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Inside the science of our continuing evolution
by Scott Solomon
UNCERTAIN times bring thoughts of human futures. Amid the fever of change that was Victorian England, H. G. Wells wrote The Time Machine, in which humans had diverged into subterranean, orc-like Morlocks and the elfin, forest-living Eloi. The cold war 1960s saw the arrival of Marvel's superpowered X-Men mutants, and, in 2009, the huge success of Avatar revealed that a surprisingly large number of people secretly wanted to be blue, 4 metres tall and have a telepathic ponytail.
But what does the future hold for ordinary mortals, and how will we adapt to it? Given our genome and the physiological, anatomical and mental landscapes it conjures, what could Homo sapiens really become - and what is forever beyond our reach?
Scott Solomon's Future Humans has only partial answers to these fascinating questions. Anyone expecting an analysis of how we might adapt to climate change’s options of aridity or inundation will be disappointed. Likewise, he does not explore how our history as a competitive but group-living primate might limit our capacity to develop strategies to cope with future challenges. Nor does he mention the evolutionary potential of switching on ancient genes to unlock long-unused options, and he sidesteps a discussion of the good-or-bad potentials of gene therapy.
Instead, Solomon focuses on our understanding of human evolution: what happened and how we know it did. He doesn't want to speculate, but to show what we know about how humans can change across generations in genuinely heritable ways.
Surprisingly, perhaps, such an effort is absolutely necessary. The idea that humans have stopped evolving is widespread, and has been supported by luminaries as diverse as Ernst Mayr, Stephen J. Gould and David Attenborough. Yes, the argument goes, humans changed in the past: skin colour was originally highly adaptive, linked via vitamin D synthesis to the need to avoid developmental abnormalities in the fetus. True, they say, adaptations to high-altitude oxygen poverty have arisen three times, each with a very different solution. And reversing lactose intolerance so adult humans could access the calcium and protein richness of dairy products is such a good idea it evolved twice.
But that was then, before the industrial revolution and the internet and the ability to swap online data with a potential partner from the other side of the world. Now, the argument goes, antibiotics, healthcare, abundant food and an absence of predators mean humans are in stasis. Evolution has effectively stopped.
But as Solomon points out, when we succeed at the extremely tricky business of separating out cultural and genetic effects, the science shows heritable changes in such things as the age of having a first child and the onset of menopause. We are also evolving resistance to malaria and HIV. On the downside, our beautifully coadapted microbiota is being hammered by antibiotics and ambient chemicals. The changes are subtle and not externally obvious, but they are there.
We know that mammals can diverge into strange and amazing forms when the need arises, as the extant water opossum and aye-aye, and sadly extinct marine sloth and dwarf elephant show so splendidly. As for our species, Solomon considers dark-skinned, light-boned, space-going humans within the realms of possibility.
Here on Earth, though, with its potential for supervolcano and asteroid-driven mass extinctions (never mind what we do to help the process along), the book only offers hints about how humans might fare.
Nevertheless, it is enjoyable and well researched, and beautifully clarifies the fact that larger populations, greater genetic interchange and ever-older breeding males all greatly increase what evolution has to work with. But what might happen and why is, it seems, the subject for another book.
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