitat fragmentation may have for woodland birds. There were two sections to the research: an experimental study investigating bird gap crossing behaviour across distances of five to 120m; and an observational study modelling woodland bird distributions in relation to local habitat and landscape scale variables in two study areas (East Loch Lomond and the Central Scotland Forest). In the experimental study it was hypothesised that bird willingness to cross gaps will decrease with increasing gap distance even at home-range scales and that the rate of decline will vary interspecifically in relation to bird morphology. Song thrush mobbing calls played at woodland edges in the West of Scotland were used to attract birds across gaps and results were compared with the response along woodland edges. Data were obtained for four species: chaffinch, coal tit, robin and goldcrest. The decline in response with distance across gaps and along woodland edge was modelled for each species using generalized linear modelling. Maximum gap crossing distances ranged from 46m (goldcrest) to 150m (extrapolated value for the chaffinch). Goldcrests responded more readily through woodlands. There was no difference between woodland edge and gap response for the coal tit. Robins and chaffinches however responded more readily across gaps than through woodland. When different response indices were plotted against bird mass and wing area, results suggested that larger birds with bigger wings responded more readily across gaps than through woodland. It is suggested that this relates to differences in bird manoeuvrability within woodlands and ability to evade a predator in gaps. Fragmentation indices were calculated for an area of the Central Scotland Forest to show how willingness to cross different gap distances influences perception of how fragmented the woodlands are in a region. Results are discussed in the context of the creation of Forest Habitat Networks. The data for the observational section of the work was from bird point counts for 200 sample points at East Loch Lomond in 1998 and 2000 and 267 sample points in the Central Scotland Forest in 1999. In addition a time series of point count data was available for 30 sample points at East Loch Lomond. Additional data was gathered for ten sample points (1998) and two sample points (2000) at East Loch Lomond to investigate effects of observer, time and weather on count data. Generalized linear and generalized additive modelling was carried out on these additional data. Results indicated that biases due to the variation in time and weather conditions between counts existed in the pure count data but that these were eliminated by reducing data to presence and absence form for analysis. Species accumulation curves indicated that two counts per sample point were insufficient to determine species richness. However a sufficiently large proportion of the species was being detected consistently in two counts of ten minutes duration for it to be valid to model them in relation to habitat and landscape variables. Point count data for East Loch Lomond in 1998 (ELL98) and the Central Scotland Forest in 1999 (CSF99) for the wren, treecreeper, garden warbler, robin, blue tit, blackbird, willow warbler, coal tit, goldcrest, great tit, and song thrush were analysed using generalized additive modelling. In addition models were built for the blackcap (CSF99) and the siskin, redstart and wood warbler (ELL98). Where all relationships were identified as linear, models were rebuilt as GLMs. Models were evaluated using the Area Under the Curve (AUC) of Receiver Operating Characteristic (ROC) plots. AUC values ranged from 0.84-0.99 for ELL98 and from 0.76-0.93 for CSF99 indicating high predictive accuracy. Habitat variables accounted for the largest proportion of explained variation in all models and could be interpreted in terms of bird nesting and feeding behaviour. However additional variation was explained by landscape scale and fragmentation related (especially edge) variables. ELL98 models were used to predict bird distributions for Loch Lomond in 2000 (ELL00) and for the CSF99. Likewise the CSF99 models were used to predict distributions for ELL98 and ELL00. Predicted distributions had useful application in many cases within the ELL site between years. Fewer cases of useful application arose for predicting distributions between sites. Results are discussed in the context of the generality of bird environment relationships and reasons for low predictive accuracy when models are applied between sites and years. Models which had useful application for ELL00 were used to predict bird distributions for 2025 and 2050 at East Loch Lomond. Habitat and landscape changes were projected based on the proposed management for the site. Since woodland regeneration rates are difficult to predict, two scenarios were modelled, one assuming a modest amount of regeneration and one assuming no regeneration. Predictions derived from the ELL98 models showed broad-leaved species increasing in distribution while coniferous species declined. This was in keeping with the expected changes in the relative extent of broad-leaved and coniferous habitat. However, predictions from the CSF99 models were often less readily explicable. The value of the modelling approach is discussed and suggestions are made for further study to improve confidence in the predictions.

