Effect of Size on Virtual Population Growth
Purpose: Observations of growth rates of wild populations of hundreds of species of fish, insects, birds and mammals show growth rates fall as population density increases, the fall expressible as a simple mathematical curve suggesting a single simple mechanism. Surprisingly, the curve is concave upward instead of falling steeper as the carrying power of the environment is approached. This suggests some mechanism lying at the very heart of evolution and genetics. We used computer programs to test various genetic mechanisms for this effect, using well known laws of inheritance.
Method: Programs were written in C++ language. A population would be modeled. Members of the population would have gene sites subject to various kinds of deleterious mutations, in particular recessive lethal mutations and mutations that detuned part of the genome against another part. Genes were passed on randomly assorted, non-randomly assorted or bound on chromosomes without crossing-over. Mates were selected at random, offspring generated, genes mutated and a new generation established. This was repeated for a number of generations and the results examined.
Results: It was possible to establish a set of parameters including both recessive lethal mutations and mutations producing detuning of one part of the genome against the other all strictly bound on two homologous chromosomes, which set of parameters produced growth rates at various population sizes (for population densities) that paralleled observations.
Conclusion: Work with anopheles mosquitoes has found that speciation genes occur in regions without crossing over. Our computer simulations showed this as well, encouraging us to think our crude model is an approximation of reality. If this is true, it must be a general principle. That implies that evolution has maximized complexity in order to maximize fitness, and the total mutational load of most populations has maximized. This may cause punctuated equilibrium.