I don't want to be a Bonobo

This Post is a reaction on the Post  from “Ariel Cast out Caliban” by Eric Michael Johnson.


There are many things in the world that annoy me: People in the bus who desperately hammer on the “stop” button to open the door, Professors who seem to know where my exact interests are although they haven’t talked in years and stupid ideologies which use biological examples to justify their view on the world.
Although I’d love to talk about all those things (especially the first one) let’s stick to the third one for now.
Every now and then, I encounter the following sentence in some way or another: “We should be like Bonobos.”


What’s really interesting is that the extremes of what could be called “human nature” are represented by our closest living relatives: Chimpanzees and Bonobos, at least if we rely on popular representations of those two species. Chimpanzees are usually presented as egoistic, brutal and aggressive. Whether Bonobos are the ultimate pacifists, their groups are led by the female individuals and conflicts and stress are usually resolved by some way of sexual interaction -instead of just bashing the head of a rival or tearing apart a helpless Colobus Monkey.
One of my favourite German biologists, Hubert Markl wrote in 1983 that all models on human nature usually have two aspects. The first one is the description of the present state of human nature, which is always pretty negative. The second one is the ideologically tainted vision of how humanity should be.

If we use this model on our closest relatives, the Chimpanzees represent our present state, while the Bonobos is the Vision of what we should become. From time to time I encounter this case, be it in the media or from people I meet and it might come up again in the next time, after some of the results of this study from Perelman et al. (2011) get more public attention.
This study, which deals with the Phylogenetic relationships of all primates, found that after the split between Chimpanzees and Bonobos, there was a higher rate of Change within the Genome of Chimpanzees as within the one of Bonobos. To make a long story short: This higher rate of change could lead to the conclusion that Bonobos are closer related to us, then Chimpanzees. Until now it was assumed that both species are equally related to us.
This of course changes everything! Our closely related living relative is the ultimate example for altruism and cooperation. The true picture of our own nature! Once again, Man cut himself from his own natural heritage. Now we simply have to return to our own biological roots and all our problems are solved! I’d bet a large amount of money that someone will write something like that, just a little more elaborated and maybe a little more esoteric. Maybe I should write this stuff myself, put in a book and sell it to bolster my very slim budget.

Jokes aside, my point is as follows:
Both Chimpanzees and Bonobos are just models for our own ancestors. Those Models fit in some cases more and in some cases less well on our past. We can’t just transfer our observations on present day animals into the past, just to help us to support some kind of weird ideology, as we can’t use them to justify acts of brutality against ourselves.
Furthermore, these genetic differences between chimpanzees and Bonobos are by now just statistical differences. We have no Idea if those differences are within regions which are related to behaviour or not.
If we look at ourselves, we can see that we’re capable of both extremes: exceptional brutality as well as exceptional altruism. Bonobos and Chimpanzees could help us to understand how we acclaimed those behaviours and how they’re funded in our own biological heritage. Sure, there’s no potentially World-saving conclusion within this stuff, but we need it, if we want to understand our biological “nature”.


Ideologies are always made by humans; and Primates, especially apes, were always used as a screen on which we can project ourselves on. The Chimpanzees were used for all that’s negative about us, while the Bonobos stand for everything positive. But we must not forget that both species are not “unfinished humans” or “almost human”, they are Apes. They got their own history, as we do. Their history might help us to understand our own history, and therefore our “nature”, in a much better way, but as closely as we’re related to them, they can never be role models for us.



References:

Markl, H. (1983) Wie unfrei ist der Mensch? Von der Natur in der Geschichte. In: Markl, H. (ed.). Natur und Geschichte. R. Oldenbourg, München, Wien. p. 11-40.
Perelman P, Johnson WE, Roos C, Seuánez HN, Horvath JE, Moreira MA, Kessing B, Pontius J, Roelke M, Rumpler Y, Schneider MP, Silva A, O'Brien SJ, & Pecon-Slattery J (2011). A molecular phylogeny of living primates. PLoS genetics, 7 (3) PMID: 21436896

Fashionably late: The 116th Four Stone hearth.

