South-to-north migration preceded the advent of intensive farming in the Maya region

Abstract

The genetic prehistory of human populations in Central America is largely unexplored leaving an important gap in our knowledge of the global expansion of humans. We report genome-wide ancient DNA data for a transect of twenty individuals from two Belize rock-shelters dating between 9,600-3,700 calibrated radiocarbon years before present (cal. BP). The oldest individuals (9,600-7,300 cal. BP) descend from an Early Holocene Native American lineage with only distant relatedness to present-day Mesoamericans, including Mayan-speaking populations. After ~5,600 cal. BP a previously unknown human dispersal from the south made a major demographic impact on the region, contributing more than 50% of the ancestry of all later individuals. This new ancestry derived from a source related to present-day Chibchan speakers living from Costa Rica to Colombia. Its arrival corresponds to the first clear evidence for forest clearing and maize horticulture in what later became the Maya region.

The immunogenetic impact of European colonization in the Americas

“…Second, the long-term isolation from other human populations implies that any immunogenetic selection taking place in Indigenous peoples of the Americas would most likely have occurred with specificity for the local pathogenic landscape, a hypothesis aligning with the Virgin Soil premise. However, these hypotheses must be taken in the context of focusing on a very broad overview of Indigenous genetic diversity as current evidence suggests that the genomic landscape of Indigenous populations throughout the Americas is far from homogenous: 1) some populations in South America and Central America exhibit differential relatedness to North Americans, carrying ancestry from the California-Channel Islands (Scheib et al, 2018;Gnecchi-Ruscone et al, 2019;Nakatsuka et al, 2020); 2) the population genetic structure in Indigenous populations of Central America and the Caribbean has been shaped by back migration of South American ancestors since the initial peopling phase (Gravel et al, 2013;Schroeder et al, 2018;Nägele et al, 2020;Capodiferro et al, 2021;Kennett et al, 2022); and 3) some South American Indigenous populations along the Pacific coast and in the Amazonian basin carry an excess of allele sharing with Australasians (Raghavan et al, 2015;Skoglund et al, 2015;Moreno-Mayar et al, 2018b;Posth et al, 2018;Castro E Silva et al, 2021). While some populations, such as the Surui, underwent extensive genetic isolation (Gnecchi-Ruscone et al, 2019), their reduced effective population size and genetic isolation have likely not carried negative implications for pathogen response as the levels of genetic diversity do not correlate with adaptive potential (Teixeira and Huber, 2021).…”

Scrutinizing the paleoecological record of the Maya forest

“…Occupation of the Maya lowlands of Mesoamerica began with the expansion of mobile foraging societies into the Americas more than 15,000 years ago (Steele et al, 1998;Goebel et al, 2003;Prufer et al, 2021). The archeological evidence for the early Holocene is growing (Neff et al, 2006;Rosenswig, 2006a,b), and data demonstrate that the Maya area was occupied early on (Kennett et al, 2002(Kennett et al, , 2020(Kennett et al, , 2022Lohse, 2010;Lohse et al, 2006), as were most areas in the Americas (Steele et al, 1998;Voorhies, 2004;Kelly and Thomas, 2013). Early populations in the Maya Lowlands inhabited an arid and cool landscape (Steele et al, 1998;Leyden, 2002;Burroughs, 2005;Piperno, 2006Piperno, , 2011; see also Caffrey et al, 2011) founded on the karstic limestone platform that forms the greater Petén of Guatemala, Belize, and the Yucatan Peninsula of Mexico.…”

Early Maize in the Maya Area

“…If this scenario depicts the direction and timing of early maize dispersal across Mexico and south to Panama, what is known of the cultigen's movement through the Yucatan Peninsula and adjacent highland volcanic chain (Figure 2)? Today, the region is known as the Maya area, but questions remain about its early cultural histories and the identities of its Archaic period occupants (Kennett et al 2022; Lohse 2010, 2020; Prufer et al 2019; Rosenswig 2021). Additionally, identifying incontrovertible evidence for anthropogenic Archaic period forest disturbance is made difficult in some cases by a Late Holocene period of climate drying that has been documented across the northern Peten and more broadly across the New World tropics.…”

“…Multiple centers of genetic improvement have been postulated, and increases in maize productivity are suggested to have occurred between about 4,400 and 2,500 years ago (Kennett et al 2017; Smith 1997)—in part as a consequence of genetic backflow as new stock was carried from South America back into Central America (Dickau et al 2007; Kistler et al 2020). An example of what this process may have looked like comes from recent genomic reconstructions from preceramic burials in the Mayahak Cab Pek and Saki Tzul rockshelters in southern Belize (Kennett et al 2022). Burial contexts here contain the remains of at least 52 individuals and yielded dates from about 9600 cal BP to AD 1000, including good continuity through the period from about 5600 to 3800 cal BP (Kennett et al 2020:Figure 2).…”

“…Burial contexts here contain the remains of at least 52 individuals and yielded dates from about 9600 cal BP to AD 1000, including good continuity through the period from about 5600 to 3800 cal BP (Kennett et al 2020:Figure 2). Genomic reconstructions indicate that, starting by 5600 cal BP, a substantial percentage of ancestry (~50%) derives from a source related to Chibchan speakers, who today occupy a region spanning lower Central America to northern South America (Kennett et al 2022). Once fully developed through these and perhaps other processes, domesticated maize became a major staple that provided caloric surpluses associated with the development of sedentary village life and complex society, defined by full-time economic specialization and stratified social statuses 2…”