From a biblical perspective: The first human, Adam, was created with a vocabulary, as well as with the ability to coin new words and thus expand his vocabulary. Without a God-given vocabulary the newly created man would have been no more able to comprehend verbal instructions from his Creator than were the unreasoning animals. (Ge 1:27-30; 2:16-20; compare 2Pe 2:12; Jude 10.) So, while only intelligent man of all earth's creatures has the ability of true speech, language did not originate with man but with man's All-Wise Creator, Jehovah God.-Compare Ex 4:11, 12.
On the origin of language, the well-known lexicographer Ludwig Koehler wrote: "There has been, especially in former times, much speculation as to how human speech 'came into being'. Writers strove to explore 'animal language'. For animals also are able to express audibly by sounds and groups of sounds their feelings and sensations, such as contentment, fear, emotion, threat, anger, sexual desire and satisfaction in its fulfilment, and perhaps many other things. However manifold these [animal] expressions may be, . . . they lack concept and thought, the essential domain of human language." After showing how men can explore the physiological aspect of human speech, he adds: "But what actually happens in speech, how the spark of perception kindles the spirit of the child, or of mankind generally, to become the spoken word, eludes our grasp. Human speech is a secret; it is a divine gift, a miracle."-Journal of Semitic Studies, Manchester, 1956, p. 11.
Language had been employed for untold ages prior to man's appearance on the universal scene. Jehovah God communicated with his heavenly firstborn Son and evidently used him in communicating with his other spirit sons. Hence that firstborn Son was called "the Word." (Joh 1:1; Col 1:15, 16; Re 3:14) The apostle Paul made inspired reference to "tongues of men and of angels." (1Co 13:1) Jehovah God speaks to his angelic creatures in their 'tongue' and they 'carry out his word.' (Ps 103:20) Since He and his spirit sons are not reliant upon an atmosphere (which makes possible the sound waves and vibrations necessary for human speech), angelic language is obviously beyond human conception or attainment. As God's messengers, angels therefore employed human language to talk with men, and angelic messages are recorded in Hebrew (Ge 22:15-18), Aramaic (Da 7:23-27), and Greek (Re 11:15), the cited texts being written in those languages respectively.
From a scientific perspective: There are two main schools of thought: vocal and gestural. The vocal school posits that human language evolved from the grunts and hoots of our early ape-like ancestors. For instance, the evolutionary psychologist Robin Dunbar theorizes that as their numbers dramatically increased, our animal ancestors had to find new ways of cementing community bounds over long distances. Therefore, Dubar thinks speaking evolved to replace grooming--the glue of ape society (see Evolutionary Psychology: Beginner's Guide, 2005). The problem with this school is that it cannot account for syntax, or proper grammar like, say, the SVO (subject-verb-object) order of English.
The gestural school posits that human language evolved from the hand gestures of our early ancestors. This is because Chimps, our closest genetic cousins, mostly communicate through visual and tactile cues like facial expressions, hand and body gestures, and bodily contact. Chimps who have been taught American Sign Language progress at the same rate as human children learning sign language or spoken language. Most importantly, they do not make grammatical mistakes. This is because syntax is built into such gestural movements. In his book Next of Kin (1997), Roger Fouts writes:
"But experts in sign language, who assume a gestural origin for language, can explain the emergence of syntax in a much simpler, more commonsense way. You can test it yourself right now by following this suggestion of David Armstrong, William Stokoe, and Sherman Wilcox from their book, Gesture and the Nature of Language:
'If you will, swing your right hand across in front of your body and catch the upraised forefinger of your left hand.'
By enacting this gesture, say the authors, you have just illustrated the most primitive form of syntax. 'The dominant hand is the agent (it acts), its swinging grasp is the action (verb), and the stationary finger is the patient or object. The grammarians' symbolic notion for this is familiar: SVO [subject-verb-object].'
It is easy to imagine our earliest ancestors using this gesture to communicate [using the hand signs], HAWK CAUGHT GOPHER. And they might have modified this sentence with adjectives (two fingers for two gophers) and adverbs (raised eyebrows for expressing disbelief: HAWK SOMEHOW CAUGHT GOPHER). These variations on a relationship are the beginnings of language as we know it" (p. 194).
But how can hand movements lead to oral speaking? Well, the area of the brain that controls detailed movements of the hands also controls the detailed movements of the tongue. Fouts, who is a Prof. of Psychology, taught American Sign Language to a pair of autistic boys who could not speak or even interact in normal social situations with members of their families. The amazing thing is that these boys gained the ability to speak within a few weeks of learning to sign. Nicholas Wade mentions in his book Before the Dawn (2006) that people with a mutated version of FOXP2, the brain gene associated with speech, have great trouble in talking because they do not have proper control of their mouth and tongue muscles. FOXP2 is located close to the gene responsible for autism; therefore, learning to control their hands through sign language helped the autistic boys gain control over their tongues, allowing them to speak.
Researchers have suggested that the FOXP2 gene evolved around 50,000 years ago because human cultural exploded after this point, probably due to language. Vocal language is far more effective in transmitting ideas than hand gestures. This suggests that humans used gestural communication for thousands of years before the gene switched on. It is important to note that a 2012 paper entitled "Monkey lipsmacking develops like the human speech rhythm" points out that the coordination of the jaw, tongue, and hyoid used in primate lip-smacking is comparable to that used for human speech. No sound is produced during lip-smacking because their vocal cords are in the wrong position. Human vocal cords are lower in our throats. Our vocal cord and tongue anatomy had to change before we could produce the sounds that we do today. In conclusion, the road to human speech involved hand gestures, lip-smacking, the dropping of the vocal cords, and the evolution of a brain gene to better control the tongue and mouth muscles.