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.

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?  Or our treaties whatever they may be worth; our symphonies however seldom they may be played; our peaceful acres, however frequently they may be converted into battlefields; our dreams however rarely they may be accomplished. The miracle of man is not how far he has sunk but how magnificently he has risen. We are known among the stars by our poems, not our corpses.

Ardrey, along with Konrad Lorenz and Desmond Morris, was much in vogue in the 1960s: Sam Peckinpah was another movie director influenced by him. The man could turn a phrase. 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 (more on this later). But where early stone tools are concerned, a different segue, from Oldowan chopper to Cuisnart may be more appropriate.

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

The Great American Interchange

2.87 – 2.72 million years ago

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.

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.)

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.

Lucy

AL (Afar locality)-288-1 is better known as Lucy: probably the most famous individual hominin fossil. Her skeleton is particularly complete, and demonstrated the existence of a previously unknown species, Australopithecus afarensis.

When she was discovered in 1974, she pushed back the hominin fossil record by over a million years. A. afarensis looked like a plausible ancestor to all the later hominins. (Things have gotten complicated since then.) “The first family” (AL 333) was discovered just a year later: bones of at least 13 individuals, a mixture of adults and juveniles, maybe all victims of a flash flood. This helped to fill in knowledge of individual variation among A. afarensis. And subsequent findings have documented the species over a million year span from 4-3 million years ago. At the same time, later discoveries have also suggested that there were likely multiple hominid species around in Lucy’s day.

Also: Her pelvis is basin-shaped, and she stood with her legs under her body, not rocking from side to side. All this is like a human, not a chimpanzee. So she was certainly bipedal, but there are arguments about just how bipedal. The initial view was that she was an efficient walker (although not much of a runner: that comes later). But another school of thought points out that she’s got very long arms, and curved finger and toe bones, suggesting she spent a lot of time in trees. Her long toes might have made her an inefficient biped (a view derided by members of the Lucy-the-proficient-walker school as the clown shoe hypothesis).

Lucy got her name from this song, played on a camp loudspeaker the day she was discovered. John Lennon, who wrote the lyrics, always denied that Lucy in the Sky with Diamonds, in spite of the initials, had anything to do with LSD. He said that it was based on picture that his son Julian (then four years old) made in school, with some Lewis Carroll thrown in.

‘I could tell you my adventures—beginning from this morning,’ said Alice a little timidly; ‘but it’s no use going back to yesterday, because I was a different person then.’

Alice in Wonderland Lewis Carroll

Four legs good, three legs better

Having grasping hands (and having them coordinate with the eyes) is one of the important things that distinguishes primates from other mammals. And a special version of bipedalism, which allows hands to specialize for manipulation, and feet for locomotion, is one of the first things that distinguishes hominins from other primates, even before hominin brains get big.

You find the same arrangement — a pair of arms with hands and a pair of legs with feet – with most science fiction aliens. (For TV and movie science fiction this just reflects the fact that aliens, pre-CGI, were mostly played by actors made up with pointy ears or fur suits or whatever.) But there are wilder possibilities, with no Earth analog. One of the most imaginative is the Pierson’s Puppeteers invented by Larry Niven:

“…. I was fed up with humanoids. Chad Oliver in particular, an anthropologist, wrote story after story claiming that this is the only workable shape for an intelligent being. The puppeteers were my first attempt to show him a shape that could evolve to intelligence. …”

The Puppeteers’ brains are safely tucked away inside their bodies, but they have two “necks” ending in “heads” each including one eye, one mouth, and a set of “fingers” around the lips. And the body has three legs. Decapitation is bad news for a Puppeteer,  like having a limb amputated, but not a death sentence.

