I had mentioned earlier that the volcanoes of the Virugna region in the Western Rift Valley (as well as other highland spots) have often been islands of rain forest separated from each other by different habitats, including grasslands and wooded savannas. this has produced an island effect that has been a laboratory for evolution, and it is likely that these forest islands (and others in the greater region of east Central Africa and western East Africa) have been the loci of evolution of many endemic species. (See Island Africa: The Evolution of Africa’s Rare Animals and Plants
It is probably not a coincidence that two of the three subspecies of gorilla live within sight of each other (and of the main subspecies, the lowland gorilla) within this region. The Virunga volcanoes are not old enough to have supported island forests for the evolution of these specific subspecies, but other highlands in the region, or other volcanoes (perhaps in the Eastern Rift) may well have been the location in which they evolved.
And, as it turns out, there is reason to believe that the split between chimps and humans occurred on one of these volcanic mountain tops several million years ago. Or, at least, in an environment geologically similar to the upper reaches of the Virunga Volcanoes. But to tell this story right, I have to go back a few years.
… distant in the background African sounding drum music, distant thunder, polyphonic singing fades to the sound of steel on rock as dozens of workers are excavating elephant bones in the dusty windswept African plain under the watchful eyes of the Rwenzori …
The Congo. Parc National de Virunga, well north of the Virunga Volcanoes, north of Lake ex-Edward. I was with a fairly large expedition. At the time we had been waiting for crucial supplies, including tents and cots and other accouterments of field life, to arrive in a truck the expedition had purchased in Kinshasa, which was being driven to the field site via the Central African Republic (there are no roads that traverse the Congo). The truck was several weeks late. So, on the occasion that we heard a vehicle on the nearby park road (once or twice a week), we had taken to chanting the name of the driver of the truck (Leo) while facing a mock-up of the truck made by a local school kid, that we had placed in a makeshift shrine under a tree near our dining area.
“Leo… Leo…. Leeeeoooooo….” we were chanting one day, in observance of our cargo cult, as we heard a vehicle driving down the road, well out of sight to the east.
When the sound of the vehicle suddenly shifted, with gears lowering, near the juncture of the main park road and the side road leading down to our research site, we didn’t think much of it. The large muddy puddle at that spot caused all vehicles to down shift and slow. But this time, the vehicle in question stayed in low gear and we could hear it getting slowly closer to us… this truck had turned in to the research camp road! It was Leo! Leo had arrived with the tents and cots and the garlic and the other stuff!
But when the vehicle finally came in sight after traversing the 3 kilometer path that lead to our camp, we were very disappointed to see that it was not The Truck driven by Leo with Our Stuff. Rather, it was someone we did not know in a Land Rover.
Visitors.
The visitors turned out to be a chimpanzee conservation specialist on contract with the United Nations and her driver. She was on her way south to the Virunga Volcanoes to habituate the chimpanzees in one of the mountain top forest patches to tourism. That is similar to habituating the chimpanzees to researchers, but instead of wearing khaki’s and carrying around notebooks … so the chimps get used to that … you wear loud print Hawaiian shirts with cheap cameras hanging around your neck and carry tour books and gin and tonics. So the chimps get used to that. I assume.
Anyway, the chimp conservation specialist eventualy moved on and went to the Virungas. I eventually (several months later) moved on and went to Cambridge Massachusetts, where I lived at the time (plus or minus) when I was not in the Congo.
And my first night in Cambridge had me crashing at the home of Irv DeVore, my advisor, the famous primatologist and forager researcher. Also crashing at DeVore’s was Richard Wrangham, famous primatologist who at the time was being courted by Harvard, and was thus visiting from Michigan.
Richard and I had a conversation. It turns out that he had met up with the UN chimpologist in the Virungas at some point when I was at the other end of the park (this park is big … traversing it the long way is not normally done, but when it is it can take a couple of days and you quite seriously risk your life). This led to an interesting conversation.
Richard and I started to exchange information and ideas. I had been looking at the use of roots by foragers in the Ituri Rainforest, and Richard had found out something interesting about the Virunga chimps:
The upper slopes of the volcanoes have porous soils and rock, and no habitual lakes, ponds or long-lived streams. Water falls from the sky and disappears beneath the surface of the volcano, to come out near the base of the mountain as springs, but in the main not accessible for drinking by the denizens of the high forest itself. Animals that live in the forest get their water mainly from very short lived puddles on the surface or from tree crotches, where branches separate and tiny puddles form, and possibly from canopy plants that hold water. During the two month dry season these sources of water dry up and any animal that requires daily drinking must migrate out of the forest or die.
But the chimps, who do require daily access to water, don’t migrate out of the forest. They can’t. The habitat they live in is circumscribed and can’t leave. Well, individual chimps probably do leave now and then and some of them manage to find other suitable chimp habitats, but for the most part the chimps are trapped in a habitat without drinkable surface water for seven to ten weeks or so per year.
