Sunday, June 14, 2015 — Yes, We Have No Savannah

Did ear­ly hominins evolve on the savan­nah? Almost any­one who reads works on pale­oan­thro­pol­o­gy would say “yes.” I would like to explain why I’m tempt­ed to say “no.”

A long time ago, I was chat­ting with an ornithol­o­gist. We were dis­cussing the Cana­di­an province of Saskatchewan, the south­ern third of which con­sists of the clas­sic North Amer­i­can prairie land­scape. I casu­al­ly referred to some “prairie birds”, includ­ing among them the wil­lett and the killdeer. My friend cor­rect­ed me. “Those aren’t prairie birds at all,” he said. “They live on the river­banks. That’s a total­ly dif­fer­ent ecosys­tem. It doesn’t mat­ter that it’s only a few hun­dred yards wide and six hun­dred miles long, it’s not the prairie. Dif­fer­ent plants and ani­mals, liv­ing a dif­fer­ent lifestyle.” This was some­thing I hadn’t grasped. The prairies of Saskatchewan sup­port species like the lark bunting, the bobolink, the west­ern mead­owlark, and the sharp-tailed grouse, which all nest, feed and frol­ic on the grass­lands, and are all bona fide “prairie birds”. Fur­ther to the north, in the great Cana­di­an for­est, you will find wood­land species like the black­poll and Ten­nessee war­bler, the pine siskin, and the nuthatch. But the wil­lett and the killdeer live and work in a ripar­i­an niche, the com­plex ecosys­tem of river­banks and lake­sides, which is fun­da­men­tal­ly dif­fer­ent from the grass­lands that sur­round them.

In the 1980’s, when I read exten­sive­ly on the sub­ject of human evo­lu­tion, I noticed that pale­oan­thro­pol­o­gists did not make this dis­tinc­tion. Vir­tu­al­ly every book and arti­cle dis­cussed some aspect of hominin evo­lu­tion “on the savan­nah.” Now, a savan­nah is a grass­land, much like the prairie of Saskatchewan, except that it is dot­ted with trees that are not suf­fi­cient­ly close togeth­er to form a canopy. Like prairie, its ground cov­er is grass, form­ing a tigh­ly woven matrix. It sup­ports a vari­ety of graz­ing ani­mals, and the preda­tors that dine on them. Most of us have a men­tal pic­ture of the African savan­nah, formed by numer­ous tele­vi­sion nature spe­cials and old films like Born Free. Almost every book or paper about hominin evo­lu­tion talks about the savan­nah as the ecosys­tem in which it took place. Yet, when­ev­er I read par­tic­u­lar reports of hominin fos­sil finds, it tran­spired that the actu­al site involved was, at the time the crea­ture was liv­ing, the banks of a riv­er, a lake or a stream. In oth­er words, from the point of view of any field nat­u­ral­ist, not on the savan­nah.

One of countless representations of homonins placing them in a savannah landscape.

One of many rep­re­sen­ta­tions of homonins plac­ing them in a savan­nah land­scape.

