Life consists of cells. All cells consist of DNA; they divide, breathe and communicate. The basic functions have remained astonishingly conserved during evolution. Genomic research is revealing to a growing extent that individual molecular constituents have also repeatedly been used during evolution. In many cases, it is possible to achieve insights into how proteins are transported in our own body cells when looking at the protein transport mechanisms in yeasts and fruit flies, for example. Experiments involving sepia or rats provide us with information on how the human neurons function. This might even pave the way for the development of methods for the treatment of diseases. The nutrition industry is one area that can make use of biological processes. Researchers are using model organisms for their research in all areas of biology. These organisms help the researchers to come to well-founded conclusions about humans without requiring experiments to be carried out on actual human beings.

Drosophila melanogaster, which is commonly known as fruit fly, also has a short generation time. The Drosophila genome is also very small and has only about 140 million base pairs. These two aspects make fruit flies excellent experimental objects for studies in genetics. In addition, fruit flies are multicellular organisms with different tissues and a nervous system, and hence more similar to humans than yeast. Between 1910 and the 1950s, Drosophila was used by famous geneticists such as Thomas Hunt Morgen to clarify the basic principles of inheritance. Over the last few years, Drosophila has also been used to study aspects of neurobiology or embryonic development. The threadworm Caenorhabditis elegans is another popular experimental organism, particularly amongst developmental biologists, due to the identical number of cells in adult threadworms (cell number constancy). Adult hermaphrodites always have 959 cells, adult males 1031 cells. The origin of the cells can be accurately followed from the fertilised egg cell. Transparent threadworms are excellently suited for the study of the mechanisms of programmed cell death (apoptosis), which is why they play an important role in ageing research.

The situation is similar for scientists investigating the human hepatitis B virus (HBV). HBV normally only infects apes and humans, neither of which can be used in experiments for ethical reasons. The exotic tree shrews (Tupaia) are a solution to this problem since they are the only known animals outside of the hominids that can serve as hosts for viruses. It is for this particular reason that Tupaia might well become a model organism in the future. This example is a perfect illustration of the fact that it is not only conventions, but often also the scientific problem that determines which organism is particularly suitable as a study object.