Life on the Edge: The Coming of Age of Quantum Biology

Overview

The Coming of Age of Quantum Biology by Johnjoe McFadden and Jim Al-Khalili isn’t about pushing yourself to the limit, but rather exploring the surprising role of quantum mechanics in biological processes.

Key Concepts

The Quantum World Meets Biology

• Why quantum biology is surprising: Classical biochemistry treats molecules as tiny billiard balls governed by thermodynamics and Brownian motion; quantum effects (superposition, tunnelling, entanglement) were thought to be washed out by the warm, wet, noisy conditions inside living cells. McFadden and Al-Khalili argue that life has instead evolved to exploit quantum phenomena precisely because they confer functional advantages
  • The measurement problem in biology: Quantum coherence typically collapses on femtosecond timescales in warm environments; the central question is how biological systems might protect or harness coherent states long enough for them to matter functionally

Photosynthesis and Quantum Coherence

• Exciton energy transfer: In photosynthetic complexes (e.g., the FMO complex in green sulphur bacteria), absorbed photon energy must travel from antenna pigments to the reaction centre with near-perfect efficiency (~95%). Experiments using 2D electronic spectroscopy (Fleming lab, 2007) revealed long-lived quantum coherences in these complexes at physiological temperatures
  • Quantum walk: Rather than hopping randomly between pigment molecules (classical random walk), the exciton may simultaneously sample multiple pathways (quantum walk), arriving at the reaction centre faster and more efficiently, though the interpretation and biological relevance of these coherences remains debated
• Implications: If quantum coherence genuinely aids photosynthetic efficiency, it suggests that ~3.5 billion years of natural selection has optimised molecular architectures to exploit quantum mechanics, a profound intersection of physics and evolutionary biology

Quantum Tunnelling in Enzymes

• Proton and hydrogen tunnelling: Enzymes catalyse reactions at rates far exceeding what classical transition-state theory predicts; one proposed explanation is that protons and hydrogen atoms tunnel through energy barriers rather than climbing over them. The particle’s wave-function has a non-zero probability of appearing on the other side of a barrier that it classically could not surmount
  • Kinetic isotope effects: When hydrogen is replaced with the heavier isotope deuterium, reaction rates drop more than classical theory predicts, consistent with tunnelling, since the heavier particle has a shorter de Broglie wavelength and tunnels less efficiently
• Electron tunnelling in respiration: In the mitochondrial electron transport chain, electrons tunnel between iron-sulphur clusters and cytochrome complexes across distances of ~14 Å through protein medium, this is well-established quantum mechanics applied to bioenergetics

Magnetoreception, The Quantum Compass

• Radical pair mechanism: Some migratory birds (e.g., European robins) navigate using Earth’s magnetic field; the leading quantum hypothesis is the radical pair mechanism in cryptochrome proteins in the retina. Blue light excites a flavin-tryptophan radical pair whose singlet-triplet interconversion rate is sensitive to the orientation of the external magnetic field
  • Evidence: Behavioural experiments show that bird navigation is light-dependent (works under blue/green light, not red), disrupted by weak oscillating magnetic fields at radical-pair resonance frequencies, and localised to the right eye, all consistent with the cryptochrome hypothesis
  • Outstanding questions: Whether the quantum coherence time of the radical pair is long enough at physiological temperatures, and how the signal is transduced into a neural percept, remain open research problems

Speculative Frontiers

• Quantum olfaction: Luca Turin’s vibrational theory proposes that olfactory receptors detect molecular vibrations (via inelastic electron tunnelling) rather than just molecular shapes, explaining why molecules with similar shapes but different vibrational spectra can smell different. The hypothesis is provocative but lacks conclusive experimental support
• Quantum mutations: McFadden explores whether quantum tunnelling of protons along hydrogen bonds in DNA base pairs could cause tautomeric shifts that lead to point mutations, a quantum-mechanical origin for some genetic variation
• Consciousness and quantum biology: The book briefly touches on (but does not endorse) more speculative proposals linking quantum processes to consciousness (e.g., Penrose-Hameroff orchestrated objective reduction); the authors maintain a more cautious position focused on well-characterised quantum effects in specific molecular systems

Personal Reflection

On the one hand, the book is a fascinating exploration of how quantum mechanics might play a role in biological systems, challenging the classical view of life as purely chemical and thermal. On the other hand, some of the claims are speculative and not universally accepted in the scientific community. The discussion of photosynthesis and magnetoreception is compelling, but the more speculative ideas about quantum consciousness and olfaction should be taken with caution. Overall, it provides a thought-provoking perspective on the intersection of physics and biology.

Related Books

• Transformer - Lane explores deep chemistry; McFadden adds the quantum dimension, both argue physics shapes biology
• An Immense World - Yong describes bird magnetoreception; McFadden explains it via the radical-pair quantum mechanism
• What is Life? - Nurse asks what defines life; McFadden suggests quantum effects may be part of the answer

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Parent: Books