I’m going, are you?

I apologize for the short notice, but I only just found out myself; this Saturday (October 6) NYU is going to host an Evolutionary Anthropology conference in honor of the work of Cliff Jolly. Jolly, basing much of his work on baboons, proposed that seed-eating could have played a significant role in hominid evolution, and the conference will primarily deal with the hypotheses and studies of Jolly. The whole program starts at 9 AM and goes until about 5 PM (with a reception afterwards), and I’ll be headed in with one of my professors Jack Harris, although I don’t know how late I’ll stay as I’ll have to take the train back (if any one has any tips on how to get back to Penn station from NYU, I’d be much obliged). If you’re interested, the program and contact information (RSVP is required) is up online, and if any readers of this blog are going to attend please feel free to drop me a message; I’d be delighted to meet any readers/other bloggers who might be there.

The Chimpanzees of Mt. Assirik

When chimpanzees (Pan troglodytes) appear in documentaries they are often shown inhabiting relatively dense tropical forest, their lives taking place within the green refuge of the forests. As with any other species that is spread over a considerable distance, however, different populations of chimpanzees have different habits, and one of the most remarkable populations are those around Mt. Assirik. Located in the southeastern part of the Parc National du Niokolo-Koba in Senegal, the chimpanzees in this area have to deal with a local ecology that is drier and more open than some of their relatives elsewhere, and their behavioral adaptations to the environment is of great interest to those study human origins.

The Mt. Assirik study area is remarkable in that 55% of the habitat is open grassland, only about 37% being woodland of varying density and only 3% being more dense forest (the remaining area being made up of bamboo forest and isolated trees). Such open spaces allow some of the major Carnivora of Africa to live in close proximity to the chimpanzees; Lions (Panthera leo), Leopards (Panthera pardus), Wild Dogs (Lycaon pictus), and Spotted Hyenas (Crocuta crocuta) are all frequently seen in the area. As if having so many predators at their doorstep were not enough, the Mt. Assirik area seems to have fluctuations of food that aren’t correlated with seasonal changes, and in the dry season water is the most prized of any resource. The apes are not entirely helpless in the face of such pressures, however, and they’ve been behaviorally adapted in some very interesting ways.

Given a choice, the Mt. Assirik chimpanzees prefer to spend their time in the denser areas of forest, but shifting food resources sometimes require them to move across large expanses of open grassland in order to find nourishment. Wandering out onto the open plains alone is so dangerous as to nearly be suicidal, and the apes form large mixed groups when they have to move across the plains. During this time they are at their most vulnerable, especially since they would be unlikely to outrun any of the major predators (especially those that hunt in packs), and they are extremely alert when undertaking such a journey. What is perhaps most striking of all, hearkening back to Raymond Dart’s “Savanna Hypothesis,” is the fact that the chimpanzees sometimes stand up to get a better look at their surroundings, potentially spotting predators before they get too close, although such an observation should not be taken as a sweeping vindication of Dart’s ideas of human evolution.

The presence of just one tree or a few trees spaced far apart doesn’t help the chimpanzees much either; mothers with children and individuals spent much less time in the sparser woodland areas than in the forest, mixed groups seemingly having to issues with the woodlands. Why should this be so? Well, leopards can climb trees (and often do so to stash their kills), as well as lions, and so simply climbing a tree does not equal escape. Lone chimpanzees are far more comfortable in a habitat where they can climb a tree and move through the canopy out of reach of their assailants, something that is not possible in woodlands. The predators may also have another effect on the diet of the chimpanzees; the Mt. Assirik chimps do not seem to eat young ungulates or monkeys, although such behaviors have been made famous where it has been observed (i.e. Gombe). This may be due to some competition, but it may also be due to the restricted forested habitat and the fact that chimpanzees would have to enter the habitat of the carnivores in order to capture young ungulates, predators being likely to quickly learn about any kills that had been made.

Indeed, the Mt. Assirik population is remarkable in that it often moves long distances in order to obtain food as it becomes available, relying on numbers and vigilance to protect itself from predators when it’s habitat only offers a few isolated islands of relief. Although humans did not evolve from modern chimpanzees, this population may give researchers some idea of the behavior patterns of our ancestors when faced with similar constraints when forests became sparser and the plains were filled with predators. Such social behavior is not the only thing that makes the Mt. Assirik chimpanzees stand out, however; they also make use of Baobab trees in a very interesting way.

By now many people are familiar with the ability of chimpanzees to use a piece of wood as a hammer to break a nut placed upon an “anvil” of rock or tree root; such footage has been shown in television programs again and again. Such behavior did not come out of nowhere, however, and the way Mt. Assirik chimpanzees open nuts may represent a stage of tool use that precedes the hammer-and-anvil technology. While it had been disputed for some time whether the Mt. Assirik population used hammers and anvils or just anvils, recent studies have shown that they are cracking open the hard nuts of the tree on branches and not using a hammer. While we might think of an “anvil” as something that can only be used in conjunction with a hammer, mechanically this isn’t necessarily so, and the Mt. Assirik chimpanzees bang the hard nuts they collect on the branches of the tree (therefore staying aloft, not coming down to use stones or the roots of the tree), the tree itself being the anvil.

Given the basal usage of anvils by the Mt. Assirik chimps and the use of hammers and anvils elsewhere, it becomes possible to hypothesize about the evolution of stone tool use in our own ancestors. The starting point was likely similar to what is exhibited by the Mt. Assirik chimpanzees, banging hard nuts on trees or rocks in order to open them (thus preventing damage to the teeth, if it even would be possible to open the nuts using their jaws). The next step would be adding a hammer, possibly wooden (as seen in some groups today) or possibly stone. At this stage any combination of wood or stone hammers and anvils could be used, but tool use would probably not progress until a population was using stone hammers and stone anvils to open foods. In such a scenario, the apes would sometimes miss their targets and flake off bits of stone, an accident that would shape the tools. When a certain cognitive leap was made, the apes could then move from accidentally flaking their tools to doing it intentionally to truly be making tools rather than making use of naturally occurring bits of wood and stone. The reality of the situation may be forever lost to us, ancient tool use before the knapping of stone became prevalent being notoriously hard to discern, but such a line of behavioral descent is not unreasonable and seems to allow further development merely by chance combinations of naturally occurring resources.

Such a discussion is only a brief sketch based upon what I have only recently learned myself, but I hope that it has been at least somewhat informative. Different populations of chimpanzees show different behaviors and live in differing ecologies, and it would be a mistake to assume what the famous Gombe chimpanzees are doing holds true for all the other populations. Another population that I soon intend to write about spends time in caves, probes trees for bush babies, and may even have the beginnings of a fire culture; others do not show the same exact behaviors, but they have their own cultures and reactions to the local ecology. While we should be careful in analyzing the living populations of chimpanzees and their perceived similarities to humans, it would be foolish to think that they can tell us nothing of our own past, and if very well may be that some of traits (behavioral or otherwise) they now exhibit were present in our own lineage, vignettes of evolutionary history being replayed with different actors in our own time.

