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Hershkovitz et al. (2007) point to the pneumatization of the mastoid region as possibly the most important test. LS patients have minimal or no pneumatization of this part of the cranial base; meaning that instead of spongy bone and open sinuses, they have dense compact bone:

Unfortunately, no radiographs of LB1's skull are as yet available and therefore appreciation of the extent of pneumatization in the LB1 skull is impossible. Non-pneumatized (acellular) mastoid process (Fig. 4), lack of (or minimal) frontal sinus (Fig. 2), and small paranasal sinuses are characteristic of LS (Kornreich et al., 2002) (Hershkovitz et al. 2007:3).

CT scans of LB 1 do exist, and they should be easy to check. Very easy. As in, somebody already knows the answer. That somebody just isn't me.

But is it a species?

What would it tell you if the hypothesis were true -- if LB 1 actually does have a mutation inducing a GH/IGR-I defect and this explains its stature, morphology, and brain size? For instance, does it represent a real ancient hominid species or just a pathological member of our own?

Hershkovitz, Kornreich, and Laron agree with Jacob et al. (2006), that many of the "unusual" characteristics of the skeleton actually are normal or reasonably common within the regional population of modern humans. For that reason, they find that the skeleton possesses no features that preclude it from membership in our species. So the short answer is, they think H. floresiensis is sunk.

But their longer answer is quite interesting as a defense of taxonomic conservatism, and is worth reading closely:

It is not the numerous conundrums that have been located by us and other researchers (Jacob et al., 2006; Martin et al., 2006a,b) in the Homo floresiensis publications which refute its status as a new species, but rather the wrong arguments brought to support it.

The combination of "modern" and "primitive" morphological characteristics is one of the major arguments raised by Brown et al. (2004) to differentiate LB1 from Homo sapiens. Nobody would argue, however, that LS patients who also manifest a similar combination (e.g., an extremely oval-shaped pelvic inlet, or a "bell-shaped" form of the thoracic cage), are direct descendents of Homo erectus (an idea advocated strongly for LB1 in the first paper) nor of the australopithecines (a notion which appears in the second publication). Based on morphological comparison between LS patients and normal short children, it is clearly evident that many of the "unique" primitive morphological traits seen in LB1 are due to her small stature (Takano et al., 1986). This also explains why LB1 shares most of her features, including the most "unique" ones (e.g., the deep fissure separating the mastoid process from the petrous crest of the tympanic bone; the absence of a true chin etc.) with local pygmoid populations (Jacob et al., 2006). Ignoring the possibility that LB1 is derived from a small stature population (Rampasasa pygmies are good candidates, as suggested by Jacob et al. in 2006) with its own distinct morphological features may lead to erroneous conclusions. For example, recently Larson et al. (2006) reported on a clavicle (short relative to humeral length) and scapula (normal) of LB1 and suggested that "A short clavicle may indicate a more protracted scapular position, raising the possibility of a previously unsuspected transitional stage in the course of hominin pectoral girdle evolution" (p A21). However, the length of the clavicle is mainly dictated by the shape and diameter of the upper thoracic cage. This is why both LS patients and KNM-WT 15000 H. erectus (both manifesting a very similar fan-shaped thorax) have a relatively short clavicle.

In contrast to Morwood's statement (2005) that LB1 manifests a combination of primitive and derived features that dictate exclusion from the species sapiens, we have herein offered evidence to suggest that LB1 is but a local individual in a highly inbred, probably pygmy-like population (of Homo sapiens) in whom a mutation of the GH receptor had occurred. (Hershkovitz et al. 2007:9).

In short, the persuasiveness of any combination of features as evidence depends on their correlation with each other. If they are all strongly correlated -- for instance, if they are effects of a common cause -- then the combination of features is best interpreted as evidence for that cause, rather than as multiple instances of evidence for some other hypothesis. In this case, Hershkovitz et al. argue that the common cause explaining the data does not require a species interpretation. Instead, they argue (following Jacob et al. 2006) that LB 1 and other specimens share many features with recent local people. So, the hypothesis that the LB hominids are Homo sapiens is well supported.

Now, what could contradict that hypothesis? In other words, what would be the right argument to support a new species?

Here, the morphology of the other specimens besides LB 1 come into play. It seems very unlikely that multiple archaeological individuals over many thousands of years would have had the same rare mutation(s) of the GH/IGR-I axis unless that mutation were very common in the local population. Richards (2006) accepted at face value the argument that these archaeological individuals were in fact of the same short stature and small size as LB 1, and suggested that the ancient Flores population of H. sapiens simply had a high frequency of this variant (in his view, possibly along with another variant affecting brain size). Hershkovitz and colleagues appear willing to accept this hypothesis, pointing out that LS patients have normal reproductive potential and are relatively more common in some populations:

As LB1 replicates most of the diagnostic features of LS patients (Table 1), as well as those of pygmoid Australomelanesians (Jacob et al., 2006), it can be assumed that the findings from the island of Flores represent a local, highly inbred, low stature Homo sapiens population in whom a mutation in the GH receptor had occurred. The long time presence of LB1-type humans on the island of Flores is not surprising considering that LS patients, and derived dwarfed populations with GHRH-R defect, reproduce normally (Laron, 2004) (Hershkovitz et al. 2007:9).

But it is not necessary to take this view of a long-term population with a variant GH/IGR-I allele, if the other specimens are not actually unusual for modern humans. That is the argument put forward by Jacob et al. (2006), and it doesn't yet seem to have been contradicted. The most persuasive commonalities among this collection of fragments are (1) that they are all small, and (2) that the second mandible LB 6/1 shares several features with the first. But Jacob et al. (2006) claim (1) that the local population was small anyway, and (2) that these features are regionally common and not persuasive as evidence for a distinct lineage.

An alternative claim might be that H. floresiensis was a genuine evolutionary species on Flores (and possibly other islands), and that local people today retain features from this ancient species due to local introgression. But of course, local ancestry of some features might occur whether the ancient Flores population was another species or not. We call the latter hypothesis "multiregional evolution." So any distinctiveness of the local people is in no respect evidence that ancient people on Flores were a different species; if anything, the long-term retention of local features into living populations is a refutation that they were a different species. There is nothing impossible about introgression -- as I've said many times -- but it actually is a bit easier if speciation has not occurred!

Picky details

As in many clinical descriptions of dwarfism, there is a lot of "SD" talk in this paper. That substitutes an absolute measure (e.g., meters) for a relative one (compared to the population variability). And in some ways, that confounds two different kinds of change. For example, after a very good discussion of the problems estimating proportions and stature of LB 1, the paper includes this:

Finally, Jacob et al. (2006) estimated that the stature of LB1 falls 3.3 SD below the local Rampasasa pygmy average stature of 1.46 m, within the range of the deviation in stature reported in some of the Israeli LS patients (Laron, 2004).