Why is this dis­tinc­tion impor­tant to the study of human evo­lu­tion? Well, in the books I con­sumed in the 1980s, the men­tal image of the savan­nah as the cru­cial envi­ron­men­tal deter­mi­nant of hominin evo­lu­tion was so pow­er­ful that it gen­er­at­ed no end of dubi­ous spec­u­la­tion. Man the Mighty Hunter still dom­i­nat­ed ideas of hominin evo­lu­tion, and vir­tu­al­ly every­thing about our pre­de­ces­sors’ bod­ies, as inter­pret­ed through fos­sil remains, invit­ed expla­na­tion as an adap­ta­tion to hunt­ing on the savan­nah — despite the occa­sion­al sar­cas­tic remark from female pale­oan­thro­pol­o­gists that, after all, the den­ti­tion of hominins and oth­er evi­dence point­ed to the impor­tance of gath­ered veg­etable food. But nobody was busy con­coct­ing sce­nar­ios in which tuber-dig­ging drove mod­i­fi­ca­tions in skele­tal struc­ture. Some of the ideas that float­ed about were down­right absurd. Hominins sup­pos­ed­ly lost their fur so they could sweat more effi­cient­ly as they ran after game on the savan­nah (despite the fact that no oth­er savan­nah hunter, such as any of the big cats, found any dis­ad­van­tage in pos­sess­ing fur). The notion that lan­guage evolved so that hunters could shout instruc­tions at each oth­er, and that upright pos­ture evolved to facil­i­tate run­ning after game still have cur­ren­cy. Even back in the 1980s, I found these inter­pre­ta­tions far from plau­si­ble. I was pret­ty famil­iar with hunters in var­i­ous envi­ron­ments, and I knew per­fect­ly well that any hunters who end­ed up doing a sig­nif­i­cant amount of run­ning were pret­ty poor, and prob­a­bly unsuc­cess­ful hunters. Suc­cess­ful hunt­ing is done by pre­dict­ing where game is like­ly to be, spot­ting evi­dence of ani­mal pres­ence, track­ing the ani­mals down, and sur­pris­ing them where they are, usu­al­ly by main­tain­ing silence and con­ceal­ment. Most tra­di­tion­al hunters have an elab­o­rate code of hand sig­nals to use when they hunt in groups, because the last thing you want to do is make noise. If the game is on the run, pur­su­ing it in the same fash­ion is like­ly to fail. Most large game ani­mals can run faster than humans. Expend­ing a huge amount of calo­ries in run­ning, on the slim chance that you will catch up with prey, is a short­cut to star­va­tion. Human beings have evolved to be pret­ty good run­ners, com­pared to oth­er pri­mates, but they are not in the league of dozens of game species that have remained res­olute­ly quadrupedal. Links between bipedal­ism and hunt­ing, and between lan­guage and hunt­ing struck me as an absurd Daffy Duck car­toon of hominins run­ning across the grass­lands, wav­ing spears and shout­ing. Few seemed to notice that such an evo­lu­tion­ary path­way would per­force lead to greater sex­u­al dimor­phism, rather than the steadi­ly decreas­ing dimor­phism in the fos­sil record. If male hunt­ing tac­tics drove skele­tal change, then there would be noth­ing dri­ving the same change in females.

So it was that, strict­ly as a read­ing observ­er, and not as any kind of pro­fes­sion­al in the field, I began to look around for a more plau­si­ble sce­nario. Now, the read­er must not get my inten­tions wrong. In some areas of sci­ence, such as ornithol­o­gy and opti­cal astron­o­my, there is a strong tra­di­tion of “ama­teur” par­tic­i­pa­tion. Ornithol­o­gy depends on the obser­va­tions of many thou­sands of non-pro­fes­sion­als, and their con­tri­bu­tion to sci­ence is respect­ed. But archael­o­gy and pale­oan­thro­pol­o­gy are fields that attract all sorts of non-pro­fes­sion­al cranks, and most pro­fes­sion­als in these fields shud­der when they hear the word “ama­teur”. I am not a sci­en­tist work­ing in any aspect of human evo­lu­tion. I am mere­ly some­one who fol­lows the sci­ence as it appears in pub­li­ca­tion, for my own edi­fi­ca­tion, and because my stud­ies of human soci­ety and his­to­ry include human evo­lu­tion and pre­his­to­ry as part of a com­pre­hen­sive overview. My spec­u­la­tions were then, and are now, mere­ly for my own enter­tain­ment.

It struck me, back then, that con­stant­ly call­ing upon the envi­ron­ment of the savan­nah was a red her­ring. Remem­ber­ing the words of my ornithol­o­gist friend, I tried to keep in mind that ear­ly hominins were ripar­i­an crit­ters, inhab­i­tants of riv­er banks and lakeshores. I sur­mised that they spent far more time near water than out on the grass­lands, a pat­tern that has been repli­cat­ed by near­ly every human soci­ety in sub­se­quent his­to­ry. Now, what are the out­stand­ing fea­tures of such an envi­ron­ment? Two come quick­ly to mind. One is that a river­bank has a com­plex ecol­o­gy with a wide vari­ety of food sources for any crea­ture that has the curios­i­ty and dex­ter­i­ty to poke and pry. The oth­er is that it is an extreme­ly dan­ger­ous envi­ron­ment. The graz­ing ani­mals that live on the grass­lands must come to lakes and rivers to get water. But they don’t stick around. It is pre­cise­ly there that they are most vul­ner­a­ble to preda­tors. In Africa, they rely on the safe­ty of num­bers, with herds accept­ing loss­es from big cats or croc­o­diles with each trip to the water source. Ear­ly hominins would have faced the same per­il, though they would be a less desir­able din­ner than a tasty gazelle or water buf­fa­lo. Being attacked by a preda­tor when going to the riv­er for water is actu­al­ly still a sig­nif­i­cant per­il for humans in rur­al Africa. But sup­pose this dan­ger could be turned into an oppor­tu­ni­ty?

