Anthropology.net

PNAS has just published a back and forth discussion between John Skoyles and Deborah Rogers and Paul Ehrlich. John Skoyles expressed beef with the paper Deborah Rogers and Paul Ehrlich recently put out. The jog your memories, Roger and Ehrlich wrote, “Natural selection and cultural rates of change.” I covered that paper in a February post, raising some questions.

I was not alone in my criticisms, Skoyles also had a set. In his letter, “Natural selection does not explain cultural rates of change,” he wonders two things. First, Skolyes addresses whether or not Rogers and Ehrlich established enough of an argument to inferring that natural selection was at play in how canoes design changed. Secondly, Skoyles takes a shot at how Rogers and Ehrlich use the term cultural evolution. Cultural evolution can be used analogous to cultural change or it can be under the principles of natural selection.

Rogers and Ehrlich defended their work in their response, “Reply to Skoyles: Natural selection does appear to explain some cultural rates of change.” Their response is pretty conservative. They write, “although it does not prove that natural selection was at work, it certainly supports that inference.” I still don’t fully see how differences in the rates of change in frequencies of various cultural traits over time infers natural selection, especially when people are the selectors. It seems like another level of selection is at play.

On that note, the University of British Columbia put out a press release on the work of Liane Gabora, who is making a computer model that will piece together the process by which human culture evolves. She’s made some comments that are directly tangential to the discussion between Skoyles, Rogers, and Ehrlich. She says,

“For one thing, artifacts do not change solely through random, ‘mutation-like’ processes. Humans innovate strategically and intuitively, taking advantage of the ability to group items that go together, like mortar and pestle, or use analogies…

…The underlying mechanisms by which culture evolves are superficially similar yet profoundly different from those through which living things evolve. A symptom of this profound difference is that biological evolution prohibits inheritance of acquired characteristics.”

Skoyles, J.R. (2008). Natural selection does not explain cultural rates of change. Proceedings of the National Academy of Sciences, 105(22), E27-E27. DOI: 10.1073/pnas.0802586105

Rogers, D.S., Ehrlich, P.R. (2008). Reply to Skoyles: Natural selection does appear to explain some cultural rates of change. Proceedings of the National Academy of Sciences, 105(22), E28-E28. DOI: 10.1073/pnas.0803570105

Seems like to today is turning into the film Fridays that I always looked forward to early on in my education. You probably deserve a break from this week’s blogging. This video that I’ll be sharing with you has many flaws, but it is a creative way to visualize the evolutionary processes. I don’t particularly appreciate how little to no effort was made to show the Cretaceous–Tertiary extinction event nor the dearth of mammalian evolution, instead they literally fast forwarded millions of years of evolution to show an ape walking bipedally in the trees… which is a somewhat dangerous interpretation.

Anyways, its flawed but it is entertaining, especially since I brought up limb evolution during the Devonian. The video also gets plus points because it plays a favorite Nine Inch Nails song of mine,

One of the hallmarks of human evolution, aside from our bipedalism and extraordinarily large brains, are our forelimbs… especially the famed prehensile thumb. Our forelimbs, or arms, are extremely flexible compared to a quadruped. For example, because of the shallowness of the ball and socket joint that connects our humerus to our scapula, our arms can rotate 180 degrees. A special thank you to our arboreal tree swinging ancestors. But our arms aren’t that different from other organisms. Actually, if you’ve spent any time reading your basic biology textbook, you probably have come across a common illustration which compares the human forelimb to forelimbs of other organisms, such as the bat, whale, etc.

In these illustrations, you are supposed to see how the bones that make up a bat’s wing are structurally analogous to both human hands and seal flippers, due to the common descent of these structures from an ancestor that also had five digits at the end of each forelimb. The bones of the bat wing are proportionately different from a human’s arm, but they still share the major components such as the humerus, radius, and ulna. These illustrations are ultimately meant to document that a lot of homology exists in the basic vertebrae body plan and establish the fact that all vertebrates share a common evolutionary ancestor.

Based off of papers such as this 2006 Science publication, we’ve come to understand that the structural homology is due to the activation and expression of several critical genes that regulate development. One of them is called sonic hedgehog or SHH, named after a favorite video game of the researcher who discovered the gene. When there are mutations in SHH, limbs do not develop normally, as illustrated in the collection of skeletons from the various mutant stocks to the right. The forelimbs of the top represent normal development with the presence of SHH. In the absence of SHH signaling, forelimbs are mutated as seen in the bottom.

