Mad cows and evolution


Researchers at the University of Oxford and the Institute of Virology and Environmental Microbiology, U.K., have shown that humans and cows share unusual similarities in two regions of the prion protein, PrP, the protein converted into the brain-destroying form in Creutzfeldt-Jakob disease of humans and ‘mad cow’ diseases of cattle.1

The sequences of amino acids in humans, cattle, and other mammals were compared. Humans, anthropoid apes (except orang-utans), and cattle, shared the same two differences to other mammals. The PrP proteins differed from other mammals in the substitution of histidine in the place of aspartic acid in another place.

Such a pattern of similarity (homology) between humans and cows cannot be explained through any conventional evolutionary just-so story of common ancestry. The probability of this being a chance coincidence was calculated at less than one in 8,000. So what is the ‘explanation’?

‘cattle and our primate ancestors were supposedly subjected to similar evolutionary pressures that drove the PrP to change in the same way. The nature of these pressures, however, remains a mystery.’2


  1. Aldhous, P., 1996. Matching proteins raise CJD fears. New Scientist, 150(2027:21). Return to text.

  3. Aldhous, Ref. 1, p. 21. Return to text.