Well that is certainly unnerving!
As defenses go, biofilm isn't a bad one. Nature doesn't like to reinvent the wheel, and biofilms are remarkably effective. Why should she tinker with what works?
from past research, I can confirm a number of those (though several aren't commercially viable). The casein in milk (one of the more famous milk proteins) is a binder used in natural glues, some paints, and plastics for the same reason. I'm guessing its an emulsifier for cosmetics?? The brain is also used for natural tanning - but that's a niche use. I don't think anyone is brain tanning at commercial scale anymore [though I could certainly be wrong].
Yes, I also was thinking a lot of these were uses at one time and now probably have been replaced by some petroleum product.
I recognize most of those as historical uses, but is much of this still true? My understanding is that in the UK at least a lot of traditional by-products are now discarded or go into pet food/snacks, because the traditional products they went into are now made of other things (e.g. tennis racquet strings, glues; interestingly china is not even listed for bones) or are obsolete, so their market has disappeared.
I think you are mostly right.
