The typical representation of primate origins is warm, leafy, and tropical: small mammals living in trees evolving in forests where fruits, flowers, and insects were accessible all year round.
A study published in *Proceedings of the National Academy of Sciences* in 2025 questions whether this portrayal starts inappropriately. Jorge Avaria-Llautureo and his team reconstructed the early geography and climate history of primates and determined that the common ancestor of crown primates likely resided in North America, experiencing a cold seasonal climate, rather than existing in a constant tropical forest. This represents one study, not a conclusive agreement.
The findings do not imply that the initial primates were traversing ice sheets, nor do they diminish the significance of tropical forests in the subsequent evolution of primates. It suggests something more precise. It indicates that the initial diversification of primates may have occurred across a broader and more challenging climatic spectrum than the typical warm-forest narrative permits, with cold, temperate, and arid ecosystems playing a significantly larger role.
### A northern beginning to a tropical narrative
For years, numerous theories surrounding primate evolution have relied on what the authors term the warm tropical forest hypothesis. Broadly, this concept links primate origins, migration, and diversification to exceptionally warm forests in northern latitudes during greenhouse periods in Earth’s history.
This hypothesis appears logical. Modern primates are closely associated with tropical and subtropical environments. Many rely on trees, fruits, young leaves, insects, and flowers. Starting with contemporary monkeys, apes, tarsiers, lemurs, and lorises, it is reasonable to envision deep evolutionary roots in warm forest canopies.
Avaria-Llautureo and his colleagues pursued a different approach. They integrated evolutionary trees, fossil and current primate distributions, paleogeographic reconstructions, and climate simulations to determine where early primates most likely thrived and what climates they inhabited over time. They also evaluated models that compelled the ancestral location to different continents to identify which scenario aligned best with the data.
The North American finding was not an isolated fragile instance. In the analyses presented in the paper, North America emerged as the proposed ancestral site for crown primates in eight out of ten primary geographic reconstructions and in all 100 median-dated trees. A sensitivity analysis indicated North America in 80 percent of 200 datasets. The authors also reported that a model confining the common ancestor to North America was statistically favored over other options.
This does not resolve every debate regarding primate origins. Fossil records are inconsistent, early primate relationships remain contentious, and methods that reconstruct ancient distributions are based on assumptions. However, it seriously challenges the notion that primates must have originated in warm tropical forests merely because many current primates inhabit those areas.
### What “cold” signifies here
The term cold requires precision. In the PNAS study, climate categories were classified using the Köppen-Geiger system, a commonly utilized method for categorizing climates based on temperature and precipitation. The inferred climate for the crown-primate ancestor was labeled as a cold climate, particularly one where the hottest month exceeds 10 degrees Celsius and the coldest month either meets or drops below freezing.
This does not imply that primates originated in a treeless polar desert. Instead, it highlights seasonal northern environments, where warmth, food, and plant growth would not have been consistently available throughout the year. The study argues that many early primates lived in cold, temperate, and arid climates, with tropical climates becoming more critical later in primate evolution.
One of the paper’s notable findings is that rising global temperatures did not solely account for primate dispersal distances or speciation rates. Local variations in temperature and precipitation were more revealing. In essence, the narrative may not be “the world warmed, and primates spread.” Rather, it may indicate that primates were repeatedly influenced by local climatic changes, geographic opportunities, and the necessity to thrive in fluctuating environments.
The authors also assert that the overarching pattern contradicts a simplistic tropical origin. Early primates seem to have migrated and diversified through non-tropical northern climates prior to later colonization and diversification in tropical areas. If this interpretation holds, tropical forests were not the original cradle of primates, but rather a subsequent destination where primates found considerable success.
### Primates near the ancient Arctic
Another fossil study aids in clarifying why this notion isn’t as implausible as it may initially seem. In 2023, Kristen Miller, Kristen Tietjen, and K. Christopher Beard identified two species of *Ignacius* from Ellesmere Island in Arctic Canada. These were basal primatomorphs, closely related to the broader primate lineage, dating back approximately 52 million years.
During that period, Ellesmere Island was situated at around 77 degrees north paleolatitude. The early Eocene climate was considerably warmer than today’s Arctic, yet the animals still lived under a polar light environment, characterized by extended dark winters and significant seasonality. The fossils were discovered in an ecosystem the authors