(published in: From Animals to Animats (page 484) 1996, MIT Press)

Sexual Swimmers

Emergent Morphology and Locomotion Without a Fitness Function

Jeffrey Ventrella


A virtual ecosystem is described which demonstrates emergent morphology and locomotion among a population of 2D figures in a virtual pond. A physics model enables a large variety of articulated figures to potentially propel themselves through simulated water. Swimmers with better skills at locomotion and turning are able to eat more food to gain energy and mate with other swimmers, thereby supplying more "fit" genetic building blocks to future generations. There is no fitness function used in this genetic algorithm scheme: fitness equals reproduction. Sexual selection is also modeled: genetically inherited preferences for mate color affect the distribution of phenotypes across the pond: swimmers of differing colors infrequently mate with each other, often breaking the population into distinct coloration groups. To witness the emergence of behavior on local scales (swimming styles), intermediate scales (family dramas), and global scales (population dynamics), this simulation can be viewed with an interactive "microscope" for panning and zooming. This work demonstrates how local behavior can affect (and be affected by) global behavior, and how these different levels of behavior evolve together.

1. Introduction

2. Related Work

3. The Swimmer World

4. Swimmers

5. Mate Preference

6. The Physics of Motion

7. Running Simulations

8. Future Work

9. Conclusion