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.

It’s still possible that hominins got out of Africa even before erectus. Just this April, an article came out suggesting 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. Erectus has a body shape and size quite similar to ours. Strikingly, the changes in body form seem to be systematically related to distance running. Tendons in the feet and calves turn into springs that put a bounce in our running stride (but also rule out serious tree-climbing). 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.

Moving from what we know to what we guess, it looks likely that Homo erectus had shifted to a new diet and a new mode of acquiring food. 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.

Like anything else in paleoanthropology, there are arguments about this. For example, fire may or may not have played a significant role at this early stage. We’ll cover some of these arguments in posts to come.

Grassroots and fisticuffs

A couple of recent perspectives on Australopithecus and early Homo:

Tropical grasses and sedges commonly use the C4 pathway for photosynthesis, which evolved from the C3 pathway used by most plants, in response to lower atmospheric carbon dioxide levels. We can trace an isotopic signature in the teeth of animals that eat C4 plants (and animals that eat those animals). From about 3.5 Mya we see evidence of hominins eating more C4 foods: either grasses (maybe including underground parts) or animals that ate grasses. Paranthropus boisei seems to be a particular champion with the C4s. Chimpanzees, even when they live in open woodlands, mostly stick to eating fruits and leaves. By contrast, exploiting grassroots and sedges to varying degrees may be an important component of australopithecine adaptation to the savannah.

Not only do australopithecines have enlarged back teeth relative to great apes, but they also have smaller canines. Canines are mostly good for fighting, so it’s nice to think that canine reduction is a sign of our ancestors becoming more peaceful. Could be. But it’s possible they just switched fighting styles. David Carrier argues that australopithecine faces are built to withstand punches, starting from the time that australopithecine hands were capable of forming fists. This might go together with high levels of sexual dimorphism – males, the more violent sex, being bigger than females (but early hominin sexual dimorphism is a contentious subject.)

Two Million BC

Two million years ago, there were multiple hominin species in Africa. There were two robust species that we know of, boisei in east Africa and robustus in southern Africa. The robusts had huge premolars and molars, and enormous jaw muscles running through a large zygomatic arch to attach all the way up to the sagittal crest in the middle of the skull. Gorillas have sagittal crests too, but with them it’s about powerful bites from incisors and canines. You, on the other hand, don’t have a sagittal crest. Your temporalis muscle only runs up to your temple.

The robusts are sometimes given their own genus Paranthropus, other times included in Australopithecus. This reflects uncertainty about their relationships. Did robust morphology evolve once, with both boisei and robustus evolving from aethiopicus? Or did it evolve independently several times, with robustus evolving from Australopithecus africanus in southern Africa?

P. boisei. Robust ancestor?

There was at least one genus of Homo around two million years ago, Homo habilis, with a larger brain than any australopithecine, but similar body size and long arms. There was also the recently discovered Australopithecus sediba, with brain not especially large, but maybe reorganized in a human direction, and teeth trending human-wards as well. . We don’t know if either of these guys was a human ancestor. Another candidate, Homo rudolfensis will show up soon.

A. sediba. Composite based on 3 individuals

Turnover pulse

Elizabeth Vrba, a South African paleontologist, coined the term “turnover pulse.” The idea is that most species most of the time are in an equilibrium with their physical and biotic environments, and not changing much. But every once in a while an environmental disturbance comes along, resulting in large scale extinctions, and a pulse of speciation. Most evolutionary change, on this theory, occurs during these pulses. Vrba saw evidence of a pulse 2.5 million years ago among South African antelopes (affecting specialized more than generalized feeders). The pulse was associated with a shift toward cooler weather, and a shrinking of forests and expansion of grasslands. Part of the turnover pulse hypothesis is that the same pulses should affect many different species at the same time: there is arguably a turnover among hominins as well, giving rise to a later generation of savannah-adapted australopithecines.

Vrba was one of a circle of paleontologists pushing the idea of punctuated equilibrium ¬– that during most of their existence species don’t change much (stasis), and evolutionary change is concentrated in the times and places when a new species branches off from another. Steven Jay Gould and Niles Eldredge were others pushing the idea. There are various possible explanations for why we might see a combination of stasis and punctuated equlibrium (assuming the theory is true in the first place). Environmental controls, as suggested by Vrba are one possibility. Or maybe species’ developmental systems are tightly integrated and resistant to change. Or (for sexually reproducing species) the need to find a similar-enough mate might foster stasis most of the time.

We’ve seen some enormous episodes of mass extinction before on Logarithmic History. The turnover pulse hypothesis implies that the same phenomenon on a smaller scale is behind most evolutionary change. Not everybody buys this though. Punctuated equilibrium is a hugely contentious topic. And plenty of evolutionary biologists think that arms races among (and within) species keep evolution running along pretty constantly even without environmental changes. We’ll see some of the same issues – punctuation versus gradualism, ecological forcing versus internal dynamics driven by arms races – when we take up human history.

Your Cuisinart, a prehistory

A famous movie cut, from 2001: A Space Odyssey, transitions from a bone club, hurled aloft by an australopithecine 2.5 million years ago, to a spacecraft in the year 2001.

2001bone

Arthur Clarke and Stanley Kubrick, coming up with the plot for the movie/book, were influenced by the popular author Robert Ardrey. In his book African Genesis, Ardrey casts human evolution as a version of the story of Cain and Abel, except in his version the peaceful vegetarians (robust australopithecines) get clobbered by the club-wielding meat-eaters (gracile australopithecines).