When your dials are pupilated…

Drop what you’re doing; Neil has one of the most singularly excellent posts I have ever seen up over at microecos about the eyes of the Aye-Aye, a very rare and bizarre endangered strepsirhine primate that is truly unusual (and, although the “rodent-like” characters of the Aye-Aye are likely derived characters, famous morphologist W.E. le Gros Clark suggested in The Antecedents of Man, truly shows that primates evolved from animals like shrews). [Many thanks to those in the comments that corrected my bad phrasing] There is such a thing as being too bizarre, however, and even though habitat loss is a huge problem for these animals, so is the local mythology; the aye-aye is so weird that local legends deem them to be evil creatures, and they are often killed to prevent them as they are seem as symbols of death and evil. Now that’s enough of my yammering; check out Neil’s essay, post haste!

A peek at my homework

Here’s the summary that I’ll be giving today in my Topics of African Prehistory course pertaining to the assigned reading Wrangham, R. 1987. “The Significance of African Apes for Reconstructing Human Social Evolution.” In Warren G. Kinzey (Ed.) The evolution of Human Behavior: Primate Models. It’s long by summary standards, but when have I been known to be succinct? In fact, I would have loved to make this even longer, but I don’t want to talk my classmates to death.

Summary

“Life is a copiously branching bush, continually pruned by the grim reaper of extinction, not a ladder of predictable progress. Most people may know this as a phrase to be uttered, but not as a concept brought into the deep interior of understanding. Hence we continually make errors inspired by unconscious allegiance to the ladder of progress, even when we explicitly deny such a superannuated view of life.” – Stephen Jay Gould, Wonderful Life, 1989

On June 30, 1860, “Darwin’s Bulldog” T.H. Huxley met Bishop “Soapy Sam” Wilberfoce in a debate on one of the most hotly contested topics ever to be put before mankind: are we evolved, or are we divine creations? While no one is quite certain as to the outcome of the debate, it is perhaps one of the most celebrated events in the history of the evolution idea, for when the Bishop rhetorically asked whether it was through his grandmother or grandfather that he was descended from a monkey, Huxley delivered this devastating rejoinder; “If then the question is put to me would I rather have a miserable ape for a grandfather or a man highly endowed by nature and possessing great means and influence and yet who employs those faculties and that influence for the mere purpose of introducing ridicule into a grave scientific discussion – I unhesitatingly affirm my preference for the ape.” Such wit did not halt the debate then and there, but as Huxley’s work Man’s Place in Nature, Darwin’s The Descent of Man, and various cartoons from Punch at the time make clear, it could no longer be denied that Homo sapiens had very close relations to the living gibbons, orangutans, gorillas, and chimpanzees, their lives providing insight into our own.

The relationship between men and apes is now taken as a “given” (and rightly so), but the question of just what living apes can tell us about our past must be asked. While the fossil record seemingly refused to give up hominid remains for some time, there is today a greater diversity of fossil hominids now known than in Huxley’s time, and what we know about living apes must be reconciled with these discoveries if we’re to accurately portray what our ancestors (even our common ancestors) may have been like. Indeed, we should not forget that our own species did not evolve from chimpanzees or gorillas but rather shared common ancestry with them in the past, and they have been evolving since the time of their separation just as we have. As Richard Wrangham rightly criticizes the approach of trying to crown a living species as the archetype for our ancestor, noting “The ideas these models generate are plausible and even thought provoking, but their value is limited by their initial assumption: they assume that the social organization of human ancestors was similar to that of living species.”

Given this potential pitfall, Wrangham suggests a behavioral sort of cladistics, surveying the social behavior of extant gorillas, chimpanzees, and bonobos in order to find the presence (or absence) of shared social behaviors. If certain behaviors exist within all the groups mentioned, then there would be reason to believe (at least in terms of parsimony) that such behaviors were inherited from a common ancestor rather than evolved multiple times. Concerning the closed or semi-closed social groups detailed in II A 2. (Grouping Patterns) of the outline, it appears that humans, chimpanzees, and gorillas all have closed or semi-closed social groups, making the behavior a shared trait that may have been shared by the common ancestor of all the groups. On the other hand, however, we have the data presented in II B 4. (Male-Male Interactions) where the variety of interactions precludes us from being able to tell what sort of behavior pattern our common ancestor exhibited in terms of male interactions.

Now that we understand the application of Wrangham’s methodology to living primates, we should consider the overall strengths and weaknesses it may have. One of its strengths may be the ability to recognize the possession of common behavior in the apes despite different ecologies. If humans, chimpanzees, bonobos, and gorillas all share certain behavioral characteristics despite living in different habitats or inhabiting different niches, the overall case is stronger for that trait being inherited from a common ancestor rather than convergent evolution. Convergent evolution can be problematic, however, as it sometimes seems to defy parsimonious explanations. Perhaps the common ancestor did not exhibit the behaviors now expressed as much carry a capacity for them through variations in populations (being that it is populations that speciate and change, not an entire species as a whole), and being that we are dealing with behavior and not morphology in this case, it might be easy to accentuate some similarities/differences while hiding others. For example, if we undertake cladistics in the traditional sense, let’s say describing a skull, the process is relatively straightforward; either a structure or trait is present or it is not. Behavior, however, can be more variable, and even in Wrangham’s description of Group Patterns there can be seen some potential for disagreement. Indeed, is there are large significance between a closed group and a semi-closed group? Again, given that we’re talking about behavior and not a morphological trait that is usually clearly present or absent, researchers would do well to be mindful of how they delineate what they consider significant behaviors and how they are measured in terms of this method.

Wrangham does not hold his method up as the one and only answer, however, and he concedes that it is more of a “quick” and “weak” starting point to determine possible similarities rather than a way to obtain ultimate answers. In fact, as he notes in the introductory paragraphs, the study of behavioral ecology weighs heavily on the issues herein discussed, although it is a discipline still in development. Even beyond modern ecology, paleoecology will have a very significant role to play in determining what our ancestors were like, especially because habitat does much to shape the bodies and behaviors of organisms through evolution. Indeed, living species can give us valuable insights into our past, but if the information gleaned is determined to be the product of convergence or is found not to be consonant with the data from the fossil record, developing understanding will have to accommodate such discoveries. Ultimately, the discovery and determination of our common ancestors with chimpanzees and gorillas will weigh heavily on this issue, but at the present time the information is overall insufficient and (as ever) there are more questions than answers. For the present, however, the behavior of living African apes can provide a sufficient framework for comparison, and Wrangham’s methodology provides a quick way to spot potential similarities that can then be checked through the study of ecology and the fossil record.

Photos from the Philadelphia Zoo, Pt. III

Here’s the last set of the photos from this past weekend, and as soon as I get the entire set uploaded to Flickr I’ll let you all know.

One of the gorillas at the Primate House. I only saw two while I was at the zoo, so I assume that most of the rest of them were inside or in an area out of view.

A Grevy’s Zebra (Equus grevyi).

A Prairie Dog (Cynomys sp.) having a snack.

