…endless forms most beautiful

Ch. Darwin, “Origin of Species”

Have you ever wondered how a rose “knows” how many petals it should have or how the zebra stripes are traced? You might most probably say, “The genome is an answer.” But think what a vast distance lies between the sequence of DNA and the actual revelation of an organism to the world as a whole being. 

This question riddled the brightest minds throughout the centuries. And not only among biologists or chemists, the famous mathematician Alan Turing also could not resist the appeal of the mystery and proposed his own theory claiming having solved it. Of course, he did not, as it became apparent quite soon, although ideas presented in his paper “The Chemical Basis of Morphogenesis” are still used in many applications. 

If you choose to believe Francis Crick, one of the discoverers of DNA double helix, and his words at some meeting on mathematical modeling, Turing once said, referring to zebra, “Well, the stripes are easy, but what about the horse part?” Obviously, he himself suspected that there is much more to it than just reaction and diffusion.

Turing’s famous paper was published in 1952, almost at the same time Belousov noticed an interesting reaction which was also destined to bring a lot of new answers and even more questions about development of the form by denying the absolute reign of the equilibrium thermodynamics, portending the advance of the non-equilibrium one heralded later by Ilya Prigogine.

So, what can be in common between modern scientists, as ones we introduced above, and ancient Greek philosophers? The answer is a bit concerning. In his article Deichmann talks about a surprisingly good preservation of the ancient dispute concerning development: What comes first, nature or nurture, in the development of forms we possess as living beings? 

It appears that two sides of this battle were defined even long before the common era and arrival of the current scientific worldview together with the crucial discoveries (unity of inanimate and animate, nature of hereditary information carriers, etc.) These views are namely of preformation (Democritus) or epigenesis (Aristotle). 

The proponents of preformation thought that an organism develops from a set of already existing “instructions” contained in some entity. In our case we are talking about genome, but ancient Greek philosophers just considered it to be a kind of “seed”. No matter the terminology the idea is that the form of an organism is totally encoded in these instructions.

Epigenesis[1], on the other hand, states that the form of an organism is realized through the influence of the environment on an initially “featureless substance”; thus, form is the result of the interplay of different physical parameters. It, therefore, places the origin of the form of an organism outside the said organism. It appears that modern proponents of neo-Darwinism are much more loyal to this concept as they extensively rely on “chance” in the formation of an organism. It is funny because Darwin disliked speaking about chance in his works.

One would think, as I did before reading this article, that scientists long ago came to a compromise concerning development where “preformation” and “epigenesis” are balanced and have their own realm each. But this is not the case, and the battle still rages on. In case you are interested in joining it or just observing from the side, you can find ample food for thought in the article “Contrasting philosophical and scientific views in the long history of studying the generation of form in development” by Ute Deichmann.

Article by Lyubov Vassilets

[1] Here I should underline that it is necessary to keep in mind that Epigenesis as described here is not in direct relation to epigenetics. Epigenesis is rather a philosophical concept (you can call it “nurture” in the famous “nature-nurture” dichotomy), dealing with general principles, intrinsically unquantifiable. Epigenetics is a branch of science dealing with modifications of proteins and nucleic acids affecting gene expression

The source article:
https://www.sciencedirect.com/science/article/pii/S030326472400145X