They found that the differences between the two species were mostly the result of 'neutral' mutations, or genetic changes with little or no consequence for the functioning of blood proteins themselves.The neutrality of these mutations meant they could be used as a yardstick of evolutionary distance - the more mutations accumulated, the longer the time since the species split.
It isn't as accurate as the geological clocks used routinely to date rocks and fossils by geologists, although, they also have their uncertainties of course.
And, rather cleverly, modern molecular clocks use dated geological events as a kind of reference or standard against which to calibrate evolutionary time, especially the 'tick rate' (or mutation rate) of the clock itself.
They are fossils captured in volcanic rock that can be given an absolute date.
(Any remnant of the past, not just bones, can be considered a fossil.) 3.6 million years ago, a volcano now called Sadiman puffed out a cloud of ash that blanketed the surrounding area.
Traditional analyses can only rely on the information gained from the study of the external morphology of specimens, and these approaches limited the study of human evolution.
The application of computed tomography (CT) has facilitated major developments in paleoanthropology.
Still, Huxley's work made it starkly clear that humans were a Great Ape, closer to our African kin than our East Asian ape cousins, the orangutan.
It was unclear, however, which of the hundreds of extinct ape species found during the nineteenth and twentieth centuries in Africa, Europe and Asia, dating from the period 10 million to 35 million years old, gave rise to the human lineage. David Pilbeam of Harvard University argued that Ramapithecus, a 14 million year old ape from the Siwalik Mountains of Pakistan, but also found in East Africa, was the earliest member of the human line.
Their findings were poised to cause a major upset among anthropologists, and would come to set the framework for understanding the origins of the human branch until today.
Emile Zuckerkandl and twice Nobel Prize winner Linus Pauling were among the many workers studying haemoglobin, and were interested in differences between humans and the gorilla.
Studies examined include virtual fossil reconstruction, the use of endocasts to elucidate brain morphology, biomechanical analyses of bone distribution, imaging of mummies and research on early human health, and skeletal and dental microanatomical research.