11.6 Biological Complexity

135

complexity ratio is only 100. This value is extremely uncertain, however; a racehorse

could cost up to 100 times more, yielding a complexity ratio considerably exceeding

that of the fighter aircraft. Similar considerations apply to dogs and other animals.

The complexity ratio concept therefore appears to be less useful when applied to

living organisms.

11.6

Biological Complexity

It has long been a tenet of biology that there has been a gradual increase in phenotypic

complexity during the history of life on Earth ¹⁵; it is “what everybody knows”, ¹⁶

although hard evidence has been remarkably difficult to come by, not least because of

a lack of consensus regarding an appropriate definition of complexity (cf. Sect. 11.5).

Some of the most convincing, albeit narrowly focused, evidence thereof has come

from the painstaking study of the evolution of ammonoid sutures (Fig. 11.1; see also

Boyajian and Lutz (1992)), which rather convincingly reveals a gradual increase of

complexity followed by degeneration (simplification) preceding extinction.

More recent and comprehensively quantitative work has explored the hypothesis

that the accumulation of mildly deleterious mutations—which occurs according to

Kimura’s theory—leads to secondary selection for protein–protein interactions sta-

bilizing key gene functions in small populations. ¹⁷ The argument of this work is that

neutral drift of the genome and, in consequence, of the proteome leads to less sta-

ble proteins because of the occurrence of dehydrons (Sect. 15.5.2). The interactome

(Chap. 23) is then developed to restore stability, ¹⁸ which leads to the epiphenomenon

of complexity. Lest it be thought that complexity is automatically a beneficial evo-

lutionary trait, it should be pointed out that the prevalence of dehydrons in complex

organisms such as ourselves leads to diseases due to unwanted protein aggregation

such as Alzheimer’s and is likely to increase the likelihood of aneuploidy and can-

cer. On the other hand, this complexity appears to have been a prerequisite for the

emergence of our brains with the concomitant ability to reflect on these matters and

even, perhaps, find ways of overcoming the physiological drawbacks.

15 For example, Lynch (2007).

16 McShea (1991).

17 See Fernández and Lynch (2011) for full details.

18 Fernández Stigliano (2015).