Read Online Malaria and Rome: A History of Malaria in Ancient Italy by Robert Sallares - Free Book Online

place. In the last few years the Duffy negative allele has also appeared in Papua New Guinea, where P. vivax is endemic. This is an example of evolution in action in human populations today in response to malaria.⁷
    Since P. falciparum was present in the heartland of human evolution in East Africa, presumably it would have been carried out of Africa by every successive wave of hominids and humans, from Homo erectus onwards. Whether it would have prospered outside Africa would have depended on the climate and on whether in new environments it encountered species of mosquito able to transmit it. These two factors are the last two pillars of the theory of the late spread of malaria into Mediterranean countries. Zulueta has quite correctly argued that the climate of Ice Age Europe was too cold both for the completion of the developmental cycle of P. falciparum itself within the mosquito and for the principal mosquito vector species in Italy, Anopheles labranchiae and A. sacharovi (= elutus ).
    He then reckoned that it would have taken thousands of years for conditions to become favourable enough for P. falciparum and its vectors to spread into southern Europe. However, this argument was based on old and out-of-date literature about the Holocene climate. It ignores the mass of evidence which is now available for what climatologists call the mid-Holocene climatic optimum, a period after the end of the last Ice Age and encompassing the Neolithic period until c .3000 , when, owing to periodic shifts in the earth’s position relative to the sun, the northern hemisphere received considerably more insolation than it does today. This resulted in the climate of many parts of the northern hemisphere being up to 2°C hotter than in subsequent millennia. Such temperatures are only now being approached again with the recent ⁷ Livingstone (1984); Zimmerman et al . (1999); Hamblin and Di Rienzo (2000).
    Evolution of malaria
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    trend towards anthropogenic global warming.⁸ The effects of these climate changes in Italy have recently attracted attention because of their relevance to the preservation of the famous ‘Iceman’ discovered in the Alps (as it turned out, just on the Italian side of the border with Austria). Fortunately for modern archaeologists, the Iceman died towards the end of the mid-Holocene climatic optimum, in the late fourth millennium , at a time when neoglacia-tion was commencing (i.e. the Alpine glaciers were starting to advance again as mean annual temperatures dropped). This covered his body with ice, preserving it until anthropogenic global warming in the last few years caused the glacier to begin to retreat again, exposing the frozen corpse.⁹
    The development of P. falciparum is heavily dependent on the temperature. Since it requires a minimum temperature of about 20°C for the completion of sporogony inside the mosquito, climatic conditions during the Neolithic period were in fact substantially more favourable for the spread of P. falciparum and its vector mosquitoes into southern Europe than they were in the first millennium 
    or any other period after the Neolithic. What are now the Saharan and the Arabian deserts also received substantially more rainfall during the mid-Holocene climatic optimum than they do today, creating more breeding sites for mosquitoes.¹⁰ This would have assisted the spread of malaria from tropical Africa towards the southern shores of the Mediterranean. It is even conceivable that the geographic range of members of the Anopheles gambiae complex, the most important vector of malaria in tropical Africa today, may have extended further north in Africa than it has done in recent times. Mosquitoes can evolve very rapidly. For example, populations of Culex pipiens confined to London Underground tunnels and separated from above-ground populations have evolved new host preferences (mice, rats, and humans instead of birds), reproductive isolation from above-ground