Comparing the SHH sequence between organisms have shown that it is a highly conserved gene, found with little difference in species as diverse as arthropods and mammals. In 2006 we also saw another paper that figured out the molecular evolution of SHH is relatively accelerated in primates, when compared to other mammals. And SHH is even more accelerated in the human lineage. Since SHH is a gene expressed during and for development, such findings implicate SHH as a potential contributor to the evolution of primate and human specific morphological traits.

Anyways, where I’m trying to go with this is that we see a conservation in limb development, both genetically and phenotypically. Neil Shubin, a professor of anatomy at Chicago University also investigated this phenomenon and published his findings in his book, “Your Inner Fish: A Journey into the 3.5 billion-year History of the Human Body“, which explores the links between humans and their most ancient forebears.

He’s analyzed the tiktaalik fossil, which is supposed to represent a transitional species of fish to amphibian. By the way, the tiktaalik discovery was announced also in 2006 by Shubin and colleagues. In his comparisons, he sees that ours wrists and unique opposable thumb, even the shape of our skulls, can be traced to origins in the tiktaalik. Shubin also found out that the tiktaalik fossil displayed similarities to the human shoulder, elbow, and forearm.

“When we study the structure of these joints to assess how one bone moves against another, we see that tiktaalik was specialized for a rather extraordinary function – it was capable of doing push-ups,” writes Shubin.

Separately, Shubin has found that modern-day fish carry genes allowing for the growth of wrists, hands and fingers. These are now “switched off” so the digits never develop in the fish.

Such findings cast doubt on the assumption that hands are a more recent evolutionary step than fins. Instead, fins may have developed as an improvement on hands.

The research also supports the argument that the majority of the human genome developed 500m years ago and is shared with most living creatures.

One of the factors that makes living forms different is the ability to switch off certain genes while retaining them in the genome.

An alternative approach is to adapt similar genes to different purposes. Some of the genes involved in the evolution of human vision and hearing play an active but very different role in the metabolism of jellyfish.

I feel that excerpt was awfully simplistic, but I want to bring to attention what I’ve bolded. The second statement, the one that says the majority of the human genome developed 500,000,000 years ago is an extraordinary but not nearly as controversial statement as the first one. We know that genes like SHH and the HOX genes are conserved… and being eukaryotes, many of the genes that encode for basic functions of the cell are conserved.

But where Shubin is paraphrased, saying fish have the developmental genes that pattern for wrists and fingers but don’t express them, is ballsy. Furthermore, saying limb patterns that makes up a hand developed before fins is even more of a contentious statement. It is reminiscent the curve ball Aaron Filler’s threw us in his human ancestor for the apes hypothesis, because the current understanding is based upon fish with fins gave rose to amphibians that have more hand-like forelimbs than their fishy ancestors. I’d like to know what genes Shubin has identified as inactivated in fish for the development of hands, wrists, fingers in fish are. But unfortunately the source article doesn’t mention them. I guess I gotta buy and read the book.

Dopamine is a fundamental neurotransmitter and hormone. You may know it as one of the neurotransmitters associated with the limbic system, being released during eating and sex, which causes a sensation of pleasure. But it is more than just a hedonistic chemical, actually many of the functions of the brain are dependent on dopamine. Memory, attention and problem solving revolve around dopamine to control the flow of information from other areas of the brain to the frontal lobes. As a hormone, dopamine acts a precursor to noradrenaline and adrenaline and thus increases heart rate and blood pressure during sympathetic nervous system response.

For this purposes of this post, dopamine is an important neurotransmitter that regulates behavioral responses. In brains of people with deficiencies in dopamine levels, attention deficit hyperactivity disorder is an all too common diagnosis. Low levels of dopamine also cause social withdrawal, apathy, and anhedonia. Furthermore, social anxiety is associated with neurons that are unable to bind dopamine. When dopamine is unregulated and in excess, extraversion or gregarious and assertive behaviors are observed.

Before I jump deep into the post, let me first run down some neuron physiology. Without an understanding about how neurons and their associated chemicals function, it’s hard to comprehend how a mutation in any one of the components leads to neurological, cognitive and behavioral disorders. Neurons are specialized cells of the nervous system that are depolarizable and this ability allows signal to be transduced. Signals come in two forms, graded or action potentials. I won’t get into the nitty gritty of how potentials are formed but just know that once graded potentials reach a threshold, an action potential is generated that rushes down the axon of a neuron. Action potentials are an all or none response.

