ABSTRACT
The thesis that hormones are tokens of evolutionary (selective) pressures is substantive only if the gradient driving the dynamics along the Z https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780429026508/4614e5f6-5f02-45e5-afec-5950c67b94fb/content/inline-math7_501.jpg"/> -coordinates is necessarily proportional to an analogous gradient in the ‘fitness’ landscape. Prior to defining the latter, the concept of fitness is explored in the present chapter. We argue that ‘empirical fitness’ is most appropriate for the present purposes as it allows us to associate an upper bound to attainable fitness to elements of X https://s3-euw1-ap-pe-df-pch-content-public-p.s3.eu-west-1.amazonaws.com/9780429026508/4614e5f6-5f02-45e5-afec-5950c67b94fb/content/inline-math7_502.jpg"/> which in turns justifies the variational principle that was the starting point in Chapter 3. Thus, provided that biological regulation operates like a gradient system (the necessity of which remains an open question), the potential function will share its major features with the fitness landscape.
