The early forest dwellers may also have found that rubbing tea on to wounds, or binding up a wound with some ground-up tea inside it, helped healing, and we know from recent accounts that tribesmen in the Naga, Shan, Kachin and neighboouring hills use tea as a medicine in this way. Such vitalising and medicinal properties would have given tea-chewing humans, and tea-chewing monkeys, a competitive advantage. For thousands of years there existed a symbiosis between tea and mammals as the latter, through their consumption and handling of the plants, unconcsciously encouraged widespread growth of the tea tree.
This isn't quite as corny as it sounds (not like saying there's symbiosis between humankind and corn because we plant corn everywhere). As the British discovered in the mid-1800s when they began trying to cultivate wild-growing tea in the Assam region of India, picking tea leaves stimulates the tea plant to grow more vigorously. That, plus the fact that early tea-harvesters probably cleared away other vegetation growing around these wild-growing plants, helped the plants spread more than they would have if left to their own devices.