We were born of risen apes, not fallen angels, and the apes were armed killers besides. And so what shall we wonder at? Our murders and massacres and missiles, and our irreconcilable regiments?

Ardrey, along with Konrad Lorenz and Desmond Morris, was much in vogue in the 1960s: Sam Peckinpah was another movie director influenced by him. Unfortunately his speculations on evolution and human behavior are probably not of enduring value: he had the misfortune to take up the topic too early to take on board the sociobiological revolution pioneered by William Hamilton, Robert Trivers, and George Williams, and popularized by E. O. Wilson and Richard Dawkins.

Ardrey may not have been off-base in thinking that weaponry and warfare have been an important motive force in human biological and social evolution. But where early stone tools are concerned, a different segue, from Oldowan chopper to Cuisnart may be more appropriate.

oldowanpiccuisinart.jpg

Recent research argues that early hominins could have dramatically increased available food energy by pounding vegetables and chopping up meat into more digestible pieces. Tool use may have been an early step in our ancestors’ move to high energy diets. Meat-eating began to be important in human evolution around 2.6 million years ago. Somewhat later we see evidence that some hominins have lighter jaws and aren’t chewing as much. So to celebrate this early dietary revolution, here’s a recipe:

Steak Tartare

Place in a food processor fitted with the metal chopping blade:

1 ½ pounds lean beef (tenderloin, top round, or sirloin) cut into ½ inch cubes

Pulse until meat is coarsely ground, 7-10 seconds. Do not over-process. Remove meat to a chilled platter or individual plates and gently form into 6 individual mounds.

[Optional: Make a spoon shaped indentation on top of each mound and crack into each

1 egg yolk.]

Divide and arrange in small piles around each serving:

½ cup minced onions
½ cup minced shallots
½ cup minced fresh parsley
¼ cup minced drained capers
8-12 anchovies (optional)

Serve immediately and pass separately:

Fresh lemon juice
Worcestershire sauce
Dijon mustard
Hot pepper sauce
Freshly ground black pepper
Salt

From The Joy of Cooking 1997

Stonecraft as soulcraft

2.71-2.56 million years ago

Until recently the earliest known stone tools dated back to the Oldowan, 2.6 million years ago, although just last year stone tools going back 700,000 years earlier were reported.

We now know that tool making is not uniquely human. But Oldowan tools – including choppers (below), pounders, and scrapers — go beyond anything chimpanzees, or other animals, do. Kanzi, a bonobo (pygmy chimpanzee, who was also taught to communicate with an artificial set of symbols) learned to use sharp stone flakes for cutting, but never mastered the art of striking a stone core at the proper angle to produce useful sharp flakes. Apparently australopithecines (or maybe early Homo or Kenyanthropus) had taken a step further by 2.6 million years ago (or earlier).

oldowan

Early evolutionary theory developed in tandem with the Industrial Revolution and included an appreciation for the importance of manual labor. Darwin, in The Descent of Man, argued for the central role of toolmaking in human evolution, and, not surprisingly, the same point was echoed by Friedrich Engels in 1876, in his unfinished essay “The Part Played by Labor in the Transition from Ape to Man.” Engels was pushing back against the attitude in most traditional stratified societies that manual labor is low class, while symbolic labor (and/or wielding weapons) is high class. For example the fingernails on this Chinese scholar advertised that he didn’t work with his hands.

fingernail

Nowadays, a common complaint about the post-industrial economy is that so much education and employment revolves around pushing symbols around that manual labor is relatively devalued. The recent book Shopcraft as Soulcraft: An Inquiry into the Value of Work is a statement of this lament. Maybe today is a good time to celebrate the part played by labor in the transition from ape to man — by making something, or mending something. I’ll be doing my part by neandering a big branch that broke off the apricot tree in my back yard. (But if food is more your thing, the next post will suggest a recipe.)

The Great American Interchange

For most of the last 100 million years, South America was an island continent, like Australia, with its own peculiar mix of species, largely isolated from other continents (although monkeys, and guinea pig relations, rafted across.) By contrast, North America was intermittently connected with Eurasia and exchanged species off and on. South America supported a rich array of marsupials, including a marsupial version of a saber-toothed tiger. It also had predatory flightless “terror birds” that seemed bent on reoccupying the two-legged predatory dinosaur niche.

terror bird

There was also a profusion of notoungulates (probably distantly related to hoofed animals in North America and Eurasia), and liptoterns. (Below is a reconstruction of a late surviving liptotern, Macrauchenia, looking like a Dr. Seuss invention.)
macrauchenia

South America was close enough to North America for the two continents to start exchanging species by 14 million years ago, but the really massive exchange began with the establishment of the Isthmus of Panama, and climate changes, about 3 million years ago. 38 genera of land mammals walked north from South America. 47 genera walked south from North America. So the initial exchange was unbalanced; the subsequent evolution was even more so. Only a handful of South American invaders – notably armadillos and (for a while) ground sloths – succeeded in establishing themselves in North America, while North American invaders generated a profusion of new species. Many of the really distinctive South American forms would go extinct over the next millions of years.

Paleontologists dispute the causes of the turnover, but it looks an awful lot like North American species had a competitive edge. This is one instance of a phenomenon we’ve seen already in animal evolution, and will see again in human history, of large land areas generating more competitive forms.