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This Week in Science: Dec 8, 2017

In this week's Science, a trio of US and European scientists present an overview of the archaeological and genetic evidence that contradict the traditional theory that modern Homo sapiens dispersed out of Africa and through Eurasia in a single wave around 60,000 years ago. They highlight the difficulties in understanding the effects of admixture between humans, Neandertals, Denisovans, and possibly other hominin taxa, and suggest that there were likely multiple dispersals predating 60,000 years ago in regions such as southern and eastern Asia. "These early human dispersals, which left at least some genetic traces in modern populations, indicate that later replacements were not wholesale," they say. 

Also in Science, a University of California, San Francisco-led team presents a new single-cell analysis of the developing human brain. They performed single-cell mRNA sequencing on areas of the developing brain that eventually become the basal ganglia and the cortex, and identify 11 broad categories of cells, as well as temporally and spatially restricted trajectories of cell maturation and neurogenesis. The scientists also find certain transcription profiles that are defined be location and not cell type, suggesting that transient transcriptional states during development influence area-specific features of neuronal identity.