Answer:
1) In language studies, displacement is the ability we have of being able to talk about unreal things, imaginary, about things in the past or future. These are qualities that only humans can do.
In 1960, Charles Francis Hockett (1916-2000) presented displacement as one of 13 characteristics that identify human language from animal communication.
2) Reflexivity, in human communication, is the attribute that allows us to use the language to talk and think about the language itself, we can review our language and make better. This is not present in other types of living thing communication. The animals can't do.
3) Language is a result from human evolution and an instrument for communication. It absorbs all our cultural aspects. In every single word has its a history and origin. It describes human development.
Our vocabulary is our intellectual achievements.
A clear example to show that language is cultural transmission:
If one child (from China) is adopted by a British family at birth, he/she will grow up speaking English (and not Chinese).
4) Allen Gardner used an experiment in which Washoe could distinguish words in the pictures. After 3 years Washoe could use more than a hundred words and put them together. Gardner showed that even without the presence of human washoe could use the right symbol to recognize things in pictures.
5) Kanzi is a rare specie of chimpanzee. He has been learning language all his life with Sue Savage-Rumbaugh, a primatologist and lead scientist from Great Ape Trust.
Kanzi born in 1980, and he is able to use than 200 keyboard symbols.
The most important point in Kanzi’s language learning is that he was showed to the language since young age, he was not taught but exposed. He could observe the language since very small.