This is not really a valid comparison. If pygmy populations of humans already have a variant of the GH/IGF-I axis that results in reduced stature, then a further mutation on that axis should not exert the same proportional effect. We ought to expect a dwarf in a population of pygmies to be close to the stature of dwarfs elsewhere.

Instead, the important comparison is the stature itself, not the number of standard deviations below mean. Hershkovitz et al. (2007) report that the stature of female Laron syndrome patients in their sample ranges as low as 95 cm, which is smaller than the minimum stature estimate of 106 cm for LB 1. Hence, it is consistent with the diagnosis.

Also, the genetic heterogeneity of LS means that there can be substantial variations among people with different mutations:

So far 57 mutations have been described in LS patients residing in various parts of the world including South Asia (Rosenfeld et al., 1994; Rosenbloom and Guevara-Aguirre, 1998; Laron, 1999; Shevah et al., 2005). These numerous molecular defects on the GH receptor gene or the postreceptor cascade (Elders et al., 1973; Godowski et al., 1989; Laron et al., 1992; Rosenbloom et al., 1999; Laron, 2004; Woods and Savage, 2004) produce a large variety of short stature phenotypes and a wide spectrum of intellectual abilities and deficits (Shevah et al., 2005), which may also explain the differences between the LS patients and LB1 (Hershkovitz et al. 2007:9).

This is the kind of quote that can drive a person crazy. The disorder is genetically heterogeneous. As reflected in OMIM, it may even include individuals with normal GHR function, but with other downstream problems that decrease IGF-I. But it is unsatisfying because it means that no comparison can necessarily capture the effects of the disorder. So for something like the exceptionally small brain size of LB 1, it is quite possible to say, "Well, there are at least 57 different ways to have this disorder, and maybe the 58th will be manifested with even smaller brain size.

On the other hand, with 57 different varieties (hmm....) we can probably say that the sample space of genetic mutations is now very large, so we are seeing possibly a good representation of the possible phenotypic effects of changes to this axis. At least, that's my optimistic answer.

Summary

This is a powerful paper. The overlap between the morphology of LB 1 and Laron syndrome symptoms is very extensive.

To my mind, much of the credibility of the species hypothesis -- that H. floresiensis really existed on Flores for a long time and evolved a mean phenotype including derived features absent in other populations -- depends on finding more specimens from earlier time intervals. If the archaeology of the island could be extended into the period after 500,000 years, it would document the long-term persistence of some hominid population across the interval from 700,000 years ago to 90,000. At 90,000 years, given ambiguities in dating, it is entirely possible that remains may be attributed to modern humans. So documenting a persistence in between those dates is important.

Likewise, the anatomical evolution of those populations would be a key piece of evidence. Were they, as Jacob et al. (2006) suggest, connected by gene flow to the Asian landmass by recurrent connections? Or were they really isolated on Flores or possibly other islands? Only a trace of the evolutionary history, through morphology or DNA, can provide evidence of this isolation.

I don't view any of this as impossible, but naturally it remains to be demonstrated. Likewise there is nothing impossible about such a population having a unique GH/IGR-I variant, either by drift or as an adaptation to the island. But we are waiting for the evidence that they were there throughout that time.

References:

Hershkovitz I, Kornreich L, Laron Z. 2007. Comparative skeletal features between Homo floresiensis and patients with primary growth hormone insensitivity (Laron Syndrome). Am J Phys Anthropol (early) doi:10.1002/ajpa.20655

Richards GD. 2006. Genetic, physiologic and ecogeographic factors contributing to variation in Homo sapiens: Homo floresiensis reconsidered. J Evol Biol 19:1744-1767. doi:10.1111/j.1420-9101.2006.01179.x

Jacob T, Indriati E, Soejono RP, Hsü K, Frayer DW, Eckhardt RB, Kuperavage AJ, Thorne A, and Henneberg M. 2006. Pygmoid Australomelanesian Homo sapiens skeletal remains from Liang Bua, Flores: Population affinities and pathological abnormalities. Proc Nat Acad Sci USA. 103:13421-13426. DOI link

Posted at 12:18 on 07/03/2007 | permanent link

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Island hopping

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This article from The Age lays out an ambitious excavation schedule for Mike Morwood and colleagues:

Professor Morwood, with a team headed by Indonesian archaeological professor Fachroel Aziz from Indonesia's Geological Survey Institute, will soon start excavations in the Atambua Basin of Timor. Afterwards, the team will begin diggings in Sulawesi and will return to the Ling [sic] Bua cave in Flores, where the hobbit species was uncovered.

"We predict a number of these islands are probably going to have their own endemic human species, and many of them will be small," Professor Morwood, from the University of Wollongong, said.

The article spends some words on size differences in island animals, raises the issue of island gigantism (hmm...does this mean we'll see the return of Meganthropus?), and this:

Professor Morwood flagged that any new human species found on Timor and Sulawesi would be called Homo timoriensis and Homo celebesiensis (Celebes being the former name of Sulawesi).

That just seems like a missed opportunity. If it were me, I would sell the naming rights to the highest corporate bidder. How about "Homo pizzahutiana". Ooh ooh! "Pan crusti!" You could probably get money for at least 20 field seasons out of them.

How sustainable was "seafaring"?

I've already heard from some correspondents (many thanks!) who consider it hubristic to predict the finding of more human species in Wallacea, when the case for one is still in doubt.

Maybe so. I think that Sulawesi and Timor, in addition to other islands including Sumba and Sumbawa, may provide an important test. The reason? Seafaring.

I haven't seen anyone comment on the seafaring issue much since the Liang Bua remains were reported. Recall that when Lower to Middle Pleistocene stone tools were originally found on Flores (from the Soa Basin), their principal importance was documenting some kind of water-crossing technology in early Homo before 800,000 years ago. That was news — with no such evidence anywhere else in the world — and was subject to some controversy.

Just how good did the "seafaring" technology have to be to establish an occupation on Flores? There were at least two water crossings (Lombok and Sape Straits) of more than 10 kilometers. Robert Bednarik has conducted a series of experiments (the First Mariners Project) attempting to assess the technological requirements for such crossings.

If the seagoing technology that allowed crossings of these straits was maintained for a long time, it surely should bolster our opinion of the cultural capabilities of the hominids. A raft -- even a simple raft made out of bamboo -- is a complicated compound tool; a tool that involves many pieces put together in a series of steps. Even though many of the steps may be completely identical to each other (that is, lash logs together, repeat), still a raft requires joining dozens of different elements on a single plan, in pursuit of a single non-immediate goal. The creation of such an object would have required a sustained, goal-oriented and design-directed cognition.

Last year, I wrote:

[W]hat happened on Timor? It seems to me that the game is over if humans were on Timor in the Middle Pleistocene. There is some indication that they were. If Homo erectus could manage sea crossings to that extent further east than Flores, then there is no way that Flores was a single, unique colonization. With an occupied Timor, we have to assume that regular contacts between Flores and mainland Asia were probable.