The action potential travels down axon to the presynaptic terminal where it causes channel proteins to open. The presynaptic terminals contain vesicles chock full of neurotransmitters. The opening of channel proteins influences the vesicles full of neurotransmitters to fuse with the presynaptic membrane. The neurotransmitter is released into the space between the presynaptic membrane called the synaptic cleft and it targets its reciprocal receptor on the postsynaptic membrane of the next neuron. The effect of the neurotransmitter on the postsynaptic membrane will depend on the nature of the neurotransmitter, the nature of the postsynaptic receptors, and whether the postsynaptic ion channels are voltage-gated or chemically-gated. In dopamine’s case, it is hypothesized to provide a teaching signal to parts of the brain responsible for acquiring new behavior.

To clean up the neurotransmitters, specialized proteins called transporters function to re-uptake the bound neurotransmitters back into the neuron. I imagine them as vacuums. In dopamine’s case, a specific transporter exits, and is called the dopamine transporter… but we’ll be calling it DAT. Since DAT cleans up dopamine, and inactivates its function, it is critical in regulating (stopping) the network of effects dopamine is responsible for. Any mutation in the DAT gene that also changes the amino acid composition of the transporter ultimately affects the ability of the protein to stop dopamine’s effects.

In humans, the DAT gene is fairly large, around 64,000 base pairs long and consists of 15 exons. Evidence for the associations between DAT and dopamine related disorders have come from a genetic polymorphisms studies of the DAT gene. Currently mutations in DAT are implicated in a number of dopamine related disorders such as attention deficit hyperactivity disorder, bipolar disorder, clinical depression, and alcoholism.

Because DAT modulates the extent of dopamine activity on the receptor, it becomes an excellent candidate to study how variants of DAT effect behavior and ultimately if the variants offer an selective advantage. In what I consider a really awesome paper in the journal, Molecular Biology and Evolution, a half dozen geneticists at the University of Pittsburg, studied DAT for sequence variation in populations of two different macaque species and humans. They calculated the extent of the different combinations of DAT alleles in their populations that would be more or less frequent than what’s expected from a random formation of haplotypes. The amount of non-random associations between polymorphisms at different loci are measured by the degree of linkage disequilibrium, which is the basically the probability to find same set of alleles at two or more loci. The key word here is non-random. In order to study whether or not a mutation in the DAT gene has any affects on survivability, we need to figure out the random variants from the ones that are seemingly selected for.

The paper, “Sequence Variation in the Primate Dopamine Transporter Gene and Its Relationship to Social Dominance,” tells us how they went about doing that. First they sampled about 760 monkeys but only 23 humans. They designed primers for the DAT gene and each exon was sequenced. That’s a lot of sequencing, if my estimations are correct, that’s around 12,000 different reactions. But I don’t know that for sure. Either way, 78 polymorphisms were identified but only two functional variants were linked to high social rank. Social rank was observed through the level of dominance (aggressive, use of attack gestures, actions, and vocalizations more frequently, and consistently defeat individuals of lower rank).

What I’m kinda iffy on is how they identified the variants, located in 5′ UTR, if they only sequenced the exons. Regardless, they realized that heterozygous individuals, with one copy of the minor 5′ UTR allele, were more likely to be of subordinate rank than those who were homozygous for the major allele. In other words,

“the odds that a subordinate individual possesses at least one copy of the minor allele… are one and a half to nearly twice the odds of it being homozygous… In contrast, subordinates were significantly less likely to be heterozygous than homozygous.”