The only visible “enrichment” the African Elephants had was a naked metal chain, and the elephant that I was told was named “Petunia” couldn’t stop fiddling with it. I have to wonder if some of this was a way to comfort herself or divert unease, as just before this picture she was driven out of the shade by the two other elephants she shared her habitat with, and overall she seemed to be restless/ill at ease the entire day.

This is “Puzzles,” the Reticulated Giraffe (Giraffa camelopardalis reticulata). I don’t know why the zoo staff has not operated on this animal, and the plaque outside the enclosure is a bit shore on details. Perhaps the condition is inoperable, and it doesn’t seem to visibly inhibit the giraffe, but I do feel sympathy for Puzzles.

The most deadly of all creatures, the Pygmy Marmost [Callithrix (Cebuella) pygmaea]. Don’t let their cute appearance fool you; they can deskeletonize a cow in seconds… or is that piranhas…

A Sable Antelope (Hippotragus niger) rests in the shade. It’s hard to tell from this angle, but this one has asymmetrical horns.

A Squirrel Monkey (Saimiri sp.) enjoying some fruit.

A Tree Shrew (Tupaia sp.), sitting still long enough for me to squeeze off a shot (albeit a blurry one).

One of the Galapagos Tortoise (Geochelone nigra) taking a dip.

A pair of Aardvark (Orycteropus afer) having a snooze in an artificial cave.

“Solstice,” a female White-Handed or Lar Gibbon (Hylobates lar). She shares her habitat with her partner Mercury (who is black rather than blonde) and an Orangutan (Pongo sp.) pair.

Solstice makes her intentions clear; she wants to be groomed by Mercury.

Mercury seemed more interested in grooming his male orang friend than his partner Solstice.

The male Orang was very shy, and carried a cardboard box on his back like a shell/shade everywhere he went.

And that’s it. Hopefully I’ll soon upload all my photos (there are thousands of them) onto Flickr soon, but I hope that you’ve enjoyed the ones I’ve put up here.

Photos from the Philadelphia Zoo, pt. I

As promised, here are some of the better shots from yesterday’s visit to the Philadelphia Zoo. I’m sorry to say that I’m going to soon write up something about the Zoo’s shady dealings involving it’s African Elephants (visit Help Philly Zoo Elephants for a spoiler), but for now I’m going to focus on some of the better photos out of the 500+ I shot yesterday. And away we go…

I absolutely love this fountain.

While not particularly exotic, Scottish Highland Cattle are still pretty neat.

A pair of rare Blue-Eyed Lemur, Eulemur macaco flavifrons. The black one is the male, the blonde the female, and they were very excited at the prospect of a snack (the mangabey next door was getting ded fed at the time)

One of my most favorite of all mammals, the Giant Elephant Shrew (Rhynchocyon petersi).

This, by far, was the thinnest Mara (Dolichotis sp.) I think I have ever seen.

The Galapagos Tortoise (Geochelone nigra) were just beginning to stir when we arrived. They weren’t nearly as randy as they had been during our last visit (I thought I had heard it all until I hear the deep tones of tortoise-lovin’)

An African Elephant (Loxodonta africana) that we were told was named “Petunia” was also up and about. The Philly elephants will soon be moved out of their rather meager accomodations, although it might not necessarily be for the better.

This little male Amur Tiger (Panthera tigris altaica) really loved his tire. He wouldn’t let any of his brothers near it without showing his annoyance.

The strangely white female lions were relaxing in the early-morning shade. I know that their condition is a regional variation, although I forget the details at the moment.

Some of my most favorite Carnivores, White-Nosed Coati (Nasua narica) were scrounging for insects and other morsels when we passed by their enclosure.

And, just for Jeremy, a Red Panda (Ailurus fulgens).

We also came across the most evil-looking Caiman I had ever seen (there was no ID plaque, so I’m not sure what species it was).

And the Clouded Leopard (Neofelis nebulosa), as ever, was asleep in it’s hammock. I have never seen this cat move a muscle in my four visits to the Philly Zoo thus far.

Just around the corner, however, was a much more active and curious cat; a male Amur Leopard (Panthera pardus orientalis). He is one of the most beautiful big cats I think I have ever seen, and it’s a shame that he’s essentially “locked up” in his enclosure, and as far as I know the zoo does not keep a female Amur Leopard to run a breeding program for this most critically endangered cat.

I still have at least 25 pictures to share, but you’ll just have to wait a little bit longer for them. Check back later tonight for more of our friend the Amur Leopard, some Giant River Otter, White-Handed Gibbons, and plenty more.

Scuttling the Aquatic Ape Hypothesis

On our occasional trips to the New Jersey shore, my wife is always the first one in the water. While I’m cautiously wading in, dreading that final slap of cold water just below my waist, she’s already frolicking in the waves, egging me on to just jump in and get it over with. Eventually I too become submerged (either willfully or by force of a wave I never saw coming), salt water inevitably shooting up my nose. Don’t get me wrong, I do enjoy warm days at the beach, but on each visit it seems that I as an individual, if not a representative of a population or species, am not well-adapted to a near-shore marine existence. Followers of the Aquatic Ape Hypothesis* (AAH), however, beg to differ.

[* I say “hypothesis” and not “theory” (AAT) because the writings of Elaine Morgan and others do not have enough supporting evidence to garner it the more prestigious title of “theory.” Given the current paucity of evidence and research, the Aquatic Ape Hypothesis is precisely that and no more.]

Before discussing the current manifestation of the AAH, we need to go back to a time when the truth of evolution had yet to fully take hold in the minds of scientists and philosophers. The Ionian philosopher Anaximander (610-546 BCE), student of Thales, suggested that the world first existed in an entirely aquatic state, the recession of the globe-consuming waters creating life. In From the Greeks to Darwin (1905), famed American Museum of Natural History president Henry Fairfield Osborn described the views of Anaximander as follows (a similar treatment is given in Osborn’s Man Rises to Parnassus, as well);

He conceived of the earth as first existing in a fluid state. From its gradual drying up all living creatures were produced, beginning with men. These aquatic men first appeared in the form of fishes in the water, and they emerged from this element only after they had progressed so far as to be able to further develop and sustain themselves upon land. This is rather analogous to the bursting of a chrysalis, then to progressive development from a simpler to a more advanced structure by a change of organs, yet a germ of the Evolution idea is found here.

We find that Anaximander advanced some reasons for this view. He pointed to man’s long helplessness after birth as one of the proofs that he cannot be in his original condition. His hypothetical ancestors of man were supposed to be first encased in horny capsules, floating and feeding in water; as soon as these ‘fish-men’ were in a condition to emerge, they came on land, the capsule burst, and they took their human form.

Like the works of many Ionian philosophers, the ideas and opinions of Anaximander do not seem to have taken hold (Aristotle ultimately becoming the preferred scientific and philosophical source for further consideration in Europe in centuries to come), and not much of his work remains. It is curious to note, though, that wrong as Anaximander was about the origins of humans, the reasons he uses to support his ideas (as relayed by Osborn) are very similar in approach to those of Elaine Morgan and some modern-day AAH adherents, as we shall soon see.