L'Amazonie a connu une longue histoire d'occupation humaine. La nature et l'échelle de l'impact des populations d'Amérindiens précolombiens sur leur environnement sont encore largement débattues. Dans une approche pluridisciplinaire, la thèse vise 1) à améliorer les estimations de l'étendue des remaniements anciens des paysages par l'Homme et 2) à comprendre comment ces remaniements affectent la structure et le fonctionnement des écosystèmes contemporains par l'étude des complexes de champs surélevés précolombiens des savanes côtières de Guyane française. Pour la mise en place d'une agriculture intensive sédentaire, les agriculteurs précolombiens ont transformé ces savanes saisonnièrement inondées en édifiant des champs sous la forme de buttes de terre circulaires produisant une hétérogénéité topographique marquée et organisée. Pour répondre au premier objectif, nous avons développé deux approches permettant de distinguer les paysages de buttes d'origine anthropique de ceux, dont la physionomie est très proche, résultant de processus naturels. Pour répondre au second objectif, nous avons décrit comment la structure des communautés d'ingénieurs naturels d'écosystèmes (fourmis, termites, vers de terre et plantes) répond à l'hétérogénéité induite par l'Homme, et comment les activités de ces ingénieurs assurent l'auto-entretien des anciens champs contre l'érosion depuis leur abandon il y a environ 800 ans. Notre travail révèle que l'étude de la dynamique temporelle de la végétation permet d'inférer l'origine des complexes de buttes uniquement lorsqu'elle combine différents proxys. L'analyse de la structure spatiale des buttes montre que les complexes de buttes de Guyane présentent une orientation souvent en grille carrée, orientation qui n'a jamais été montrée ni prédite pour des paysages d'origine naturel, indiquant que la géométrie du paysage peut porter la signature de l'intervention de l'Homme. Depuis l'abandon des champs surélevés, les communautés d'ingénieurs naturels se structurent, et concentrent leurs activités, dans les buttes. Nous avons montré que ces activités contribuent à maintenir des habitats surélevés contre l'érosion mais que les rétroactions qu'ils conduisent sur le sol sont modulées par les conditions initiales du milieu. Le paysage observé actuellement dans les savanes de Guyane n'est ni entièrement façonné par l'Homme, ni entièrement naturel mais résulte de l'interaction complexe entre les composantes physiques et biotiques et de l'héritage des activités anciennes de l'Homme. Le résultat de ces interactions est reflété par une mosaïque de buttes plus ou moins érodées. Notre travail représente la première étude montrant l'impact à long terme des activités anciennes de l'Homme sur les écosystèmes de savanes en Amazonie. Nos résultats présentent des applications importantes dans le domaine de l'ingénierie écologique pour la conception de nouveaux agroécosystèmes durables. / Amazonia has a long history of human occupation. The nature and scale of the impact of pre-Columbian humans on their environment are still hotly debated. In a pluridisciplinary approach, this thesis aims 1) to improve estimations of the scale of ancient landscape transformations by humans and 2) to understand how these transformations influence the structure and the functioning of contemporary ecosystems, by studying the particular exemple of pre-Columbian raised-field complexes in coastal savannas of French Guiana. To conduct sedentary intensive agriculture, pre-Columbian farmers transformed these seasonally flooded savannas by building raised fieldsin the form of circular moundscreating a marked and organized topographic heterogeneity. To accomplish the first objective, we developed two approaches to distinguish anthropogenic mound-field landscapes from others, of similar physiognomy, resulting from natural processes. To accomplish the second objective, we described how the structure of the community of natural ecosystem engineers (ants, termites, earthworms and plants) is influenced by human-induced heterogeneity, and how feedbacks generated by these engineers can lead to self-organized maintenance of the ancient fields against erosion since their abandonment around 800 years ago. Our work reveals that the study of the temporal dynamics of vegetation can be used to infer the origin of mound complexes only when it combines different proxies. The analysis of spatial structure of mounds shows that mound complexes of Guiana are strongly oriented, often in a square lattice, an orientation that has been neither demonstrated nor predicted for natural landscapes, indicating that landscape geometry bears a diagnostic signature of human activities. Ever since raised fields were abandoned, the community of natural engineers is structured, and its activities are concentrated, on mounds. We showed that these activities cont ribute to maintaining these raised features against erosion, but that the effectiveness of engineer-feedbacks on soil in countering erosion are modulated by initial conditions of the environment. The current landscapes of French Guianan savannas are neither solely modeled by humans nor entirely natural, but result from the complex interaction between physical and biotic components and from the legacies of past human land use. The result of these interactions is reflected in a mosaic of more or less eroded mounds. Our work represents the first study showing the long-term impact of ancient human activities on Amazonian savanna ecosystems. Our results can have important applications in the framework of ecological engineering to conceptualize new durable agroecosystems.

