Early primates may have evolved in cold North America not tropical forests; study suggests

For decades, the story of primate origins seemed straightforward. Early primates were thought to have emerged in warm, humid forests before spreading across the world. The idea fitted neatly with what we see today: most living primates are concentrated in tropical regions, from the rainforests of South America to the forests of Africa and Southeast Asia.Yet a growing body of evidence has been making that picture harder to sustain. Fossils recovered from northern continents have not always matched the tropical settings long associated with early primate evolution. Now, a study suggests the earliest members of our lineage may have begun their journey somewhere far less familiar. Instead of dense tropical forests, the first primates may have lived in colder, more seasonal environments, facing conditions that demanded flexibility and movement long before their descendants reached the tropics.

Fossil evidence suggests early primates thrived in cold climates

According to the research published in Proceedings of the National Academy of Sciences of the United States of America, titled “The radiation and geographic expansion of primates through diverse climates”, it revisited one of the most widely accepted ideas in evolutionary biology: that primates originated and diversified in warm tropical forests.Using a combination of fossil evidence, climate reconstructions and models that tracked ancestral geographic locations across deep time, the researchers arrived at a different conclusion.

Their analysis found that many early primate ancestors occupied climates that would not be considered tropical at all.As the paper states, “Early primates dispersed and radiated in higher latitudes, through diverse climates, including cold, arid, and temperate conditions.”Rather than seeing tropical forests as the cradle of primate evolution, the findings point towards a much broader climatic history. Early primates appear to have lived across changing environments, adapting to conditions that ranged from dry landscapes to cold seasonal regions.

North America may be the birthplace of modern primates

One of the study's most striking findings concerns location. After comparing several possible regions of origin, including Africa, Asia and Europe, the researchers found the strongest support for North America as the ancestral home of crown primates. Climate reconstructions linked to that location suggested conditions far removed from the permanently warm environments usually associated with early primate history.The study reports that the common ancestor of modern primates most likely inhabited a cold climate category, one characterised by pronounced seasonal variation. Winters could reach freezing temperatures, while summers remained relatively warm. According to the researchers, “the common ancestor of primates was found in a cold climate within North America.” That conclusion challenges a narrative that has shaped textbooks and scientific discussions for more than forty years.

Environmental instability may have driven early primate evolution

The research does not simply argue that early primates tolerated colder conditions. It suggests environmental instability may have played a major role in their success.The study found little evidence that warmer global temperatures increased primate dispersal or accelerated the formation of new species. Instead, periods of changing local temperature and rainfall appeared to have a stronger influence.According to the authors, “Warmer global temperatures had no effect on dispersal distances or the speciation rate.”What mattered more was environmental fluctuation. Regions becoming wetter, drier, warmer or cooler over time created pressures that rewarded mobility. Species capable of moving into new areas were more likely to survive and diversify, while less adaptable populations disappeared.The researchers suggest that changing local climates may have encouraged repeated movement across landscapes, helping primates spread into new territories and eventually occupy a wider range of environments.

Modern primates reached tropical forests after millions of years of adaptation

Modern primates are strongly associated with tropical forests, but the study indicates this was not always the case.Climate reconstructions across the primate family tree revealed that cold, temperate and arid environments dominated much of the group's early history. Tropical climates became increasingly important later, after millions of years of expansion and adaptation.The authors write that “most early primates occupied cold, temperate, and dry climates.” Over time, some lineages moved into warmer and more stable regions, eventually giving rise to the tropical distribution that characterises most primate species today. In that sense, the tropical primate world we know may represent the outcome of a long evolutionary journey rather than its starting point.