To the best of my current understanding, the hypothesis that man was a product of the sea did surface again until 1942 when Max Westenhofer of the University of Berlin published the book The Unique Road to Man. According to Donna Kossy’s book Strange Creations, Westenhofer’s treatment of an aquatic origin of mankind consisted of little more than mention of it as a promising hypothesis, however, and the outbreak of war prevented the professor from pursuing the line of inquiry further. The hypothesis would have to wait until March 5, 1960, when marine biologist Sir Alister Hardy presented a lecture on “Aquatic Man: Past, Present, and Future” to the British Sub-Aqua Club. The address caused quite a stir and led Hardy, who had been inspired by the layers of sub-cutaneous present in humans and some marine mammals he had seen skinned on a journey to the Antarctic in 1927, to write a series of articles in the magazine New Scientist to clarify his position on the subject. Kossy relates the words of Hardy from an April issue of the magazine (although the year is not specified);

My thesis is that a branch of this primitive ape-stock was forced by competition from life in the trees to feed on the seashores and to hunt for food, shell fish, sea-urchins, etc., in the shallow waters of the coast. I suppose that they were forced into the water just as we have seen happen in so many other groups of terrestrial animals. I am imagining this happening in the warmer parts of the world, in the tropical seas where Man could stand being in the water for relatively long periods, that is, several hours at a stretch. I imagine him wading, at first perhaps still crouching, almost on all fours, groping about in the water, digging for shellfish, but becoming gradually more adept at swimming. Then, in time, I see him becoming more and more of an aquatic animal going further out from the shore; I see him diving for shell fish, prising out worms, burrowing crabs and bivalves from the sands at the bottom of shallow seas, and breaking open sea-urchins, and then, with increasing skill, capturing fish with his hands.

Thus the more familiar image of the amorphous “Aquatic Ape” was born, wading out into the surf and feeling in the shallow sands for food. The early stage of such a transformation is awfully raccoon-like, as raccoons have incredibly sensitive hands that they use to feel about in streams and shallow waters for mussels, crayfish, and other morsels without being driven to become fully aquatic themselves. Nevertheless, the idea that man had his origins in a shallow sea rather than on a hot and brutal savanna was certainly controversial. Ever since Raymond Dart described the skull of the Taung Child in 1925 (shifting attention away from Europe and Asia for the origins of man) and the fossil assemblages of the South African caves were discovered, humans were thought to have evolved through a hunting culture, nearly every specialization that separates us from living primate relatives being due to our meat-craving societies. Indeed, the remains of Australopithecus found in South African caves (especially the jaw of a 12-year old child whose jaw appeared to have been fractured by a direct and accurate blow) like those Makapansgat suggested to Dart that these “proto-men” were not only skilled hunters, but also murderers and cannibals. Even though our understanding of these assemblages has greatly changed since Dart’s time (see C.K. Brain’s The Hunters or the Hunted?), the overall image of human evolution being intricately linked to meat-eating and hunting has dominated the discussion of our origins. Even more specifically, the considerations of our ancestors have nearly always focused on the male of the species, and even Hardy’s early ideas of an aquatic ape focused primarily on males.

In 1964, zoologist Desmond Morris published the bestseller The Naked Ape. Today the book is nearly useless outside of understanding the history of thought about human evolution, but when it was first published a short discussion of the AAH caught the attention of a woman named Elaine Morgan. On page 37 of the 1967 paperback edition, Morris states;

Another, more ingenious theory is that, before he became a hunting ape, the original ground ape that had left the forests went through a long phase as an aquatic ape. He is envisaged as moving to the tropical sea-shores in search of food. There he will have found shellfish and other sea-shore creatures in comparative abundance, a food supply much richer and more attractive than that on the open plains. At first he will have groped around in the rock pools and the shallow water, but gradually he will have started to swim out to greater depths and dive for food. During this process, it is argued, he will have lost his hair like other mammals that have returned to the sea. Only his head, protruding from the surface of the water, would retain the hairy coat to protect him from the direct glare of the sun. Then, later on, when his tools (originally developed for cracking open shells) became sufficiently advanced, he will have spread away from the cradle of the sea-shore and out into the open land spaces as an emerging hunter.

…

Unfortunately, [searching for fossils in marine or fluvial deposits or further research into the AAH] has yet to be done and, despite its most appealing indirect evidence, the aquatic theory lacks solid support. It neatly accounts for a number of special features, but it demands in exchange the acceptance of a hypothetical major evolutionary phase for which there is no direct evidence. (Even if eventually it does turn out to be true, it will not clash seriously with the general picture of the hunting ape’s evolution out of a ground ape. It will simply mean that the ground ape went through a rather salutary christening ceremony.)

[Emphasis mine]

Elaine Morgan read the brief treatment and qualifications (some of which has been omitted here for the sake of brevity) and wanted to know more about the possibility of our ancestors going through an aquatic stage of evolution. No information seemed to be available, and so Morgan wrote to Hardy in 1970, and he encouraged Morgan to push ahead with her research and desire to write a book about the AAH. The result was the bestselling The Descent of Woman, published in 1972. My copy is a little bit newer than that, being the Bantam 1973 edition, and featuring what appears to be a nude mother and child on the cover. Closer inspection reveals that something isn’t quite right, however; the mother I previously assumed was a representative of Homo sapiens looks like she’s been hit in the face with a frying pan. I didn’t know it at the time, but the text would reveal that the plump, nude, and long haired female on the cover was not drawn from life, but rather was Morgan’s idea of the Australopithecus specimen “Lucy” as Aphrodite.

Morgan’s first book is certainly a unique one, weaving in between “Just-so story” type paleo-fiction and long arguments about the female orgasm, including it’s fallacious mythical status. Indeed, the AAH only seems to occupy the first 1/3 of the book, only cropping up here and there in the following chapters, and receiving only a brief mention in the conclusion. Still, the way Morgan structures her argument in her first book will tell us much about her later works and the rise of the AAH as a popular idea. Early on in the work, we are introduced to a hypothetical female ape, not unlike Proconsul, living in Africa sometime during the Pliocene (~5.3-1.8 million years ago). During this time a hard life trying to find food and avoid predators was becoming even harder, Morgan hypothesizing that a terrible heat wave would change the way of life for many populations of these unnamed apes (from what I understand, however, the climate of the Pliocene began to approach our own and became cooler, drier, and had more seasonal distinctions rather than being a global hot-house).