Much depends on what the people were doing with watercraft -- were they using them for fishing? River crossings? Short island-hopping? Ecologies that encourage the use of watercraft exist in the region today, for all of these reasons and more. We can infer that if people were capable of exploiting these ecologies in the past, then the opportunity to do so would have been recurrently (or constantly) present during the last 800,000 years. Like any cultural tradition, seagoing rafts might have been lost over time. But even if people forgot how to make watercraft, the fact that they could invent them in the first place suggests that they should have invented them repeatedly. Humans certainly have done so recently.

The paradox is that regular crossings of the straits would have prevented isolation of the island populations. It would seem that the hypothesis of isolation entails that seagoing technology was not a sustainable development, and that the initial occupation of Flores (and by extension, Lombok and Sumbawa) was a matter of chance. If this is true, then early evidence of water crossings itself has little, if any, import to our interpretation of early human cognitive evolution.

Consider that other than this evidence for crossing the Lombok and Sape Straits, there is no evidence for compound tools of any kind before the Middle Paleolithic-Middle Stone Age. If Lower Pleistocene humans were capable of making a raft, this would be a major addition to the evidence for their technological competence.

Well, I don't know the answer, but I think that finding hominids on Timor would pretty much end the story in favor of more capable seafaring rather than less.

Sulawesi is less certain; it may have been too easy to get there by chance to really establish that water crossings were controlled and sustained. Sulawesi seems like a great prospect for hominid occupation; the fauna is more Asian than Flores, so it must have been comparatively easier to make the crossing. The Makassar Strait probably was not narrower than the corresponding water crossings from Bali to Lombok and Sumbawa to Komodo, but the opposing coastlines of Sunda and Sulawesi were very long, perhaps providing a greater chance of making a successful crossing without being washed clear of landfall. Of course, that makes isolation much less likely also.

The more regular water crossings were, the less likely isolation on Flores would have been. It's certainly important to look for hominids on those islands, but maybe not for the reasons everyone seems to be assuming.

Posted at 15:42 on 05/12/2007 | permanent link

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A guide to fantasy science

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I'm about two-thirds of the way through Mike Morwood's new book, The Discovery of the Hobbit, and I'll be posting a review when I'm through. Generally, I have a positive opinion of the book so far.

Henry Gee has reviewed the book in this week's issue of Nature. I wanted to point out my generally positive attitude about the book, so that you'll know that my miserable opinion of Gee's review has little to do with the book's merits.

Consider how Gee starts his review:

The unicorn, wrote Jorge Luis Borges (in Kafka and His Precursors), is universally regarded as a supernatural being of good omen. But there's a problem: despite its folkloric familiarity, we wouldn't know how to recognize a unicorn if we met one in real life. It "does not figure among the domestic beasts, it is not always easy to find, it does not lend itself to classification," Borges continues. "It is not like the horse or the bull, the wolf or the deer. In such conditions, we could be face to face with a unicorn and not know for certain what it was."

Is Gee smoking crack? What kind of blather is this?

First of all, I know I'm being terribly literal, but a unicorn is a horse with a horn. One horn. Not so hard to recognize! Maybe my 3-year-old daughters could help edit at Nature.

Let's see, where have I seen one of those that Gee might recognize? Oh, yeah:

Photo credit: Simon Stratford (via stock.xchng)

There it is, sound as a pound.

Next, Gee spends several paragraphs expositing on his own role in the publication of the Homo floresiensis announcement. We learn some interesting little facts, like how the authors wanted to name the species "Sundanthropus floresianus" until a reviewer pointed out that future students would confuse the name with a flowery butt.

I kid you not. Nature has a layer of reviewers to take tushie references out of taxonomy. Somehow they can't tell a left femur from a right, but they're on the watch for sphincter-species!

The review is entirely self-serving -- there are only three paragraphs that include any reference to the book! In the midst of this babbling about unicorns and hobbits, Gee tells us that skepticism at new hominid discoveries should be dismissed as the predictable result of "mindsets" of the skeptics:

Such reaction is common in the wake of new hominid discoveries, which are routinely dismissed either as pathological humans (Homo neanderthalensis) or apes (Australopithecus africanus and Sahelanthropus tchadensis). Such reactions say less about the facts than the mindsets of commentators, who might be unwilling to have their comfortable views of the world so forcibly changed. Confronted with what might be a genuine unicorn, many would prefer to see a pantomime horse with a spike glued to its head.

Ooooh! Since I'm one who has been notably skeptical of Sahelanthropus and have approached H. floresiensis skeptically, I'm obviously a prime target for this paragraph. It is so comfortable to stay in my view of the world where hominids interbreed with each other. Clearly, a bestiary that includes small-brained island bipeds must shake me out of my comfort zone.

How could I have been so wrong! When every species ever proposed has faced the same resistance? Sure, Tim White says that Kenyanthropus is a glued-together matrix-filled A. afarensis, but that's just his mindset. Or how about Eoanthropus? Sure, Franz Weidenreich thought that it was just a concoction by "English authors," but couldn't he tell that it was more than just a pantomime skull with an orangutan jaw? Why couldn't I see that these petty minds were just holding back the important work of taxonomy!

No, no, no. You see, if we approach things skeptically, we won't dare to dream about the unicorns:

The unicorn remains as it always did, frustratingly elusive. This year, the researchers will return to Liang Bua to see if they can discover more. But stories such as this demand a mythological beast altogether less serene. It is as if the researchers had set out to discover some new form of fossil mouse, only to find that they had grabbed a dragon by the tail instead. And as any devotee of Harry Potter will remind you: Draco dormiens nunquam titillandus.

The theme of the review is perhaps to be expected from Gee, otherwise known as the author of The Science of Middle-Earth. But I find his mixture of fantasy and science to be especially malaprop in the context of the Flores fossils, since with every fantasy word he detracts from the credibility of the journal's review process!

Some of you will have seen the episode of The Simpsons, titled "Lisa the Skeptic," where Lisa excavates an "angel" from the ground. Here's part of the synopsis from Wikipedia:

As Homer attempts to get a motor boat, a new shopping mall in Springfield is being built on an area where a large number of fossils were found. Lisa condemns and protests the building of the mall. Thanks to her protest, it prompts the school to conduct an archaeological dig. When Lisa is digging, it reveals a human skeleton with wings. Springfield's residents are convinced it is an angel, and Homer cashes in by moving the skeleton into the family's garage; however, Lisa is skeptical, believing it may not actually be an angel, and even has Stephen Jay Gould test a sample of the skeleton. The next day, Dr Gould runs to the Simpson house and said the tests came out inconclusive and after Lisa on television compares belief in angels to belief in unicorns and leprechauns, Springfield's religious zealots riot and destroy all of the scientific institutions.

Later, we find out that the "angel" is a publicity stunt for the new mall; Guest voice Gould confesses that he never really performed any tests on the "angel". This is one of my favorite episodes: it's a rare one where Lisa's preachy skepticism is entirely justified, and the "expert" doesn't care enough to do anything at all.