Even more exotic are Vernor Vinge’s “Tines.” These are dog-like aliens who have evolved a short-range ultrasonic communication system that transmits information at such a high baud rate that a pack of half a dozen separate organisms is integrated into an enduring single individual with a shared consciousness. Losing one member of the pack is more like losing a limb, or having a stroke, than like the death of an individual. The mouths of the pack act together, as coordinated as the fingers on a hand, allowing the Tines to build up a medieval level civilization. (Vinge is a computer scientist, not an evolutionary biologist, however, and he glosses over some potential problems in Tine sociobiology: “all for one and one for all” is all very well, but which member of the pack actually gets to pass on their genes when it’s time to mate?)

But we don’t have to travel to other planets to find alternatives to two hands / two feet:

Elephant trunks, for example, let elephants browse while avoiding the need for a giraffe/diplodocus-style long neck. The trunks even have “fingers” (2 for African elephants, 1 for Asian elephants) that are sensitive enough to pick up a single piece of straw.

Even more exotic are octopuses (octopi, octopuses) – easily the smartest invertebrates, solitary creatures with little social life, but very handy with their tentacles. Peter Godfrey-Smith, philosopher and scuba diver gives his take here.

We’ll spend a lot of time on Logarithmic History asking how human beings got to be such an extraordinary species. Hands are an important part of the story, although the elephant and octopus cases suggest that hands (or their near-equivalent) are merely unusual, not absolutely unique to humans and near relations.

Ardi

4.4 Mya

We’ve got earlier hominins – Sahelanthropus, Orrorin tugensis, even an earlier species of Ardipithecus – but Ardi (her nickname, her species is Ardipithecus ramidus) stands out because she left us an exceptionally complete skeleton. 

And she helped to upend a lot of theories based on drawing a straight line between modern chimpanzees and later australopithecines. She was a biped. Her legs tucked under her pelvis, with a short lower spine, and a broad pelvis (all closer to modern humans than to chimps). Her outer foot was adapted for walking on the ground. But her toes were long-ish. And her big toe stood way off to the side: well-adapted for grasping branches. So when she was walking on the ground, she had to use her second toe to push off, instead of – like you and me – her big toe.

Ardi really shifted people to realizing that gorillas and chimps are specialized beasts, specialized in being big apes adept at climbing trees, grasping branches, swinging around, and pulling themselves up by their arms, but paying a price in inefficient knuckle walking when down on the ground. Ardi was taking up a different specialization, still a tree climber (her habitat was woodland, more than savannah), but ambling around (not quite striding yet) two-legged on the ground. 

So the common ancestor of chimps and humans, back before Ardi, apparently didn’t look all that much like either. In some respects she might have been somewhat closer to humans. She might even have been a sometime biped on the ground.

For a great recent summary, including lots of information about Ardi, and also about the politics, academic and otherwise, of digging fossils, check out Fossil Men: The Quest for the Oldest Skeleton and the Origins of Humankind.

The bottomlands

5.31 – 5.03 million years ago

There’s a book from back in 1954, now out of print, called Engineer’s Dreams by Willy Ley (who was most notable as a spaceflight advocate). The book lays out various grandiose engineering projects that people have proposed over the years. Some of these dreams have actually been realized: after centuries of people talking about it, there is now a tunnel under the English Channel.

Others … well …

One project the book discusses is damming the Congo River, creating a huge lake in the Congo basin, then sending the water north to create another huge lake in Chad. (There’s a small lake there now, almost dried out, which was a lot bigger 10,000 years ago when the Sahara was wetter.) From Lake Chad, the water would be sent further north to create a great river – a second Nile — running through Libya into the Mediterranean. All that fresh water is just running uselessly into the Atlantic now. Why not send it someplace where it’s needed?

Another engineer’s dream is to refurbish the Mediterranean Sea by building a dam across the Strait of Gibraltar. This actually isn’t an impossible project. The strait is less than nine miles across at its narrowest, and about 3000 feet deep (about 900 meters) at its deepest. A dam across the strait would have some dramatic consequences. The Mediterranean loses more water from evaporation than it gains from the rivers running into it. The difference is made up by a flow of water from the Atlantic. Cut this off, and the sea will start shrinking. You could let the Mediterranean drop 330 feet (about 100 meters) before stabilizing it, run a huge hydroelectric plant at Gibraltar, and open up a whole lot of prime Mediterranean real estate.

