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Form and function

Two sides of the same coin

Living systems are all different, but at the same time they have common characteristics. Some of them are always present, so that in some way they contribute to define our concept of life itself.

There is a common premise to these characteristics, and especially to our way of contemplating and telling them. It is the relationship between the form and function of a biological structure.

Biological systems have a structure, i.e. their parts are organized in space according to a precise scheme that connects them. The functioning of a biological system emerges because of this organization, which in turn evolves as a result of the biological processes that involve the system. Even more so, we can consider form and function as two sides of the same coin, two interdependent aspects that make us understand different things about a system, and affect each other at different stages of a process.

Biological systems have multiple organizational levels, and the relationship between form and function is realized in each of them: from molecule, to cell, to group of cells, and so on.

The diversity of structure underlies a diversity of function. In an organism composed of many cells, there are different cell types, i.e. different functional specializations for different cells that have different roles in contributing to the organism's life. The set of these different cells makes up the structural and functional complexity of an organism, where different interdependent functionalities result in an overall functionality. Such functional diversity corresponds to an equally rich structural diversity.

Each cell is specialized to perform a number of functions. When comparing two cells that perform different functions, their morphological difference, i.e. relative to form or structure, is often also evident. For example, a squamous epithelial cell has a flat shape, which allows the formation of layers of cells with a covering and protective function, such as that of the epithelium, i.e. the skin layer in contact with the outside.

(Squamous cells - Wikimedia commons)

A neuronal cell, on the other hand, has branched structures of different types to allow the exchange of signals with other nerve cells.

(Diagram of a complete neuronal cell - Wikimedia commons)

This great diversity of cell types within an organism has emerged during evolution, creating a variety of functions that are increasingly broad and effective in responding to the challenges posed by the environment to the organism.

In this process of mutation and selection, selective pressure is exerted on function, not directly on structure.

In fact, the organisms that stand out in evolutionary competition are those that are best suited to the environment in which they are located. These organisms structure themselves, generation after generation, supporting the functional capacity that makes them evolutionary advantaged.

Since different environments sometimes present similar evolutionary challenges, the same functionality is selected positively several times, throughout the evolutionary history, because it responds effectively to these challenges. This means that structural solutions that nature brings out have very different starting points, but become similar during evolution.

This is the case of convergent evolution, i.e. the process (defined in evolutionary biology) whereby organisms that are not closely related evolve, independently, similar traits. This results from the need, which they share, to adapt to similar evolutionary environments or niches.

An example of this phenomenon is the similarity between the structures of pterodactyls, insects, birds and bats for flying. All of them perform the same function of "wings", and to do so they are articulated in very similar structures, but they do not derive one from the other:evolutionally: they have evolved independently.

(© Sinauer Associates 2001 )

Looking at biology from the perspective of the relationship between structure and function, it can become a catalogue of optimal solutions to inspire engineering problem-solving and design. Biomimetics indicates the transfer of biological processes from the natural to the artificial world, making the imitation of solutions found by evolution a real design process.

Nature is of great inspiration to find new technological and design solutions to formalize and implement. However, it is fundamental, in order to admire biological systems in their complexity, to understand that they do not derive from the implementation of a rational design aimed at solving a problem. Rather their functional, and therefore structural, complexity emerges through processes of random mutation and natural selection without guidance. These processes are in fact local and distributed, i.e. they are not related to any intelligence that coordinates them, but happen depending on the specific circumstances in which the organisms find themselves at a specific time, and depending on what has happened before. This makes the beautiful - and functional - forms of nature even more interesting.

Roberta Bardini is a researcher in computational Biology and systems. She currently works at the Sysbio Group, Polytechnic of Turin, where she obtained her PhD. She deals with the development of multicellular organisms, and their enhancement in the business environment.
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