Reconstructing human diffusion and collapse in the Americas


The Americas, with their relatively recent history of population diffusion and collapse after European contact, represent an ideal case-study for testing the genetic footprints left by such demographic changes. Evidence from different disciplines suggests that a reduced number of founders entered this landmass with a major migration in the late Pleistocene, where they spread and diversified until the encounter with European conquistadores; this contact was followed by a demographic decline, testified from historical sources. The population movements and the diversification which took place from the colonization until the European conquest was intense enough to result in one of the highest cultural and linguistic diversity described for living populations. This case of conspicuous language diversity led some scholars to propose a time frame of 35,000 years for the colonization (Nichols, 1990), while other scholars reconciled the pattern of diversity with a recent colonization, compatible with the archaeological dates (Nettle, 1999).

The human migratory trajectories within the continent are particularly difficult to reconstruct, and leaving many question unanswered: How did populations diffuse in North America? Which role was played by Central America as a corridor? Can we predict a second bottleneck after the passage through Panama? How was the interaction between the Andean and the Amazonian ecological and cultural domains? Which routes did people take before they reached the foremost south? How did the Pacific coast act as a preferential route for the spread of maritime cultures?

John Everett Millais - Pizarro seizing the Inca of Peru (1845)
John Everett Millais – Pizarro seizing the Inca of Peru (1845)

With the arrival of the Spanish conquistadores a process of systematic population decline started to take place. The spread of diseases to which the Native Americans were never exposed fostered the extermination of the native groups. The activity of the Jesuit and Franciscan missions pushed communities into relocations and language shifts, contributing to shaping the current linguistic diversity and language distribution. Which kind of traces could such a phenomenon bring to the present day genetic makeup of native populations? Did the phenomenon affect the whole continent at the same time and with similar proportions?

In this project I aim at analyzing the diversity of populations from different regions of the continents with high-resolution uniparental markers, testing for different models of expansion and collapse. The final objective is to reveal to which extent we can distinguish between different population histories in the heavily bottlenecked genetic makeup of Native populations. Bayesian simulation analyses are performed in collaboration with Dr. Silvia Ghirotto, University of Ferrara.

  • Nichols J (1990) Linguistic diversity and the first settlement of the New World. Language (Baltim) 66:475–521.
  • Nettle D (1999) Linguistic diversity of the Americas can be reconciled with a recent colonization. Proc Natl Acad Sci U S A 96:3325–3329.