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Sequence comparisons reveal evolutionary relationships between proteins(rate of evolution varies from protein to protein); protein families evolve by following

• duplication
• divergence of genes encoding protein domain

A protein having the same function in different species, e.g., the cytochromes c, is called orthologous proteinsas they have similar functions; therefore, having similar sequences, and such proteins evolved from a common ancestor through gene duplication.

Two independently evolving genes derived from a duplication event are

said to be paralogous proteins. In prokaryotes, approximately 60% of protein domains have been duplicated; in many eukaryotes, duplication is approximately 90%, and in humans, it is approximately 98%.

Changing amino acids on a protein's function is a significant factor in how quickly a protein evolves. Multidomain proteins, such as blood clotting proteins, are derived from sequence variation.