Comparative biochemistry provides a strong evidence in favour of common ancestry of living beings.

Convincing evidence of common ancestry comes from similarities in biochemical composition and physiological activities, such as metabolic processes, enzymes, and proteins like cytochrome C, insulin, and hemoglobin. The genetic code, which is the sequence of $DNA$ nucleotides determining the amino acid sequence of proteins, is read in triplets called codons and is applicable universally from viruses to trees to humans. For instance, $mRNA$ from a chick oviduct introduced in $E.coli$ produces an ovalbumen exactly similar to one formed in chick. Both statements are true and the universality of the genetic code (the reason) provides a specific biochemical basis that supports the evidence for common ancestry (the assertion).