Much like photosynthesis in plants, can human beings utilize light and water for their energy needs? New evidence suggests that it may be happening right now in each cell of your body.
In response to the title question, my answer is a definite “maybe.”
On the positive side, a recently published paper by Herrera et al. (1) argues that the answer is yes. The authors pinpoint melanin as the central player in the drama of photosynthesis, arguing that melanin, a black substance prominent in certain tissues, absorbs all visible wavelengths. Those concentrated photons could then drive the photosynthetic process in the same way as photons do in green plants and many single celled organisms.
The authors focus on the eye, which absorbs abundant light. They address a mystery of ocular function that remains unsolved: the retina stands as one of the most avid of the body’s consumers of energy; yet nearby capillaries are remarkably sparse, and therefore seemingly unable to meet those energy needs. Herrera et al. argue that the missing link could be melanin, which exists in unexpectedly high concentration in the eye. If melanin were a light antenna, collecting numerous photons, then that concentrated energy could drive metabolic processes just as they do in green plants. Melanin could resolve the energy problem.
Melanin exists not only in the eye, but also in many tissues. In a comprehensive review, Barr et al., (2) discuss many relevant features of melanin that support the authors’ hypothesis. First, melanin is an ancient protein, which may have been present at the inception of life. Second, its distribution is ubiquitous not only within, but also among, living organisms. Third, melanin in brain tissue increases with ascent up the phylogenetic ladder, reaching a peak concentration in man; it is invariably found in the brain’s strategic, highly functional loci. And, melanin responds to light, with semi-conductive properties. Hence, the provocative idea that melanin may be centrally involved in transduction of light energy into chemical energy gains traction from this evidence.
Our own work lends strong support to the idea that humans exploit light energy. Although we have not studied melanin, we have studied in considerable detail another light-absorbing substance that exists in higher concentration in the human body: water. Given water’s simplicity and pervasiveness through nature, many presume that water must be completely understood, but in fact little has been known about how water molecules organize themselves, and especially how they respond to light — until recently.
Students learn that water has three phases: solid, liquid and vapor. But there is something more: in our laboratory we have uncovered a fourth phase. This phase occurs next to water loving (hydrophilic) surfaces. It is surprisingly extensive, projecting out from those surfaces by up to millions of molecular layers. And it exists almost everywhere throughout nature, including our bodies.