Paleo Phil wrote:
>> This may be an area where the "blood type diet" theory has some merit.
>> It is a fact that people with type A blood make less gastic HCl than
>> those with type O blood.  It also appears to be true that the frequency
>> of type A blood in human populations increased about 40,000 years ago,
>>     
>
> Interesting, do you have a reference where I can learn more on this? 
>   

Nothing that I can put my hand on, unfortunately.  When Peter D'Adamo's 
"Eat Right 4 Your Type" book came out, we had a flurry of discussion 
about it on this list, and I did a little research at that time.  I 
recall that I was able to confirm that type As produce less gastric HCl, 
and that the A phenotype became more common about 40,000 years ago.  
There's also a difference in production of alkaline phosphatase.  
D'Adamo claims that this makes type As less able to digest fat, but I 
was never able to find support for that.

>> although there's no reason to suppose that it *began* then.  
>>     
>
> Indeed, we know that it didn't begin then because type A blood is found in
> other primates, such as chimps, and it predates the human race (more than
> 2.5 million years ago).
>   

Yes.  This point was made on D'Adamo's forum, but I don't recall his 
response to it.

>> So one theory is that gastic HCl also serves to kill food-borne
>> microorganisms (dogs and other carnivores also produce high levels of
>> HCl), and the cooking of meat became common, this defense became less
>> important, resulting in a proliferation of the type A phenotype that,
>> prior to cooking, was held back.
>>     
>
> That would appear to presume a very late start to cooking prevalence of
> around 40k years ago, whereas the recent evidence has been pushing cooking
> back further and further--more than 200k years ago.
>   

I'm more persuaded by that evidence than by my half-baked conjecture, 
frankly.  Still, the differences in HCl production are interesting, 
including the fact that dogs and cats produce more than humans.  It 
seems likely that the HCl has a purpose beyond adjusting the pH to 
activate the protease enzymes, so it certainly makes one wonder what it is.

Todd Moody
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