Morgan’s ape was in a bit of a jam, that’s for sure. The water holes are said to be stalked by hungry cats and food was becoming scarce, and the imaginary female was not as fearsome or powerful as the males in her group. Eventually she was chased into the water by a large cat, and decides that, despite her distaste for water, “the seaside not at all a bad place to be. She found to her delight that almost everything on the beach and in the water was either smaller or more timid than she was herself.” Indeed, Morgan’s ape appeared to have found paradise. While other animals cooked during the “dog days of the Pliocene”, her ape (and by extension the population of apes) found what seems to be a sheltered and peaceful lagoon devoid of predators, scavengers, or other threats from either land or sea. “Leopards don’t come so far into the sea, nor sharks so near to the land,” we are told, and while leopards may not be attracted to water, sharks are well-known for their shallow water hunting habits. Crocodiles are not even considered, nor are stingrays, poisonous urchins, jellyfish, disease, infection, or any of the other biological problems that may come with an aquatic existence or change in ecological setting. The new home of the apes sounds better than Club Med, a watery Eden lacking in devious serpents and forbidden fruit.

As suggested by Morris and Hardy, the population of apes gets by on a diet of shellfish and relatively stupid sirenians that happen to come by, males making short work of the water-going creatures with rocks found along the shore. Given the amount of time that the apes would be spending in the water (they couldn’t have just subsisted by wading in or eating what washed up, or at least this is what is implied), bodies started to change. Males are paid little attention by Morgan, and the warm relationship between mother and child takes center stage. While most of the hair on the body would be lost as an adaptation to water (an odd conclusion given that otters, seals, and sea lions all are covered in hair), the hair on the head would be allowed to grow long, the water babies being able to curl their fingers into it and stay close to mom for a nap when they got tired of exploring off on their own. Conversely, breast feeding would still have to take place on shore, but the upright posture of the females (acquired from so much time in the water) would require the baby to be held at an awkward position in which they could not reach their mother’s nipples. This was solved by developing larger “hemispherical” breasts to reach down to the infant, even though larger breasts may cause infants problems when they try to get their mouths on them to breast feed (if the breast is so large that the infant’s nose is covered by it, breathing and feeding becomes difficult).

In searching for an aquatic example of such a striking characteristic, Morgan turns to the Florida manatee and other sirenians, many who have seen females with young noting the presence of “breasts” on the aquatic mammals. Interestingly enough, however, the manatee shares it’s ancestry with living elephants, the females of which also exhibit some rather sizable swellings when lactating. Robert Sapolsky, in his book A Primate’s Memoir, describes seeing such an unexpected shape on the chest of a female elephant for the first time;

Did you know that female elephants have breasts? I do not mean rows of teats, a mama elephant lying on her side with dozens of little piglet elephants nursing with their eyes still closed. I mean breasts, two huge voluptuous billowy mounds, complete with cleavage. I bet you had no idea, did you? Nor did I – it is a subject rarely broached in our public schools. I’m out in the bush that first month, armed with binoculars and stopwatch and notepad, spending the days carefully watching baboons mating left and right. And then, suddenly, some pachyderms come cruising past, and I see some elephant with these, well, breasts. And the natural first reaction is to think, Oh, great, I’m such a horny lascivious pathetic adolescent that after a mere month of isolation in the bush I’ve already cracked, I’m hallucinating breasts the size of Volkswagens on the elephants. Horrors, to have one’s psychotic break occur so soon, and to have it take the form of a puerile sexual obsession many embarrassing steps below gawking at National Geographic nudies. I was greatly relieved to eventually discover that the elephant’s breasts were real, that I was not having some Marlin Perkins wet dream.

It should be noted, however, that Morgan attributes an aquatic origin to elephants as well, primarily based upon their ability to shed tears (and therefore salt), as well as the ability of living Indian elephants to swim long distances in the ocean. Such considerations are a side trip from the main thrust of her argument, and no detail is given as to when, where, why, or how elephants arose from a water-dwelling species, only that a few characteristics in living animals point to an Aquatic Pachyderm Hypothesis.

Going back to the AHH, given about 10 million years in the water Morgan’s ape is substantially different than the one that was first driven into the waves by a predator. Referring to her as “Mrs. Australopithecus,” Morgan paints the following portrait (the artistic manifestation of which is found on the cover of the book);

So our hominid has a nose. I have no doubt that she also had fleshy nostrils, but considerable doubt that they evolved to make sex sexier for her mate. I think she was by no means the simian, cadaverous, lipless creature that artists sometimes reconstruct by covering her dug-up skull with a tightly fitting layer of hairy skin. The layer of fat which was rounding out her arms and legs and adding bulk to her breasts was also filling out her cheeks, and her nostrils, and her earlobes, and everting her lips… We would not have accounted her beautiful, with her low forehead and prognathous jaw, but the chances are that she was a chubby little creature with several superficial features resembling our own more nearly than they resembled any ape’s. And as for the expressions that flitted across that prehistoric countenance, her millions of years in the water had certainly left their mark on those also.

This is quite a different picture of “Lucy” than is often seen, but is there anything to it? Part of the advantage of the AAH is that Morgan doesn’t specify her ideas down to a scientific level, allowing her to poetically play with her ideas in any way she wishes, the female becoming more beautiful while the men continue to try and kill dugongs with rocks. This type of feminist reaction to the “Man the Hunter” narrative is the main connective feature throughout the book, and Morgan’s writing is far more concerned with the more graceful and beautiful evolution of woman, with sex ultimately bringing “sin” into the Garden.

In Morgan’s story, the genitals of the ancestral females went from facing backwards (making rear-mounting positions by the male easy) to facing downwards, a position that Morgan insists will not work for males, face-to-face mating being adopted as a must. Morgan’s reasoning for the change is that aquatic animals often undergo this type of genital shift (cetaceans are her primary example), but she generally ignores why the genitals should be shifted in the first place. In terms of cetaceans, the ancestors likely had their anal-genital openings in the position typical for quadrapeds; facing backwards at the location of the pelvis just under the tail, usually being at the most distal end of the body. As they evolved, the archaeocetes lost their hind limbs and their spines elongated, being the main source of propulsion, so rather than keep moving backwards with the spine the genitals stayed in the pelvic region “settled” on the ventral side of the body; where else they would have gone, I do not know. Given this morphological necessity, face-to-face mating became the only way cetaceans could copulate. Seals and sea lions, on the other hand, still have their anal-genital openings near the distal most parts of their bodies because that is where the pelvis is and there was no need to change mating styles, and males still mount females from behind. Even beyond such considerations, I do not see how the rear-mount strategy can be dogmatically ruled out, and I have a feeling that because such a position is considered “kinky” by some it was essentially ruled not to have happened. In fact, the retention of rear-mounting with the shift in female genitals could help explain elongation of the penis in males (they’d have to extend a bit farther), although this matter is far from settled. Curiously, Morgan generally ignores the bonobo and it’s face-to-face mating habits, even in her later books. She’s clearly aware of these apes (she does mention them and one graces the cover of The Descent of the Child), but they are conspicuously absent from discussions about sex.

Still, if we are to follow Morgan’s model, the apes would have to switch from mating using a rear-mount position to face-to-face (the males, we are told, couldn’t penetrate any other way), such a position causing much trauma for females. Males wouldn’t know how to calm the female for a face-to-face encounter, and it essentially led to either rape or an unfruitful attempt to mate. Morgan describes such a scene;

The primate was a totally different shape. Her new aquatic streamlining had been unable to prevent her becoming lumpy in the middle, and as a littoral biped her legs were developing in the opposite direction from the seal’s – they were becoming not smaller and thinner but farther apart, but longer and thicker and closer together. The seal’s solution was impossible for the aquatic apes. Their dilemma was unique.

