Chapter 2 – Orientation for the Bio-Curious  47

of enormous complexity called emergent structures, which often have properties that are

difficult to predict from the fundamental simple sets of rules of individual interacting units.

There is good evidence that although evolution is driven at the level of DNA molecules,

natural selection occurs at the level of higher-​order emergent structures, for example,

cells, organisms, colonies, and biofilms. This is different from the notion that higher-​order

structures are simply “vehicles” for their genes, though some biologists refer to these emer­

gent structures as extended phenotypes of the gene. This area of evolutionary biology is still

hotly contested with some protagonists in the field formulating arguments, which, to the

lay observer, extend beyond the purely scientific, but what is difficult to deny is that natural

selection exists, and that it can occur over multiple length scales in the same organism at the

same time.

The danger for the physicist new to biology is that in this particular area of the life sciences,

there is a lot of “detail.” Details are important of course, but these sometimes will not help

you get to the pulsing heart of the complex process, that is, adaptation from generation to

generation in a species in response the external environment. Consider, instead, an argument

more aligned with thermal physics:

KEY POINT 2.15

Biological complexity is defined by local order (e.g., more complex cellular structures,

or even more complexity of cells inside tissues, or indeed more complexity of individual

organisms within an ecology) implying a local decrease in entropy, which thus requires

an energy input to maintain. This is a selective disadvantage since competing organisms

without this local increase in order benefit from not incurring a local energy loss and

thus are more likely not to die (and thus reproduce and propagate their genetic code).

Therefore, there has to be a good reason (i.e., some ultimately energy gain) to sustain

greater complexity.

This, of course, does not “explain” evolution, but it is not a bad basis from which the physi­

cist has to start at least. Evolutionary change is clearly far from simple, however.

One very common feature, which many recent research studies have suggested, which

spans multiple length scales from single molecules up through to cells, tissues, whole

organisms, and even ecologies of whole organisms, seems to be that of a phenomenon known

as bet hedging. Here, there is often greater variability in a population than one might normally

expect on the grounds of simple efficiency considerations—​for example, slightly different

forms of a structure of a given molecule, when energetically it may appear to be more effi­

cient to just manufacture one type. This variability is in one sense a form of “noise”; however,

in many cases, it confers robustness to environmental change, for example, by having mul­

tiple different molecular forms that respond with different binding kinetics to a particular

ligand under different conditions, and in doing so that organism may stand a greater chance

of survival even though there was a greater upfront “cost” of energy to create that variability.

Unsurprisingly, this increase in noise is often seen in systems of particularly harsh/​competi­

tive environmental conditions.

Note that although natural selection when combined with variation in biological properties

between a competing population, at whatever disputed length scale, can account for aspects

of incremental differences between subsequent generations of cell cycles and organism life

spans, and ultimately evolutionary change in a population, this should not be confused with

teleological/​teleonomic arguments. In essence, these arguments focus on the function of a

particular biological feature. One key difference in language between biology and physics is

the use of the term “function”—​in physics we use it to mean a mapping between different sets

of parameters, whereas in biology the meaning is more synonymous with purpose or role. It is

not so much that new features evolve to perform a specific role, though some biologists may

describe it as such, rather that selective pressure results in better adaptation to a specific set

of environmental conditions.