**Botany online** 1996-2004. No further update, only

- Growth, Reproduction Rate
- Regulation of the Population Size,

Capacity of the Habitat, Density-Dependent Growth,

r- and K-Strategies - Competition
- Mutation, Gene Flow, and Recombination. Drift and Selection
- Polymorphism, Genetic Load
- An Attempt of Population Genetics Considering Selection and Fitness
- Literature

The examples discussed in the previous topics helped to illustrate evolutionary processes. The results of many experiments show that certain properties provide the individual organism with a real selective advantage over those individuals lacking this property. The often quick dispersal of new genotypes hints at an enhanced fitness of these genotypes as compared to their predecessors. How are fitness and selection connected, how are they defined, and what mathematical formulations are required for the quantification of a given selection and for making up models that help to predict the success of a given strategy?

The English mathematician and geneticist R. A. FISHER (1890 – 1968) developed the necessary mathematical aids during the 1920^{th}. The American S. WRIGHT (1889 – 1988) gave further decisive imputs.

Evolution can be regarded as a change of the genetic constitution of a population. Two independent reflections allow the understanding of selection and fitness:

- It is necessary to have a good look at reproduction rates and growth functions.
- The basis for further calculations have to be the HARDY-WEINBERG formulas of population genetics.

A theory of natural selection has to consider the growth rate, the mortality, the size of the population, the capacity of the habitat, and the laws of genetics. This is the only way to organize experimentally collected data in a calculable formula helping to understand the changes of a species in regard to its environment.