Now I know, that the episode was missing a scientific editor to encourage Lisa to forget about her doubts, and just to accept the "angel" for what it is. After all, every new discovery has its skeptics.

Well, there is a lesson to take away from all the unicorn talk. If you are in Cardiff and find the skeleton of a giant, be sure to send your report to Nature, where you'll find a receptive editor. Despite what they may say, there's not one of those born every minute.

UPDATE (4/26/2007): A reader e-mails, "Remember that Borges was blind." True. Perhaps we can extend this analogy further?

Another reader: "Well, at least we can expect a fair set of reviews on the Sahelanthropus postcrania...D'oh!"

References:

Gee H. 2007. In a hole in the ground.... Nature 446:979-980. doi:10.1038/446979a

Posted at 22:10 on 04/26/2007 | permanent link

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Floresiensis presentations

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I'm at the AAPA meetings in Philadelphia this week, which were preceded yesterday and today by the meetings of the Paleoanthropology Society.

There were several interesting papers given today, but I wanted to pass along the abstracts of the two pertaining to the Flores hominids:

"Allometric Scaling of Craniofacial Shape: Implications for the Liang Bua Hominins"

K. Baab, K. McNulty, and P. Brown

There has been considerable controversy concerning the taxonomy and evolutionary history of the hominin fossils recovered from the Indonesian island of Flores. One hypothesis is that these individuals were the result of insular dwarfing of H. erectus or a small bodied and as yet unknown hominin from the Asian mainland (e.g., Brown et al., 2004). Alternatively, some have claimed that LB 1 is a microcephalic modern human. This study will take a new approach to investigating the affinities of the Flores hominins by focusing on the three dimensional shape of the LB 1 craniofacial skeleton. To address the possibility of dwarfing in the evolutionary history of the Flores hominins, we also examined allometric scaling of craniofacial shape within the African apes and humans. As a first step, generalized Procrustes analysis was performed and principal components analysis (PCA) was used to explore the shape of the LB 1 neurocranium within a broad range of specimens representing both fossil and extant Homo species using geometric morphometric techniques. PCA indicated that the shape of the neurocranium was aligned most closely with H. erectus. A landmark set which also incorporated facial landmarks again showed similarities with H. erectus, particularly Asian H. erectus, but also with modern humans. The second set of analyses occurred in size-shape space, which, in addition to the Procrustes shape coordinates, also includes the logarithm of centroid size as an additional variable (Mitteroecker, 2004). By performing a PCA in size-shape space, we were also able to explore allometric patterns within and between Gorilla, Pan and Homo. While the apes, modern humans and archaic Homo all have separate trajectories, their slopes are quite similar. The position of LB 1 in size-shape space is compatible with its interpretation as a scaled down version of an archaic Homo species.

The second paper was much more interesting:

Morphological affinities of the wrist of Homo floresiensis

M. Tocheri, W. Jungers, S. Larson, C. Orr, T. Sutikna, Jatmiko, E. Saptomo, R. Due, T. Djubiantono, M. Morwood

The shape of the trapezoid in Homo sapiens is derived in comparison to the shape in other primates. Whereas the trapezoid of nonhuman primates is shaped like a pyramidal wedge (the narrow tip is palmar while the wide base is dorsal), that of H. sapiens is boot-shaped, resulting from a radio-ulnar and proximo-distal widening of the palmar half of the bone. The human trapezium, scaphoid, capitate, and second metacarpal base exhibit a derived complex of features that correlates with the distinctive shape of the trapezoid. Current paleontological evidence indicates that this derived complex of features evolved as early as 800,000 years ago and is a synapomorphy of H. sapiens and Homo neanderthalensis. The Homo floresiensis type specimen (LB1) includes a trapezoid, scaphoid, and capitate, all well-preserved and non-pathological. These small carpals display none of the aforementioned shared, derived features of H. sapiens and H. neanderthalensis. Rather, these bones are morphologically identical to the conditions seen in all African apes and in Australopithecus afarensis. The trapezoid is wedge-shaped with a small, dorsally-placed facet for the capitate and a large, triangular-shaped facet for the scaphoid, while the capitate and scaphoid exhibit the morphology that is typically correlated with the primitive trapezoid condition. As might be expected, the scaphoid and os centrale of H. floresiensis are completely fused, which is a synapomorphy of Gorilla, Pan, and Homo. The primitive carpal morphology of H. floresiensis is not consistent with hypotheses of a congenital or developmental abnormality afflicting a modern H. sapiens. Rather, the evidence is more consistent with hypotheses that H. floresiensis is descended from a hominin ancestor that migrated out of Africa prior to the evolution of the shared, derived carpal morphology characteristic of H. sapiens and H. neanderthalensis.

OK, after pasting that and fixing all the markup, I have to say that abstract drops entirely too many taxonomic names. But the basic point of the paper was that the wrist bones associated with the LB 1 skeleton don't look like modern humans. They look like the wrist bones of OH 7, which for these particular bones (trapezoid, scaphoid, and capitate) are similar to chimpanzees and other apes. Tocheri was fairly compelling in the description of the initial shape formation of the wrist bones prior to week 10 of fetal development; any genetic change that affected these shapes would have to be expressed very early. That would tend to make it unlikely that a single developmental change could have caused a modern human to have both the cranial form and the wrist morphology of LB 1.

There were some missing parts that should be fleshed out -- for instance, how much interpopulational variation is there in these bones in recent humans? The Neandertals overlapped with the modern human distribution, but there was no comparison of means.

Still, this may be a compelling argument for LB 1 not being modern, assuming the association of the wrist is good.

In the morning, I'm moderating a session with some more papers about the Flores hominids. I'll report anything interesting (including fights!).

UPDATE (4/2/2007): Sharp-eyed reader Brian Witte found an html error that spread a case of the italics across the site; many thanks for pointing it out!

In the last couple of days, I have had correspondence with a number of people about the wrist. Again, I should note that this is an area where a publication will really be required to evaluate the claims; particularly concerning developmental stability as a function of early differentiation.

Posted at 00:36 on 04/03/2007 | permanent link

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Size, shape, and microcephaly

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I've been taking quite a lot of notes while studying last week's paper by Dean Falk and colleagues.

The lede in all the articles about Falk and colleagues' paper is that they show that LB1's endocast is normal. But is it?

As Ralph Holloway and colleagues (2006) have noted, LB1 is not the same shape as an average-sized human endocast. It has strange protrusions in Brodmann's area 10 of the prefrontal cortex, it is very flat from top to bottom (platycephalic), it has an unusual proportion of cerebellum to neocortex, and it is quite asymmetrical. There seems to be no substantive disagreement about these features. These features do not show that LB1 had any of the spectrum of microcephaly disorders. But they do show that it's abnormal, at least in the context of modern humans.