I know I’m late, so let us don’t waste any more time with weird stories how I managed to completely forget that I canceled my Internet-contract a few months ago, leaving me in a completely Internet-less home and therefore making such mundane tasks like reading Blogs a pretty complicated and time consuming issue.

So instead, let us concentrate on more important things, like Anthropology and Blogs and what happens if you combine those two things. Personal submissions were nonexistent this time, so I dug around and tried to gather all the interesting stuff I can find.


Probably one of the more popular topics was the “Gay Caveman Story”, which was covered by three Blogs:
"The Gay Cavemen" -John Hawks
"Gay Caveman ZOMFG!" -Christina Killgrove
"Gay Cavemen & Buried Shamans" -"Genealogy of Religion"

It’s interesting to see how the most popular story of the last two weeks intertwines with the saddest news this week, as Lewis Binford, the “inventor” of Archeological middle range-theory, died this Monday. Christina Killgrove at (Bone Girl) wrote a nice obituary and although I'm not very interested in Archeology, the news of Binford's death really affected me.
I first heard of Binford’s work as I read Robert Foleys “Just another unique species” where he adapts Binford’s middle Range theory to evolutionary model-building. I still keep this theory in the back of my mind when I try to think about a proper approach to scientific modeling in Paleoanthropology.




On the front of behavioural studies, there are two Posts worth to be mentioned.


I’m happy, that there’s at least one Post which deals with primates in this weeks edition:


Jason Goldman, wrote about a study dealing with contagenious yawning in Chimpanzees.
"Sleeping or empathic: What does yawning mean?"
I yawn a lot, so this is a story in which I’m naturally interested, although I have some problems with the study itself. But on the other hand, I have Problems with almost every behavioural study. But I think, there are some nice things to discuss in this Post.


Same goes with the next Post:
"If I objectify you, will it make you feel bad enough to objectify yourself? On shopping sexiness and hormones, by Cathrine Clancy, of "Context and Variation".


Furthermore, John Hawks wrote a nice little piece about data sharing in paleontology:
"Opening up paleontology" 


The next one already is pretty dusty, but it’s my favourite Post so far in this year and I think everyone in the world should read it. "Evolution: What it is and why humans aren't immune to it." by Zaccharoo over at Lawn Chair Anthropology. Probably one of the best summaries on the general principles of evolutionary theory I’ve read so far.


I wasn’t the only one who had his birthday in the last days. In fact, “This is serious monkey business” turned One year old  a week ago and celebrated this event with a collection of its most popular posts. So, if you haven’t already stopped by, do it right now.




That's it for this week. I really hope you enjoy this edition and I really hope, I'd be able to host another one sometime soon. The next edition (April 27th) is still vacant, so if anybody wants to fill in this position, just tell Krystal D'Acosta.

Let me close this edition with the only funny photograph of an Ape I got (I really need a bigger collection of those).



Dunja, a female Orang-Utan of the Leipzig-Zoo, probably commenting the request of some visitor to "do something".
The Photograph was taken sometime around 2008/2009 by "David B." a good friend of mine and excellent Photographer.

A special Announcement

This Year’s April 13th is a very special day. First of all, it’s my birthday, but there is nothing special about birthdays, since you got them each year on the same day besides, everyone has a birthday. So what makes this date so special to me this year? Well, it’s because it will be the first time that I have the honour to host the “Four Stone hearth”.



The four Stone hearth is a bi-weekly Anthropology (in the broadest sense possible)-related Blog Carnival. This means that every two weeks, one person has the duty to sum up and present a conglomeration about what happened across the whole Anthropology-Blogosphere (I hate those buzzwords). So, if you have a Blog and want to submit one of your posts, or if you found a post from which you thought it might fit within the four stone hearth, just write me an Email (my Address is somewhere on the right sidebar, or under the “about” tab). Depending on the number of submissions I might add additional Posts, even if their authors didn’t submit them on their own.


