Molecular evolution is the change of amino acid composition at locus specific positions of proteins for maintaining structural and functional integrity over long periods of time. In orthologous protein sets, adapted in different environmental conditions such as normal, high temperature and high ionic condition might have different or identical evolutionary characters. To understand the basis of this fact and to assess the differentials, if any are there, I perform detailed computational analysis on clusters of orthologous protein sequences procured from halophiles, thermophiles and mesophiles using authentic web based and our laboratory-developed programs. Results reveal domain of lives and orthologous protein specific variation in these sets. Unlike thermophiles which show higher usage of hetero-pairs with dominant pair from hydrophobic ones, halophiles, show lower usage with dominant hetero-pairs as ED. Maximally diverse residue is from bulky hydrophobic class in thermophiles and that in the halophiles is acidic ones. Overall, the study demonstrates domain of lives and orthologous proteins specific evolutionary characteristics, the information of which has potential application in biological evolution of homologous proteins under different solvent conditions.