The two DAT 5′ UTR variants fall at a putative transcription factor–binding site. They don’t get deep into a discussion on how the variants affect the transcription factor-binding site (other than the minor allele abolishes the core sequence) nor what the putative transcription factor that binds to it, which would be two a really cool study in itself. If one could take the 2 variants and compare how levels of gene expression vary, then we can get an idea if the homozygous alleles allow for less DAT to be transcribed and ultimately allow for more dopamine to float around causing extraversion and socially dominant behavior. But they do identify NFAT as a regulator,

“…these transcription factors thus play a crucial role in shaping long-term changes in neuronal function. They are also sensitive to secondary messenger systems activated by brain-derived neurotrophic factor (BDNF) which regulates expression of the dopamine D3 receptor. It is thus possible that NFAT and/or BDNF also modulates expression of DAT. “

I consider this study extremely enlightening in understanding the biological mechanisms behind primate social behavior and ultimately evolution. See we have behavior, social dominance, that for the most part we think has evolutionary significance and has something to do with dopamine and the regulation of this neurotransmitter. In order to figure out if the two are linked, one needs to correlate that a variation in any portion of the gene that regulates dopamine activity (DAT) is linked to a heterozygote or homozygote state.

In this case, Robert Ferrell and his lab identified a difference in an area slightly upstream of DAT that controls the rate it is transcribed in macaques. By looking at the variants in each individual and the observations of the social behavior, his lab figured out heterozygous individuals we’re as bossy. Pretty amazing, if you ask me. But this putative binding site is not found in the homologous region of human DAT, which is also really interesting! Has social dominance by way of the dopamine network not been positively selected or lost in the human lineage? Or have we humans found another biochemical pathway to influence dominant behavior?

I try to avoid filling up this site with anti-creationism banter because other people do so much of a better job with that sort of blogging, and I like to focus on new things in anthropology. But since the National Academy of Sciences and the Institute of Medicine pooled their resources and minds together and put out a comprehensive 88 page book titled, “Science, Evolution, and Creationism” I feel obliged to share it with you. The book was put together in order to explain the overwhelming evidence in support of biological evolution, and slam the shortcomings in creationism thought, including “intelligent design.” From the description of the book,

“The book explores the many fascinating inquiries being pursued that put the science of evolution to work in preventing and treating human disease, developing new agricultural products, and fostering industrial innovations. The book also presents the scientific and legal reasons for not teaching creationist ideas in public school science classes.

Mindful of school board battles and recent court decisions, Science, Evolution, and Creationism shows that science and religion should be viewed as different ways of understanding the world rather than as frameworks that are in conflict with each other and that the evidence for evolution can be fully compatible with religious faith. For educators, students, teachers, community leaders, legislators, policy makers, and parents who seek to understand the basis of evolutionary science, this publication will be an essential resource”

You can read the full text of the book for free, chapter by chapter or download a free PDF of the Science, Evolution, and Creationism summary brochure. I can’t seem to find a free full text PDF of the entire book, but you can order 2 copies for $9 which ain’t a bad deal.

In other evolution news, John Hawks has a run down on 2008 predictions in physical anthropology. To add to one point he makes about three papers with new Ethiopian fossils coming out this year, I know of at least one major find that we’ve all been waiting to be published should be published in the near future. I’m really interested in the bonus prediction, the, “dramatic development in the problem of pre-2.0-million-year-old Homo,” point.

Both Nature and PNAS have put out two fascinating papers on the evolution of language.

Nature‘s “Quantifying the evolutionary dynamics of language,” studies how grammatical rules change over time, a term the authors call regularization. The authors specifically studied the regularization of English verbs over the past 1,200 years. Here’s a summary of what they concluded from the abstract,

“We have generated a data set of verbs whose conjugations have been evolving for more than a millennium, tracking inflectional changes to 177 Old-English irregular verbs. Of these irregular verbs, 145 remained irregular in Middle English and 98 are still irregular today. We study how the rate of regularization depends on the frequency of word usage. The half-life of an irregular verb scales as the square root of its usage frequency: a verb that is 100 times less frequent regularizes 10 times as fast. Our study provides a quantitative analysis of the regularization process by which ancestral forms gradually yield to an emerging linguistic rule.”

I’ve bolded what I consider important because this conclusion has some tangents to protein evolution as well. Often proteins that are less vital are mutated much more frequently than vital proteins. It is remarkable to see the authors quantified a similar phenomenon in language evolution.