I’m really looking forward to next week and I’m pretty sure it’ll be a very interesting edition.

GfA Fail

Yesterday, while I did some research for a Post I originally intended to write today, I visited the Homepage of the "Gesellschaft für Anthropologie" (GfA), which is the Association for Anthropologists in Germany. There I found a public “statement” of the GfA regarding the debate of evolutionary theory “vs.” Creationism. This statement had a very interesting, and somewhat disturbing back-story:



Back in 2009, due to my raising concerns about the situation of Anthropology on German Universities, I attended to the Congress of the GfA in Munich, so that I could get a better picture about, what exactly Anthropologists in Germany do. On the general Assembly of all GfA-Members, which I attended to as a non-member, a debate was opened whether or net, the GfA should make a public Statement on this issue. During this debate, one person stood up and said, the she would appreciate it, if kids in school were lectured in both “visions” (in German it was “Vorstellungen” –I have no Idea how to translate it properly), Evolutionary Theory AND Creationism.


Now you must know, that German Anthropology contains only of what most of you might describe as “physical” or “biological” Anthropology.
During the arising ruckus, which lead to a statement from myself and after it to the request that only members of the GfA should say something, the debate was more or less aborted.

Well, after almost 2 years, there finally is a statement, which you can read here. You'd probably have no problem reading it, because it’s in English. Why in English you might ask?
Well, because the GfA kindly got the permission to use the Statement of the AAA regarding the debate on creationism. Now let us ignore all the fuss about this “AAA-Fail”* thing, and that the statement itself seams a little bit watered down to me. I’m bothered about something else, which in my opinion leads to the reasons why Anthropology in Germany is on the way to becoming an insignificant part at German Universities.


As I said, German Anthropology is foremost a biological discipline. And we all know which theory is the central, and maybe the only theory in biology. Dobzhansky even said that nothing in biology would make sense without it.


And now, if we look at this statement again or more on the fact that they had to use the Statement of the AAA instead of making their own statement, it seems that there is no one within the GfA with enough competence to actually write something about evolutionary theory, human evolution and creationism. Well, there are people in Germany who would be able to do something like this, in fact they would probably do a great job, but they don’t want to be affiliated with the GfA. How could this happen?


Throughout its history, Anthropology in Germany remained an almost complete descriptive and somewhat atheoretic  discipline. It might claim, that its goal is to understand “the evolution of man in time and space” (or something like that -all those descriptions are horrible), but in reality only a small part of it, tried to do this.


Almost thirty years ago, in 1982 the German anthropologist Christian Vogel, who was a Professor at the University of Göttingen and was one of the establishers of Socio-biology and modern Primatology in Germany, addressed this issue in his Essay “Biologische Perspektiven der Anthropologie: Gedanken zum sog. Theorie-Defizit der biologischen Anthropologie in Deutschland” (“Biological perspectives of Anthropology: Thoughts on the so called ‘Theory-deficit’ of biological Anthropology in Germany”-my translation).


You probably can compare his appeal to the appeal of Sherwood Washburn to the AAPA back in the 1950s.


I read his essay back in 2009 as I prepared myself for the GfA Congress and I wanted to know, how much of the problems Vogel addressed in his paper, were even considered by German Anthropologists. After my visit and my disturbing experiences on the general Assembly, I dare saying, that none of them were considered. In fact, I think things even got worse.

