Early primates survived in cold, not tropical climates
Japanese snow macaque - unusual for a modern primate but our common ancestor may have lived in a similar climate.
Ever-hopeful creationists will no doubt seize on this as evidence that science keeps “getting everything wrong” and is now supposedly admitting that humans did not evolve in Africa but… somewhere else. (Not in Mesopotamia either, and certainly not just 10,000 years ago, but we can worry about that later — the important thing is that science got it wrong again, right?).
But of course, this is a distortion. The new findings don’t overturn evolution, nor do they suggest humans suddenly popped up in the “wrong” place. The study doesn’t even concern early human ancestors directly. Instead, it examines the very earliest primates — the common ancestor of the entire primate clade, which includes monkeys, apes, and humans, but also tree shrews, tarsiers, bush babies, and lemurs.
So the debate here isn’t about whether primates share a common ancestor — that fact is firmly established — but about where that ancestor first evolved. The conventional view has long been that primates arose in warm, tropical forests, because that’s where the majority of them live today. But by examining genetic data, ecological modelling, and the fossil record, Avaria-Llautureo and colleagues argue that the earliest primates actually adapted to cooler conditions. In other words, the roots of the primate family tree may lie in temperate regions, not the tropics.
Far from being a “crisis for evolution”, this is science doing what it always does: refining our understanding in light of new evidence. No biologist doubts that primates, including humans, share common ancestry going back tens of millions of years — far beyond the Bible’s compressed and mythical 6,000–10,000-year timeline. What changes is our picture of the environment in which those ancestors thrived.
As Dr Jason Gilchrist of Edinburgh Napier University — who was not involved in the study — points out in his article in The Conversation, this research challenges old assumptions but also enriches our understanding of primate resilience. If our lineage began in colder settings, it helps explain how primates could later spread and diversify into such a wide range of habitats, from the tropics to the highlands, deserts, and even urban environments where some species now live.
So the take-home message is not “science was wrong again” but rather “science is working as it should”. Each new finding gives us a sharper, more accurate picture of our evolutionary story — a story that remains completely at odds with creationist myth-making, but endlessly fascinating in its complexity.
Timeline of Primate EvolutionThe research is published in the Proceedings of the National Academy of Sciences of the USA, and is also summarised in a news release from the University of Reading.
- ~66 million years ago (end of Cretaceous) Dinosaurs (except birds) go extinct; mammals rapidly diversify.
- ~60–65 million years ago
Earliest proto-primates appear — small, nocturnal, tree-dwelling insect-eaters.- ~55–58 million years ago
First true primates (strepsirrhines) emerge, resembling modern lemurs and bush babies.- ~40–45 million years ago
Tarsiers and early monkeys split from the lemur line. Anthropoids (monkeys, apes, and humans) begin to develop larger brains and forward-facing eyes.- ~25–30 million years ago
Old World monkeys (baboons, macaques) and apes diverge from one another in Africa.- ~13–15 million years ago
Early great apes diversify across Africa and Eurasia; ancestors of orangutans, gorillas, and chimpanzees appear.- ~6–7 million years ago
Human lineage (hominins) splits from the chimpanzee lineage in Africa.- ~2–3 million years ago
Homo genus emerges, with larger brains and more sophisticated tools.- ~300,000 years ago
Anatomically modern humans (Homo sapiens) appear in Africa.
Early primates survived in cold, not tropical climatesThe article in The Conversation by Jason Gilchrist is reprinted here under a Creative Commons licence, reformatted for stylistic consistency:
Primates - the group of animals that includes monkeys, apes and humans - first evolved in cold, seasonal climates around 66 million years ago, not in the warm tropical forests scientists previously believed.
Researchers from the University of Reading used statistical modelling and fossil data to reconstruct ancient environments and trace where the common ancestors of all modern primates lived.
The study, published today (Tuesday, 5 August) in the journal PNAS, says these first primates most likely lived in North America in a cold climate with hot summers and freezing winters, overturning the long-held "warm tropical forest hypothesis" that has long influenced evolutionary biology.
For decades, the idea that primates evolved in warm, tropical forests has gone unquestioned. Our findings flip that narrative entirely. It turns out primates didn't emerge from lush jungles - they came from cold, seasonal environments in the northern hemisphere. Understanding how ancient primates survived climate change helps us think about how living species might respond to modern climate change and environmental changes.
Dr Jorge Avaria-Llautureo, lead author.
