International Balzan Foundation Luigi Luca Cavalli

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1999 Balzan Prize for Science of Human Origins Genetics is a quantitative science, though errors in measurements and predictions are usually much greater. But in the study of human evolution we are beginning to have reasonable measurements, for instance, of the rates of expansions. [Ten years on, reading this after it was published and translated into Italian, genome analysis has led to the complete sequencing of DNA, resulting in a level of precision which is one thousand times greater, and precision is increasing.] In Europe, the average rate of the advance of farming was of the order of one kilometre a year, somewhat faster in the expansion from its area of origin in the Middle East westwards, via the Mediterranean, than towards the north-west, to Turkey, Greece, the Balkans, and Central Europe. We have approximate measurements of other rates. That of the Bantus , which started in Cameroon about 3,000 years ago and ended around 300 years ago in South Africa, where they met Boer farmers, was 50% faster on average (they were able to make use of iron). The Malayo-Polynesian expansion originated in South-east Asia – the precise area of origin is debated – and crossed the Pacific Ocean. It reached Easter Island about 1,500 years ago, in many jumps from island to island, and was about five to six times faster. It also expanded towards the west, reaching Madagascar only slightly later. For earlier expansions we have only one estimate of some precision: during the last glaciation, between 29,000 and 13,000 years ago, the ice covered most of northern Europe and the population retired into two non-communicating refuges: south-western France, and the Balkans and the Ukraine. At the end of the glaciation Palaeolithic hunters began resettling the north, at a rate of about 0.7 kilometres a year. This rate must have been to some extent controlled by the rate at which ice withdrew. In general, rates of expansion are determined by an average (a geometric mean) of the rate of population growth and that of individual migration. The first extension of Homo Sapiens from East Africa to South America took approximately 50,000 years to cover 25,000 kilometers (0.5 km on average per year), though it is possible that the settlement of South America by hunter-gatherers from Alaska to Chile was much faster. The limit to the quality of such estimates is set by the quantity and quality of archaeological findings. Thinking of the genetics of the future, a very serious limit is set by ethical and practical considerations. Today we know about 10,000 genetic diseases. They are all Mendelian, that is, they follow Mendel’s laws for characters determined by single genes; fortunately, they are very rare, as almost all are very serious. The most important and common diseases, like arthritis, diabetes, hypertension, 34
Luigi Luca Cavalli-Sforza many immunological diseases, schizophrenia, manic-depressive syndrome, are very poorly known. We are sure there is a genetic component, but there is potentially a multitude of genes involved in each one, as well as external factors that are difficult to pin down. Knowledge of the human genome will help, but there is still much work to do. This ’polygenic or multifactorial inheritance’ can be studied in animals, in which controlled crosses and experimental treatments unthinkable in humans are possible, so there is hope, and there has already been some success in getting help from animals for solving human genetic problems. But there are serious ethical limits to understanding human physiology and pathology, caused by the unacceptability of almost all experimentation. Even so, when I try to imagine what science and technology can do in the remote future, I find it very difficult to foresee serious limits to our knowledge. All the imaginations of Jules Verne have come true, plus many more. Perhaps whatever limits we picture today will be food for laughter among our descendants. The most serious limit to growth is of another kind: will the world survive the machinations of a technologically very knowledgeable, very depressed Luddite? There is a finite probability, fortunately very small for the time being, that this may cause the end of the only part of the universe where, as far as we know, science is being practised. 35
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International Balzan Foundation Luigi Luca Cavalli

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