Recently I read some Posts where people tried to describe what they love about Anthropology, or why they love it. And although I would probably have some difficulties to answer this question for myself, I can say for sure, that my fascination is mostly based on the aspects of our own evolutionary history and its implications for our present day life.
And it makes me mad, how these aspects are treated within the GfA. Anthropology deals with some of the most important questions we can ask (“Where do we come from?” “What is human nature” “What defines a human?”) and the GfA abandons these question in favour of being a helper for Archaeologists who want to know what kinds of skeletons they have excavated.** Instead of a flurish discussion about how evolutionary theory could help us to understand ourselves in a much better way, my experiences as student of Anthropology looks like this:
In some of my Psychology-courses (Psychology is one of my minor subjects) people started to groan as soon as I tried to put certain phenomena in a evolutionary perspective.
A friend of mine, who, besides studying Anthropology, also studies Ethnology faced open hostility when he mentioned the word “Socio-biology” in one of his courses.
Some of our (Anthropology) Students have no idea about human evolution or even the basic principles of evolutionary theory, because they think it’s not important for them and our curriculum enables them to ignore courses about this topic.
Every time I tell someone what I study, the first question I’m being asked is: “Ah, and what exactly are you doing there?”***.
And the worst part of all, those people who try to explain evolutionary theory on a public level, have absolutely no Idea about human evolution and always present it in a “march of progress”-like manner, speaking about “missing-links” and “chimpanzee like ancestors”****.


Here, the GfA had the opportunity to make not only a statement against the equal teaching of creationism and evolutionary theory; they had the opportunity to make a statement why Anthropology is an important science, and how it can contribute to modern day issues.


The GfA completely failed at this. Instead they gave a statement about their own incompetence. 

Right now, Anthropology in Germany is a descriptive, atheoretic and almost abiologic “science”, which is doomed to become an insignificant hoard for people who don’t find a place within their own field of science (such as medicine, educational science, psychology etc.) and I don’t want to be represented by this kind of association.
Surely, many people from the GfA will disagree with me on this point. On their next congress, which is in September, they’ll probably say again (as they did in 2009) how important they are and at the same time, wonder why they're the only ones who think that.


In the past months I often tried to compare the situations of Anthropology in Germany (and my own experiences with it) with the events around the AAA last year. And although I don’t think, we can directly compare them; there are some parallels, when it comes to questions what Anthropology exactly should try to achieve.

Looking at both stories, the only thing I learned so far is that you never should rely on scientific associations to define and defend your field of research. If you want to keep aspects of your field which are important to you, then do it yourself and think of means to convince other people, that those aspects are worth to be kept..



*Although I have to admit this story leaves a somewhat bitter taste.
** This is no degradation of Archaeology or prehistoric Anthropology, I just think, that Anthropology can do more then just this.
*** This I wanted to know for a long time: How often do Anthropologists from other countries get asked this question?
**** Besides, most of them are arrogant douchebags.




References:

Vogel, C. 1982. Biologische Perspektiven der Anthropologie: Gedanken zum sog. Theorie-Defizit der biologischen Anthropologie in Deutschland. Z. Morph. Anthrop., 73, 225-236.

What happened to Sahelanthropus tchadensis? (Part 2: Conclusions)

Two weeks ago, I finished my Post regarding the (almost non-existing) controversy about Sahelanthropus tchadensis with a more or less cryptic statement, which I thought should deserve a separate post to elaborate.

I ended my post asking the question whether or not the exclusion of Sahelanthropus would diminish this fossil from its scientific value. Well, the answer itself is pretty easy: Of course it wouldn’t do it. The more interesting question is: Why?


To answer this question we should take a closer look at the situation on the base of human evolution:


Timeline showing the estimated age of the earliest putative homids. As indicated by the red circle, these fossils almost perfectly fall inside the timeframe of the Chimpanzee/Human divergence based on molecular-clock estimations. (pictures taken from Johanson & Edgar, 2006; Suwa et al. 2009)



As we can see on this picture, we’re more or less in the right time frame when it comes to finding putative hominid ancestors, since we’re pretty much inside the estimated date of divergence between humans and chimpanzees (as indicated by the red circle). On one hand, this is pretty great because now we have much better resources to actually build up and test hypothesises about human origins. On the other, we got the problem that it’s actually pretty hard to classify these fossils in a proper way. The reason why there is this problem is because the closer we get to the actual date of divergence between humans and Chimpanzees the more the fossils we find will resemble the most recent common ancestor (MRCA). This means that these fossils to a great extant would still reflect the ancestral condition of the MRCA and would not have developed a huge amount of derived characters which could provide us with enough information to classify them properly.

