Free The Incredible Human Journey by Alice Roberts Page B

difference in the thermal responses; 10 indeed, he wrote, ‘If anything, the thin and hawk-like visage of the European is better protected from cold than that of
     the Asiatic.’ Evolutionary biologist Brian Shea 11 looked at the facial anatomy of Eskimos; he suggested that the internal architecture of
     the nose and sinuses might show some evidence of cold adaptation, but concluded that there was nothing to support the general
     idea of Asian faces being ‘cold-engineered’.
    Having eliminated cold adaptation, we are still left with the question of why (or indeed where and when) typically East Asian
     features arose. I will return to these questions later in this chapter, with the fossil and genetic evidence that I explored in China.
    Staying with cold adaptation for a minute, though, there does seem to be some interesting recent research suggesting that
     there may be some adaptive changes in northern populations – not in faces, but deep inside cells. There are very few examples of definite Darwinian or genetic adaptations among modern humans. Sickle cell anaemia and Stephen Oppenheimer’s thalassaemia in South-East
     Asian populations are rare examples, and the links in the chain are understood: the gene(s) responsible, the effect on phenotype
     (the observable characteristics: in these examples, the effect on blood), and the way in which a mutation confers its selective
     advantage (protection against malaria infection in these cases).
    The boosting of thyroid hormones and metabolic rate discussed earlier is a short-term, physiological mechanism that allows
     the body to effectively turn excess food into heat, not an example of a Darwinian adaptation to cold. The proposed genetic
     adaptation to the cold is related to the efficiency of mitochondria. In these minute ‘power stations’, of which there are
     thousands per cell, dietary calories are transformed into a package of energy that can be used by the cell (adenosine triphosphate,
     or ATP). Mitochondrial DNA contains the genes coding for just thirteen proteins, all of which are employed in energy production.
     Doug Wallace of the University of California, aficionado of all things mitochondrial, has studied how genetic mutations in
     mtDNA could alter the efficiency of mitochondria. A less efficient system produces less ATP per calorie, and loses energy
     as heat. So here comes the adaptation: Wallace argues that, in the tropics, mitochondria tend to be very efficient and generate
     little heat, whereas, in the Arctic, mutations make the mitochondria less efficient, and they produce heat. 12
    So while I was relying on chemical reactions inside bags of hand-warmer granules to keep my fingers going, it seems that the
     Evenki may have been benefiting from their own internal heat generation. And the short-term physiological response stimulated
     by the Evenki’s meaty diet would have further amplified that effect: thyroid hormones mainly work on mitochondria. Native
     Siberians have higher metabolic rates than non-natives on a similar diet. Even if I’d eschewed my vegetarianism and eaten
     reindeer meat, I still wouldn’t have been able to compete in the production of metabolic warmth.
    It does seem that modern humans are the only hominins to have colonised the Arctic and subarctic regions of the far north.
     This feat of survival may have depended on a whole range of adaptations, biological, behavioural and cultural, which together
     made it possible for humans to flourish in Siberia, and heat-generating mitochondria may be among those adaptations. But one
     other adaptation seems even more important: it was reindeer hunting, providing a meat-rich diet and fur for cold-weather clothing, that paved the way for colonisation
     of the north.
    Back to the Evenki, and the camp was getting busy as the brigade prepared to move house. It was remarkable how quickly a chum
     could be taken apart and packed up ready to be moved off on reindeer-drawn sledges. Once the