On that note, PNAS ran this paper about a week ago, “Coevolution of languages and genes on the island of Sumba, eastern Indonesia.” Here’s the abstract,

“Numerous studies indicate strong associations between languages and genes among human populations at the global scale, but all broader scale genetic and linguistic patterns must arise from processes originating at the community level. We examine linguistic and genetic variation in a contact zone on the eastern Indonesian island of Sumba, where Neolithic Austronesian farming communities settled and began interacting with aboriginal foraging societies ~3,500 years ago. Phylogenetic reconstruction based on a 200-word Swadesh list sampled from 29 localities supports the hypothesis that Sumbanese languages derive from a single ancestral Austronesian language. However, the proportion of cognates (words with a common origin) traceable to Proto-Austronesian (PAn) varies among language subgroups distributed across the island. Interestingly, a positive correlation was found between the percentage of Y chromosome lineages that derive from Austronesian (as opposed to aboriginal) ancestors and the retention of PAn cognates. We also find a striking correlation between the percentage of PAn cognates and geographic distance from the site where many Sumbanese believe their ancestors arrived on the island. These language–gene–geography correlations, unprecedented at such a fine scale, imply that historical patterns of social interaction between expanding farmers and resident hunter-gatherers largely explain community-level language evolution on Sumba. We propose a model to explain linguistic and demographic coevolution at fine spatial and temporal scales.”

Like genes, words can be compared to one another and scrutinized with phylogenetic analysis to understand their origins. In this situation the authors found a correlation within individuals with similar Y chromosome lineages and cognates, words so similar from one language to the next that they suggest both are variants of a single ancestral prototype.

In preparation for today’s Nature paper on Dmanisi, yesterday I went over some of the hot Homo fossils that have come from Dmanisi. But I focused only on remains of the head. And of those remains, what I went over was a whole range of features, proportions, and sizes, that showed a lot of variation in early Homo cranium from Dmanisi. Size-wise, the fossils have been more in the range of H. habilis than erectus, but feature by feature each one seemed to have bits and pieces of what we acknowledge as H. erectus.

The paper that I’ve been waiting for, “Postcranial evidence from early Homo from Dmanisi, Georgia,” reminds me that there are other fossils than ones from the head, to analyze. Especially from such a rich site.

In this new paper, David Lordkipanidze and all the other authors, describe new fossils of the postcranial, of a teenager that is associated with D2700 cranium and 2735 mandible as well as three adults who are also associated with other fossils. The elements analyzed are pictured to the right. This last section of the abstract is the most important,

“This material shows that the postcranial anatomy of the Dmanisi hominins has a surprising mosaic of primitive and derived features. The primitive features include a small body size, a low encephalization quotient and absence of humeral torsion; the derived features include modern-human-like body proportions and lower limb morphology indicative of the capability for long-distance travel. Thus, the earliest known hominins to have lived outside of Africa in the temperate zones of Eurasia did not yet display the full set of derived skeletal features.”

So we’re looking at at least four people in this collection of bones. As I mentioned, the authors think they have the teenager’s skull and mandible. The other parts, such as a left clavicle, some ribs, a set of cervical and thoracic vertebrae with one lumbar vertebrae, both humeri but one is broken, a left femur, and several bones of the hands and feet, of this youngin’ are the seen in “a”, all the bones in the left half of the above image.

So how do they know that these are the bones from the same individual? Well, I’m pretty sure they don’t know for sure because they did say a minimum of four people… But because the bones were found in the same stratigraphic layer, in close proximity to one another…. And that the cranial and postcranial bones both show similar developmental stages, such as fusion patterns in the sutures of the skull and fusion patterns of the epiphysis (ends) of long bones to the shaft, or diaphysis, they can make this claim with some confidence.

The other three individuals, two small folk and one larger person, weren’t anywhere close to the teenager. The large adult is represented by a big right femur, whole tibia, and a patella… which all articulate snuggly. That’s how they figured out this was one individual. The other two small ones are represented by metatarsals and bones of the feet from different stratigraphic layers.

This is an impressive collection of bones. Having more than one individual from the same place and time helps paint a much better picture of what was going on with early Homo than would a single skeleton. In the following paragraphs, I’m gonna summarize the analysis of each element.

D4166 – The Adult Right Scapula
This element has a short and wide coracoid process and a narrow glenocoracoid angle, which are primitive, great-ape like traits. But the position of the glenoid to the spine as well as the breadth of the spine fall right at the bottom of modern human variation and resemble Turkana Boy.

D2724, D4161 & D4162 – The Clavicles

These clavicles represent the right and left sides. As you can see, both D4161 and D4162 are missing the sternal and acromial ends. D2724 is a bit better and is similar to modern day teenagers in shaft length. Since all of these clavicles have a middle portion, the cross sectional shape was analyzed. That feature resembles H. habilis.