In their supplementary material, Falk and colleagues show that the frontal lobes of microcephalics generally have a flattened orbital surface. In other words, they don't project downward into the space between the orbits so much. LB1 does not share this flattening -- it is like normal humans in this anatomy. I think this is an important observation, though it is not entirely clear how diagnostic it is for microcephalics.

But the main evidence in the paper relates to their use of a discriminant function to classify LB1:

As shown here, the frontal breadth relative to cerebellar width and lack of cerebellar protrusion of LB1's endocast classify it with 100% probability with normal H. sapiens rather than microcephalics (2516).

Them's strong words. Like most biological anthropologists, I have some experience with discriminant functions. It can be easy (although certainly not always!) to get highly significant statistical results, when the original samples are small as they are in this study. Small samples by chance exclude much of the variation that makes classification errors apparent.

So I looked carefully at the details of the discriminant analysis in this paper. I'm not so convinced they've shown the skull is "normal". I think that another way of looking at the same data makes the endocast look even more unusual.

See more ...

Posted at 09:18 on 02/07/2007 | permanent link

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"I'd be very surprised if the hobbits didn't fall down there."

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So says Mike Morwood about the discovery (reported in The Australian) of a newfound chamber behind and beneath Liang Bua cave:

The unexpected discovery of a chamber in the Flores island cave was made last year by an Australian-Indonesian team - led by ANU paleoclimatologist Mike Gagan - while they were investigating ancient climates.

An expert caver assisting in sample retrieval abseiled down a 23m-long sinkhole, inaccessible to the original team, at the back of Liang Bua Cave and found the chamber.

...

Dr Gagan said he and his Indonesian colleagues surveyed just the top 5cm of a 5m-deep layer of mud in the 430sqm cavern. "Imagine what's below," he said. "It might have been a split-level home for hobbits."

That sounds more like something out of A Very Brady Christmas than the Mines of Moria...

This creates two teams searching for hobbit bones at Liang Bua:

Dr Gagan's team will return to the cave in June, with additional members, including Alan Cooper, an expert in ancient DNA with Adelaide University, and CSIRO mammalogist Ken Aplin. Professor Morwood's group will also return to Liang Bua this year, after previously being denied access by Indonesian officials.

Both groups will continue to collaborate with the Indonesian National Research Centre for Archaeology. Dr Gagan's group is also working with the Indonesian Institute of Sciences.

That should be interesting. Now that they're going back to work, I wonder if we will hear more about the rumored hair in the strata. (via Afarensis).

Posted at 16:19 on 01/30/2007 | permanent link

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Another brain scan hobbit paper coming

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LiveScience writer Ker Than on the hobbits:

"What we have is a little tiny brain that has four features that you can see with your eyes that are advanced and distributed from front to middle to back," [Dean] Falk said. "In other words, this thing appears to be globally rewired. Those are really advanced features. They're not like humans, they're not like anything."

Robert Martin, curator of Biological Anthropology at the Field Museum in Chicago, is not convinced by the new evidence.

One of his major criticisms has to do with the sample of microcephalic skulls the team used.

"They're being a bit naughty about this," Martin said in a telephone interview. "Four of the nine microcephalics were not adults."

Well, we'll just have to wait for the paper to show up at PNAS. Bernard Wood seems convinced:

"Dean Falk and her colleagues have injected some much needed scientific rigor into the debate about the brain of Homo floresiensis," Wood said. "They show that the microencephaly 'explanation' for its size and morphology is untenable. I hope we can now get down to the important task of trying to understand the biology of H. floresiensis without the distraction of non-existent pathology."

Well, that settles that!

Posted at 20:02 on 01/29/2007 | permanent link

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Is this the end for Homo floresiensis?

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The paper by Teuku Jacob and colleagues is being published in PNAS today. Today's papers haven't appeared yet, but the press release is available online at Science Blog. Here's a quote:

To study LB1's traits, 94 cranial features and 46 features of its mandible were compared to values for modern humans. All fell within the normal range of variation for Australomelanesians. Two anatomical details, particular grooves in the cranial base singled out as "not seen in modern humans," in the 2004 new species announcement are, according to Alan Thorne, archaeology and natural history, Research School of Pacific and Asian Studies, Australian National University, Canberra, commonly found in Australian and Tasmanian crania.

I will post a link to the paper when it appears online. (UPDATE (8/23/2006): Now available online, open access.) In the meantime, I have a copy and I'll post some comments about what it means.

John Noble Wilford has an article with extensive quotes from both Bob Eckhardt and Peter Brown.

Asymmetry

To me, the most important point raised by the new paper is the asymmetry of the skeleton. Here's a picture:

Liang Bua 1, in normal (l), right mirrored (c) and left mirrored (r) views. Photo courtesy of D. W. Frayer.

The authors argue that this asymmetry is a sign of developmental abnormality. This is from the paper (Jacob et al. 2006:3-4, citations omitted):

After allowance for left orbital region damage, asymmetry affects frontal breadth, position and contour of the lower orbital order, angle of inferior nasal margins, location of the (broken, off-center) nasal spine, and expression of the canine juga. Asymmetry also extends to other areas on the cranium. Detectable in the original figure 1 in ref. 1 but not mentioned, and more clearly here, the palate midline is rotated 4-5 [degrees] from the midsagittal plane, so that a line extending the midpalatine suture does not bisect the foramen magnum. In addition, right parietal and left occipital bones are flattened compared with their more rounded antimeres. The nuchal torus is markedly asymmetrical, and the antimeric mastoid regions differ greatly. This pervasive asymmetry suggests growth anomalies producing a vault and face with substantial lateral contrasts.

Patterns of asymmetry in the human skull are well documented, with typically greater neurocranial asymmetries than in the face, where asymmetries are slight overall .... These differences represent small (typically <1%), fluctuating asymmetries. Reanalysis of these data (citation) supported the earlier statement that "[t]he face is the most symmetrical region of the skull." ... Studies of facial asymmetry are medically important and have diagnostic applications, with low single-digit lateral deviations in percentages or millimeters marking thresholds for clinical intervention.

We quantified craniofacial asymmetry for LB1 to the extent possible by dividing digital photographs of the cranium into right and left halves along the midsagittal plane by using Photoshop, then making composite images by mirroring the left and right sides. On a digital image of the face, we also measured left and right deviations from the midline. Six of seven measures were larger on the right, by amounts ranging up to nearly 40% (distnace from mental foramen to midline). The only measurement larger on the left was the 6% for distance from the orbit lateral rim to midline (see Supporting Text). Gauged by anthropometric and clinical standards, LB1 asymmetry exceeds clinnical norms where determinable, providing evidence for rejecting any contention that the LB1 cranium is developmentally normal.

I quoted this extensively because the details are important as a response to an obvious criticism. The criticism is raised by Peter Brown in the Times article:

Dr. Brown said the critics' claim of "the asymmetry of the skull being the result of abnormal growth is fiction." The skeleton was buried deep in sediment, he said, and this brought on "some slight distortion."

