If there is one thing that all biologists agree on, it is that homeostasis is essential for life. You might reply that this sounds all very well, but what does it mean? We soon realize however that the issue is important for understanding living organisms when we hear that homeostasis is a unique property of living organisms without which the organism dies or never was able to live in the first place.

Suppose we consider a single cell. In order to live, it needs to maintain its interior with conditions that are ideally suited to its life processes. Outside the cell, the environment may be subject to major shifts in conditions, many of which are unfavourable to life. Inside the cell, however, the life processes need close to ideal conditions. Obviously, the interior of the cell needs protection, provided by a cell (plasma) membrane. But how does the cell membrane protect the interior? It has to be very selective as to what products it allows to enter the cell, and what products it encourages to exit the cell.

The cell membrane thus is a major contributor to homeostasis, a dynamic process that can change internal conditions as required to survive external challenges. The problems faced by the cell membrane mean that it needs multiple fancy proteins which penetrate through the membrane. These proteins allow for passage through the membrane of certain very specific products. In order to maintain interior stability, the cell/organism needs the complex interactions of multiple feedback systems. Thus the membrane gateways are not just passages for products.  Homeostasis of a cell or even of a whole organism is a complicated process.

From the 19^th century on, some biologists reflected on the amazing property of living organisms to maintain interior ideal conditions. An American physiologist Walter Cannon (1871-1945) coined the term homeostasis from two specially chosen Greek words. He chose homoios, meaning “similar” and stasis meaning “standing still.” He wanted to communicate that by means of feed-back controls, conditions inside the cell keep reverting to close to ideal.

The interesting thing about homeostasis is what it tells us about the origin of the living cell (and by extension all organisms). In view of the fact that organisms cannot live without homeostasis, which involves a lot of precise proteins working closely together, this means that without a lot of initially provided information and systems in the cell, there never was any life. A French physiologist from the mid-19^th century pointed out that: “the stability of the ‘milieu interieur’ [cell interior] was antecedent to (i.e., required for) and not the consequence (outcome) of a free and independent life.” [cited in George E. Billman. 2020. Homeostasis: the Underappreciated and Far Too Often Ignored Central Organizing Principle of Physiology. Frontiers in Physiology vol 11 pp 1-12  doi:10.3389/fphys.2020.00200  see p. 4]

There you have it!! No cell can live without the massive information content and complex controls of homeostasis. The cell could not develop gradually, with a lipoprotein membrane first organizing itself around some pre-cellular contents (because the system would soon be overloaded with waste or lack of resources). It has to be complete from the start, or dead!

Nevertheless, since few biological articles these days omit a favourable mention of evolution, this physiologist included the remark: “it took time to appreciate that natural selection provided the means by which regulatory control could evolve.” [p. 4] He did not say anything more on this topic like how this could happen. Since natural selection only works on systems that are fully functional, this remark by Dr. Billman does not communicate any insights about origins to us. Of course, he had already stated the opposite idea, that the cell had to exhibit fully functioning homeostasis if it were to be living at all.

So, homeostasis provides dramatic testimony that the living cell was created and did not evolve. This indeed sums up the whole message of cell biology.

Related Resources

Origin of Life: the Problem of Cell Membranes (YouTube,  11 min)