Researchers discovered a universal temperature curve that governs how temperature affects biological performance across all life studied so far. No species has escaped the constraints this curve imposes.
Every organism has a thermal performance curve — a function relating temperature to some rate process (growth, metabolism, locomotion, reproduction). These curves share a shape: performance rises with temperature, peaks, then crashes. The rise is gradual; the crash is steep. The asymmetry is universal.
The conventional view was that evolution could reshape this curve — that organisms adapting to extreme environments would develop fundamentally different thermal responses. They don't. Thermophilic bacteria, Antarctic fish, desert lizards, and tropical insects all obey the same functional form. Evolution shifts the curve's position along the temperature axis (where it peaks) but cannot alter its shape (how it rises and falls).
The constraint is thermodynamic, not genetic. Enzyme kinetics set the rising phase: reaction rates increase with temperature following the Arrhenius equation. Protein denaturation sets the falling phase: above a threshold, three-dimensional protein structure unfolds. The asymmetry — gradual rise, steep fall — reflects the difference between these two processes. Activation energy is continuous; denaturation is cooperative.
Evolution can move the peak by modifying protein stability — making enzymes that denature at higher temperatures. But it cannot change the fundamental shape because the shape is dictated by physics, not biology. The curve is not a biological fact. It is a physical law that biology inherits and cannot override.
The boundary between what evolution can change and what it cannot is the boundary between biology and physics.