So we left her on her back, kicking and struggling and frightened out of her tiny anthropoid mind, with her mate beginning to get irritated. When she saw him snarl and bare his canines she was finally convinced that he wanted her for dinner, and that her last hour had come. Further resistance was useless. She stopped fighting and signaled her submission, defeat, and appeasement as strongly as she could with so little room for maneuver.

Immediately, the incident was over. The male was a properly programmed animal, and it was impossible for him to go on clobbering a member of his own species that was giving clear indications that it had stopped fighting back. He moved a little way off, wearing a puzzled expression. He had thought for a moment that he was on to a good idea, but obviously there was a snag to it.

Such events removed us from our Eden along the shores, males taking up hunting on the plains soon after the eviction. Rains that quenched the African drought allowed the apes to leave the habitat that they had become so accustomed to (it seems like the males led the charge, being sick of their prolonged day at the beach), moving on to evolve in ways that fit the scientific orthodoxy of the times a bit more closely. Even so, Morgan suggests that women have retained the peace, beauty, and grace of their aquatic origins while males are more shaped by violence and hunting, her parting words being;

He is the most miraculous of all the creatures that God ever made or the earth ever spawned. All we need to do is hold out our loving arms to him and say: “Come on in, the water’s lovely.”

Oddly enough, such arguments seem more specific and in-depth than those in Morgan’s later works The Descent of the Child (1995) and The Scars of Evolution (1990). The Descent of the Child can largely be ignored, being that it’s primary focus is on doing for human babies (from conception through early childhood) what The Descent of Woman did for women, all-in-all being a string of facts presented to the reader in an easy-to-digest manner but without much further discussion. In covering past evolution, the “savanna hypothesis” and “man the hunter” are both alluded to or pointed out to be wrong, although no rigorous refutation is made. Instead the reader is referred to the earlier The Scars of Evolution for the “scientific” argument, but Morgan’s earlier poetry contains far more detail than the 1990 work. I breezed through the 178 pages of the book easily enough, but there was little positive evidence within it’s pages for the AAH. Certain physiological systems were pinpointed and deemed to be of aquatic origin since Morgan deemed no other hypotheses to be adequate (which, of course, assumes that all possibilities have been discovered and have received proper consideration).

I actually would love to write up a longer discussion of The Scars of Evolution but there is surprisingly little actual AAH evidence to be considered, and Morgan even makes some fairly basic mistakes about fossil preservation. Early on in the book she writes;

So if the prospecting had started in the north [of the Rift Valley] and worked down, popular illustrations of groups of Australopithecus would have shown them reclining under a shady tree at the water’s edge, living perhaps on fruit and greenery and fish. Instead, they are depicted as shaggy creatures trekking through parched grass and a scatter of stunted thorn bushes, turning to scavenging and hunting to supplement their diet.

This conclusion comes from Morgan’s assertion that some specimens of Australopithecus are found associated with fossils like crocodile remains and turtle eggs, suggesting an aquatic habitat. This largely ignores taphonomy, however, and an animal that dies in or near water being much more likely to be preserved and fossilized than one that drops out on the plains, the body undoubtedly being ripped apart by scavengers and leaving little or nothing to the fossil record. Most of the rest of the book covers material already mentioned in The Descent of Woman, like the fallacious notion that pheromones are essentially nonexistent or non-influential in humans because we went through an aquatic phase of evolution where scent wouldn’t have counted for much. Also curious is one of Morgan’s final statements about how evolution works, especially in regards to water. Rather than gaining specializations mentioned in so many of her works (i.e. the ability to cry and remove saline from the body, nostrils with possible flaps to keep water out, enlargement of the female breasts), a kind of de-volution of our ancestors is favored;

Conceivably, a species finding itself in a radically new environment (such as water) begins to shed the more advanced features which fitted it for its old environment. It back-tracks to a more unspecialized foetus-like form, before re-adapting to the new habitat. If that were the case, then our own ancestors, having moved from the land to the water and subsequently from water to land, would have been subjected to an impetus towards neoteny on two successive occasions. It would explain why in our case the trend was unusually powerful.

In all, Morgan’s work seem to be lacking of any rigorous research or hypotheses, and it led me to wonder why the AAH will simply not go away. Perhaps some of it is the mental appeal and the common error of linking correlation in evolutionary convergence to causation, working backwards to whatever ideal we hold most dear. Even if I’m incorrect as far as social motivation goes, the AAH has shown up in the scientific literature in the past few years, and it’s primary advocate seems to be Marc Verhaegen. Although the majority of his papers seem to be currently unavailable online, there is no name that more frequently appears in terms of AAH literature in scientific journals, giving the hypothesis some visibility (and credibility, as far as AAH advocates may be concerned). Some of the papers published on the AAH I could find are;

Bender R, Verhaegen M, & Oser N. “Acquisition of human bipedal gait from the viewpoint of the aquatic ape theory” Anthropol Anz. 1997 Mar;55(1):1-14.

Cunnane, S.C. “The Aquatic Ape Theory reconsidered” Medical Hypotheses Volume 6, Issue 1, January 1980, Pages 49-58

Ellis, D.V. “Wetlands or aquatic ape? Availability of food resources.” Nutr Health. 1993;9(3):205-17.

Rhŷs Evans, PH. “The paranasal sinuses and other enigmas: an aquatic evolutionary theory” J Laryngol Otol. 1992 Mar;106(3):214-25.

Vaneechoutte, M. ” Report of the Symposium ‘Water and Human Evolution’, Gent, Belgium, April 30th 1999” Human Evolution. 2000 Volume 15, Numbers 3-4

Verhaegen, M.J.B., Puech, P.F., & Munro, S. “Aquarboreal ancestors?” Trends in ecology & evolution (Amsterdam). 2002 Vol. 17, Issue 5, page 212

Verhaegen, M.J.B. and Puech, P.F. “Hominid lifestyle and diet reconsidered: paleo-environmental and comparative data” Human Evolution. 2000 Volume 15, Numbers 3-4

Verhaegen, M.J.B. “The Aquatic Ape Theory and some common diseases”. Medical Hypotheses
Volume 24, Issue 3, November 1987, Pages 293-299

Verhaegen, M.J.B. “The Aquatic Ape Theory: Evidence and a possible scenario”
Medical Hypotheses Volume 16, Issue 1, January 1985, Pages 17-32

Verhaegen, M.J.B. “Aquatic ape theory and fossil hominids” Medical Hypotheses Volume 35, Issue 2, June 1991, Pages 108-114

Verhaegen, M.J.B. “Aquatic ape theory, speech origins, and brain differences with apes and monkeys” Medical Hypotheses Volume 44, Issue 5, May 1995, Pages 409-413

