Global temperatures have been climbing steadily for decades, and biologists have long debated how much flexibility different species retain in the face of that pressure. Researchers at Trinity College Dublin have now published findings that suggest the answer may be far less than assumed.
The team reports the discovery of what they call a “universal thermal performance curve” — a single underlying pattern that, according to the announcement, governs how organisms across the entire tree of life respond to changes in temperature. The study, published in PNAS, draws on tens of thousands of previously separate performance curves gathered across thousands of species.
The pattern is consistent. Biological performance improves gradually as temperatures rise, peaks at an optimal point, then drops sharply once that threshold is passed. That steep decline after the optimum is the detail that carries weight: overheating moves quickly from reduced performance toward physiological breakdown.
One Shape, Every Species
What makes the finding notable is its reach. The curve holds whether researchers are measuring how fast lizards run on a treadmill, how sharks move through water, or how quickly bacterial cells divide. It applies to bacteria, plants, reptiles, fish, and insects alike. Each species has its own preferred temperature range — optimal temperatures in the dataset span from 5°C to 100°C — but the shape of the curve remains the same across all of them.
Professor Andrew Jackson, Professor in Zoology in Trinity’s School of Natural Sciences and a co-author of the study, described what the team found: “Across thousands of species and almost all groups of life including bacteria, plants, reptiles, fish and insects, the shape of the curve that describes how performance changes with temperature is very similar.”
He added that the relationship between peak performance and maximum survivable temperature appears fixed. “What we have shown here is that all the different curves are in fact the same exact curve, just stretched and shifted over different temperatures. And what’s more, we have shown that the optimal temperature and the critical maximum temperature at which death occurs are inextricably linked.”
Evolution Facing Hard Limits
Scientists had previously proposed many separate models to account for the variation in temperature responses observed across species. The new research collapses those into a single framework — and in doing so, points to a constraint on evolutionary adaptation that has not been widely recognized.
The implication, according to the study, is that evolution has limited room to maneuver. No species examined so far has managed to escape the shape of this curve. Jackson noted that above the optimum temperature, the viable range for survival becomes structurally narrower: “Whatever the species, it simply must have a smaller temperature range at which life is viable once temperatures shift above the optimum.”
With warming continuing across much of the planet, the study suggests species may face stronger limits in coping with future temperature increases than existing models have accounted for.
Senior author Dr. Nicholas Payne, also from Trinity’s School of Natural Sciences, noted that the conclusions rest on an extensive dataset spanning thousands of thermal performance curves drawn from across the tree of life.
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