The oppor­tu­ni­ty I had in mind was theft. What if you could take advan­tage of the fact that game ani­mals will come to the river­side or lake­side, and that preda­tors would fol­low them and kill them? What would be need­ed would be some way of dri­ving the preda­tors away after they made their kills, then steal­ing the fresh kills. There had been, even back then, some spec­u­la­tion about ear­ly hominins being scav­engers rather than hunters, but I think those who were advanc­ing this idea were think­ing more of the kind of scav­eng­ing that is done by minor car­ni­vores that “clean up” the kills of major preda­tors, who usu­al­ly leave sig­nif­i­cant amounts of left­overs after they have gorged them­selves on the best bits. This is not what I had in mind. I was think­ing, rather, of hominins divid­ing their atten­tion between gath­er­ing the numer­ous tid­bits that can be found on river­banks — birds’ eggs, cray­fish, nuts, tubers, small bur­row­ing ani­mals, fruit, berries, frogs, fish — and the theft of fresh kills from preda­tors. How do you steal from a big cat? You let it make its kill, then you dri­ve it away. But, how do you dri­ve it away?

You throw rocks.

The more I looked at the phys­i­o­log­i­cal changes that dis­tin­guished ear­ly hominins from their simi­an rel­a­tives, the more they seemed to me to line up with throw­ing rocks. Chim­panzees reg­u­lar­ly throw things (usu­al­ly excre­ment, which they fling as a sign of hos­til­i­ty), but they are not very good at it. Their wrists are not well-shaped for it, their fin­gers are too long, and their arms and shoul­ders don’t have the right con­fig­u­ra­tion for pitch­ing things accu­rate­ly. But it is pre­cise­ly these fea­tures that are dra­mat­i­cal­ly mod­i­fied in ear­ly hominins, and the changes are as dra­mat­ic as those in the low­er body and spine that favour bipedal­ism. Human beings, the inher­i­tors of these changes, may not be able to run like a chee­tah, or out­per­form oth­er ani­mals in many tasks, but they are spec­tac­u­lar­ly good at throw­ing things. One has only to look at chil­dren play­ing base­ball or crick­et to see that humans have evolved phe­nom­e­nal throw­ing skills. Ear­ly hominins had all these fea­tures — they have remained remark­ably sta­ble ever since. They prob­a­bly were as good at throw­ing rocks and hit­ting the mark as we are. 

This sce­nario also plays into the riverside/grasslands dichoto­my. Walk around on a grass­land and try to find a rock that will fit into your hand. You won’t. It’s along riv­er banks that you find peb­bles and rocks, and espe­cial­ly rocks that have been round­ed by tum­bling to make them fit in the hand, and deposit­ed in handy piles. A small group of hominins, able to col­lect and stock­pile throw­ing rocks, able to throw them accu­rate­ly, able to work togeth­er, some­times throw­ing from con­ceal­ment, some­times sur­round­ing and attack­ing from all sides, should have been able to dri­ve away even a top preda­tor like a big cat, leav­ing a fresh kill for the tak­ing. Hominins would not have had to find ani­mals, because ani­mals would have come to them, to known drink­ing places. Hominins would not have had to bring down an impala or a buf­fa­lo, because a preda­tor would have done it for them. It would have been dan­ger­ous work, requir­ing as much courage as any form of hunt­ing, but it would have been a viable strat­e­gy, one that could have pro­vid­ed the inter­me­di­ate evo­lu­tion­ary feed­back that ulti­mate­ly lead to pur­su­ing large game. Bipedal­ism, the good binoc­u­lar vision already extant among pri­mates, and strate­gic muta­tions in the struc­ture of the wrist and shoul­der, would have con­sti­tut­ed a deal­ing of the cards that would have trumped the big preda­tors. Observ­ing when and where game ani­mals would come to drink would have been in har­mo­ny with the con­stant obser­va­tion that accom­pa­nied all the oth­er forms of food acqui­si­tion char­ac­ter­is­tic of a ripar­i­an envi­ron­ment. Unlike the savan­nah graz­ers who came to the water hes­i­tant­ly and depart­ed as quick­ly as they could, hominins would have been able to stick by the shore and exploit its resources thor­ough­ly.