One of the major challenges that persists in postsecondary foreign language (FL) education in the US today is how to implement a more integrated approach to language and literature instruction, that is, one that fosters critical awareness on multiple levels and prepares learners to be globally-connected and engaged citizens (MLA, 2007; Swaffar & Urlaub, 2014). Major contributions for achieving these goals have come from an array of pedagogical approaches that share in common their focus on language as a resource for making socially and symbolically rich meanings that do more than convey facts or express objectives. These include those designated as multiliteracies and genre-based approaches, as well as those that promote intercultural, symbolic and literary competencies as integral to the language learning experience. All of these frameworks acknowledge to some extent the fact that ambiguity-understood here as the multiplicity, indeterminacy, or destabilization of meaning-characterizes language itself and thus also our day-to-day and global communication, as well as the experience and process of FL learning. This dissertation, based on a qualitative classroom-based research study, considers how ambiguity can more be comprehensively integrated into FL learning and in particular into text-oriented teaching practices. The approach taken was a pedagogy that embraces ambiguity by providing learners and educators with strategies for navigating the moments of indeterminacy, uncertainty, and doubt that they will inevitably encounter in and out of the FL classroom. The study, set in an intermediate German language and culture course at a large public university, investigates 1) how to incorporate and assess moments of ambiguity more comprehensively across the curriculum and 2) how learners responded to various encounters with ambiguity, including ambiguity of genre, perspective, and silence. Data analysis revealed that purposeful integration of induced ambiguity can facilitate more comfort with those three dimensions and that it complements the principles of a multiliteracies-based FL pedagogy.

Dans un contexte de grandes transformations économiques imposées par la mondialisation, le développement d’innovations et la financiarisation de l’économie ont profondément atteint les villes mono industrielles de la période fordiste. L’industrie automobile, grandement influencée par les restructurations économiques globales, a elle aussi été profondément touchée. Ce faisant, les paysages urbains des villes dépendantes de cette industrie, comme Windsor en Ontario, ont été construits et détruits par le processus de destruction créative, dont nous soulignons la composante spatiale. La structure paysagère de Windsor s’est ainsi transformée : alors que des aires importantes dans différents quartiers attendent d’être réinvesties, donnant lieu aux paysages abandonnés, d’autres paysages sont créés. Cette recherche est basée sur l’étude de trois quartiers bordant la Rivière Détroit ayant subi d’importants changements dans leurs paysages. L’objectif principal de ce mémoire est donc de déterminer comment le processus de destruction créative s’opère à Windsor et quels en sont les impacts spatiaux. Afin de parvenir à cet objectif, des observations du paysage avec la création du répertoire photographique, accompagnées d’entrevues directes, ont été les méthodes privilégiées La recherche a permis de déterminer que le processus de destruction créative a lieu dans des contextes de déclin, mais également de croissance. Avec les restructurations économiques globales de l’industrie automobile, les paysages de Windsor se sont créés, déstructurés, et parfois restructurés, grâce aux interventions des acteurs locaux. Face à l’abandon progressif de certains espaces, ces acteurs ont dû réfléchir à de nouvelles stratégies en réponse aux transformations paysagères, comme le néolibéralisme urbain. Nous avons ainsi pu conclure que la destruction créative des paysages est donc en relation avec les processus économiques globaux et négociée par les acteurs locaux. / In a context of great economic transformations imposed by globalization, the development of innovations and the financialization of the economy have deeply affected the mono industrial cities of the fordist period. The automotive industry, largely influenced by global economic restructuring, was also deeply touched. In doing so, the urban landscapes of cities dependent on this industry, such as Windsor in Ontario, were built and destroyed by the process of creative destruction, by it’s spatial component. Thereby, the landscape structure of Windsor has been transformed: while important areas in different neighborhoods are waiting to be reinvested, giving rise to abandoned landscapes, other landscapes are created. This research is based on the study of three neighborhoods along the Detroit River that has undergone significant changes in their landscapes. The main objective of this research is to determine how the process of creative destruction takes place in Windsor and what are the spatial impacts. To achieve this goal, observations of the landscape with the creation of the photographic repertoire, accompanied by direct interviews were the preferred methods. Research has determined that the process of creative destruction takes place in contexts of decline, but also growth. With overall economic restructuring of the automotive industry, the landscapes of Windsor have been created, unstructured, and sometimes restructured through the efforts of local actors. Faced with the phasing out of certain areas, these actors had to think about new strategies in response to landscape transformations, like urban neoliberalism. Therefore, we can conclude that creative destruction of the landscape is related to global economic processes and negotiated by local actors.

