What I am wondering is how much of an impedance is cellulose to assimilation of nutrients.
It's a stonewall impediment. We can't digest enough of the nutrients embedded in uncooked cellulose to pay us back for the energy of chewing. As I mentioned earlier on this thread, fire is on the short list of nominees for the Breakthrough Technology that allowed
H. sapiens to become us. One of the many things that cooking does is simply make food easier to eat. I recently saw a calculation that even if we didn't have to hunt our meat, it would take about four hours a day to eat a day's ration of it raw. That alone gives us a lot of time for other pursuits that advance civilization.
but we are very much refined by millions of years of evolution from ancient primates... so, evolution should bring some beneficial characteristics and add more and more abilities to that organism.... even we are omnivorous... why we would lose that ability to digest cellulose?
Because we didn't need it any more. Grazing is an incredibly time-consuming activity. If you think spending four hours a day eating raw meat would be a bummer, try spending most of your waking life munching on raw plants. As we developed into hunters and adapted to a more carnivorous diet, we just didn't need to bother wasting our time chewing on roots, leaves and bark. A digestive system more compatible with a carnivorous diet would have been a favorable adaptation and evolution would have selected for it when it occurred. Herbivores have huge guts that would not make them nimble hunters.
in the previous replies, we read that cellulases are secreted by some bacteria present in the guts of herbivorous animals.. so did our ancestors eat some kind of food that would lead to formation of these bacteria???? did these bacteria come from the food they ate??
It's a stable bacterial culture that regenerates itself. Once it becomes established in the gut of a young animal a steady state exists in which the existing bacteria eat the cellulose and transform it into new bacteria, while at the same time the animal is digesting the protein-rich bacteria cells and keeping the population constant. I'm not sure how each species of herbivore establishes the initial culture, but baby rabbits, for example, eat the feces of adults in which there is inevitably some bacteria still alive.
The digestive help of bacteria is not limited to herbivores. Dogs and other canids have such short guts that they maintain a bacterial culture to help digest their food. In the wild they eat the intestines of their prey (and the leftovers from the meals of more finicky carnivores) to keep that culture going. If you see your dog out in the yard eating the feces of other animals, it's probably because you feed him commercial food full of preservatives and it's killing off his intestinal culture. He might even eat his own poop if he's desperate, some bacteria will have survived the onslaught of preservatives.
I thought it would be cool to develop a pill that would contain cellulose degrading bacteria. You would dump a bunch of grass, leaves, whatever in a pot, throw in a pill, and after some (lots) stirring, it could be edible. Does anyone see why this couldn't be done?
Because it's so much easier to simply apply a nice flame to that pot and accomplish the same result by cooking.
High heat breaks down cellulose into simpler molecules like starches that we can digest. That's where this whole discussion started!
