Infant-carrying and bipedalism in humans

Way back at least to H. erectus times, pair bonding and neoteny meant that both parents were needed to care for infants. And they had to travel with them: at least one infant or toddler (interbirth interval may have been longer, like in bush-living !Kung, 4 years, instead of developed-world humans, less than 2 years) and another one or two dependent juveniles. They travelled widely, all the way to Java and China (well, strictly speaking, the population expanded that far, but individuals must have travelled widely for that to happen). They had to cross rough terrain, like canyons, and wade innumerable creeks and streams (how they got across big rivers like the Indus, Ganges and Irrawaddy is another question). So the mother carries the infant or toddler, and the man does what? Go to any urban park and you’ll see: human males universally carry toddlers on their shoulders, leaving one hand free to lead a pre-adolescent. We need a strong vertebral column for this, and a very upright posture. You must have noticed that when carrying anything heavy, your back could support way more weight than your arms, and the weight forced you to walk very erect. Humans are so programmed to carry heavy weights on our backs that we go backpacking for fun. I think the human vertebral column is way stronger than needed for ordinary and infrequent carrying, like meat back from a hunt. We had to be carrying toddlers. I’ve even been tempted to wonder the sexually dimorphic width and strength of men’s shoulder girdles might have been involved in toddler-carrying. Women can’t carry kids on their shoulders, which are too narrow, for any length of time—the kids slip off.

Homo erectus crossed the Indus, Ganges, and Irrawaddy

An interesting news item (Zach Zorich, Palaeolithic Tools, Archaeology, January/February 2011), but why the surprise that H. erectus/ergaster could cross 40 miles of open sea to reach Crete?

When I was little, my family often went camping and many times my brother and I made use of a drift log to reach islands out in a lake, or to cross a river. As a young field biologist working in remote wilderness in northern Canada, we often lashed a few logs together to make a raft to cross rivers; the photo is an example. It seems obvious that Homo erectus , who clearly had the tool-using skills, would have done so.

Much earlier than the Crete crossing, H. erectus evidently crossed Mab el Mandeb at the mouth of the Red Sea (although it was probably narrower then), and reached the islands of Java and Sumatra (but the Sunda Shelf may have been exposed). Regardless of these uncertain sea crossings, they must have also crossed the Indus, Ganges, and Irrawaddy Rivers to reach Java, and the Mekong River to reach China, in addition to countless smaller, though still daunting, rivers. These crossings imply technology for river/sea transport, not only of people (including infants and toddlers who could hardly have straddled a floating log, for example) but also of tools and supplies.

Crossing to Crete is another matter: 40 miles is a long way. But I feel certain that if any homonids from H. erectus on could see land across the water, they could reach it.