This paper explores the intersections between national identity and the production of medical/population genomics in Mexico. The ongoing efforts to construct a Haplotype Map of Mexican genetic diversity offers a unique opportunity to illustrate and analyze the exchange between the historic-political narratives of nationalism, and the material culture of genomic science. Haplotypes are central actants in the search for medically significant SNP’s (single nucleotide polymorphisms), as well as powerful entities involved in the delimitation of ancestry, temporality and variability ( www.hapmap.org (...) ). By following the circulation of Haplotypes, light is shed on the alignments and discordances between socio-historical and bio-molecular mappings. The analysis is centred on the comparison between the genomic construction of time and ethnicity in the laboratory (through participant observation), and on the public mobilisation of a “Mexican Genome” and its wider political implications. Even though both: the scientific practice and the public discourse on medical/population genomics are traversed by notions of “admixture”, there are important distinctions to be made. In the public realm, the nationalist post-revolutionary ideas of Jose Vasconcelos, as expressed in his Cosmic Race ( 1925 ), still hold sway in the social imaginary. In contrast, admixture is treated as a complex, relative and probabilistic notion in laboratory practices. I argue that the relation between medical/population genomics and national identity is better understood as a process of re-articulation (Fullwiley Social Studies of Science 38:695, 2008 ), rather than coproduction (Reardon 2005 ) of social and natural orders. The evolving process of re-articulation conceals the novelty of medical/population genomics, aligning scientific facts in order to fit the temporal and ethnic grids of “Mestizaje”. But it is precisely the social and political work, that matches the emerging field of population genomics to the pre-existing projects of national identity, what is most revealing in order to understand the multiple and even subtle ways in which population genomics challenges the historical and identitarian frames of a “Mestizo” nation. (shrink)