It turns out that the plants that live in this habitat are also water stressed, and some of them have interesting evolved adaptations to this. One viney plant, a kind of yam, has evolved a huge underground storage organ that swells as it collects water all year, then provides water during the dry season.
This yam is about the size of a coffee table or maybe a small couch. That is quite large for a yam. And it is loaded with water.
And … you guessed it: The chimps dig these tubers up and drink from them during the dry season.
This may or may not impress you but it should. Of all the species of vertebrates, hardly any use roots of any kind for any reason. Probably only mammals. Of mammals, bears, pigs, and rodents include species that use roots to some extent. Among primates it is not generally thought of as a major adaptation. Nearly 300 species of primates have fewer than four or five (including these chimps and humans) that ever use roots. And these chimps are the ONLY chimps known that dig for roots.
There is a lot more to this story than the Virunga chimps or my work with foragers in the Ituri. There is work by other people on pigs and bears, there is work by my friend Betsy Burr on rodents, and there is information from the fossil record. But the conversation I mention above at DeVore’s house led, after considerable time dicking around with it, to this: The rise of hominids as an adaptive shift in fallback foods: Plant underground storage organs (USOs) and australopith origins. In which:
We propose that a key change in the evolution of hominids from the last common ancestor shared with chimpanzees was the substitution of plant underground storage organs (USOs) for herbaceous vegetation as fallback foods. Four kinds of evidence support this hypothesis: (1) dental and masticatory adaptations of hominids in comparison with the African apes; (2) changes in australopith dentition in the fossil record; (3) paleoecological evidence for the expansion of USO-rich habitats in the late Miocene; and (4) the co-occurrence of hominid fossils with root-eating rodents. We suggest that some of the patterning in the early hominid fossil record, such as the existence of gracile and robust australopiths, may be understood in reference to this adaptive shift in the use of fallback foods. Our hypothesis implicates fallback foods as a critical limiting factor with far-reaching evolutionary effects. This complements the more common focus on adaptations to preferred foods, such as fruit and meat, in hominid evolution.
I don’t think this happened in the Virungas, because as I mention above, they are relatively young volcanoes. It may even be that nothing like this happened at all. The significance of the observation may be simply that chimps can make use of USOs. The last common ancestor of humans and chimps was probably a lot like a chimp. So, the Virunga chimps simply demonstrate that this early population may have been able to use roots for something (water or food) and further demonstrates that the use of this resource could be not only something that some groups use, but that a particular group can survive because of. That is important because of all the interesting things chimps do, like using tools to get termites or various “symbolic” behaviors to communicate, none are done by all groups of chimps, and most or all of these behaviors seem to come and go randomly and do not have a high impact on survival. But the root digging and drinking of the Virugna chimps can’t disappear as a strategy in this one group; They depend on it for survival.
It is also not certain that such a context (a truly dry two months or so per year) requires volcanic sediments, but this does seem like a very likely location for such a thing. A similar thing happens on the Kalahari sand sheet, where water is abundant, but only if you are able to get at the water which is meters, or tens of meters, below the surface. However, I am pretty sure that there is not a huge water-abundant tuber of this type in th Kalahari. But perhaps at one time there was.
Evolving away on the upper slopes of a volcano would have other effects a well. Like, unfortunately, occasional local extinction. Of course, it would also be a great place to “discover” fire … But that is an entirely different story, for another time.
Recent Kenyan Newsreel:
Earlier film on the Nyiragongo volcano (near Nyamuligira) and the region:
LADEN, G., & WRANGHAM, R. (2005). The rise of the hominids as an adaptive shift in fallback foods: Plant underground storage organs (USOs) and australopith origins Journal of Human Evolution, 49 (4), 482-498 DOI: 10.1016/j.jhevol.2005.05.007
Have you read the breakthrough novel of the year? When you are done with that, try:
or Paperback
*Please note:
Links to books and other items on this page and elsewhere on Greg Ladens' blog may send you to Amazon, where I am a registered affiliate. As an Amazon Associate I earn from qualifying purchases, which helps to fund this site.
It certainly doesn’t — there are big parts of the “desert” Southwest that have two-month or longer dry seasons. The “sky island” habitats such as Arizona’s Mount Graham are isolated arboreal environments separated by some extremely dry country, and the arboreal biomes indeed include not only deep-rooted plants able to reach groundwater but also tuberous water-storing plants — as do the lowlands, with plants such as Macfadyena unguis-cati and Antigonon leptopus, which thrive on intermittent rainfall in sandy soils.
Well, what is needed specifically here is a dry season in a rain forest where the groundwater does not produce streams that run all year. All the East African and Central African chimps live in a rain forest with a dry season of about 2 months or so (and when I say “dry” I mean nothing other than “no rain at all”) but the streams continue to run because there is enough rainfall.