Sadly, whenever people have dreamed great dreams, there have always been small-minded carpers and critics to raise objections. Okay, so maybe the mayors of every port on the Mediterranean would complain about their cities becoming landlocked. And maybe massively lowering the sea level in an earthquake-prone region would lead to a certain amount of tectonic readjustment before things settled down.

So probably the Gibraltar dam will never be built (although Spain and Morocco are considering a tunnel). But we’ve seen already that Mother Nature sometimes plays rough with her children, and it turns out (although Ley couldn’t have known this back in the 50s) that damming the Mediterranean has already been done. The story begins back in the Mesozoic (late March), when the Tethys Sea ran between the northern continent of Laurasia and the southern continent of Gondwanaland. The sea was still around 50 million years ago (April 11) when whales were learning to swim. But it has been gradually disappearing over time. When India crashed into Asia and raised the Himalayas, the eastern part of the sea closed off. And as Africa-Arabia moved north toward Eurasia, a whole chain of mountains was raised up, running from the Caucasus to the Balkans to the Alps. The Tethys Sea was scrunched between these: what’s left of it forms the Caspian, Black, and Mediterranean seas.

Starting about 6 million years ago, the story takes a really dramatic turn. The continents were in roughly there present positions, but the northern movement of the African tectonic plate, plus a decline in sea levels due to growing ice caps, shut off the Strait of Gibraltar, sporadically at first. With water from the Atlantic cut off, the Mediterranean began drying out. By 5.6 million years ago, it had dried out almost completely – the Messinian Salinity Crisis. (The Messinian Age is the last part of the Miocene Period). There were just some hyper-saline lakes, similar to the Great Salt Lake in Utah or the Dead Sea in the Near East, at the bottom of an immense desert more than a mile below today’s sea level. The Nile and the Rhone cut deep channels, far below their current levels, to reach these lakes. This lasted until 5.3 million years ago, when the strait reopened and a dramatic flood from the Atlantic restored the Mediterranean.

All this was happening just around that time that hominins were committing to bipedalism. Did the cataclysmic events in the Mediterranean basin have some influence on hominin evolution in Africa? At this point we can’t say.

Harry Turtledove, prolific writer of alternative history, has a novella, Down in the Bottomlands, set on an alternative Earth in which the Mediterranean closed off, dried out, and never reflooded. In the novella, terrorists are plotting to use a nuclear weapon to reopen the Mediterranean desert to the Atlantic – sort of Engineer’s Dreams in reverse.

And here’s a completely unrelated post about bottoms.

Grasses and gases for a cooling world

The standard sort of photosynthesis uses a so-called C-3 chemical pathway. But  maybe from 8-7 million years ago there’s an increasing proliferation of so-called C-4 plants. They are more tolerant of low carbon dioxide levels, using an alternative, more-efficient pathway to incorporate carbon from C0₂. C-4 plants evolved independently 45-60 times.

Tropical grasslands are mostly C-4. The profusion of grasses, herbivores, and carnivores on tropical savannahs will owe a lot to C-4 plants. This evolutionary transition is probably a sign that C0₂ levels are declining, and have reached a threshold where C-4 plants are favored.

Going back about 7 million years, C0₂ levels stood at maybe 1500 parts per million (ppm). (They were higher earlier in the Miocene.) Levels decline pretty steadily, leading to global cooling and eventual Ice Ages. But things never again reach the extremes of Snowball Earth 750 million years ago.

At the beginning of the Industrial Age C0₂ levels stood below 300 ppm. They went above 400 ppm a few years back.

Toumaï

7.04 – 6.67 million years ago

Sahelanthropus is a 7-6 million year old species whose remains have been found in Chad. “Toumaï” (“hope of life” in the Daza language) is the nickname for one individual, represented by a fairly complete skull. Otherwise Sahelanthropus is known from some jaws and teeth.

