Swift-footed erectus

… trembling took hold of Hector, and he could no longer endure

there to stand his ground, but left the gates behind and, terrified, he ran.

The son of Peleus charged for him, trusting in the swiftness of his feet;

as a mountain hawk, lightest of all things on wings,

easily swoops after a terror-stricken dove,

which, away from under, flees, but crying sharply near

he swoops continuously and his spirit drives him to take her;

so Achilles flew straight for him, ravenous, and Hector fled

under the walls of Troy, working his swift knees.

…

… they ran, one fleeing, the other behind pursuing;

outstanding was he who fled ahead – but far better was he who pursued him

swiftly; since it was not for a sacral animal, nor for an oxhide

they contended, prizes in the races of men –

but they ran for the life of Hector breaker of horses.

…

Relentlessly, swift Achilles kept driving Hector panicked before him,

as when a dog in the mountains pursues a deer’s fawn …

so Hector could not elude Achilles of the swift feet

…

Iliad 22:156-193. translated by Caroline Alexander 

By today’s date on Logarithmic History, human ancestors have been walking bipedally for millions of years. But with the arrival of Homo erectus (more or less), a new mode of bipedalism appears on the scene: endurance running.

Human beings, walking, operate an inverted pendulum, trading off kinetic energy and a lower center of gravity at toe-off, for potential energy and a higher center of gravity at midstride. 

Human beings, running, adopt a different energy conservation strategy, storing potential energy in elastic “springs”: the Achilles tendon and other muscles and tendons in the legs, and in the feet. A number of other adaptations, evident in comparing later Homo with other apes, contribute to our aptitude for endurance running. Our lower joint surfaces are expanded, making them better (albeit imperfectly) adapted to handle the pounding stresses of running. Running also calls for counterbalancing the forces acting on alternating sides of the body. Lacking the tails of other bipedal runners (e.g. some birds and dinosaurs), we rotate our trunks. Our neck gets longer and shoulders and head get more independent so we can swing arms for balance without twisting our heads from side to side. And the gluteus maximus becomes the largest muscle in the body, to prevent our bodies from toppling forward with each step. Homo erectus is the first hominin with a serious butt.

https://scholar.harvard.edu/files/dlieberman/files/2004e.pdf

David Carrier argues that H. erectus was a persistence hunter, running after prey until they were exhausted. Human beings, although pretty poor sprinters, have a big advantage in distance running, in that our breathing is uncoupled from our running. This lets us run efficiently at whatever speed we choose. Most mammals, by contrast, have to breathe and run in synch, and pay a heavy price – wasting energy and overheating – for running at non-optimal speed. Bipedal dinosaurs enjoyed a similar advantage. And a recent article backs this up with some further calculations of running energetics, and with wide-ranging ethnographic evidence for endurance running in pursuit of prey.

But running for dinner is not the only possible selective pressure for endurance running in Homo. Violent conflict, including warfare, may have been an important selective pressure in human evolution. Sometimes, like doomed Hector,Homo erectus may have found himself running for his life.

And one more artistic note, that brings us closer to hunter-gatherers: Achilles is not the only legendarily speedy hero. Atanarjuat – The Fast Runner is a cinematic retelling of an Inuktitut Inuit legend, in the Inuktitut language, with an Inuit director and cast. It includes an extremely memorable sequence with the eponymous hero, victim of an ambush, running and running, naked and barefoot, through a snowy Arctic landscape, with his enemies in pursuit.

Homo erectus

Evolutionary theory implies that the transition from one species to another takes many generations. There’s never going to be a point at which a non-human animal gives birth to a human offspring. But on the scale we use to measure things at Logarithmic History, the time 1.8 million years ago has a good claim to be the time when human beings began. Genus Homo has been around for a while, but there are major evolutionary changes around now in the human direction. We can start with geography. It’s now that we find the first hominins outside of Africa, at least as far as Georgia in the Caucasus. The Dmanisi fossils from Georgia can probably be assigned to the new species Homo erectus, albeit somewhat shorter and smaller-brained than later erectus. Homo erectus also appears around this time in Africa (or maybe a bit earlier in South Africa, according to recent findings.)

It’s still possible that hominins got out of Africa even before erectus.  A recent article came out suggests that Homo floresiensis, the famous diminutive “hobbit” from Flores island, Indonesia, has its closest affinities with African Homo habilis, raising the possibility of an earlier exit. It’s even possible that H. erectus evolved outside Africa from this earlier emigrant (so far undiscovered), and then some migrated back to Africa.

H. erectus has a bigger brain than earlier forms, and reduced jaws and teeth. And there are dramatic changes below the neck. 

To be continued …

Amplifier lakes

Paleontologists and paleoanthropologists are busy sorting out what was special about the climate and ecology of Africa, especially East Africa, that contributed to various phases of hominin evolution. (“Hominin” is the current label for everyone more closely related to us than to our closest living relatives, i.e. chimpanzees and bonobos. My spell checker wants me to change it to hominid, the old label.) For example, Elizabeth Vrba, a South African paleontologist, argued that about 2.5 million years ago East Africa experienced a “turnover pulse” that affected a number of species. As the climate shifted toward cooler weather, and grasslands expanded, there was a wave of extinction and speciation among antelopes and (arguably) hominins as well.

More recently, paleoanthropologists have argued that not just cooling or aridity per se, but climate variability played a major role in driving hominin evolution, with episodes of greater variability leading to various responses ­– extinction, habitat tracking, or greater behavioral flexibility – as suggested in the diagram below.

More specifically, it looks like there were particular times when lakes were flickering in and out of existence along the Eastern and Western arms of the East African Rift Valley. Between just under 3 million years ago and just under 1 million three episodes stand out: around 2.7-2.5 mya, 1.9-1.7 mya, and 1.1-0.9 mya. These happen at intervals of 800,000 years, and may be tied to very long cycles in the eccentricity of Earth’s orbit. Within each of these episodes, the Rift Valley was home to large numbers of “amplifier lakes.” These lakes formed briefly during short intervals of high precipitation, and then evaporated quickly, making for a rich (sometimes) but also a particularly challenging environment.

Tellingly, it looks like these episodes were also associated with important events in hominin evolution. of 15 hominin species that evolved in this period, 12 appeared during these episodes.

This story, and much more, are set out in Lewis Dartnell’s excellent recent Origins: How Earth’s History Shaped Human History. However it is a ways from being settled science: here is a review of some of the problems with identifying ecological drivers of human evolution (behind a paywall unfortunately). The coauthors include some of my colleagues at the University of Utah.