The cloud forests are one possibility, but there are no “cloud forests” that know of that have no streams or other surface water in central or east Africa (though maybe in Sierra Leone in West Africa).
But yes, there are probably other ways for this to happen. But you need a lot of permeable depth.
If I remember correctly, there was a paper in Science a few years back showing gene flow between humans and chimps up to 2 mya, until we had that little chromosomal accident. Wouldn’t that suggest the kind of allopatry you’re talking about? “Islands” of this kind would minimize gene-flow between sister species, allowing inter-fertile species to remain isolated for extended periods of time, with intermittent periods gene exchange when the islands became temporarily connected and populations shifted.
It also suggests different kinds of biogeographic isolation that must have been involved in our bushy ancestry — who believes that if chimps and australopithecines could interbreed, that later Homo’s couldn’t as well?
That is exactly what I would expect a frog to say.
Your paper is very interesting, particularly the difference between food abundance in rainforest vs savanna. The relative deficiency of edible roots in the rain forest vs the savanna might explain why the people that inhabit rainforest (the pygmies) tend to have short stature, it could be an adaptation for reduced food supply (as also occurs on islands) rather than an adaption for early reproduction. Since non-pygmies in the west go through menarche at less than age 12, earlier menarche would seem to be easier to evolve than differential regulation of growth.
In looking at wikipedia, there are indigenous pygmies in Africa, Asia, South America and in Australia, and they all seem to live in rainforest.
You could call this the “Mole Ape Hypothesis”. People would give TED talks about it. You might even get on Oprah. (Oops, too late!)
Curtis Marean was insisting recently that a bottlenecked human population of ~150Kya? survived because they, uniquely, had learned to exploit shellfish. Each bottleneck would have its own success story, because all their descendants would know the secret, but only one group among them survives the next one. Maybe tubers get a bottleneck of their own.
A view of human evolution as a series of bottlenecks each conditioned on a seminal invention starts to resemble your typical cheap TV drama.
Hominid Lost. Then Found. Then Lost Again. Then Found.
It could be better than a lot of what is on TV now.
Cool. Interesting idea. It is fun to get a look at how the science works behind the scene.
The concept of habituating chimps for tourists strikes me as both very funny and a very bad idea. Wouldn’t this leave them more vulnerable to human depredation?
Peter: Yes, indeed! It is a questionable practice if you have a lot of poachers.
On the other hand, chimps can learn the difference between poachers/hunters and tourists. In this particular region, habituating the gorillas to tourists changed the local economy and saved the gorillas. Temporarily.
It is no doubt not an easy decision to make.
So diplomatic. I would have said “couldn’t be worse”.
But there are people who would insist that the appeal of this sort of presentation amounts to a racial memory: everyone alive today is descended from a long series of subpopulations selected for interest in how the elders survived adversity. Tragically, such interest is equally satisfied by falsehoods; hence, religion. And TV.
Some chimps use digging sticks to dig up tubers during the rainy season; during the dry season these tubers become increasingly poisonous from alkaloids IIRC.
Interesting that the volcanic soil there is similar to coral atoll soils in that both drain rainwater immediately, so a long dry season is difficult. Technically a “rainforest” which has a long dry season is a monsoon forest, a true rainforest produces its own rain throughout the year, reducing but not stopping during the dry season.
Shallow-water habitats as sources of fallback foods for hominins
R Wrangham, D Cheney, R Seyfarth & E Sarmiento 2009 AJPA 140:630-642
“Underground/underwater Storage Organs (rhyzomes) consumed by hominins could have included both underwater and underground storage
organs, ie, from both aquatic and terrestrial habitats.”
Some chimps use digging sticks to dig up tubers during the rainy season; Which chimps? Are you referring to the chimps at Tai? That may actually be one of those behaviors that has come and gone rather than that is required for survival and known to have persistence.
There is also a group of chimps that digs for water. But that is a whole other story and they are not really digging for water, IMO, though I’m not sure if the researchers and I agree on that interpretation.
Technically a “rainforest” which has a long dry season is a monsoon forest, a true rainforest produces its own rain throughout the year, reducing but not stopping during the dry season.
Not according to the classification systems of which I’m aware. However, it is worth noting that if you take the minimum required annual rainfall to be a rain forest and apply it to Africa, there is only one tiny itty bitty rain forest in West Africa and not one bit elsewhere. So, we Africanists tend to ignore that and refer to the parts with the closed canopy and all the rain as rain forests. The problem is that when the classifications were worked out the data from Africa was rare and that which existed was not really used. So there is a Brazilain/Borneo standard, if you will.
Yes, the Wranngham et al paper you cite is one of several extensions of the work that Wrangham and I did earlier.
Interesting that the volcanic soil there is similar to coral atoll soils in that both drain rainwater immediately, so a long dry season is difficult.
Yes indeed, very similar!