A unique combination of transcription factor expression and projection neuron identity demarcates each layer of the cerebral cortex. During mouse and human cortical development, the transcription factor CTIP2 specifies neurons that project subcerebrally, while SATB2 specifies neuronal projections via the corpus callosum, a large axon tract connecting the two neocortical hemispheres that emerged exclusively in eutherian mammals. Marsupials comprise the sister taxon of eutherians but do not have a corpus callosum; their intercortical commissural neurons instead project via the anterior commissure, similar to egg-laying monotreme mammals. It remains unknown whether divergent transcriptional networks underlie these cortical wiring differences. Here, we combine birth-dating analysis, retrograde tracing, gene overexpression and knockdown, and axonal quantification to compare the functions of CTIP2 and SATB2 in neocortical development, between the eutherian mouse and the marsupial fat-tailed dunnart. We demonstrate a striking degree of structural and functional homology, whereby CTIP2 or SATB2 of either species is sufficient to promote a subcerebral or commissural fate, respectively. Remarkably, we reveal a substantial delay in the onset of developmental SATB2 expression in mice as compared to the equivalent stage in dunnarts, with premature SATB2 overexpression in mice to match that of dunnarts resulting in a marsupial-like projection fate via the anterior commissure. Our results suggest that small alterations in the timing of regulatory gene expression may underlie interspecies differences in neuronal projection fate specification.

Can ten weeks of archival research be considered a re-enactment of the daily life of black African clerks who created the records? What would such a claim entail when it is made by a white female scholar? Drawing from my experience of archival research in Zambia, and from recent enthusiasm in historical geography for "enlivening" or "animating" the past, I analyse what parameters would be necessary for this re-enactment to be considered a success. This paper explores how breaking up historical situations into units of gesture and experience affects the narrating of history. It asks what models of the self are implied by re-enactive historical investigation; in relation to the agency of historical actors, and also to the performativity of their original gestures. It argues that performative investigation of the social and cultural geographies of the subaltern sits uncomfortably with current scholarly practices in historical geography. This is in part because that work is largely carried out by lone scholars, but also because of the highly individualised, self-conscious and self-possessed modes through which the outcomes of performative research are narrated. Finally, borrowing the term "acts of transfer" (from the performance scholar Diana Taylor), this paper proposes that this contemporary performance of clerical work is only one route through which the colonial past resonates, or acts, in the present. The lives of the colonial clerks were locked into structures of racial and socioeconomic inequality that survive outside my performance. Does "performing" the past overwrite or obscure these other continuities? To avoid such an erasure, both the ethical consequences and epistemological goals of performative research in historical geography need to be more clearly articulated in relationship to the sociomaterial geographies of the present. K E Y W O R D Sacts of transfer, archive, colonial history, material culture, re-enactment, Zambia

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This article explores the uneven patterns of topographic mapping of colonial Northern Rhodesia (today Zambia). These patterns were generated in the years 1927-1931 and have an enduring effect today. Previous accounts describe colonial mapping in Africa as 'incomplete', but this is an inadequate conclusion. The article proposes that these unsatisfactory narratives of cartography can be corrected by applying the model of a cartographic economy to the close reading of archival sources. This model is used to interrogate topographic unevenness within the framework of the interests of diverse parties, with differing values and resources. It reveals that the patterns of topographic production were particularly strongly linked to aerial photographic projects. These projects documented areas that were preconceived as valuable. However, the article reveals that the cartographic economy was determined by more than just the value of the land, as the value of the cartographic representation itself could be manipulated independently. This perspective should be considered in the study of British mapping of other colonial territories.