Samuel Cobb (2008) came to the same conclusion, when he tried to reconstruct the facial morphology of the MRCA:

„In light of the problem summarized above and the paucity of the fossil evidence of the face in the hypodigms of these four taxa [Sahelanthropus tchadensis, Orrorin tugenensis, Ar. ramidus, Ar. ramidus kadabba -my addition], it is not possible to determine with any confidence whether any of them is the LCA , or a stem taxon in either lineage, or a member of an extinct, and until now unrecognized, hominid lineage.” (Cobb, 2008; p.482)

So, in the end we’re stuck in a situation which looks something like this:

Possible classification of the earliest putative hominid fossils. Because of their (probably) very ancestral condition, they could be either stem hominids, on the lineage to the Chimpanzee/Huma LCA, stem Chimpanzees or stem Gorillas.

On the first hand this picture might look a little bit depressing (at least I found it to be depressing), but, and now I finally come to my original statement, even if we’re not able to classify these early putative hominids with absolute certainty, they’re still providing us with lots of valuable information. Each fossil from this specific timeframe helps us to reconstruct the ancestral morphology of the Chimp/Human common ancestor, to reconstruct the original ecological niche of the MRCA and they help us to build up and test hypothesises on how exactly and under which circumstances the divergence of the Chimpanzee/Human clade took place.
All these things actually are much more important then the exact classification of the fossils we use dot draw conclusions from. Sure it might not sound very spectacular if someone publishes the description of a new putative hominid and states that he isn’t sure where to exactly place It., but it’s probably much closer to reality then all those ground breaking discoveries we encountered in the last 10 years.


Ok, this doesn’t sound very optimistic, but I still think that we, even if it seems futile, should still try to classify each fossil we find. I also want to add that this might look futile, from a present day perspective. But right now we also have to face the fact that there is one huge, but very critical gap in the fossil record. I’m of course speaking about the almost non-existent fossil record in the Chimpanzee and Gorilla lineage. Right now we have actually no Ideas how and in which way these genera evolved since they split from our lineage. Usually the lack of a Chimpanzee/Gorilla fossil record is explained by the fact that rainforests don’t provide the circumstances for good fossilisation. Right now this sounds like a sorry excuse, at least in my eyes.

In the last century we were able to get a very good coverage about the whole timeline of human evolution. We got this coverage, because there were huge efforts put into the search for fossil hominids. And right now, I’m pretty sure that, if we put even a small bit of this effort into the search for Chimpanzee and Gorilla ancestors, we will find them. On the other hand it’s pretty clear that if we do not search explicitly for these kinds of fossils we pretty sure won’t find any.

Just to show that I’m not the only one with this opinion and since it’s always good to support one’s argument with some famous words, here’s one of my favourite quotes from the paper of Esteban Sarmiento (2010), whose critique on the classification of Ardipithecus I start to like more and more:

“(...) it is curious that in a century-old race for superlative hominid fossils on a continent currently populated with African apes, we consistently unearth nearly complete hominid ancestors and have yet to recognize even a small fragment of a bona fide chimpanzee or gorilla ancestor.” (Sarmiento, 2010 p.1105b )



References:
 
Cobb, S. (2008). The facial skeleton of the chimpanzee-human last common ancestor Journal of Anatomy, 212 (4), 469-485 DOI: 10.1111/j.1469-7580.2008.00866.x

Sarmiento, E. (2010). Comment on the Paleobiology and Classification of Ardipithecus ramidus Science, 328 (5982), 1105-1105 DOI: 10.1126/science.1184148

Pictures:

Johanson D., Edgar, B. (2006). From Lucy to language. Simon and Schuster, New York
Suwa G., et al. (2009). The Ardipithecus ramidus Skull and Its Iimplications for Hominid Origins. Science 326, 68.