One of the things that distinguishes hominins (the human line) from great apes is that the front teeth – canines and incisors – are reduced. (Back teeth are another story. They stay big, or even get bigger, for a long time.) By this standard, Sahelanthropus looks like an early hominin. It’s got reduced incisors and canines and a short mid-face. And depending on who you talk to, it might or might not have been bipedal, although the foramen magnum (where the spine enters the skull) was maybe not positioned to balance the skull on top of the spine. Not that there was much brain inside the skull: the cranial capacity (maybe 360 cc) would be at the low end for a chimp.

So Sahelanthropus could be one of the very first species related to us after the chimp/human split. Chad, where Sahelanthropus was found, is a long way from East Africa, where most other hominins have been found, which suggests there may have been a profusion of hominins across Africa, waiting to be discovered.

The face in the Logarithmic History banner for the month of May is a Sahelanthropus.

Two roads diverged

7.88 – 7.46 million years ago

There was a lot of hullabaloo a few years back over claims that a jaw assigned to the 7.2 million year old Graecopithecus freygbergi represents the earliest known human relative after the hominin/chimp split. The jaw was found in Greece, which suggests that the split happened around the Mediterranean, rather than in Africa. (This doesn’t take anything way from the claim that Africa is the main center of later human evolution, up to 2 million years ago, which would have taken place when Graecopithecus’ descendants migrated to Africa).

All this needs to be taken fairly skeptically: a mandible with one tooth isn’t overwhelming evidence.

The date for Graeccopithecus is at the upper end of dates given for the chimp-human split. The TimeTree site, sponsored by Penn State, Arizona State, the National Science Foundation, and NASA, lets you enter any pair of species you want (common names or Latin) and find out the time since they split from a common ancestor. You get a range of estimates from the scientific literature, along with means and medians. The site lets you track down sources if you want. Entering Homo sapiens and Pan troglodytes gives you a median estimate of  the time of the split of 6.4 million years, a mean estimate of 6.7, and a whopping confidence interval of 5.1 to 11.8 million years, based on 79 studies.

Bottom-up apes

According to the latest research, chimpanzees recognize other chimps not just by their faces but by their butts. 

Which raises the further question: Why are chimps down on all fours, while we’re not? This and related matters are subjects of a major recent review, “Fossil apes and human evolution,” which contrasts “top-down” and “bottom-up” approaches to understanding comparative ape and human ancestry. The authors write “top down approaches have relied on living apes (especially chimpanzees) to reconstruct [human] origins.” By contrast, “bottom-up” approaches pay more attention to the fossil record. The review brings to the fore something that’s been brewing for a while: fossil apes from the mid to late Miocene, leading up to the time that gorillas, chimps, and humans go their separate ways, are a varied bunch, and the last common ancestors of gorillas, chimpanzees, and humans, and of chimpanzees and humans, may be creatures that didn’t look all that much like any of the three. More specifically, the common ancestors may have been “orthograde,” standing upright and using both feet and hands to clamber vertically through trees. From ancestors like this, gorillas and chimps may have evolved similar innovations in parallel, getting bigger, evolving longer arms, larger palms, and shorter backs – all of which helped them as big animals to get around in trees, but also led them to take a more crouching posture, and to adopt the expedient of knuckle-walking on the ground (and hence to spend a lot of time looking at one another’s butts). The ancestors of humans, on this account, followed a different path, adopting bipedalism – not such a big step, already a big part of their postural repertoire – when walking on the ground. 

In some ways, gorillas and chimps seem to be caught in a “specialization trap.” This seems to show up in the energetics of locomotion. For a human being, it takes about 50 kilocalories to walk a mile (or about 30 kcal to walk a kilometer). This is about the same as you’d expect for a standard mammalian quadruped of our size. But for chimpanzees, committed to knuckle-walking, the energy cost is about double.