D2680, D2715, D4507 – The Humeri

The Dmanisi have straight humeri but a lot of torsion and lateral epicondyles that are higher than the lateral condyles which are all seen in most great apes, and other ancient hominin humeri. Modern humans do not have as much torsion.

D2673, D2674, D26721, D2713, D2672 – The Vertebrae

These vertebrae, such as the slope of the articular processes, represent primitive australopithecine-like or even great-ape like form. But since the spinal process is short, narrow, and the canal shapes of all the vertebrae are wider side to side, these bones represent more modern traits.

D4167 – The Femur

This is the most complete femur of an early Homo individual. It has a defined linea aspera, a ridge on the femur that serves as an attachment for the adductors and the intermuscular septa. It is very robust, straight. The neck of the femur, where the leg is attached to the hip, is similar to the autralopithecines and the bicondylar angle, a measurement of how the femur rests on the tibia, is similar to australopithecines too.

D3901 – The Tibia

This is the first complete fossil hominin tibia, pretty cool. It too is robust, and the joint surfaces on the top and bottom are large. The mid-shaft, though, is less robust and the degree of torsion is similar to modern humans…. something not seen that much in other great apes.

There are other bones, such as the the patella, the talus, and metatarsals which I’m not gonna review for several reasons, one of which is that this post has gotten long enough already. The second reason is that I think you can see that Lordkipanidze et al., have been really thorough in documenting how these specimens are a hodgepodge of archaic and modern traits. Very indicative of some sort of transition going on.

In their conclusion, the authors say, the most definitive, ancestral trait is the torsion seen in the humerus. And since the Dmanisi postcranial remains and endocranial volumes are awfully close in size to H. habilis that suggests the first hominis out of Africa weren’t completely like the H. erectus originating in Africa. What does that mean really? That means a wave of more primitive Homo fled Africa, all the while African hominins were doing their own thing. Does this mean once the African H. erectus figured it out and moved out of Africa, that these primitive Homo were replaced? This study certainly suggests that.

Tommorrow, Nature will be publishing a new study of the Dmanisi fossil specimens. In preparation, I’m gonna introduce you to the importance of the Dmanisi site, overview the human fossils that have come out of it, and the related debates.

Firstly, Dmanisi is a rich paleoanthropological and archaeological site in Georgia. Multiple lines of evidence date the human occupation at Dmanisi as early as 1.85 million years ago, putting it in the Pleistocene. You ask, “What sort of data?” Layers of ash and sandy sediment, which contain remains along with numerous crude stone tools and flakes, have been dated radiometrically at 1.7 to 1.85 million years old.

Other dating techniques, such as isotopic potassium-argon (K-Ar) and argon-argon (⁴⁰Ar/³⁹Ar) dating give an age of 1.8 million years ago. Paleomagnetic analysis of the units around the fossil layer, hold a record of change in magnetic polarity about 1.77 million year ago, which correlates to other dated sites, most notably Olduvai Gorge in Tanzania. All of these dating techniques help place Dmanisi as one of the most ancient human habitation sites in Eurasia. Dmanisi is approximately equivalent in age to the oldest H. erectus localities in eastern Africa. The remains found from Dmanisi have become crucial, and at the same time very controversial, to the study of human evolution.

The remains I want to segue into have consistently brought up a heated debate. And since we’re talking early Pleistocene, i.e. 1.8 mya, we are in the Homo lineage. For anyone not in the know, the fossils record for early Homo is spotty. Trying to make sense of the spottiness, many anthropologists have been butting heads about what has been happening to Homo erectus and Homo habilis during a 2 to 1 million year ago time frame. John Hawks reviewed Brown’s revised chronology in 2006. And the most recent debate, the Ilert hominids, have complicated our understandings of what was going with these two taxa in Africa. So to say that H. erectus has a problematical heritage is to grossly simplify matters.

The best Dmanisi fossils from this time frame haven’t, as of yet, clarified the conundrum outside of Africa for us. The first hominid fossil from Dmanisi was a mandible, was found on the last day of the 1991 field season, by Antje Justus. This mandible was assigned as D211.

