A multidisciplinary overview on the Tupi-speaking people expansion

The cultural and biological diversity of South American indigenous groups represent extremes of human variability, exhibiting one of the highest linguistic diversities alongside a remarkably low within-population genetic variation and an extremely high inter-population genetic differentiation. On top of that, this region has seen some of the most dramatic demographic events in human history unleashed by the European colonization of the Americas. As a result of this process, the distribution of indigenous populations has been radically changed. In this review we focus on the Tupi, the largest and most widespread linguistic family in eastern South America. Tupi are believed to have originated in southwestern Amazon, from where some of its subfamilies expanded into other parts of the Amazon and, in the case of the Tupi-Guarani, beyond its borders. Recent evidence from archaeology, linguistics, and genetics aligns with José Brochado's Tupi Expansion model. He proposed that the gradual development of agricultural systems within the Amazon resulted in population growth and, eventually, territorial expansion. This model also supports separate Tupi Expansion branches: Tupinambá (Atlantic coast) and Guarani (south, midwest Brazil). Although being the most populous group on Brazil's Atlantic coast, which was the most affected by European colonization, the Tupi still account for roughly 20% of the country's overall indigenous population. Finally, despite its importance and more than a century of research on the Tupi and their expansion history, many key questions remain unanswered, which we attempt to summarize and explore here.

A genomic perspective on South American human history

It has generally been accepted that the current indigenous peoples of the Americas are derived from ancestors from northeastern Asia. The latter were believed to have spread into the American continent by the end of the Last Glacial Maximum. In this sense, a joint and in-depth study of the earliest settlement of East Asia and the Americas is required to elucidate these events accurately. The first Americans underwent an adaptation process to the Americas' vast environmental diversity, mediated by biological and cultural evolution and niche construction, resulting in enormous cultural diversity, a wealth of domesticated species, and extensive landscape modifications. Afterward, in the Late Holocene, the advent of intensive agricultural food production systems, sedentism, and climate change significantly reshaped genetic and cultural diversity across the continent, particularly in the Andes and Amazonia. Furthermore, starting around the end of the 15th century, European colonization resulted in massive extermination of indigenous peoples and extensive admixture. Thus, the present review aims to create a comprehensive picture of the main events involved in the formation of contemporary South American indigenous populations and the dynamics responsible for shaping their genetic diversity by integrating current genetic data with evidence from archeology, linguistics and other disciplines.