Ecology and Evolutionary Biology Division
School of Biological Sciences
University of Reading, Reading, U.K.
Moving to survive
Primates that could travel far when their local weather changed quickly were better at surviving and having babies that lived to become new species.
When primates moved to completely different, more stable climates, they travelled much further distances - about 561 kilometres on average compared to just 137 kilometres for those staying in similar, unstable climates. Early primates may have survived freezing winters by hibernating like bears do today - slowing down their heart rate and sleeping through the coldest months to save energy. Some small primates still do this - dwarf lemurs in Madagascar dig themselves underground and sleep for several months when it gets too cold, protecting themselves from freezing temperatures under layers of roots and leaves.
Primates didn't reach tropical forests until millions of years later. They started in cold places, then moved to mild climates, then to dry desert-like areas, and finally made it to the hot, wet jungles we see them in today. When local temperatures or rainfall changed quickly in any direction, primates were forced to find new homes, which helped create new species.
Publication:
Our primate ancestors evolved in the cold – not the tropics
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Japan’s famous snow macaques are an exception among primates today. But our early ancestors often lived through weather like this.
R7 Photo / shutterstock
Jason Gilchrist, Edinburgh Napier University
Most people imagine our early primate ancestors swinging through lush tropical forests. But new research shows that they were braving the cold.
As an ecologist who has studied chimpanzees and lemurs in the field in Uganda and Madagascar, I am fascinated by the environments that shaped our primate ancestors. These new findings overturn decades of assumptions about how – and where – our lineage began.
The question of our own evolution is of fundamental importance to understanding who we are. The same forces that shaped our ancestors also shape us, and will shape our future.
The climate has always been a major factor driving ecological and evolutionary change: which species survive, which adapt and which disappear. And as the planet warms, lessons from the past are more relevant than ever.
The cold truth
The new scientific study, by Jorge Avaria-Llautureo of the University of Reading and other researchers, maps the geographic origins of our primate ancestors and the historical climate at those locations. The results are surprising: rather than evolving in warm tropical environments as scientists previously thought, it seems early primates lived in cold and dry regions.
These environmental challenges are likely to have been crucial in pushing our ancestors to adapt, evolve and spread to other regions. It took millions of years before primates colonised the tropics, the study shows. Warmer global temperatures don’t seem to have sped up the spread or evolution of primates into new species. However, rapid changes between dry and wet climates did drive evolutionary change.
One of the earliest known primates was Teilhardina, a tiny tree dweller weighing just 28 grams – similar to the smallest primate alive today, Madame Berthae’s mouse lemur. Being so small, Teilhardina had to have a high-calorie diet of fruit, gum and insects.
The first primates were about the size of a mouse lemur: tiny.
Jason Gilchrist.
It is easy to see why scientists had assumed primates evolved in warm and wet climates. Most primates today live in the tropics, and most primate fossils have been unearthed there too.
But when the scientists behind the new study used fossil spore and pollen data from early primate fossil environs to predict the climate, they discovered that the locations were not tropical at the time. Primates actually originated in North America (again, going against what scientists had once believed, partly as there are no primates in North America today).
Some primates even colonised Arctic regions. These early primates may have survived seasonally cold temperatures and a consequent lack of food by living much like species of mouse lemur and dwarf lemur do today: by slowing down their metabolism and even hibernating.
Challenging and changeable conditions are likely to have favoured primates that moved around a lot in search of food and better habitat. The primate species that are with us today are descended from these highly mobile ancestors. Those less able to move didn’t leave any descendants alive today.
Over 56 million years, primates have evolved into all sorts of shapes and sizes.
Monkeys: Our Primate Relatives exhibition at the National Museum of Scotland. Jason Gilchrist
The study demonstrates the value of studying extinct animals and the environment they lived in. If we are to conserve primate species today, we need to know how they are threatened and how they will react to those threats. Understanding the evolutionary response to climate change is crucial to conserving the world’s primates, and other species beyond.
When their habitats are lost, often through deforestation, primates are prevented from moving freely. With smaller populations, restricted to smaller and less diverse areas, today’s primates lack the genetic diversity to adapt to changing environments.
But we need more than knowledge and understanding to save the world’s primate species, we need political action and individual behaviour change, to tackle bushmeat consumption – the main reason primates are hunted by humans – and reverse habitat loss and climate change. Otherwise, all primates are at risk of extinction, ourselves included.
