This article is prefaced with the simple statement that there is almost nothing known about prehistoric cooking or the first culinary use of fire, and that all that is contained in this article is conjecture.
Prehistoric mankind was at a challenge from everything in life; hungry predatory animals, unremitting weather, insidious diseases, afflictions, and even finding adequate drinking water. They were fortunate to even reach middle age, due to a lack of vitamins, malnutrition, poisonous plants, contaminated kills and the like. They took up a lifestyle that revolved around their food supply, either becoming stationary dwellers scouring the surrounding area for nuts, plants and local animal life, or nomadic types by following the seasonal migrations of the animals they desired to eat.
For the stationary "gatherers", root vegetables must have had preferred liking, because the root was buried underground, and protected from most of the ravages of nature. Above-ground vegetables were also prized, including the cabbage and shoots from young trees, ferns and nettles, gourds and fungus, as well as fruits and berries. These were gathered and eaten daily, because the plant-life would usually spoil within a day or two. The smaller animal life for the gatherer is available to augment their diet, even down to snails and insects, when their natural plant life is at a low.
For the nomadic "hunters", they most undoubtedly preferred to kill an unsuspecting prey, primarily because it would be much easier and safer that way, but perhaps they discovered what us modern folk have, that a relaxed and unsuspecting animal that is killed will yield tastier meat than one that is panicked and frightened. We can also infer the occasional vegetable and small mammal and insect overlap that the gatherers were exposed to, when their prime food source was scarce.
The prehistoric peoples most likely spent many thousands of years eating their food raw. However, soon after they discovered the friendly and warmth-giving fire, charring the food in it must soon have followed. The main conjecture for this is from our own modern experiences - anyone who has sat around a campfire will be tempted to play with it, by throwing twigs in, or leaves, etc. Perhaps the prehistoric folk found, that by "playing" with the raw food such, made them easier to eat because the fire softened them from an indigestible state to one that could be metabolized.
More likely, though, because "playing" with your food in an era when just being able to eat it was at a premium, someone accidentally dropped a piece of meat or a vegetable into a fire and was unable to retrieve it until the fire died down, only to discover later that the charred item was tastier than before, because (most certainly unknown to them), fibers in the food were broken down to release more nutrients than eating it raw. They then may have grown tired of reaching directly into a bed of coals and, having realized that rocks heat up when near a fire, placed a flat one directly on the coals to make it easier to retrieve the item from the fire. This may be considered the first use of grilling.
While cooking cuts of meat on this flat rock, it may well have been noticed that pieces that had fat in it were more tender and juicy than pieces that contained little fat, so the notion of gathering up fat, or scraping the rendered fat from a cooking stone after it had cooled for reuse next time may have come into being. By using the rendered fat over again, the first use of frying may have been born.
Because small animals took too long to cook on a flat rock, perhaps the next step occurred when someone carelessly placed a soiled and mud-caked piglet into a fire. After retrieving it from the coals, they found it was much more juicy and succulent than its cleaner counterpart; the protection from the charring heat and the sealing in of juices afforded by the mud must have become apparent.
Then there is the ground under the fire. They must have known that the ground under and around a fire heated up, because sleeping next to the fire is much preferred, and that the ground next to a fire of coals is warmer than a few feet away will feel. The prehistoric must have found that the ground itself was a natural oven, so why not bury some vegetables, build a fire above them, and then later dig them up. Root vegetables, such as tubers or potatoes, or gourds, like squash or pumpkins would be a prime example of this type of experimentation. It was only a short step to bury the piglet under the fire after the mud-cake adventure described above. The two previous examples might represent a primitive example of baking.
Roasting might have been the most intuitive and cognizant invention made by prehistoric mankind. Although the "dropping a piece of meat into the fire" scenario described earlier can, by our modern nomenclature, be described as roasting, the roasting in question here is spit roasting. It can be imagined that they became tired of reaching into the coals, or onto a flat stone to retrieve a cooked item. They must also have realized that the air directly above a fire was very hot, almost as hot as the fire itself. In order to make use of this fact, and to avoid reaching into a hot fire, they could suspend the meat over the fire into the super-heated air.
Some scrappy and enterprising caveperson may have discovered that by erecting two elongated "Y" shaped tree limbs on either side of a fire pit, and after skewering an animal with a pole, and placing it over the fire between the two "Y"'s, was able at once to solve the problem of reaching into the fire, and to cook the animal first without cutting it up and then throwing it directly into the flame or onto the flat rock. But then, it was soon discovered that one side of the animal (closest to the flame) became very cooked, burned, and dried out, while the other side (farthest from the flame) remained almost raw. Only the meat in the center of the animal was cooked to primitive perfection. The art of rotating the pole every so often to allow for even cooking must then have been discovered, and as a bonus, they must have discovered that the rotating animal basted in its own fats and juices, which approximated the taste they came to savor from cooking a mud-caked piglet directly in the fire. This is the prehistoric offering for the discovery of spit roasting.
Boiling, on the other hand, has a much more dubious prehistoric past, because of the very few natural hot springs occurring in the world, AND because boiling cannot occur without the intentional creation of containers that are both heatproof and waterproof. The following argument is offered for prehistoric boiling of water:
A pit in the earth is lined with stones to prevent seepage
Water in the pit is brought to boil by heating stones and submerging them in the water
Any veggies or meat is placed in the water and continued to boil by rotating heated stones
This pit method, although tedious, may have been used as a ceremonial act, designed for a large social gathering to honor other tribe members, or perhaps members of other tribes, but probably wasn't a main staple of their diet, due to the large amount of fuel needed to boil a chunk of food.
Other cooking revelations most likely had to wait for the invention of pottery, and further explorations with the use of fire. With the discovery of fire itself, early Earth dwellers were able to secure a somewhat safer living environment and perhaps extend their own lifespans!


Comments: 4
It is easy to see how such people would deduce that the fire is what caused the meat to be more tender and better tasting, and thus why they began to approach the fire as a potential tool rather than something to fear. These same people would have had fewer food-borne ilnesses, and thus would have flourished.
An interesting hypothesis, at any rate. To this day we are the only animal that applies heat to our food.
best
Ian