'Horizon' documentary notes:

Horizon is a documentary that investigates how we learn to speak.
It says that language is part of what defines and distinguishes us as humans as we are the opnly ones who can speak.
Children learn to speak a complex language and a sophisticated skill with minimal effort without being explicitly taught which suggests its a natural process ingrained in humans. However how we learn to speak is still a mystery to the experts.
Deb Roy is a cognitive scientist who said that in order to examine how a child learns to speak they must be observed 24/7 while they were developing speech. To do this he turned his own home into an experiment to observe his own son, which is the first experiment of this type. He called it The Speech Home Project and watched how his son's speech developed until he was 3 years old. He discovered there was many stages of learning to talk, including the early 3 stages, which are the one word stage, the two word stage and then further complex language stage, where the children would start to say sentences including more than two words.
The way the children are interacted with and spoken to when learning to speak affects how they learn, for example, when given a positive reaction to something that the child has said they're then more likely to say it again. Adults often simplify their speech when talking to children/each other when the child is around. This includes elongated pauses between words to simplify the lexis and syntax. this is an example of convergence where the adults make the language appropriate for the children. Once the child then begins to speak more and more complexly, the parents speech mirrors that and then becomes more complex as a result.
Children listen to the tone and intonation of the voice to gauge the mood of the speech, not the lexis. Their phonological awareness outstrips their lexical awareness as they are first learning to speak.
By the child is 5 they will have learn approximately 5000 words. Of these, most of them are nouns and they will be beginning to learn to use more determiners, such as 'that's'. After the age of 5, its estimated that they will be learning around 3000 new words a year and will use 15000 words a day as an adult.
An animals voice box is higher which gives them a shorter vocal track, compared to humans lower voice box and longer vocal track. This was thought to be the reason why humans could speak, but animals couldn't. However animals can lower their voice box when the make sounds, meaning their vocal track can be elongated, giving them enough room to form the more complex sounds needed to speak so the theory was proved incorrect and so it was estimated that the main reason humans can speak and animals can't must be something in the brain.
New born babies respond to their mother voice in a way that they don't to other voices, this is due to the fact they began to learn language and sounds by hearing the mothers voice while still in the womb. All of this points towards an innate ability to develop language and that humans are born with the tools needed to speak within our brain.
Noam Chomsky is often called the godfather of linguistics who stated that the basis of our ability to speak is innate and to be able to stimulate the part of our brain which allows us to speak we must be exposed to language from a young age and throughout the 'critical acquisitional period'. His theory was called the L.A.D theory, that we are born with language, but to be able to learn and speak it properly we must be surrounded by language from and early age.
The forbidden experiment would be one way of figuring out if we are born with the ability to speak, however it is forbidden due to ethical issues because it would involve taking a child out of their natural habitat and isolating them, forcing them to grow up in silence and observing if they would develop language on their own.
Gene Fox-P-2 was found in a specific family who gave the the impression that they were deaf due to unclear speech inherited from the grandmother. The scientists found that the thing that affected their speech was found on chromosome 7, but they didn't know where or which gene of chromosome 7. They the discovered that part of chromosome 7 was broken off, which was why their speech was affected. This supported Chomsky's L.A.D theory and the reason we can speak is nature, not nurture. However behaviorists say that it must be stimulated in the critical acquisitional period so humans to be able to develop speech to a proper communicative level. All animals have this gene but the slight difference in the human version of the gene must be responsible for why humans can speak instead of just making noises.
Scientists think that language developed about 50,000 years ago, when art and technology boomed abruptly and they think that language was developed subconsciously over a process of time.