Similar to the chicken or egg problem, which came first, language or metaphor? The classic book Metaphors We Live By (1980) by Lakoff and Johnson explores how metaphors shape our understanding of the world, because they help us understand one thing in terms of another. The authors provide many examples, such as Time is Money or Life is Hard. But they do not explore the origin of metaphors. What was the evolutionary advantage to think about the world in terms of metaphors?
The answer lies in that animals and humans can only experience the world first hand. We can only see our own point of view, only know our own mindset and only feel our own feelings. Our senses provide direct contact with the world around us, but as individuals we are self-contained. Hence, we can never truly understand The Other. The ideas of love and relationship are self-induced fiction.
Metaphors, however, bridge the gap between our own, self-contained experiences and those of others. The Other can explain to us his personal experiences in terms of experiences that we both share. A simple analogy explains why. For example, one hunter who has hunted both horses and fish may teach another hunter, who has only hunted horses, how to hunt fish as well. Both types of hunt may involve a spear. The less experienced hunter can learn to use his familiar spear in a new context.
Similarly, more abstract analogies become the metaphors we live by. Metaphors thus help build a common grounds upon which groups of individuals may further their understanding of the world. With metaphors we can share our personal experiences with others in ways The Other can understand them.
So, which came first, metaphor or language? Even animal brains can (learn to) understand one natural phenomenon in terms of another phenomenon, either one they instinctively understand, or one they experienced through trial and error. Even without the capacity for language, wild animals can understand abstract metaphors. For example, a tiger may instinctively live by the metaphor Patience is Food. The patient hunter that does not scare off his prey has best chances of winning his kill. Herd animals may instinctively understand the metaphor Together is Better. Staying together provides herds better defense against predators.
Therefore I believe that metaphors not only came before language, but that metaphors drove the evolution of language as a means to efficiently communicate them. The ability to verbally express metaphors offers groups of individuals an exponential evolutionary advantage. Among other causes, the ability to communicate metaphors thus explains the success of Homo Sapiens.