Babel's Dawn and the Evolution of Vocalisation

A copy of Edmund Bolles' book, Babel's Dawn, A Natural History of the Origins of Speech, has just arrived and tells a fascinating story of how humanity has developed from just being a great ape over the last six million years. He uses a series of verbal snapshots to reconstruct what life was like for the Last Common Ancestor and their descendants. At each stage he discusses the findings of recent research, the uncertainties of reconstructing the past of our species, and the many gaps that still have to be filled. For each episode there are brief notes that re-direct you to the extensive bibliography.

So far, so good, but I have two major problems with the book. Before I retired I used to review books for the New Scientist, and also was the book review editor for an online discussion forum called HICOM, which was an early UK based interactive forum discussing a very wide range of subjects relating to the way humans interacted with information and computers. This book might even have been included on the possible review list as it is about how humans came to communicate with each other.

The first question I would ask in picking up any book to review myself, or to allocate a suitable specialist to review, is “What is the market for this book?” In the case of Babel's Dawn I am not sure. The story is told as if the reader was was walking through a museum with dioramas representing different periods in the past, with a verbal commentary being given as you go. For school children and the generally interested public the book would have been far more effective if each vista had been described with an associated picture with the pre-human figure in a reconstructed view of the landscape, and the amount of more formal scientific discussion significantly reduced. On the other hand, the serious scientific reader might find the faction approach annoying and the lack of an index frustrating. However my knowledge of the modern US university student book market is very limited, and it could be a useful reader, rather than reference book, in introducing a subject which many students might find controversial because of their religious beliefs – a problem which is far less an issue in the UK.

I also had a serious problem with Edmund's treatment of vocalisation and its relevance to speech, Without vocalisation there can be no speech as we know it and in my opinion the book fails to examine the evolutionary pressures that lead to the changes in the vocal tract which makes speech possible.

To be fair there is a very real difficulty in reconstructing this aspect of mankind's part as sound is about as ephemeral as one can get, and there is no possibility of any direct fossil evidence. Even indicator evidence, such as the changes in a tiny bone in the larynx, is hard to find, as the bone is rarely found in fossil deposits. In practice all one can do is to speculate on the evolutionary pressures that might lead to the evolution of vocalisation, which in turn lead to speech.

So lets step away from the book and speculate as to how the story might have been told.

Undoubtedly a very important aspect of the evolution of the human body was the move from living in forests to living in far more open and dryer environments. As the forests dried out they would have initially fragmented, depending on soil, altitude and drainage conditions locally, leading to a series of forested “islands” that would eventually vanish entirely. Forest species trapped on these islands, including our ancestors, would either have to adapt or become extinct. Such environmental changes, temporally trapping creatures in small habitat areas which are in the process of disappearing, are powerful evolutionary workshops and if we look at the human body most of the changes make sense. Descending from the trees and walking in more open areas is an obvious driver for changes in our lower limbs. Such changes also free our forelimbs for gathering food, tool making and throwing things. As a vulnerable animal, which no longer has trees to climb to escape, and who is not agile enough to catch fast moving prey or run from the larger predators, early man would need a degree of cunning and planning which will be helped by a larger and more imaginative brain.

The relevant evolutionary pressures are not so obvious when it comes to vocalisation. The modern human has a very powerful and flexible vocal system – which can produce a wide range of noises, including whistles and clicks, with significant control over pitch, volume and timing. However a modern human language may only use about 30 phonemes to express meaning – so it would seem that our vocal system has developed to a far greater extent than is necessary to support speech.

Of course social bonding might have been a factor, as Edmund suggests, but our great ape ancestors would almost be using facial expressions, body language, grooming and gestures to communicate when they are close together, and it has been suggested that the reason that we have developed whites to our eyes is to make it easier to “read minds” by observing our social companion's eye movements. It is easy to see why, if vocalisation changed for other reason it might have been adapted for social communication but it is not obvious why, if stronger social bonding was an advantage, that this should not have been done by a cultural change affecting the existing bonding techniques, rather than the far slower method of, for example, evolving a more versatile larynx.

One must realise that when man's forebears first came down from the trees the use of sound would have had its snags. Using sound is a very public way of communicating – and while someone might be able to signal to a colleague on the other side of a valley one must remember that every prey or predator in the neighbourhood would pick up the sound and turn to look at where the sound indicating danger or food came from.

However there is one area where improved vocal ability could have a significant advantage and that is if used as a tool when hunting. After all, in evolutionary terms getting enough to eat must be the top priority after avoiding being eaten yourself. If the aim is to catch a medium-sized herbivore such as an antelope a good technique is to drive the animal towards an ambush, but this needs a number of hunters working as a team, and this involves signalling at a distance. The ambushers need to tell the drivers when they are ready while it could increase success if the drivers warn the ambushers that the prey is approaching the killing area. Initially an ape-like grunt to indicate that the ambusher is ready might be adequate – but over time evolutionary pressures on the prey would alert it to the fact that ape noises can indicate danger – so the signalling method would need to change. As the long time battle between prey and hunter continues the hunter must improve his tactics – so an innocent imitation call of an owl hooting, or the whistling call of a bird would be a far better signal. But as the hunters vocal skills develop it will become possible to lure other animals by making, for example, mating calls at the right time of year.

If we consider that the ability to mimic other animals is an advantage to the increasingly intelligent hunter we now have an evolutionary pathway that will lead to the development of a very wide range of vocalisations - which is what the human species possesses. But this also leads to a possible start for using vocal symbols to communicate. After all, using an animal call to symbolise an animal is the equivalent of using a simple picture as a symbol in the early days of writing. Perhaps, in the same way that pictorial languages simplifies to alphabetic languages using words, vocal languages developed in a similar way by using special combinations of sounds to symbolise names of individual members of the group, perhaps naming them after animals. Vocalisations might then be extended to other objects. Further moves towards the rudiments of language would involve reducing the number of phonemes needed to be accurately recognised and generated by combining groups of sounds into words.

But that is a story for another day.