Research published in the July issue of Trends in Immunology, shows how a more advanced immune system in humans could explain why the human genome may have only a slightly greater number of genes than the plant Arabidopsis thaliana, and probably less than rice, Oryza sativa.

The human genome is estimated to have as few as 30-45,000 functional genes, while  Oryza sativa has between 32,000 and 56,000 functional genes. The earthworm, Caenorhabditis elegans, has 19,000 genes and the plant, Arabidopsis thaliana has 25,000 genes.

Dr Andrew George, reader in molecular immunology at the Hammersmith campus explained: Although humans are normally thought to be considerably more complex than organisms, such as plants, rice, yeast and earthworms, this is not reflected in their number of genes - humans have less than other supposedly less complex organisms.

The limited number of functional genes in the human genome may be a result of the presence of a more advanced immune system designed to protect us from disease, the doctor pointed out. It is important that the cells of the immune system do not recognise our own tissues or cells, as this would lead autoimmune disease, he stressed.

The limited size of the human genome could make further evolution for humans difficult.  Fortunately, the human genome has been able to create genes which have multiple uses, thus making the best use of a limited number of genes, the doctor concluded.