A study published in *Nature Genetics* (2015) identifies two clock-like mutational processes in human somatic cells. These processes generate mutations at a steady rate throughout life, with the number of mutations in a cell proportional to the person's age. Using data from 10,250 cancer genomes across 36 cancer types, the researchers found two mutational signatures with clock-like properties. These signatures exhibit different mutation rates in various tissues and are influenced by distinct biological factors. Signature 1, associated with C>T mutations at CpG dinucleotides, shows a strong correlation with age of diagnosis. Signature 5, with a different mutation pattern, also shows a correlation with age but is less consistent across cancer types. The study highlights that the mutation rates of these signatures vary significantly between cell types, with signature 1 being influenced by cell proliferation rates. Signature 5 may be affected by non-clock-like factors or the neoplastic process. The findings suggest that these clock-like mutational processes are fundamental to understanding cancer development and aging. The study provides the first comprehensive analysis of these processes in human somatic cells, revealing their roles in different tissues and cancer types. The results indicate that the mutation rates of these signatures are influenced by different biological factors, with signature 1 being more closely related to cell division rates. The study also notes that the presence of these signatures in cancer genomes may be obscured by mutations from other processes, but the clock-like nature of these signatures is still detectable in most cancer types. The research underscores the importance of understanding these mutational processes for future studies on cancer and aging.A study published in *Nature Genetics* (2015) identifies two clock-like mutational processes in human somatic cells. These processes generate mutations at a steady rate throughout life, with the number of mutations in a cell proportional to the person's age. Using data from 10,250 cancer genomes across 36 cancer types, the researchers found two mutational signatures with clock-like properties. These signatures exhibit different mutation rates in various tissues and are influenced by distinct biological factors. Signature 1, associated with C>T mutations at CpG dinucleotides, shows a strong correlation with age of diagnosis. Signature 5, with a different mutation pattern, also shows a correlation with age but is less consistent across cancer types. The study highlights that the mutation rates of these signatures vary significantly between cell types, with signature 1 being influenced by cell proliferation rates. Signature 5 may be affected by non-clock-like factors or the neoplastic process. The findings suggest that these clock-like mutational processes are fundamental to understanding cancer development and aging. The study provides the first comprehensive analysis of these processes in human somatic cells, revealing their roles in different tissues and cancer types. The results indicate that the mutation rates of these signatures are influenced by different biological factors, with signature 1 being more closely related to cell division rates. The study also notes that the presence of these signatures in cancer genomes may be obscured by mutations from other processes, but the clock-like nature of these signatures is still detectable in most cancer types. The research underscores the importance of understanding these mutational processes for future studies on cancer and aging.