In the early 1960s, Zuckerkandl and Pauling sequenced amino acids of hemoglobin of several different species and counted the differences. They insightfully observed that number of amino acid differences among these species correspond roughly in portions to geological time, when they juxtaposed these two lines of evidence.
Primate (human), horse and mouse lineages were thought to have originated about 70 mya, birds about 270 mya, frogs (amphibian origins) about 350 mya and sharks (cartilaginous fish origins) about 450 mya. Hemoglobin was acting like a molecular clock. Thus, it is clear that biomolecules changes at a somewhat regular rate over hundreds of millions years.
Sarich and Wilson found that albumins of humans, chimpanzees, and gorillas differ by 1%. Each of them differed from albumins of Old World monkeys by 6%. Sarich and Wilson picked an event from fossil record to calibrate their molecular findings. The event they chose was the divergence of hominoids and Old World monkey lineage and estimated time 30 mya.
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Therefore, 1% differences among African hominoids represents one sixth of 30, or 5. Sarich and Wilson were then able to deduce that humans, chimpanzees and gorillas had a common ancestor about 5 mya. The 14 million years old Ramapithecus could not have been a hominid. These finding were first reported in 1967 as controversial.
Many paleontologists insisted that dental morphology of Ramapithecus proved it to be hominid, denying validity of molecular clocks and rejected a 5 million year ape human divergence as being too recent. Subsequently, more molecular data supported the idea of a 5 million year divergence. Fossil bones indicated Ramapithecus was a tree living ape, not a upright walking human. Hominid fossils, 3 to 4 million years old, are very like chimpanzees.
The 5 million year estimate for common ancestor of apes and humans fits with current hominid fossil record. Fossils tell us when and where ancient ancestors lived and they might have looked alike. Molecular data provide quantitative information on species relationships and estimates of when in the past the lineages diverged. These two kinds of information, paleontological and molecular, are complementary, not contradictory and both are essential for reconstructing evolutionary history.