[And for an opposing view see Langdon, J.H. “Umbrella hypotheses and parsimony in human evolution: a critique of the Aquatic Ape Hypothesis” Human Evolution. 1997, Volume 33, Number 4, pp. 479-494(16)]

As is immediately apparent, the great majority of the papers have appeared in one journal (Medical Hypotheses) and can be attributed to one author, Verhaegen. Judging from what I was able to find, many of the arguments that Verhaegen employs are very similar to those of Morgan, working backwards from somewhat contested or enigmatic human features to an aquatic origin to the exclusion of other hypotheses. Where Verhaegen differs, however, is that his aquatic hypothesis is far more broad than that of Hardy or Morgan. While Morgan implied that the aquatic apes were an isolated group that ended up leading to man (what happened to populations elsewhere is never spelled out), Verhaegen suggests that the last common ancestor of living gorillas, chimpanzees, bonobos, and humans was at least semi-bipedal and semi-aquatic, likely living in a habitat like a mangrove swamp. From the paper “Aquaborel ancestors?”;

A vertical posture and an ability to climb with the arms raised above the head could have helped a wading primate to enter or leave the water by grasping overhanging branches or waterside vegetation, and to grasp fruits above the water. Body enlargement and tail reduction would hinder agile arborealism, whereas a larger body is more easily supported in water and helps reduce heat loss (explaining why aquatic mammals are larger than related terrestrial forms). Tails would be of little use for a wading and/or swimming primate and would cause both drag and heat loss.

Thus Verhaegen attempts to separate New and Old World monkeys from apes by making the ancestors of all living apes at least partially water-bound, standing up to wade through water. Ultimately humans would have stayed in the pool while gorillas and chimpanzees got out, although gorillas, chimpanzees, and bonobos do not seem to show the same signs of being adapted to water that are often associated with humans under the AAH. Of further note is the fact that living primates like baboons, macaques, and proboscis monkeys have been known to swim and stand upright in water, although none seem to show signs of becoming exclusively adapted to an aquatic lifestyle. In the recent BBC series Planet Earth, baboons of the Okovango Delta in Botswana were shown wading through the water;

The baboons are not especially comfortable in the water, just as many other animals in the delta like cheetahs and lions don’t especially like crossing the waterways. Indeed, crocodiles are the primary danger in the water, and many animals seem to know of the threat all too well (but must cross from time to time, anyway). Such modes of moving through water, also seen in chimpanzees (see the final episode of the BBC’s Life of Mammals, entitled “Food for Thought”), seem to constitute the “weak” version of the AAH, and isn’t entirely unreasonable in explain possible motivation to become bipedal. It does require a certain ecology, however, (i.e. flooded plains, a swamp, shallow mangrove forest, lagoon, etc.) and has little explaining power out of such a context. Still, there are even more aquatic primates that were also featured in Planet Earth; the crab-eating macaques.

If we’re looking for a model of what an aquatic ape would look and act like, surely these monkeys would be it, and Morgan does note some of the aquatic habits of macaques (especially the behavior of washing food in water, as seen in Japanese Macaques). The problem is that macaques are monkeys, not apes, although they seem to get along in the water just fine. Unfortunately the adaptation of these primates to water is going to be slow and take many generations, but the study of these animals could give us some clues as to what the AAH can and cannot explain, although it seems that many of the features explained by the AAH don’t fit with what we see in the macaques. Looking at the underwater behavior, it would seem that the monkeys would be adapted to swim in a matter similar to that of quadrupeds rather than to start wading in, becoming bipedal, and then doing a breast-stroke. Indeed, the video shows that becoming bipedal is not a necessary precursor to being able to swim or becoming semi-aquatic, and it is quite possible (even probable) that primates could abandon the upright stage altogether. Standing upright seems to be generally uncomfortable for many primates, and it’s hard to see how primates introduced to a fruitful aquatic habitat would want to stand up before just jumping in if there was really nothing to fear in the waters. Even in the weak version of the AAH, it is hard to see how standing upright while crossing a river would have selected for bipedalism as it seems that many primates are capable of doing it over short periods and it does not hold any strong advantage that would relate to mating success or overall survival. Unless the hypothetical apes lived in an area constantly flooded, requiring them to stand up much of the time, it is difficult for me to imagine how water could have helped to select for an upright posture.

The overall problem I have with Morgan’s hypothesis about apes becoming almost exclusively aquatic is that it forces us to make a choice of one habitat or another. Mentions are made of Proboscis Monkeys and Macaques enjoying a swim, washing off food, or living near water, but they don’t seem to be bent on the same path as the one Morgan proposes. Organisms certainly are plastic, and they don’t rigidly abide by the “rules” set down by those that describe them as to where to live, what to eat, and how to act properly. In fact, it seems more reasonable to me that primates past and present would take advantage of an aquatic resource if readily available, but still maintain their terrestrial life unless they were so isolated that they had no choice for food other than the water. Time will tell if some of today’s semi-aquatic primates ever become more fully at home in the water, but I see no reason to believe that our ancestors decided to take a prolonged summer vacation on the beach, proceeding in a way that just so happened to explain everything neatly (if un-parsimoniously).

The AAH hinges on apes willingly going into the water for safety from predators, but this is only a Just-So story without the details. It also ignores the fact that the water can be almost as dangerous, if not moreso, than the land, and there are predators in the water just as there are in terrestrial habitats, not to mention rip-tides and other problems inherent to the ocean itself. While Morgan, in The Descent of Woman, states that newborns could be left to paddle about on their own while mom went about her own business, such maternal inattention doesn’t seem like it would be especially effective in making sure that young made it to adulthood. Only the calmest, most sheltered, and safe of lagoons would have allowed for this. If the AAH is to be taken seriously in whatever form, it is going to require rigorous ecological study, and so far it seems that it relies far more on post hoc arguments than actual evidence.

While Jim Moore has already done a fantastic job dismantling the various problems with the AAH, I hope I have helped to illuminate the overall lack of evidence for the idea. As an idea it’s not a bad one, but it seems to have never gone beyond hypothetical situations and Just-So stories, and most of the ideas associated with the AAH seem to be criticisms of other hypotheses, therefore leaving the AAH as the only alternative. While I can certainly appreciate the frustration Morgan and others must have felt (and even still feel) towards a male-dominated field in science and consideration being mainly given to the strong, archetypal male, I feel that the AAH is taking things too far in the other extreme. It is hard to ignore the feminist underpinnings of Morgan’s writing and the overall disregard for the big picture in order to bring women and children into closer focus. Combating a hypothesis you don’t like with an equally narrow one, just reversed, is not the way to bring greater understanding of our evolutionary history, and given that hominids and apes are so close to us, it’s easy to fall into trapping of preference. Being that I am no expert on the matter, however, I will close with T.H. Huxley’s final words from his work Man’s Place in Nature, as they seem to resonate with the big questions about our origins that remain unknown;

Where, then, must we look for primeval man? Was the oldest Homo sapiens pliocene or miocene, or yet more ancient? In still older strata do the fossilized bones of an Ape more anthropoid, or a Man more pithecoid, than any yet known await the researches of some unborn paleontologist?

