Evidence for evolution

Macroevolution, which cannot be observed directly, is studied through indirect evidence. Molecular biology: in all organisms hereditary information is in DNA (RNA in some viruses), the genetic code is almost the same (one codon – one amino acid), protein synthesis takes place on ribosomes, ATP is the universal energy carrier – this points to a common origin of life. Protein and DNA sequences are compared between species: close species differ little, distant species much. For example human and chimpanzee DNA sequences are about 98–99 % identical; cytochrome c of human and macaque differs by only 1 amino acid, of human and horse by about 12. Because differences accumulate over time, a “molecular clock” helps estimate when species diverged. The α and β chains of haemoglobin (141 and 146 amino acids) have similar sequences – they result from duplication and divergence of one ancestral gene. Cytology: all organisms are made of cells (cell theory), and cells share organelles and membranes. Embryology: vertebrate embryos are similar at early stages (gill slits, tail, notochord), and class-specific features appear later (K. von Baer’s law). E. Haeckel proposed the biogenetic law (ontogeny is a brief repetition of phylogeny); in the modern view ontogeny repeats the embryonic stages, not the adult forms, of ancestors, and some stages drop out or change (A. Severtsov’s theory of phylembryogenesis: useful mutations change embryonic stages and thereby change phylogeny).