How Death Played a Role in the Evolution of Human Height
How Death Played a Role in the Evolution of Human Height
Perhaps no other human trait is as variable as human height. At 5’4″, I’d be dwarfed standing next to 6’3″ Kerri Walsh, the 2012 Olympic gold medalist in beach volleyball. But next to an African pygmy woman, I’d be a giant. The source of that variation is something that anthropologists have been trying to root out for decades. Diet, climate and environment are frequently linked to height differences across human populations.
More recently, researchers have implicated another factor: mortality rate. In a new study in the journal Current Anthropology, Andrea Bamberg Migliano and Myrtille Guillon, both of the University College London, make the case that people living in populations with low life expectancies don’t grow as tall as people living in groups with longer life spans. They also argue changes in mortality rates might account for the jump in body size from Australopithecus to Homo some 2 million years ago.
From an evolutionary standpoint, Migliano and Guillon note, it’s beneficial to start reproducing as soon as possible if you live in a society where individuals typically die young. That way you can have as many babies as possible in a short amount of time. Thus, you should stop growing relatively early in life and start devoting your energy to having children and taking care of them. Having a shorter developmental period means you can’t grow as tall, on average, as someone who has more time to mature. But getting big has reproductive benefits: Larger individuals tend to take in more energy and therefore can invest more energy in reproducing. So in societies with lower mortality rates, and longer adulthoods, it’s better to mature slowly and grow bigger and taller. Over time, populations experiencing different mortality rates will adapt to have shorter or longer developmental periods—and therefore be shorter or taller. (Of course, there is also variation within a population. But here, and throughout the post, I’m talking about population averages.)