If we want to know where our capability for complex language came from, we need to look at how our brains are different from other animals. This relates to more than just brain size. It is important to know what other things our brains can do and when and why they evolved that way. One thing we can see in the remains of early humans, is the development of the mouth, throat and tongue, which allowed language to evolve.
At some point, our brains became able to make our mouths produce vowel and consonant sounds, and we developed the capacity to invent words to name things around us. These were the basic ingredients for complex language. The next change would have been to put those words into sentences. However, no one knows if the next step - adding grammar to signal past, present and future, for example, or plurals and relative clauses - required a further development in the human brain or was simply a response to our increasingly civilized way of living together.
Between 100, 000 and 50, 000 years ago, we start to see the evidence of early human civilization through cave paintings, though no one knows the connection between this and language. However, human brains did get bigger at this period. Moreover, humans did become more complex and more intelligent. Was it using language that caused their brains to develop, so that human could produce cave paintings? Or did their more complex brains start producing language? It was not clear yet.
More questions lie in looking at the influence of genetics on brain and language development. Are there genes that mutated(突变)and gave us language ability? Researchers have found a gene mutation that occurred between 200, 000 and 100, 000 years ago, which seems to have a connection with speaking and how our brains control our mouths and faces. Monkeys have a similar gene, but it did not undergo this mutation. It's too early to say how much influence genes have on language, but one day the answers might be found in our DNA.
