Hello lovely biologists, I hope the beautiful world of nature is treating you well.

I've got a question that has been stinging me lately, and all the answers I've found have been a bit circular in their logic. The question is:

Why has salivary amylase evolved to be basic in pH, and not acidic?

The further wondering is: What is the evolutionary benefit of having separate pH levels in the mouth and in the stomach? Why can the human mouth not be slightly acidic and use other enzymes (or amylase had it evolved for an acidic medium), to break down starch? Is there a specific scientific reason that states that starch can only be really effectively hydrolyzed by a basic pH enzyme? Does not a single pH level for the mouth and stomach seem evolutionary more expedient?

I know a bit about the roles of the acidic medium of the stomach and it's benefits in the denaturing of proteins and killing of bacteria, so I'm just wondering, aside from amylase evolutionary dependency on a basic pH, what real benefits are conferred only by a basic mouth medium.

This isn't for an assignment, just desperate for some biology curious sated, as always. Thanks so much for your time.

The pH of saliva is 6.2 to 7.4 so slightly acidic. Its main function other than lubrication is to reduce dental caries which requires mild acidity without damaging the enamel of the teeth.

alpha-amylase starts the digestion of starch before the food is swallowed and thus unsurprisingly has an optimal pH of 7.4 consistent with saliva. In contrast, lingual lipase has an optimum pH ~4.0 so is not activated until entering the acidic environment of the stomach.

From an evolutionary perspective I suspect it's simply difficult. Your stomach has t be resistant to the acid it produces and not much else. But your mouth holds your teeth, and the tongue is quite a delicate muscle and with much sensory apparatus, and of course your mouth opens up to your sinuses and airway. It's quite possibly impossible to protect your teeth from dissolving in a high-acid environment, or producing tastebuds that can resist such things, and of course vapours extending into your nasal cavity or accidently being taken into the lungs would be painful and harmful. Best to keep all that strogn acid locked up in one place.