It is probable that the use of fire drives to herd game and burning to stimulate new growth, attracting game animals and improving the production of some nuts and seeds pre-dated the use of fire for cooking. This pre-cooking use of fire was the only use of fire for which there is evidence for most of human evolution.
Cooking food - the use of fire - changes the bioavailability of some nutrients. Some are destroyed or reduced (e.g., vitamin C); some are enhanced nutritionally (e.g., the proteins in legumes) and other foods have their natural protective toxicity reduced (e.g., the green skin on potato tubers - and other plants with toxic proteinaceous chemicals evolved as a defence against animal predation) and others are unaffected (the mineral content). Cooking can also sterilize foods by killing bacteria, parasites and fungal infections. Cooked flesh (and plants) are made more tender and more easily shared and this, in itself, would have increased the utility of the cooked foodIt goes - almost - without saying that cooking, more than anything else, has transformed food preparation from a simple utilitarian operation into a complex cultural ritual, seen by some to mark off the uncivilized (the raw) from the civilized (the cooked), both actually and symbolically.It is worth noting, then, that the evidence for the controlled use of fire has been found for only the last 1.2 million years of five million years of human evolution. It is likely, too, that cooking was rare through to about 300,000 years ago from when the first hearths survive (Terra Amata, southern France). This places the use of cooking well toward the end of the Palaeolithic period. As meat appears to have become the main source of nutrition from about 2.5 mya, for most of our history as omnivores, we ate all our food raw.What implications does this have for us today, choosing whether we cook our food or eat it raw? This is a personal choice which depends primarily upon your cultural preferences, up-bringing and the extent to which you are concerned about your dietary preferences. Those who want to pursue raw food (particularly raw meat and fish) might like to read Aajonus Vonderplanitz's book "We Want to Live" and to join the Primaldiet forum on Yahoo. Vonderplanitz's book does not begin from a human evolutionary perspective but is probably the single most persuasive and complete book on this confronting topic. Check Karl Loren's website for an enthusiast's views.
Tony McMichael, in Human Frontiers, writes "The enhanced social cohesion resulting from the use of fire for warmth, nocturnal security and prolonged group interaction may have further impelled the emergence of early language in the Pleistocene" (p.49).