Time will show. But, in the meanwhile, if any form of the doctrine of progressive development is correct, we must extend by long epochs of the most liberal estimate that has yet been made of the antiquity of Man.

Which way to the Tendaguru beds?

Hat-tip to Matt for the tag. If you want to make one of these yourself, leave a comment/link back here.

Update: Bora shows us what telecommuting looks like, Julia is hard at work in the library introducing Tyrannosaurus to some modern country music, and I’m sure more will show up throughout the day.

Photo of the Day: Gorilla mother and babies

I know I’ve posted this picture before, but it’s one of my favorites and I thought I would drag it back out to the top of the blog again. It probably has to do with my current dilemma of whether to stay the course in Ecology & Evolution to just “get it over with” or switch over to Evolutionary Anthropology to make the most out of my last year (as long as it won’t keep me back again). What to do, what to do…

Carnivory in Hippos

Replica of the skull of the Hippopotamus, Hippopotamus amphibius, at Disney’s Animal Kingdom Park (via Wikipedia)

Hippos are one of those animals that are sometimes used to drive home the point that appearances can be deceiving; despite their fearsome dentition, they’re really herbivores. They may have bad attitudes and be a terror along African waterways, but at least they’re not carnivorous. At least, that’s the story.

It’s easy to see why the hippopotamus got it’s name, meaning “River Horse.” Taken at the Philadelphia Zoo, August 2006.

While the vast majority of the hippo’s food intake is short grass that grows along river banks, this doesn’t exempt them from eating meat every now and then. In 1996, J.P. Dudley published the paper “Record of carnivory, scavenging and predation for Hippopotamus amphibius in Hwange National Park, Zimbabwe,” followed two years later by “Reports of carnivory by the common hippo Hippopotamus amphibius.” I do not have access to either of these papers, but as far as I understand it, they are the best scientific accounts that we have that hippos do sometimes eat meat. A pdf file announcing the Dudley’s work, states that not only was carnivory witnessed among the hippos, but even cannibalism, the strange habits of the studied group perhaps contributing to an anthrax outbreak that ended up killing 300 hippos in the area.

Taken at the Philadelphia Zoo, August 2006.

More clues are offered up by a short summary from a 1999 issue of Natural History;

Although the hippopotamus’s usual fare is this habitual vegetarian can occasionally turn carnivore. Field biologist Joseph P. Dudley, formerly at Hwange National Park in Zimbabwe, observed a male hippo killing an impala ram that had swum through a pond to evade a wild dog. After eating some of the meat, the hippo returned to his herd.

A few minutes Later, ten more individuals from the group gathered at the floating carcass for a communal feast. Later a few of them climbed the pond’s banks to wrest another dead impala from wild dogs. “It seems almost incredible,” writes Dudley, “that carnivorous feeding behavior by hippos, even if of very infrequent occurrence, could have gone unreported for so long.” Perhaps, he opines, the behavior may have been attributable to “nutritional stress caused by severe drought conditions.”

Taken at the Philadelphia Zoo, August 2006.

Even last night I caught a few moments of a nature documentary showing hippos mouthing/playing with bloated carcasses of wildebeest that drowned in an attempt to cross a river during their annual migration between the Serengeti National Park and Masai Mara National Park. The segment was short, but overall it didn’t seem that the hippos were very interested in consuming the dead antelope as much as mouthing it a bit before moving on. Likewise, hippos in captivity have been known to “play” with/harass other animals in their enclosures, especially birds. At Adventure Aquarium in New Jersey, many Turacos ended up dying of stress when they would fall into the hippo enclosure, the mammals taking the birds into their mouths and lashing them about, keepers frantically trying to rescue the birds with a dip net. Darren Naish has also posted anecdotal evidence of carnivory in captive hippos before, as well.

As I said before, I don’t have access to the scientific papers, but it seems that many of the hippo predation/scavenging events occur in years of drought, where large groups of the animals are brought together in one area when grasses and other “normal” foods are scarce. This could be why hippos in the documentary I mentioned above only “mouthed” the carasses of the wildebeest; they may have had plenty of food so there was no need to eat something that’s not a regular part of their diet. Still, as has been mentioned by Dudley, hippos often eat at night, and their nocturnal eating habits have generally kept us in the dark as to what they might be munching on other than grass.

But what about cannibalism and anthrax? A 2004 article in NewScientist suggests that the spread of anthrax in hippos was actually helped by a particularly harsh year where carnivory and cannibalism came apparent. The problem probably started in water contaminated with anthrax or grass containing anthrax spores. The problem with the hypothesis that hippos were initially infected by anthrax-contaminated water, however, is that the park in which the outbreak occurred is said to have plenty of flowing water, not the stagnant pools typical of an environment that harbors anthrax.

Regardless of how it got into the local ecology and transmitted to hippos, however, a particularly harsh or lean year could have easily caused rapid transmission in a population, even if only a small group were infected. If resources were scarce and hippos (known for their aggressiveness) were pushed closer together in the remaining areas of water and food, there would be much more fighting, and hippos leave tremendous gashes (prone to infections) on each other during these fights. This would make the animals more susceptible to infection, and because hippos appear to eat meat more when other food is scarce, the infected hippos would be more likely to be consumed, infecting even more hippos and leading to a runaway outbreak.

Looking at the dentition of hippos, part of the reason why I wouldn’t necessarily expect carnivory to be common is that their teeth seem to be more adapted to be weapons than efficient cutting/slicing teeth. Hippos may have a good amount of power behind their bite, and the teeth in the front of their jaw are certainly powerful when it comes to puncturing, but it would seem to me that they would have to puncture carcasses with their massive front teeth and then try to rip off bits to then swallow whole; they lack the more efficient piercing and cutting teeth of carnivores like dogs and big cats. The apparently get by well enough without it when times get hard, but it doesn’t seem like they’re particularly well-adapted to carnivory. The following clip gives us a brief glimpse of a hippo scavenging from a buffalo carcass, although it doesn’t seem particularly interested in consuming much or fighting the lions for the carcass;

While it may be easy to write off such behaviors as aberrant or abnormal, they are very important to our understanding of ecology. Many people have a somewhat Disney-esque idea of what nature is like, with the “great Circle of Life” allowing each animal to have their own niche and live in harmony with each other; carnivores only eat other animals, herbivores only eat plants, and mammalian babies are cared for by both the “mommy and daddy” until they grow up. The truth of the matter is that ecological interactions are far more complex than we realize, sometimes revealing a “darker” side of nature than some people care to acknowledge (but again, this is putting a moral judgment on nature, which does not operate by a moral code or “Law of the Jungle”). There is cooperation in nature, but there is also fierce competition, and when ecologies start to become strained, whole new dimensions of behavior that are otherwise hidden or only barely visible come into play in an attempt to allow for the survival of the individual animal. Why should we expect otherwise?

Hippo Skeleton. Via Wikipedia.