Abbreviations BMC -Biomedical CenterBMC GSTSE -Biomedical Center globally subtracted, tumor-specifically expressed BMC GSTSE-X non-coding sequences -Biomedical Center globally subtracted, tumor-specifically expressed non-coding sequences located on X chromosome CDD -computer-assisted differential display CT antigen gene -canser/testis antigen gene TSEEN genes -tumor specifically expressed, evolutionarily novel genes Ma -million years ago PPOD -Princeton Protein Orthology DatabaseCT-X antigen genes -CT antigen genes located on X chromosome Abstract Earlier we showed that human genome contains many evolutionarily young or novel genes with tumor-specific or tumor-predominant expression. We suggested to call them TSEEN genes, i.e. Tumor Specifically Expressed, Evolutionarily New genes. In this paper we performed a study of the evolutionary ages of different classes of human genes, using homology searches in genomes of different taxa in human lineage. We discovered that different classes of human genes have different evolutionary ages and confirmed the existence of TSEEN gene classes. On the other hand, we found that oncogenes, tumor-suppressor genes and differentiation genes are among the oldest gene classes in humans and their evolution occurs concurrently. These findings confirm predictions made by our hypothesis of the possible evolutionary role of hereditary tumors.