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Re: [palanthsci] 'From one microcephalic to twenty by John Hawks'

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  • Ralph Holloway
    ... For whatever it is worth, the Weber et al stuff proves nothing. None of the so-called 19 microcephalics studied by Weber et al have the shape of LB1.
    Message 1 of 4 , Oct 14, 2005
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      Mikey Brass wrote:

      >*/http://johnhawks.net/weblog/fossils/flores/weber_microcephaly_comment_2005.html/*//
      >
      >
      >
      >
      >*From one microcephalic to twenty by John Hawks *
      >Falk et al. (2005a) compared the LB1 endocast to one microcephalic skull
      >and concluded it didn't match. Now Jochim Weber and colleagues (2005)
      >have compared the endocast to nineteen additional microcephalic modern
      >human crania. They argue that LB1 is likely microcephalic. Falk et al.
      >(2005b) disagree. So who's right?
      >
      >Weber et al. (2005) make four points:
      >
      > The endocranial volume of LB1 (417 ml) is well within the range of
      > the modern human microcephalics (280 to 591 ml).
      > Modern microcephalic endocasts are "extremely heterogenous" in
      > their morphology, but some of them grossly resemble early hominid
      > endocasts.
      >
      > One endocast in particular from their sample has a volume of 415
      > ml, and the ratios of its dimensions are all within 0.01 of the
      > matching ratios from LB1. This appears to indicate an extremely
      > close similarity of overall endocast shape.
      >
      > A substantial proportion (7 out of 19) of the microcephalics
      > exhibit relative enlargement of Brodmann's area 10, the area that
      > is also extremely enlarged in LB1
      >
      >Falk et al. (2005b) criticize the latter two of these points. Taking the
      >last one first:
      >
      > Weber et al. assert that seven of their microcephalic endocasts
      > have a relatively expanded Brodmann's area 10 similar to LB1, but
      > none of the five microcephalic endocasts in their figure 3
      > reproduce the two distinct, enlarged convolutions seen in the
      > region of area 10 in LB1 (Falk et al. 2005b:236).
      >
      >Their other criticism focuses on the apparent similarity in ratios
      >between one microcephalic and LB1. This point is somewhat involved,
      >because it relies on a technical difference in the orientation of
      >endocasts. As they describe, the microcephalic pictured by Weber et al.
      >(2005) as well as that pictured by Falk et al. (2005a) both have
      >relatively large cerebellar volume compared to overall brain volume.
      >This results in a cerebellum that takes up a broader area in the back of
      >the endocast.
      >
      >I've Photoshopped the figures together to make the orientation clearer:
      >ole0.bmp
      >/Microcephalic skull pictured by Weber et al. (2005) in the orientation
      >of Falk et al. (2005b) (L); Same skull in orientation of Weber et al.
      >(2005) (C); LB1 in orientation of Falk et al. (2005a) (R). For all
      >three, the position of the transverse sinus is marked "TS"./
      >
      >The disproportionate reduction of the cerebrum compared to the
      >cerebellum in these microcephalics complicates the comparison of
      >endocast shape. For Falk et al. (2005b), the main implication is that an
      >incorrect orientation may result in an incorrect measurement of endocast
      >dimensions, and thereby to incorrect ratios of those measurements. The
      >end result may be that the "closely matching" ratios may not be so close.
      >
      >On the other hand, the shape of the forebrain in these endocasts is
      >still broadly similar, and the size of the microcephalic is if anything
      >smaller than LB1. Thus, the disagreement comes down to anatomy, and
      >questions that cannot be answered by ratios.
      >
      >For example, even though the cerebellum of LB1 appears relatively small
      >compared to those of the microcephalics illustrated in these studies, it
      >actually appears relatively large compared to humans,/ Homo erectus/ and
      >chimpanzees pictured in Falk et al. (2005a). Is this a consequence of
      >allometry, or is it actually abnormally large relative to brain size?
      >Are there microcephalic crania whose cerebellar size is more similar to
      >LB1? Are there any modern humans that have pronounced area 10
      >convolutions like LB1?
      >
      >*What I think*
      >I'm not sure we will ever have answers to some of these questions, at
      >least those requiring comparison to microcephalic crania.
      >
      >Of course, there is at least one kind of "smoking gun" proof: if we find
      >another endocast of similar size. Unless another small-brained specimen
      >were found in a death embrace with LB1, the existence of a second small
      >endocast by itself would be enough to show that a small-brained
      >population really existed.
      >
      >But is there any/ other/ kind of smoking gun evidence? Suppose for
      >example that we found a modern microcephalic skull in a museum that was
      >identical to LB1. Would that be enough to prove the skull was pathological?
      >
      >As Weber et al. (2005) note, some microcephalics approximately have the
      >shape of early hominid endocasts. Even if it were pathological, LB1 is
      >clearly one of those: its shape is grossly similar to that of/ H.
      >erectus/, although much smaller. This similarity may have been
      >overstated, since the proportions of individual parts of the endocast
      >surface and the details of its surface have not been reported fully. But
      >considering the extensive variability of/ normal/ modern human
