(Attractiveness vs. Efficiency)

1 Introduction

In the natural world, there are particular instances of form and motion which are the direct result of a phenomenon known as sex. The exuberant display of colored feathers during courtship in some bird species is an example. Much of the amazing variety of form and motion in nature which has become such a basic part of our aesthetic lives can be traced to the need for organisms to reproduce sexually.

Many fish species possess body plans and coloration strongly adapted for sexual attraction, and exhibit elaborate displays of dance, often causing risk to their own safety, in order to attract mates. Can the need to attract mates in some species be demanding enough on the evolution of a body plan to adversely affect other needs, such as locomotion?

What is the importance of 'attractiveness' in evolution? In what ways does mate preference affect the overall fitness of individuals or species? While this paper does not attempt to address the deep questions concerning the subtle interactions between natural selection and sexual selection, it does offer a context in which to explore this subject, by describing a simulation which produces intriguing forms and motions, resulting from a simple form of mate choice. The hypothesis is that mate preferences for arbitrary features in phenotypes can inhibit the evolution of energy-efficient locomotion.

In this simulation, a population of coexistent organisms evolves optimized morphology and motor control for locomotion in a viscous fluid, through competition for mates and food. There is no distinction between male and female in this simulation(it is not meant to model sex, but simply to introduce mate preference as a factor in the evolution of physically-based locomotion.

In a preliminary version of this model, the criteria for choosing mates involved a minor genetic component. But for the sake of clarity in observing results, the genetic component was replaced with a set of pre-defined criteria for attractiveness, so that the results of different kinds of mate preferences could be studied and compared. The simulation demonstrates how preferences for specific phenotypic features in the bodies of potential mates can alter, and sometimes inhibit the optimization of energy-efficient locomotion in the population. The emergence of peculiar motions and forms is then observed qualitatively, compared with results of simulations in which organisms choose mates randomly.

2 Background

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