Yes, it is true that any archaeological specimen is likely to be distorted to some extent by reconstruction or postdepositional deformation. That might be true of this skull also. But in this case, the asymmetry clearly extends to morphological characters that should be relatively unaffected by such distortion. For example, the position of the mental foramen shouldn't change by 40 percent from being buried in wet ground. And while distortion might affect the curvature or flatness of the occiput, it shouldn't affect the relative development of the nuchal torus or mastoid regions on each side, which must be a consequence of different muscle development or configuration.

That muscular problem appears to be reflected in other areas of the skeleton also. For instance, the authors argue that the humeral torsion is a correlate of "extremely weak muscle development indicated by muscle insertions", and may reflect a "response to the dynamic forces exerted by shoulder rotators on the growing bone" (p. 5).

Likewise, the femora are asymmetrical and show odd muscle features:

Proximally, the intertrochanteric crests on the femora are highly asymmetrical (larger on right), with sizes and positions of lesser trochanters differing substantially between sides. On the right, the spiral line, adductor insertions, and lateral gluteal lines converge toward the midshaft, where they run parallel for only ˜30 mm before dividing again into borders of the popliteal surface. These lines are barely visible, even in the middle of the shaft, unlike a normally robust and prominent linea aspera. The arrangement of muscle attachments is similar on the shaft of the left femur, but lines are not visible distally. Such atypical features imply severe muscle hypotonia (paresis) during life, associated with complications of abnormal growth (ibid.:5).

The authors consider that it seems incongruous to find such apparently weak musculature for a skeleton that has been described as morphologically robust. But so far, the only evidence for "robustness" has been the large diameters of the long bones in comparison with their short length. Of course, this may result from change in the denominator (shorter bones) as well as in the numerator (thicker bones).

So they scanned the bones. They discovered that the long bones have thin cortical bone:

Inflated circumferences, combined with very thin cortical bone showing very weak muscle markings, indicate not robusticity but long bone overtubulation indicative of disordered growth (5).

To me, all of these features make a very compelling case for pathology. The asymmetry is clear and widespread throughout the skeleton (this is not to mention the evidence for asymmetry in the endocast, which remains to be reported). The remaining traces of muscle attachments and bone thickness all are either asymmetrical or unusually weak. The humeral torsion is extremely unusual, and is apparently not explained by functional comparisons with any hominoids. From top to bottom, this skeleton has obvious problems.

The authors here argue that the pathology is likely some form of microcephaly, but they do not offer a specific diagnosis. However, they do note that many documented conditions involving microcephaly also involve small stature.

Comparisons with local pygmies

The other main element of the paper is the comparison of the Liang Bua morphological characters with those found among local people, as a result of the Rampasasa expedition:

From the beginning, the "H. floresiensis discovery" was treated as a matter of hominid taxonomy and phylogeny. Curiously, however, comparisons of LB1 were made mostly with H. sapiens from other geographic areas of the world, principally Europe. Yet it would have been logical even for a supposedly novel human species from the Australomelanesian region to have been compared with other human populations, present as well as past, from that region (2).

So they did the comparisons:

Aside from abnormalities discussed below, not one of the 94 descriptive features of the LB1 cranium or the 46 features observed on both mandibles lie outside the range for modern humans from the region. The form of the superciliary area, nasal floor, subnasal region, orbits, and occipital superstructures of LB1 all are encountered routinely among Australomelanesians.... Purportedly, the LB1 cranium displays two skeletal features "not seen in modern humans." In one, "a deep fissure separates the mastoid process from the petrous crest of the tympanic" bone. The other is "a recess between the tympanic plate and the entoglenoid pyramid" on the medial part of the mandibular fossa. Australian and Tasmanian crania commonly display both these features. The latter trait is also present in two Pleistocene Australians, Kow Swamp 5, and, in a reduced form, Keilor.

Personally, I have to observe that "not seen in modern humans" is like a hanging death sentence for any paper that uses the phrase. Somebody is always going to check that in museum collections, and they are always going to find humans that have the "never seen in humans" feature. I think there must be some cryptosadistic editors that let this phrase stay in papers because they secretly enjoy seeing the authors get their comeuppance.

They find many other "distinctive" features of the skeleton in local or regional samples. A strong majority (>90%) of the Rampasasa people sampled had "neutral or negative chins." Many of them had rotated teeth. There is a high regional frequency of third and fourth premolars with Tomes' roots. And the authors argue that a wide pattern of not-so-unusual morphological features of the teeth may be evidence of a link to local peoples:

Other dental traits linking LB1 to modern pygmies from the Liang Bua region include a tendency for the longitudinal fissure to shift away from the buccolingual axis on lower molars, tremata (spaces between teeth), squared lower molar outlines related to hypoconulid loss, and large buccolingual P₃ diameters. Overall, the dentition of LB1 exhibits modern human traits, with bilateral rotation of the upper fourth premolars and tooth shape deviations in lower premolars, both of which seem to occur at elevated frequencies in the Rampasasa (4-5).

This echoes the Gary Richards' conclusion that the fossils share features with modern humans that would have to be explained by parallelism under the species interpretation, but with much more detail.

I can imagine a response for this argument is that these features are "plesiomorphic", shared from some ancestral species of Homo. But you can only push something so far before it starts to be pulled by something else. In this case, if these features of the skeleton that are shared with modern Australomelanesians are really primitive features that were inherited from some distant ancestor, then you have to wonder whether any features really mark modern humans in contrast with that surprisingly derived primitive ancestor. And just where is that ancestor supposed to have lived, hiding its derived morphologies from our prying eyes? The plesiomorphy explanation always seems to me like a stretch, because it depends so strongly on unobserved facts, but in this case it stretches the imagination. No, if Liang Bua represented a different species from modern humans, I think these features must certainly be explained as parallelism, which demands some account of how they could have evolved in common.

In any event, the authors in this case present their conclusions in terms of a null hypothesis that the Liang Bua fossils are the same species as us, and they conclude that the null hypothesis is not refuted by the features of the specimens. They don't measure or attempt to estimate whether the apparent parallelisms would be impossible if Liang Bua were a different species, but they conclude that they would be unlikely.

Island biogeography

They present two additional reasons to think that in situ evolution of a dwarf hominid species on Flores was unlikely. First, they argue that Flores just wasn't all that isolated over the relevant time period. They note that only two short water gaps separated Flores from mainland Asia during glacials, and there were at least two dispersals of elephants to the island during that time. They argue that this is evidence against isolation.

Second, they note that even though Flores is a large island, it wouldn't support a very large population at typical human hunter-gatherer population densities. With a probable census population size on the order of a few thousand (they estimate between 500 and 5000), the population would be continually in danger of extinction during the past 800,000 years.