      >endocasts, we should expect a range of variability in fossil endocasts
      >as well. Thus, LB1 may well lie within the range of/ shapes/ of several
      >early hominid species, even though it does not match those populations
      >in/ size/.
      >
      >So as long as LB1 is plausibly within the shape range of early hominids,
      >even a perfect match with some microcephalic cranium is unlikely to
      >convince some people that it is pathological. No smoking gun there.
      >
      >At the same time, I don't think we should/ expect/ to find an identical
      >microcephalic anywhere. Weber et al. (2005) write that microcephalic
      >crania are "extremely heterogenous", and this would be my assessment
      >also from the few I have seen. Microcephaly is a developmental pathology
      >with many causes, many different manifestations, and consequently many
      >different morphological possibilities. To me, this means that no two
      >microcephalics may be alike, and we may never find an exact match for
      >any ancient microcephalic skull.
      >
      >For this reason, the idea that we/ should/ expect to find an exact match
      >is far too stringent a requirement. After pointing out the possible
      >discrepancy of orientation, and noting that none of the endocasts
      >studied by Weber et al. had exactly the pattern of area 10 convolutions
      >as LB1, Falk et al. (2005b) end their comment:
      >
      > If this is the best evidence that can be produced from a sample of
      > 19 microcephalics, we suggest that the authors reconsider their
      > position on the microcephalic hypothesis regarding/ Homo
      > floresiensis/.
      >
      >I have the opposite opinion. I might well expect to study several
      >hundred microcephalic crania and never find an exact match for LB1. Even
      >so, if this sample, like the 19 studied by Weber et al. (2005), has over
      >30 percent of endocasts with enlargement in Brodmann's area 10, and if
      >it has some endocasts that are relatively broad with low transverse
      >sinuses, it would be hard to say that LB1 lies outside their range of
      >variability.
      >
      >One may reasonably wonder where the burden of evidence lies in this
      >case, particularly now that we have additional evidence for small-bodied
      >individuals in the Liang Bua sample. Some may presume that the
      >hypothesis of pathology for the endocast must be accompanied by a
      >specific diagnosis that matches the details of the entire skeleton.
      >After all, microcephaly is a very rare condition, and it must be the
      >rare case indeed that survives in a Late Pleistocene population and
      >exhibits morphology that is broadly similar to that of early hominids.
      >
      >But the hypothesis that the specimen is a normal member of a dwarf
      >population of/ H. erectus/,/ H. sapiens/, or/ Australopithecus/ brings
      >its own strong problems that we should not gloss over.
      >
      > o If it derives from/ Homo sapiens/, what pattern of selection
      > caused its brain to shrink? What accounts for its limb
      > proportions and strange long bone, pelvic, and mandibular
      > morphology?
      > o If it derives from/ Australopithecus/, how did it get there?
      > How did it survive so long? How did it get human-like teeth?
      > o If it derives from early/ Homo/,/ none/ of these questions
      > have good answers.
      >
      >So pathology solves a lot of problems with the sample, even if it
      >creates others. I don't know that we can weigh these options relative to
      >each other: the likelihood of microcephaly versus the likelihood of a
      >"Lost World" australopithecine scenario, for example. But if we are
      >going to act like Sherlock Holmes, we will have to start eliminating
      >options. And Weber et al. (2005) do a good job of showing that we can't
      >yet eliminate microcephaly.
      >
      >*References:*
      >Falk D et al. 2005a. The brain of LB1,/ Homo floresiensis/. Science
      >308:242-245._ __Full text (free)
      ><http://www.sciencemag.org/cgi/content/abstract/308/5719/242>_
      >
      >Falk D et al. 2005b. Response to comment on "The brain of LB1,/ Homo
      >floresiensis/". Science 310:236._ Full text (subscription)
      ><http://www.sciencemag.org/cgi/content/full/310/5746/236c>_
      >
      >Weber J, Czarnetski A, Pusch CM. 2005. Comment on "The brain of LB1,/
      >Homo floresiensis/". Science 310:236._ Full text (subscription)
      ><http://www.sciencemag.org/cgi/content/full/310/5746/236b>_
      >
      >*/Posted at 01:24 on 10/14/2005/*//
      >
      >~~~
      >
      >
      >
      For whatever it is worth, the Weber et al stuff proves nothing. None of
      the so-called 19 microcephalics studied by Weber et al have the shape of
      LB1. Microcephalics do not have large cerebral lobes over-riding small
      cerebellar lobes, and that is what LB1 has. The size issue cannot be
      used to claim microcephaly as pathology. However, I think Falk is wrong
      concerning the area 10 region. I have seen at least one true
      microcephalic which shows very narrow superior frontal gyri, and
      depressed sulci adjacent to these. These are reminiscent of a condition
      known as microgyria, where the cortex is formed of four rather than the
      normal six layers. One cannot, from an endocast, determine if the area
      10 configuration being bruited about is normal, advanced, or
      pathological, without studying many more microcephs, and including the
      full spectrum of that condition, which must included nanocephalics,
      which appear to have very small brains, small stature, but little if any
      actual brain pathology, at least from gross neuroanatomical examination.