"The degree of consistency between our theoretical knowledge of the world and the real world remains unknown to us, even if it's complete."

(From: Vollmer G. (1975) Evolutionäre Erkenntnistheorie Hirzel, Stuttgart, Leipzig, p. 137, (probably horribly) translated.)




So much for the proposition that something is "fact".

What happened to Sahelanthropus tchadensis?

This Wednesday I had to do a Presentation on the description and classification of Sahelanthropus tchadensis for my Seminar on Human Evolution. I loved working on this topic, because two years ago, while I already attended a similar course, I watched a pretty impressive presentation about the same topic. This Presentation was one of those “enlightening” moments I had in this time and I always wanted to dig deeper into this whole story.
Anyways, I think I did pretty well, although I again realised that many other students do not share my enthusiasm for cladistics and the search for “good” characters. This or maybe it was just boring.


To come to my original reason for this post: While I prepared my talk, reading all those papers about the original discovery of Sahelanthropus and the upcoming critique of its classification, I could not help but ask myself: “What happened to this discussion?”
To give short recap on this story: Michel Brunet and his colleagues base their interpretation of Sahelanthropus tchadensis being a hominid on the following traits:


-A large supraorbital Torus, which Brunet et al. (2002) associated with a male individual (this sex estimation is pretty important for the next trait).






Brunet et al. (2002)


-A small canine, with  a  distal and apical wear facet and no C/P3 honing facet. (There were more characters described for the Canines, but I will skip them here)

-An enamel thickness between the chimpanzee and the Australopithecus condition.

-A flat, horizontally orientated Planum nuchale

-A more anterior positioned Foramen magnum

Zollikofer et al. (2005)

-A more perpendicular angle between the Foramen magnum and the Orbital Plane


The last three characters were associated with the probability of Sahelanthropus being a Biped.



Now, two years ago when I first heard about above listed traits I nearly went mad on their assumption that Sahelanthropus was a male. I just couldn’t, and still can’t understand how you’re able to estimate the sex of a single individual without knowing how those characters you use for your Sex estimation vary within this species.
This estimation is crucial because if we look at the canines, they are only small if Sahelanthropus was a male individual. If it was female, the size of the canine falls within the variation of other female Miocene apes and becomes much less diagnostic.

Speaking of canine morphology, there is a huge probability, that the morphology of the canine and its wear pattern is not an apomorphic character for hominids, but in fact a plesiomorphic character of at least all African Apes, which renders it almost useless for classification. Wolpoff and Colleagues (2006) stated that the wear pattern of the Sahelanthropus canines is probably the result of powerful masitcation, because similar patterns could be found in other Miocene Ape Taxa, such as Ouranopithecus and Gigantopithecus.

Canine of Gigantopithecus showing slight distal and apical wear. According to Wolpoff et al. (2006) this tooth shows an earlier stage of the wear pattern of Sahelanthropus tchadensis. (Wolpoff et al., 2006).

They continue in their critique, showing that none of the traits, Brunet et al. (2002) and Zollikofer et al. (2005) showed, could be interpreted as clear signs for bipedalism. This doesn’t mean of course, that those traits couldn’t be seen as apomorphic for hominids*, but at least you’re not able to state that it’s more possible that Sahelanthropus was a biped, than that it was not (as ist was by Zollikofer et al., 2005).