While the H. erectus versus H. ergaster debate is largely settled in favor of calling everything that was once ergaster synonymous with erectus, at the time, D211 opened a Pandora’s box of sorts because it differs from known H. erectus specimens. D211 has certain similarities to ER992 (pictured) and ER730, both assigned as H. ergaster from Africa. D211 shares the following similarities:

• General form and robustness of the jaw
• Anterior position of the ascending ramus, including the edge of the retromolar space
• The absence of a trigonum mentale

D211 differs from ER992 and ER730 because it has smaller molars and premolars as well as a less receding anterior surface of symphysis. Despite these differences in size, and Brauer and Schulz’s contention that D211 is a representative of H. erectus, D211 was placed closer to H. ergaster group.

Even though the debate over classifying D211 was between calling it H. ergaster and H. erectus, and not H. habilis vs. H. erectus, it did set the tone for agreeing about future hominid finds from Dmanisi.

Fast forward to 1999, when D2280 and D2282 surfaced from the same stratigraphic level as D221. D2280 is an almost complete calvaria. It includes most of the left mandibular fossa of the temporal, a partial cranial base with a damaged occipital, and parts of the greater wing of the sphenoid. It is pictured in the photographs to your right.

You can see it is rounded, and doesn’t have such an angular posterior side, traits seen in H. habilis. The endocranial volume for D2280 is about 775 cm³, making it small… closer to the size of H. habilis than H. erectus. But because D2280 included a supraorbital torus, and shared some proportional similarities to H. ergaster (like WT15000 and ER3733), it was assigned as such.

D2282 is a much more complete specimen. As you can see, it is a cranium with many of the bones of the face and cranial vault. The major problem with D2282 is that it has been kinda deformed throughout the ages, the occipital and temporal ares are crushed on the left side, as are the zygomatic bones making a lot of the measurements and proportions convoluted.

To complicate it, much of the median upper facial skeleton is missing including the supraorbital torus at glabella, nasal bones, and frontal processes of the maxillae. Which makes it even harder to compare feature to feature to D2280.

However, all hope was not lost with our friend D2280. With a well persevered maxillae that still holds the right P⁴-M² and the left M¹ and M², as well as the alveoli of all other adult teeth including those of M³, a more thorough comparison was done. The comparison of the teeth lead to the conclusion that D2282 represents H. erectus. One example, the presence of singler roots in the upper premolar teeth is a H. erectus trait that.

D2282 is still small; the smaller of the two crania; 650 cm³ small; small like habilis.

Right above the tuff that locked away D211, D2280, and D2282, came another set of findings in 2001 and 2005, the D2700 cranium and the D2735 mandible, and the D3444 cranium and D3900 mandible.

The cool thing about D3444 cranium is that he was an old guy, completely toothless. His toothlessness was not something new, he had been toothless for several years before death, judging by the complete resorption of the tooth sockets. The implications of how he was cared for in his old age, were outstanding.

And about the D2700 cranium. It is even smaller than D2282, at 600 cm³. D2700 has many characteristics which resemble H. ergaster but also a handful that resembles the ER1813 H. habilis skull. Vekua et al., write in their 2002 paper that,

“In overall shape, D2700 is similar to D2280 and D2282, and D2735 resembles D211. Despite certain differences among these Dmanisi individuals, we do not see sufficient grounds for assigning them to more than one hominid taxon. We view the new specimen as a member of the same population as the other fossils, and we here assign the new skull provisionally to Homo erectus.”

So, other than showing you how bountiful Dmanisi has been in yielding Homo fossils, what else is going on here? We have a lot of small habilis-like skulls coming out from Dmanisi which have erectus-like features.

Do we go with size or do we go with morphology? As of right now, we’ve gone with morphology, but that’s problematic, especially dealing with heavily fragmented remains. Better yet, do the Dmanisi fossils represent a transitional species, one were humans were similar in size to habilis but similar in shape and form to erectus?

I think that will be answered in tomorrow’s Nature.

I don’t know really, but I’d like that to be answered because I’m pretty sure all you see right now is the great flaw in understanding evolutionary relationships and ancestors from fossil remains; when determining taxonomies with many traits, measurements, and damages to consider, it seems to be nothing more than a big pissing match between respective paleoanthropological groups.

References:

• Taxonomy of the Dmanisi Crania
• The morphological affinities of the Plio-Pleistocene mandible from Dmanisi, Georgia
• Earliest Pleistocene Hominid Cranial Remains from Dmanisi, Republic of Georgia: Taxonomy, Geological Setting, and Age
• Anthropology: The earliest toothless hominin skull