Smoke and Perfume.

Since most predators rely upon a keen sense of smell to detect and track their prey, one human device may have been to try to confuse predators with powerful fragrances. Just as intense light brings temporary blindness, so intense odour would produce temporary loss of a predator's sense of smell, preventing them from detecting and tracking humans.

A whole arsenal of fragrances have been bequeathed by antiquity. Lavender, lemon grass, frankincense, civet, musk. Asafoetida grass, garlic, cedarwood, sandalwood.

Fire may not only have served for heating and cooking, but also to mask human natural odour with acrid smoke from predators downwind. Keeping a smoky fire burning at all times, even while on the move, may have been essential. The custom of pipe-smoking may have arisen as a way of keeping something continually burning, using human lungs as bellows. With this smouldering material, a camp fire could be readily lit.

Fire could also have been used not only to mask human odour, but also to defend against predator attack. When predators closed in on a human group, they may have responded by setting fire to everything that would burn, to drive back the predators, and provide a visual smokescreen under cover of which they could make their escape.

One result of living continually in a heavily scented, smoky environment would have been a gradual degeneration, over many generations, of the human sense of smell, which would have been permanently overloaded, and relatively useless.

The corollary of these attempts to mask human odour was the attempt to minimize human body odour. The practice of bathing was intended not to achieve personal cleanliness, but to wash off those bodily secretions which gave rise to human odour. Also the habit of defecating in places apart may also arisen for the same reasons. If humans defecated into pits, these could then be backfilled to ensure that the odour of their contents would not be released. Otherwise, faeces lying on open ground would have drawn predators onto the human trail.