To learn more about primate diversity, behaviour, and threats to their survival, see Monkeys: Our Primate Family, as the exhibition ends its international tour with a return to the National Museum of Scotland in Edinburgh.
Jason Gilchrist, Lecturer in the School of Applied Sciences, Edinburgh Napier UniversityThis article is republished from The Conversation under a Creative Commons license. Read the original article.
What this research really demonstrates is the strength of evolutionary science. Far from being static or dogmatic, science constantly tests, questions, and refines its conclusions as new evidence emerges. That willingness to update our understanding is precisely what makes it reliable — and why it has delivered an ever-more detailed account of our shared history.Significance
Textbooks often portray primates as originating, evolving, and dispersing exclusively within warm tropical forests. This tends to come from fossil evidence distributed across northern latitudes typically characterized as tropical. However, accumulating independent evidence suggests that nontropical climates were common across these regions during early primate evolution. By employing a geographic model capable of inferring ancestral locations within a phylogenetic framework while accounting for continental drift, we find that, contrary to widespread assumptions, early primates primarily inhabited cold and temperate climates. This research suggests that primates evolved and dispersed through diverse climates before becoming largely confined to modern warm tropical forests.
Abstract
One of the most influential hypotheses about primate evolution postulates that their origin, radiation, and major dispersals were associated with exceptionally warm conditions in tropical forests at northern latitudes (henceforth the warm tropical forest hypothesis). However, this notion has proven difficult to test given the overall uncertainty about both geographic locations and paleoclimates of ancestral species. By the resolution of both challenges, we reveal that early primates dispersed and radiated in higher latitudes, through diverse climates, including cold, arid, and temperate conditions. Contrary to expectations of the warm tropical forest hypothesis, warmer global temperatures had no effect on dispersal distances or the speciation rate. Rather, the amount of change in local temperature and precipitation substantially predicted geographic and species diversity. Our results suggest that nontropical, changeable environments exerted strong selective pressures on primates with higher dispersal ability – promoting the primate radiation and their subsequent colonization of tropical climates millions of years after their origin.
The idea that early primates—including both modern primates and those belonging to the broader Euprimates clade (1)—originated, radiated, dispersed, and thrived in the tropical forests, has been the dominant narrative for more than four decades (2–18). It is often reported that the primate radiation dramatically expanded, both geographically and taxonomically, in association with the global warming of the Paleocene–Eocene Thermal Maximum (PETM), when the range of the tropical forest presumably reached high latitudes in the Holarctic continents (3, 10, 17–22). We henceforth refer to these collective notions as the warm tropical forest hypothesis–i.e. that warm tropical forests have been instrumental in defining primate origins and evolution. The fact that the current distribution of extant primate species is largely restricted to a narrow range of tropical temperatures is also used to bolster support for the warm tropical forest hypothesis. However, current paleoclimatic evidence derived both from spore-pollen fossils and general circulation model simulations does not indicate tropical climates at the key locations where early fossil primates have been discovered or in the continents where they most likely originated (23–25). For example, climate reconstructions indicate that the Bighorn Basin and Chalk Butte in North America, as well as key fossil-bearing sites in Western Europe, were not tropical before and during the PETM (23).
The apparent discrepancy between the expectations of the warm tropical forest hypothesis and that early primate fossils are found in nontropical climates could stem from two factors. First, there are inherent temporal, spatial, and taphonomic biases in the fossil record. These biases have made the warm tropical forest hypothesis a longstanding challenge to evaluate. This is because the fossil record may tell us about the places, times, and, most importantly, the climates where fossilization was most likely—rather than where primates evolved and diversified. That is, a higher probability of fossilization in nontropical climates (26) could lead to the apparent lack of tropical climates in the early fossil record of primates. Second, despite the prevalent notion of warm tropical forest origins of primates, there is still considerable ambiguity in the terminology used to define and classify climate. Indeed, previous work on primate paleo-environments (27) has noted the extent of this issue: “it seems that every work on the paleoecology of ape’s environments adopts one or other of the numerous classifications of vegetation structure, never the same”. A nonexhaustive literature search retrieves at least 10 names associated with the type of climate where primates are proposed to have originated—all incorporating concepts like tropical, warm, and wet: tropical rainforest (17), tropical climate (3), tropical flora (16), continuous evergreen forest belt (18), tropical plants (10), lush forest (10), paratropical forest (17), tropical angiosperm biome (11), warm forest (12), and wet forest (12).
