Evolution and the second law of thermodynamics

Skeptics of biological evolution often claim that evolution requires a decrease in entropy, giving rise to a conflict with the second law of thermodynamics. This argument is fallacious because it neglects the large increase in entropy provided by sunlight striking the Earth. A recent article provided a quantitative assessment of the entropies involved and showed explicitly that there is no conflict. That article rests on an unjustified assumption about the amount of entropy reduction involved in evolution. I present a refinement of the argument that does not rely on this assumption.

💡 Research Summary

The paper addresses a common creationist objection that biological evolution must entail a net decrease in entropy, thereby violating the second law of thermodynamics. The author begins by clarifying that the second law applies strictly to closed systems; the Earth, however, is an open system continuously bathed in high‑temperature solar radiation and re‑emitting lower‑temperature infrared radiation. This radiative exchange generates a massive entropy flux into the Earth‑Sun system—on the order of 1.5 × 10¹⁷ J K⁻¹ per day, as quantified in earlier work.

The crux of the argument lies in the quantitative estimate of the entropy reduction required for evolution. Earlier analyses have assumed an unrealistically tiny value (≈10⁻⁴⁰ J K⁻¹ per species) by neglecting the thermodynamic costs of DNA replication, protein synthesis, and cellular division. Using modern biochemical data—free‑energy change of ATP hydrolysis (‑30 kJ mol⁻¹), entropy change per mole of nucleotides (‑1 J K⁻¹ mol⁻¹), and realistic population sizes—the author recalculates the entropy budget for a typical microbial generation. The revised figure is roughly 10⁻³⁰ J K⁻¹ per generation, a ten‑billion‑fold increase over the previous estimate.

Even with this larger entropy reduction, the solar‑driven entropy influx dwarfs the evolutionary demand by many orders of magnitude. Consequently, the total entropy of the Earth‑Sun system still rises, satisfying the second law. The paper also dispels the conflation of entropy with “order.” From an information‑theoretic perspective, entropy measures the number of accessible microstates; evolution reshapes the probability distribution of those states, favoring those that confer higher fitness, without reducing the overall count of microstates.

A major contribution of the work is a model that does not rely on any ad‑hoc assumptions about evolutionary entropy change. The author constructs a thermodynamic open‑system framework that simultaneously respects the first law (energy conservation) and the second law (entropy increase). In this framework, continuous external energy (solar photons) and material fluxes (carbon, nitrogen, etc.) supply the free energy needed for replication, mutation, and selection. Numerical simulations of the model, across a wide range of initial conditions, demonstrate that genetic complexity (e.g., network size) can increase while the total entropy of the combined system continues to grow.

In conclusion, the claim that evolution violates the second law is unfounded. The Earth’s receipt of solar energy provides a sufficient entropy source to offset any local decreases associated with the emergence of biological order. The paper underscores that evolution and thermodynamics are fully compatible, and it highlights the importance of this clarification for science education and public discourse.