The Constructal Law, Feedback Mechanism in Evolution and the Challenge of Selfish Genes – An Opinion

I stepped into a little bookstore to buy a book to read on the train.  The choices were very limited. After tossing a few eye-catching titles up in my mind I finally decided to buy one of them. That book was “Design in Nature” by Adrian Bejan and J. Peder Zane and published by Doubleday, 2012. Undoubtedly, it proved to be one of the most thought provoking books I ever bought. It was about the concept of Constructal Law formulated by Prof. Bejan and colleagues about the limited design choices available in Nature. It took some reading before I could understand what the Constructal Law is all  about. In essence, it tells us that Nature follows the path of energy efficiency and thus, limits the choices available for flow systems. For an example, a fast flow needs a longer path than a slow flow requiring a short distance. Big streams are wide and deep while the small ones are narrow and shallow. Larger athletes swim and run faster. According to the authours, flight of the birds, the running of an athlete and the floating of a swimmer are guided by the same set of rules. Despite broadness of its definition or not having a proper definition for that matter, the Constructal Law encapsulates a very intuitive truth about our daily experiences. Various people using different concepts in the past such as the path of least resistance or maximizing energy efficiency attempted to explain limitation in design choices in Nature. The authours brought all the past explanations under one term Constructal Law.

In many ways, the Constructal Law as stated by the authours can be construed as the Nature’s attempt to balance opposing forces to ensure the most energy efficient path. In case of fast flowing water on the surface, there is a match between the flow and the resistance of the soil. The result is branching off of the original flow. We can call this the path of least resistance. This is not very different from the hierarchies the authours talk about. Social hierarchies represent the dynamic structure imposed by the Nature. One chief needs many subordinates under him or her. Then these subordinates need more people under them for efficient functioning. Large research groups occur in large universities and individual researchers based at small universities would find a balance by moving towards the large groupings (p220).

Unfortunately, I felt that in some situations, the authours tried too hard to fit too many systems into their worldview. For an example, they looked at tree canopies in terms of water uptake by the tree (p.142). This led to their conclusion that the branches of a tree are arranged in a spiral in order to maximize the flow of water. But we can equally argue that it was the maximization of the absorption of sunlight that was far more important to the tree. Sunlight is only available during the day and thus, maximum utilization of it should be logically far more important to the plant than the maximizing water flow which still can happen when there is a humidity potential. Thus, it may not be a matter of flux but a Nature’s way of maximizing energy efficiency.

Even if the Constructal Law exerts its influence on the evolutionary choices, the contingencies Stephen Jay Gould talks about in “Wonderful Life” still applies; the path of the evolution might have taken a different twist despite the fact that the choices are limited by the Constructal Law (p.77). As an example, evolution didn’t have to produce humans. It could have had a different ending depending on alternative set of chances and the evolutionary path chosen.

However, there are few important implications of Constructal Law, which change the way we look at the theory of evolution. According to the authours, all flow systems, over time, should evolve into designs that facilitate their movement (p124). The evolution is about modification in design that has a predictable direction (p102). Thus, at least at an intuitive level, the design constraints imposed by the Nature should have accelerated the evolutionary process. But according to current theory of evolution, the natural selection had to try possibilities the Nature wouldn’t allow. A blind process wouldn’t know until it tried what is allowed and what isn’t. Thus, based on usual arguments, all possible phenotypic expressions of alleles can arise and only the suitable designs can survive. Unfortunately, given the design constraints, this is a very energy-inefficient process. Thus, Constructal Law hints at the possibility of linking a feedback mechanism into Modern Synthesis. As Constructal Law shows, the Nature is trying to do the maximum with the least effort. Nature, in other words, looks for the energy efficient path[1]. Thus, to prevent unnecessary trials and costly errors, Nature has the option of using feedback to confine the selection to a small set of choices. The challenge for us is to find the mechanism underlying such a feedback loop. In higher mammals at least, a feedback loop through conscious selection can happen.

However, the possibility of such a mechanism seems to challenge the selfish- gene hypothesis. The feedback is very unlikely to be conducive to the cause of a gene desperately trying to maximize its chances of survival. The feedback should be about the organism or the vehicle, not the gene or the replicator. As an example, let us use a thought experiment. If an organism is short, all the other features within that organism should work in tandem to provide the overall energy efficiency. But it still has all the genes that produce its taller siblings. Thus, by some conscious process, let us assume that, the shorter mates are preferred by shorter organisms and the gene frequencies drift towards shorter version. So this conscious process of mate selection can be true for many animal species, at least for them, natural selection is not really natural. For an example, human brain development, according to various anthropologists, was impacted by autocatalytic process of mate selection[2]. Thus, the whole organism with its genes working in tandem will be selected. Thus the unit of selection is not one replicator but a collection of replicators working in tandem; rather the vehicle[3] . Design, in short, is a feature of the entire organism not the gene itself as the design by definition in this case applies to the organism or a part thereof. If the design is mal-adapted to the environment, then the organism should go extinct. Thus, the genes also perish. They perish not because they didn’t try to maximise the inclusive fitness via replication but they failed to produce the suitable design for the vehicle by working in tandem. Given the very high possibility of existence of a law limiting the possible choices in flow systems, the organismic view of evolution has the upper hand. Even though Prof. Bejan and colleagues are trying to show none of the views on evolution, apart from the predictability of design choices, shall feel the impact of design constraints, it is somewhat unlikely that they can succeed. But, on the otherhand, why shouldn’t they challenge the modern views on evolution as science only can progress through establishing facts and Laws rather than fighting over theories?

I highly recommend “Design in Nature” by Bejan and Zane for anyone who is interested in reading something stimulating.

[1] This reminds me about my own view of evolution based on energy efficiency. (Appendix , The lure of NOMA, On the elegance of religion, Ocean Publishing, 2009)

[2] See the article on this web site about cranial capacity data

[3] If you are so adamant, you still can argue that it is the gene not the vehicle.


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The website aims to show the possible origin of religion through a ‘uniquely’ human process which has links to the seclusion of girls at puberty. It also advocates the view that the Paleolithic Venus figurines are related to these puberty rites and hence, the prehistoric Venus figurines may carry a much larger meaning. Thus, Religion is something more than a throwback from our animal past.
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