From the Editor – JASON KARP, PHD, MBA
Symmorphosis
In 2004, while working on my PhD in exercise physiology, I was assigned a research paper on evolution and the limits of athletic performance. I was asked to outline what I considered to be crucial evolutionary improvements in humans, when those traits first showed up in our evolutionary history and how they enabled humans to become a successful species, and how, given these evolutionary traits, I can explain and quantify human diversity to answer the question, “How does an understanding of evolution contribute to the understanding of human athletic achievement?”
I was given one week to write the paper.
Of course, it was a difficult paper to write. I highlighted traits like the opposable thumb, upright posture, enlarged neocortex, aerobic and anaerobic metabolic capacities, and the quantities of muscular force and mechanical power that can be generated and sustained, and then discussed them in light of evolutionary theories like Darwin’s natural selection, genetic drift and gene flow, divergence of character, and an esoteric anatomical theory called symmorphosis.
First proposed by Swiss anatomist Dr. Ewald Weibel in 1981, symmorphosis suggests that an organism’s structural design is regulated by its functional demand. As Weibel wrote, “…the quantity of structure incorporated into an animal’s functional system is matched to what is needed: enough but not too much.”
Weibel proposed that demand, which occurs over millions of years as the body interacts with its environment, drives a change in an organism’s structure. And any extra baggage is not supported and becomes extinct. From an evolutionary perspective, the human body can change, and the limits of human athletic performance can only be exceeded, if the demand on the human body increases.
One example of symmorphosis is the human lung, in which the structure of the lung’s alveoli—an ultrathin wall that’s scrunched up like a head of broccoli to maximize its surface area—is precisely matched to the body’s oxygen needs. It is neither under-designed nor over-designed for its function of oxygen diffusion into blood vessels, and any significant change in its structure would compromise its function.
Like the long, evolutionary process of symmorphosis that is experienced by a species to give us the lungs we now have, remarkable microstructural changes also occur on an individual level in the short term (weeks to months in our lifetime) in response to specific demands, physical training being the most potent.
For example, in response to specific physical training, the athlete’s muscle fibers increase their metabolic machinery, bones increase their density, cardiac and skeletal muscles enlarge, new blood vessels sprout around muscle fibers, and more neurons are formed that connect the central nervous system to muscle. Singularly and collectively, these structural changes, which are quite sensitive to imposed demands, enhance the athlete’s function. Indeed, the human body — and the structure of all organisms — evolves to cope with all but the most extreme demands to which it is subjected.
In this April 2025 issue of Track Coach, my first as editor, we remember symmorphosis and focus on the biomechanics of track and field, placing demands on the athlete’s structure (technique) to enhance his or her function.