I rea­soned that bipedal­ism was more use­ful in this con­text than in chas­ing game on grass­lands, and that
most of the rather odd changes in skele­tal struc­ture that appeared among ear­ly hominins fit in bet­ter with this sce­nario. Tool use, which appears quite ear­ly in the form of mod­i­fy­ing hand-sized rocks and peb­bles, also seems to unfold nat­u­ral­ly from it. First you throw rocks, then you begin to select rocks that throw best, then you stock­pile rocks, then you devise ways of car­ry­ing rocks, then you start break­ing rocks up to get the size you want, then you start mod­i­fy­ing them by strik­ing them against each oth­er, then you start devis­ing new uses for them (scrap­ers, pounders, cut­ters, wedges). The need to car­ry throw­ing rocks and the need to make food caches, hang­ing from trees, or buried in riv­er banks, would have stim­u­lat­ed anoth­er range of tools: con­tain­ers. Unfor­tu­nate­ly, con­tain­ers tend to be made from per­ish­able mate­ri­als that leave no remains, so they have been sore­ly neglect­ed in stud­ies of ear­ly tech­nol­o­gy. All these process­es, includ­ing the throw­ing, would not be gen­der-depen­dent. Even if males took the lead in the “theft-hunt” there would still be suf­fi­cient rea­son for females to devel­op along sim­i­lar lines, and most of the skills and con­se­quent attrib­ut­es would over­lap with oth­er forms of food gath­er­ing. Hunt­ing on the savan­nah would not have been some­thing that drove evo­lu­tion­ary changes, but a lat­er exten­sion and mod­i­fi­ca­tion of the orig­i­nal strat­e­gy. Even today, the hunt­ing under­tak­en on the savan­nah by tra­di­tion­al-style hunters in the Kala­hari or the Aus­tralian out­back has more in com­mon with ripar­i­an food-gath­er­ing tech­niques than it does with the hunt­ing done by ani­mal preda­tors. It’s all based on close, calm obser­va­tion, and coor­di­nat­ed activ­i­ty, not on the abil­i­ty to exert ener­gy in sprint­ing.

Some of these points had been made long before, by the advo­cates of the “aquat­ic ape hypoth­e­sis” (Max West­en­höfer, Alis­ter Hardy, and Elaine Mor­gan), but their view­point was not tak­en seri­ous­ly by the great major­i­ty of sci­en­tists when I was doing my first read­ing, and is still not tak­en seri­ous­ly today. Nor am I an advo­cate of it. How­ev­er, while some of the points over­lap, rec­og­niz­ing that our ances­tral envi­ron­ment is bet­ter described as ripar­i­an than savan­nah-based is not the same as the aquat­ic ape hypoth­e­sis. The stone-throw­ing sce­nario did not play any part in the aquat­ic the­o­ry. I have a feel­ing, how­ev­er, that focus­ing on the ripar­i­an envi­ron­ment is some­what taboo, because it sug­gests an “edg­ing toward” a the­o­ry which is usu­al­ly con­sid­ered to be cranky.

So, in the 1980s, I set­tled on this image of hominid evo­lu­tion, pure­ly for my own way of envi­sion­ing human ori­gins. I occa­sion­al­ly dis­cussed it with friends, but lit­tle else. Now, here we are, decades lat­er, and I’m in the mid­dle of one of my cycli­cal read­ing binges in pale­oan­thro­pol­o­gy. How is my imag­ined sce­nario look­ing now?

Well, I’m hap­py to say that many lines of inquiry have been mov­ing things in its direc­tion. Most of the trends make me feel that my spec­u­la­tions were anticip­i­to­ry. There is still a lin­ger­ing habit of describ­ing our ances­tral habi­tat as the “savan­nah”, but there’s been a steadi­ly grow­ing real­iza­tion that the eco­log­i­cal issues are more com­plex. The envi­ron­men­tal back­ground of hominin evo­lu­tion was not just a sta­t­ic repro­duc­tion of the mod­ern African veldt. The “mighty hunter” theme is con­sid­er­ably toned down, and there is more atten­tion giv­en to food gath­er­ing (though it is rarely linked to major phys­i­o­log­i­cal changes). The skele­tal changes have been recon­sid­ered from a greater vari­ety of the­o­ret­i­cal view­points. There have been sig­nif­i­cant stud­ies made, in recent years, of the phys­i­ol­o­gy of human and pri­mate throw­ing skills. One recent researcher even casu­al­ly men­tioned that rock-throw­ing might have been used to dri­ve away preda­tors. All that’s miss­ing is a small shift in view­point, a real­iza­tion that all these mod­i­fi­ca­tions of the old­er views can be reshaped into a coher­ent whole.

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