These two arguments are sort of a pincer-effect on the possibility of endemic dwarfing on the island. If the island was really isolated enough for the evolution of an endemic species, then it couldn't have supported a large enough population to ensure survival. On the other hand, if it wasn't really isolated, then people could more easily have survived (with gene flow from outside), but they wouldn't be endemic.

I am less convinced by this element of the paper. For one thing, elephants swim, and their ability to colonize the island twice doesn't necessarily mean that humans could have done so. Of course, since the first humans got there by boat 800,000 years ago, we have to wonder why they subsequently lost that ability (otherwise, no isolation). But it would be more convincing if there were clear evidence of other Asian species appearing, and there isn't. It is, after all, Wallacea.

For another thing, the density estimates from modern human hunter-gatherers don't necessarily apply to super-small-bodied pygmy hunter-gatherers. If the reason that selection favors dwarfism on islands is limited resources, and if small body size really adapts species to those limited resources, then small-bodied hominids should have had much smaller areal requirements than large modern humans.

I don't think these criticisms refute the paper's arguments about biogeography, just that they aren't the strongest aspect.

Conclusion

So, is this the end for Homo floresiensis? I'm sure it won't be. But there are some things that I hope will come to an end.

First of all, it is now abundantly clear that some kind of microcephaly can explain the small size and small brain size of the LB1 specimen. Moreover, the specimen exhibits other very obvious signs of developmental pathology. It is a bad specimen on which to base the diagnosis of a new species; its most important features are quite plausibly caused by its manifest pathology.

The argument so far against pathology has been that it cannot explain other unique morphologies, like the lack of a chin, and Tomes' root, and so forth. But this paper shows that none of these other features are necessarily unusual for modern humans, in the local and regional context. So that argument is dead, unless someone can show that there is some unique character to the combination of traits in the specimen. Since most of the features that would differentiate it from Homo erectus -- purportedly due to endemic dwarfism -- are also shared with modern humans, that seems like a problem for the species idea.

So I completely accept the argument that LB1 is pathological. A corollary is that the skeleton cannot be a convincing type specimen for a new species.

But this isn't only about LB1: there are the other small specimens. This paper makes clear that none of the features of the LB6/1 mandible are outside the range of local peoples. This is not a case of two specimens that must share some rare pathology; the paper argues that they are two specimens that share a regionally-common suite of characteristics. They aren't, in other words, unusual.

The paper is silent on the other postcranial remains, except for the very short tibia LB8, about which there is this comment:

[T]he LB8 tibia, with an estimated length of 216 mm, is used to reconstruct a stature of 1.09 m, greater than that of LB1 at 1.06 m, although LB1 tibia length is 235 mm.

That says to me that there is still work to be done in establishing exactly what the body size of the other individuals was. Maybe they will all turn out to be very small, but it is hard to extrapolate because they are outside the range in which modern human regressions will be accurate -- even on modern-day pygmies. In short, the paper does not claim that the Liang Bua fossils do not sample an exceedingly small-bodied population. That population must itself be explained in evolutionary terms. Since we don't yet have a particularly good explanation for small-bodied human populations anywhere, this is certainly a worthwhile topic to consider further.

Another argument, about the tiny-brained humans making the modern human stone tools, was to me a nonstarter from the beginning. The thing is that all early humans were under selection for smaller brains -- for energetic reasons -- and all early humans were under selection for more complex culture. If there were a way to combine small brains and complex culture, some other population of humans would have found it, and that population wouldn't be a small population trapped on an island. So the Liang Bua tools should be sufficient to demonstrate the presence of modern humans.

I would be focused like a laser on three things. First, what happened to the early colonists of Flores? Do any 200,000-year-old archaeological sites survive? What was the ecology of the earliest Flores people?

Second, when did modern humans really show up in southeast Asia and Java? One of the only supports left for the idea of a Flores species is that the earliest levels at Liang Bua (>70,000 years) supposedly predate modern human arrival. Were modern humans there at that time? Are those levels just inaccurately dated?

And third, what happened on Timor? It seems to me that the game is over if humans were on Timor in the Middle Pleistocene. There is some indication that they were. If Homo erectus could manage sea crossings to that extent further west than Flores, then there is no way that Flores was a single, unique colonization. With an occupied Timor, we have to assume that regular contacts between Flores and mainland Asia were probable.

References:

T. Jacob, E. Indriati, R. P. Soejono, K. Hsü, D. W. Frayer, R. B. Eckhardt, A. J. Kuperavage, A. Thorne, and M. Henneberg. 2006. Pygmoid Australomelanesian Homo sapiens skeletal remains from Liang Bua, Flores: Population affinities and pathological abnormalities. Proc Nat Acad Sci USA. PNAS published August 23, 2006, DOI link

Posted at 22:32 on 08/23/2006 | permanent link

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Pygmoid, Australopithecus, Homo, yada yada...

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I can't help noting the contrast between these two quotes. First, from Argue et al. (2006:18-19):

A cranial morphometric and morphological comparison of LB1 with microcephalic individuals suggests that LB1 is unlikely to be a microcephalic H. sapiens, at least not of the MOPD II type. In the craniometric analyses, the Minoan and Sano 3 microcephalics are within the range of H. sapiens, although the Minoan is on the edge of the range of this species. LB1 is outside the range of H. sapiens and separated from the two microcephalics. For the microcephalics to cluster with LB1 in the analyses, they would have to possess a greater degree of prognathism, a lower vault, and wider biauricular breadths, which one might consider an unlikely set of characteristics for H. sapiens. We note, however, that we were only able to include two microcephalic individuals in the metric analyses for want of published data. Microcephaly is an extremely heterogeneous condition and, while our results are suggestive, it may be that they would differ should a larger sample of microcephalics be studied.

When the cranial morphology of MOPD II individuals is compared to that of LB1, however, the only condition they have in common is a small cranial capacity. In no other way does LB1's cranial morphology correspond to that of MOPD II. Further, except for a bowing of the tibia, LB1 does not display any of the postcranial morphologies commonly found in these individuals. Likewise, LB1 separates from the LT 'pygmoid' in the cranial metric analyses and does not display its modern human morphological features. LB1 is separate from the Andaman sample in the cranial analyses and does not reflect the postcranial proportions of any African pygmy populations. It would appear unlikely, then, that LB1 is either a microcephalic or pygmoid H. sapiens.

And then this quote from Richards (2006:15):

Many of the post-cranial features described for the Flores remains (Brown et al., 2004; Morwood et al., 2005) are consistent with those found in human populations that have undergone stature reduction by way of a modification of the GH-IGF-I axis. Brain size in humans can be reduced through the MCPH gene family or changes in IGFs and GHs (via GHRH-R inactivation) to the size of that found in H. floresiensis without significant impacts on the viability of a majority of the affected individuals. Genetic mutations that produce such reductions can be present at high frequencies in small, consanguineous groups in relatively isolated contexts. MCPH individuals show developmental delay and, in some, a reduction in stature. However, despite considerable effort I have been unable to uncover data on how MCPH impacts somatic development and, by extension, how this might impact craniofacial development. I have also been unable to discern how changes resulting from MCPH might interact with developmental modifications expressed in GH-IGF-I axis defects. Nevertheless, based on available data, a basic model that accounts for the morphology of H. floresiensis can be constructed.