Des souris aux baleines en passant par les humains, la diversité écologique des mammifères placentaires est des plus fascinantes. Bien qu'il s'agisse là d'un des groupes les plus étudiés, leur origine fait pourtant l'objet de bien des mystères. Leurs relations de parenté les plus basales restent en effet incertaines, et l'on ignore encore beaucoup du mode de vie qu'avaient nos ancêtres du Crétacé, ces mammifères placentaires qui auraient côtoyé les dinosaures pendant plus de 30 millions d'années.Afin d'aborder ces questions, cette thèse a utilisé l'outil de la génomique comparative. L'une de ses principales originalités est la prise en compte d'un distorteur majeur de notre évolution moléculaire: la conversion génique biaisée. Truquant la loterie génétique, ce mécanisme associé à la recombinaison méiotique avantage les nucléotides G et C au détriment des nucléotides A et T. Façonnés par son influence, nos paysages nucléotidiques présentent ainsi ponctuellement des taux de GC anormalement élevés.Jusque là, ce phénomène n'avait été étudié que chez une poignée d'organismes modèles. Son analyse chez plus d'une trentaine de génomes mammaliens a mis en évidence une série de résultats clés. En particulier, l'évolution du contenu en GC des gènes s'est avéré dépendre de la masse corporelle et la longévité des espèces. E nreliant ainsi évolution moléculaire et traits d'histoire de vie, des reconstructions de séquences ancestrales ont permis d'estimer la durée de vie des premiers mammifères placentaires à plus de 25 ans. Cette longévité va bien au delà de ce que peuvent espérer atteindre les souris ou musaraignes actuelles, des animaux au mode de vie pourtant jusqu'ici supposé comme étant proche de celui de nos ancêtres.Parallèlement à ces résultats, une tendance à produire des phylogénies inexactes a été détectée chez les gènes les plus GC-riches. Moins soumis à la conversion génique biaisée, les gènes AT-riches se sont montrés plus fiables, tout en soutenant que les espèces originaires d'Afrique sont situés à la base de l'arbre des placentaires. Ce résultat suggère ainsi la possible résolution d'un des noeuds les plus controversés de notre histoire évolutive.Du simple nucléotide à la naissance d'une infraclasse de plus de 4000espèces, ce travail révèle comment l'évolution moléculaire peut porter un nouveau regard sur nos origines les plus profondes. / From mice to whales through humans, placental mammals present astunning diversity. Despite being one of the most studied group ever,mysteries persist about their origin. Indeed, their most basalrelationships still remain uncertain, and nothing is really knownabout the lifestyle of our cretaceous ancestors, these placentalmammals which lived side by side with non-avian dinosaurs during 30My.To answer these evolutionnary questions, comparative genomic studiesof placental mammals have been conducted. One of its originalities isto take into account biased gene conversion. Rigging the geneticlottery, this recombination-associated mechanism involves a reparationbias favouring the G and C nucleotides over the A and T ones, whichmark the mammalian genomic landscapes by inducing localized peaks ofGC-content.This phenomenon has been so far studied in few model species. Theexploration of biased gene conversion in more than 30 mammal genomesled to several key results. In particular, GC content evolution hasproved to be correlated to the longevity and the body mass of species.By linking together molecular evolution and life history traits, thereconstruction of ancestral sequences allowed us to estimate alife-span above 25 years for early placental mammals. This value ismarkedly different from that of mice or shrews, although our mammalianancestors have often been represented as such. In addition to these results, GC-rich genes were found to be prone toproduce false phylogenies. Less affected by recombination associatedartifacts, AT-rich genes are shown to be more reliable, and to supportspecies of African origin as the sister group of all other placentalmammals - perhaps resolving one of the most controversial nodes of themammalian tree.From nucleotide to the birth of a 4,000 species infraclass, this workreveals how molecular evolution can shed new light onour deepest origins.