Linus Pauling: I had a man come from Paris to work with me, presumably for a short while, on the oxidation reactions in marine organisms.
But I asked him if he would get some hemoglobins, some blood from different species and run these protein patterns. This was
before the days of amino acid sequences. And human, fish, lungfish, echiurid worm, shark. It's obvious that the hemoglobins
are much different. Here, human, cow, pig, they're beginning to be more similar. In fact, when it became possible to determine
amino acid compositions or sequences, it turns out that the difference between human and cow in the alpha chain is about 20
residues out of the 140. So you're getting close. Here we have human, chimpanzee, gorilla, orangutan, rhesus monkey. Well
there are about six residues difference between rhesus monkey and humans, and about one residue between the alpha chain or
beta chain in the chimpanzee. In fact, one of the chains is identical. So this is a way of setting up an evolutionary chart.
Dr. Emile Zuckerkandl and I wrote a paper in 1962 on this subject. This was the start of molecular evolution. He is the editor,
has been for fifteen years of its existence, of the Journal of Molecular Evolution, Emile Zuckerkandl. Here back 20 years ago a number of differences. We started with horse and human, and put down 80 million
- that's high, it should be about 60 million years - between the separation of horse and human probably. And horse and rhesus
monkeys, their six differences, if you take this proportionality and say that there's one evolutionarily-effective mutation
every 4 million years, from twenty to eighty, then the six [differences] would mean that human beings separated from rhesus
monkeys 24 million years ago. Gorilla and chimpanzee it's two or one or zero [differences], average would be about 4 million
years, for the time when we separated from those anthropoid apes.
This evolutionary clock seems to be reasonably good. You have - I don't know whether I have, oh yes, here's the slide - this
is for Cytochrome-C, has about 100 or 105 amino acid residues in the polypeptide chain. Man and rhesus monkey only one. I
haven't seen that anyone has studied man and the anthropoid apes, but probably there is no difference. One instead of six
here, man and other mammals about eight instead of twenty, man and the birds about fourteen, man and tuna fish twenty-one,
man and the moth thirty, man and baker's yeast forty-five. So in sixty of the positions, human beings and baker's yeast are
analogous. We're moderately closely related to baker's yeast. Somewhat more closely related to the moths, and still more to
tuna fish, and almost identical with the anthropoid apes.