...

Such a scenario would account for the reduced body and brain size found in the LB1-LB9 individuals, but it does not fully reveal the underlying biology of the craniofacial skeleton. Any attempt to reveal this biology and construct a basic explanatory model is complicated by the lack of: (1) individuals possessing a combined GH-IGF-I/MCPH malformation; (2) documentation on specific changes and geographic variation in skeleto-dental features in individuals possessing either of these conditions and (3) knowledge of the change that results in the modification of the GH-IGF-I axis in pygmy populations.

Completely opposite conclusions!

Now, Richards focuses his paper far more on the medical and genetics literature related to microcephaly and small body size; Argue et al. include metric comparisons with a small number of microcephalic humans as well as normal humans and fossil hominids.

Richards discusses a wide range of microcephaly-inducing pathologies; Argue and colleagues also discuss a broad range but focus their comparisons on one. Richards doesn't really provide any comparisons.

Argue and colleagues conclude that LB1 is not any of the other things, because it falls metrically (and nonmetrically) outside the range of the other things. Richards proposes that it falls outside the range of other things because it has a combination of two things.

Richards relies on parsimony for his arguments about the phylogenetic relationships of LB1 -- in particular the shared features with modern humans that would have to have evolved in parallel on Flores if that population emerged from some earlier hominid. Argue and colleagues discuss some parallelisms with modern humans, but do not apply any arguments based on parsimony.

All this goes to explain how two groups of people can look at exactly the same data and come to opposite conclusions. I suppose I should be worried that I read all this and come to yet another conclusion.

References:

Argue D, Donlon D, Groves C, Wright R. 2006. Homo floresiensis: Microcephalic, pygmoid, Australopithecus, or Homo? J Hum Evol in press. DOI link

Richards GD. 2006. Genetic, physiologic and ecogeographic factors contributing to variation in Homo sapiens: Homo floresiensis reconsidered. J Evol Biol in press DOI link

Posted at 09:18 on 07/20/2006 | permanent link

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Narrowing down Flores microcephaly

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Well, I'm still writing from Zagreb, so I don't have a lot of time for review. But I do want to point out the new paper by Gary Richards in Journal of Evolutionary Biology (DOI link).

It is clear from the paper that Richards really knows his microcephaly, from a clinical medical perspective. This is the kind of knowledge that the skeletal biologists should have brought in from the beginning, as I've argued for since early 2005:

Has anyone involved any experts in human brain pathologies in studying the skull yet? Is there even a single expert on microcephaly who has said anything about the skull? I know enough not to pretend that I can say this is or isn't pathological. I suspect that any qualified clinician would say the same; there is just no telling how microcephaly would manifest in a Stone Age specimen.

At this point, after this new paper, I think I can restate that question a different way: Has anybody with clinical knowledge of microcephaly now argued in support of the idea that this is a new species? Because we have now had three published arguments about the specimen (from Weber and colleagues, Martin and colleagues, and now Richards) that support the hypothesis of microcephaly, based on comparisons with endocasts, critiques of the original descriptions, and now physiological and anatomical comparisons with human pygmy populations.

There is an enormous amount of detail in this new paper about the genetic mechanisms behind small body size in pygmies, the genetics of primary microcephaly, the clinical and developmental manifestations of different types of microcephaly, and the consequences of all these for interpreting the Liang Bua remains. Richards has studied microcephaly and dwarfism in archaeological remains before, and clearly knows this literature. He is critical in several places of the original descriptions of the fossils, for their failure to cite pertinent recent clinical literature and their misuse of terms; either by failing to note changes in definitions in modern practice, or by failing to note variability in the diagnoses and manifestations of different conditions.

However, Richard's conclusion is not that the LB1 specimen is pathological. He is persuaded by the evidence of additional individuals from the site, and concludes that the sample represents a population with a distinctive suite of genetic characteristics due to insular isolation and dwarfism. I can't explain it better than citing his conclusion:

I agree that these remains do not represent diseased, pathological, or aberrant individuals. I consider these individuals to manifest physiological differences from other modern humans in similar ways to modern pygmies and additional modern humans possessing MCPH or GHRH-R mutations. When developmental differences result in divergent morphologies that then define a population, they can provide the basis for speciation, but by themselves they do not confer specific status. The fact that the Liang Bua remains present with a currently distinct suite of characters relative to modern humans does not necessarily mean that they represent a separate species. We currently lack the kind of detailed morphological assessments of both pygmy populations and individuals possessing the kinds of anomalous conditions suggested to account for the observed morphology. Prior to suggesting that the observed morphological suite of the LB1-LB9 individuals is indicative of speciation, it will be necessary to collect a substantial amount of new data.

When one applies the concept of maximum parsimony to the totality of evidence available on the Flores remains, one finds significant support for the remains being a variant of H. sapiens and little support for a species-level distinction. Given this position, I suggest that the LB1-LB9 individuals represent the remains of a H. sapiens group which became dwarfed in an island environment via changes in the GH-IGF-I axis. Acquisition of a dwarfing condition may either have occurred prior to or after the group arrived on the island. If it can be demonstrated that the totality of the recovered remains sample the same population, it appears that a mutation in the MCPH gene family or a secondary modification of the GH-IGF-I axis arose in teh later part of their occupation of the island and was transmitted within a local group. Whereas I consider the 'primitive' features identified in the LB1-LB9 individuals to be consistent with the scenario presented above, only a detailed analysis will be able to clarify the value of these features for phylogeny reconstruction (Richards 2006:19).

So the hypothesis is that this actually was a distinctive local variant population, but not a species that had diverged from some earlier hominid, like H. erectus. That is a fair enough hypothesis, but it doesn't quite make sense to me as following from the evidence presented. The only specimen for which there is any evidence about the brain at all is LB1. Now, Richards presents several examples of microcephaly variants that are very common in consanguineous marriages or small villages. So there is the possibility of such a condition becoming locally common even in modern humans. But in this case, we really have no reason to think that the condition was locally common. There is only one skull!

But I think the paper is a very important source of information, not only about the clinical manifestations of microcephaly and genetic mechanisms of small stature in human populations, but also because it draws together more considerations of how LB1 and the other specimens compare to different populations of modern humans, and not "modern humans" as a whole. Quite clearly, when you consider a small subset of modern humans as a comparative sample, some individuals who were not part of this small sample are going to look different or even strange. But you have to consider the full extent of variation in humans -- especially local humans -- when considering whether an unusual feature is part of the range of modern human morphology:

Brown and Morwood (2004) have recently argued that the LB1 mandible possesses a combination of nine features that eliminated any possibility it could derive from a modern human. At first glance this feature set would seem to