Here, we overcome the enduring difficulty of evaluating the warm tropical forest hypothesis through the resolution of those two main problems. First, we combine climatic inferences from the fossil record with inferences based on the location of common ancestors–i.e. internal nodes within the most recent and comprehensively sampled Euarchonta phylogeny (28). To do this, we use a modified version of the Geographic (Geo) model implemented in BayesTraits v5 (29, 30) that accounts for historical inhabitable environments (e.g. ancient seas)—as well as incorporating phylogenetic and topological uncertainty (Materials and Methods). Such an approach complements data derived from fossils and extant species locations as it can reveal hitherto unknown historical climates in unsampled regions where ancestral primates lived. Ancestral species could have dispersed over vast distances, potentially up to about 20,000 km in just 20,000 y (18), resulting in significant geographic and climatic differences between fossil sites and ancestral species locations. Second, after extracting geographic and climate data for fossils and ancestral species, it was essential to use a formal and standard climate classification criterion to make the hypothesis testable and reproducible, avoiding the ambiguity and complexity of climate definitions found in the literature. It is possible to achieve this by using climatic data derived from the Hadley center general circulation Coupled Model (Materials and Methods) (31–33) to classify the paleoclimates using the Köppen-Geiger (KG) classification system (34, 35).
Our approach brings the unique opportunity to explicitly and quantitatively test the various predictions made by the longstanding warm tropical forest hypothesis. If ancestral species evolved and relied on tropical forests for their dispersal, we would expect to find most early phylogenetic nodes to be reconstructed within the KG climate category Tropical (the type “A” climate, SI Appendix, Fig. S1 A and S1 B) (35). The Tropical climate category refers to an environment that is hot all year round with average annual temperature over 18 °C (34, 35). This climate includes multiple subcategories: Tropical Rainforest (wet), Tropical Monsoon (short dry season), and Tropical Savannah (distinct dry season), which each differ in the annual amount and pattern of rainfall (34, 35). Since the KG Tropical category encompasses a wide variety of subclimate categories, we are adopting a conservative approach in what constitutes a tropical climate. Furthermore, if early primates dispersed greater distances during the warmest global conditions of the PETM – when the tropical forests reached their widest latitudinal extension (17, 18, 20) – we would expect to observe a negative association between the total distance traveled across the globe for each species (pathwise, from root to tip—henceforth DPATHWISE) and time (SI Appendix, Fig. S1C). Similarly, we expect to observe a positive effect of global mean temperature on DPATHWISE (SI Appendix, Fig. S1 E). If early primates were also more speciose during the PETM, we would expect to observe a negative association between pathwise node count (the pathwise number of nodes, from root to tip, henceforth NCPATHWISE) and time (SI Appendix, Fig. S1D). NCPATHWISE can be regarded as a speciation rate metric (36). Finally, we should observe a positive effect of global mean temperature on NCPATHWISE (SI Appendix, Fig. S1F).
To test these predictions, we carried out phylogenetic generalized least squares (PGLS) models using DPATHWISE as the response variable, with time and global temperature as predictors. Then, we carried out phylogenetic generalized linear mixed models (37) (PGLMM) using the same predictors but using NCPATHWISE as response variable with a Poisson distribution (Materials and Methods).
J. Avaria-Llautureo, T.A. Püschel, A. Meade, J. Baker, S.L. Nicholson, & C. Venditti
The radiation and geographic expansion of primates through diverse climates Proc. Natl. Acad. Sci. U.S.A. 122(32) e2423833122, https://doi.org/10.1073/pnas.2423833122 (2025).
Copyright: © 2025 The authors.
Published by The National Academy of Sciences of the USA. Open access.
Reprinted under a Creative Commons Attribution 4.0 International license (CC BY 4.0)
For creationists, this is not good news. Each discovery pushes the timeline of life further back and shows ever more clearly how interconnected the living world is. The primate family tree stretches tens of millions of years into the past, leaving no room for a recent, miraculous creation. Instead, humans are revealed as part of a vast evolutionary story, one twig on a branching tree that also gave rise to lemurs, tarsiers, monkeys, and apes.
In the end, the story of our origins is not diminished by finding that our earliest ancestors may have survived in colder climates rather than tropical forests. If anything, it enriches our understanding, showing that resilience and adaptability were present in primates from the very beginning. That legacy of flexibility is what allowed our lineage not only to survive, but eventually to flourish across almost every environment on Earth.
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