From my point of view, Wolpoff et al. (2006) raised some serious doubts on the classification of Sahelanthropus being a hominid and I was pretty sure that there should be some kind of answer on these issues by now. Well, apparently I was wrong about that,The only thing I found so far was this little passage:


“Scientifically it is impossible to understand why some authors ignore these derived characters and concentrate on primitive ones to reach the conclusion that S. tchadensis is related to modern apes and even more precisely to a palaeogorilla (Wolpoff et al. 2002, 2006; Pickford 2005). This attempt to undermine the clear affinity of the Chadian hominid is curious mainly when it is coming from, among others, two who have not yet had the opportunity to check Toumaı¨ casts in their laboratory. Is it what they believe, or is it only because they want to keep Orrorin as the earliest hominid?“ (Brunet, 2010, S.3318)


I found this to be pretty disappointing. Mostly because, a little bit before that passage, Brunet listed exactly the same “derived” characters, Wolpoff et al. criticized in their 2006 paper.

And instead of countering the critique on a scientific base, Michel Brunet points to the involvement of two of his “critics” (Martin Pickford and Brigitte Senut) into the discovery and description of Orrorin tugenensis. Well you can do exactly the same kind of argument with Michel Brunet, pointing out his extensive work in Tchad and the fact that it surely is pretty lucrative to announce an “earliest known hominid”.

Surely, there might be some kind personal interest behind many critical papers, but you still have to confront those critics in a scientific way. And the only way to get some kind of scientific progress is to falsify hypothesises of other people. In fact, the only thing we can be sure of in science is that if something is false, it is false (to put it simple). So the best way, to show that you’re right, is to show to other people that they are wrong.  But if we look at this case here, I can’t see that this process is happening right now.

Judging from what I know so far about this story, I would not classify Sahelanthropus tchadensis as a hominid. This doesn’t mean on the other hand that this conclusion diminishes the scientific value of Sahelanthropus.
What I exactly mean by this sentence I will explain in my next post, which I hopefully manage to put in a few days.




* I’m a little bit confused about that right now, since I got this thought while writing this post.


References:

Brunet, M., Guy, F., Pilbeam, D., Lieberman, D., Likius, A., Mackaye, H., Ponce de León, M., Zollikofer, C., & Vignaud, P. (2005). New material of the earliest hominid from the Upper Miocene of Chad Nature, 434 (7034), 752-755 DOI: 10.1038/nature03392
Brunet, M., Guy, F., Pilbeam, D., Mackaye, H., Likius, A., Ahounta, D., Beauvilain, A., Blondel, C., Bocherens, H., Boisserie, J., De Bonis, L., Coppens, Y., Dejax, J., Denys, C., Duringer, P., Eisenmann, V., Fanone, G., Fronty, P., Geraads, D., Lehmann, T., Lihoreau, F., Louchart, A., Mahamat, A., Merceron, G., Mouchelin, G., Otero, O., Campomanes, P., De Leon, M., Rage, J., Sapanet, M., Schuster, M., Sudre, J., Tassy, P., Valentin, X., Vignaud, P., Viriot, L., Zazzo, A., & Zollikofer, C. (2002). A new hominid from the Upper Miocene of Chad, Central Africa Nature, 418 (6894), 145-151 DOI: 10.1038/nature00879
Brunet, M. (2010). Two new Mio-Pliocene Chadian hominids enlighten Charles Darwin's 1871 prediction Philosophical Transactions of the Royal Society B: Biological Sciences, 365 (1556), 3315-3321 DOI: 10.1098/rstb.2010.0069
Wolpoff, M. H., Hawks, J., Senut, B., Pickford, M., & Ahern, J. (2006). An Ape or the Ape: Is the Toumaï Cranium TM 266 a Hominid? Paleoanthropology, 36-50
Zollikofer, C., Ponce de León, M., Lieberman, D., Guy, F., Pilbeam, D., Likius, A., Mackaye, H., Vignaud, P., & Brunet, M. (2005). Virtual cranial reconstruction of Sahelanthropus tchadensis Nature, 434 (7034), 755-759 DOI: 10.1038/nature03397