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14

The Nature of Living Things

Fig. 14.5 Waddington’s sketch of the epigenetic landscape (from C. H. Waddington, The Strategy of

the Genes: A Discussion of Some Aspects of Theoretical Biology, London: George Allen & Unwin,

1957; reproduced with permission). Some explanation is given in C. H. Waddington, Principles

of Embryology, New York: Macmillan, 1956: the spheroid represents a genotype and it has some

bias (which in a physical realization of the model could be achieved by departures from sphericity,

or an asymmetrical internal distribution of mass) corresponding to the particular initial conditions

in some part of the newly fertilized egg. The surface slopes down towards the observer and at the

saddle points (cf. Fig. 12.3 and the associated text), the genotype will move unpredictably to the left

or to the right. The endpoint of the sequence of bifurcations will correspond to some typical organ.

Waddington further proposed that the topography of the landscape, formed from a thin skin of some

material, arose through a layer of genes beneath it, attached with guy-ropes to various points on

the underside of the surface, the guy-ropes representing the “chemical tendencies which the genes

produce”

a very low fitness relative to other species. The most successful beings are likely to

be old and wise. Theupper KK-selective régime is the scenario for classical progressive evo-

lution, characterized by a primary rôle for increasingly specialized morphology in

adaptation, a tendency for size to increase, and hypermorphosis (the phyletic exten-

sion of ontogeny beyond its ancestral termination) enabled by delayed maturation.

This also applies to human beings, who in our currentlyupper KK-limited environment will

evolve as much as they can, within phylogenetic constraints, towards more sophis-

ticated forms. In this way economic growth can continue. Nevertheless, the human

population has grown to such an extent that resources are being used at such a rate that

some of them might actually be used up, for all practical purposes, in the near future.