      I must say, I find John Hawkes blogs surprising, as he was in my hotel
      room during the April 2005 AAPA Meetings in Milwaukee when I showed him
      and several colleagues the actual LB1 endocast that I had made, and
      explained these various issues to them.

      Best,

      Ralph Holloway
    • Mikey Brass
      ... To plagerise from Jaime Headden, what about a late microcephalic Homo erectus?
      Message 2 of 4 , Oct 16, 2005
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        Ralph Holloway wrote:

        > For whatever it is worth, the Weber et al stuff proves nothing. None of
        > the so-called 19 microcephalics studied by Weber et al have the shape of
        > LB1. Microcephalics do not have large cerebral lobes over-riding small
        > cerebellar lobes, and that is what LB1 has.

        To plagerise from Jaime Headden, what about a late microcephalic Homo
        erectus?
      • Dale Hoogeveen
        There are both genetic and non-genetic causes of the various types of micro- and nano-cephaly. These pathologies are variable enough in their development that
        Message 3 of 4 , Oct 17, 2005
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          There are both genetic and non-genetic causes of the various
          types of micro- and nano-cephaly. These pathologies are
          variable enough in their development that even in the
          extremely rare cases of siblings or even identical twins the
          final phenotypes are quite variable with the final
          development very often quite distinctive with some similar
          types of pathologies even showing sublethal for one
          identical twin while the other completely matures.

          It is very likely that any microcephalic offspring of known
          modern parentage is quite likely to be unique enough to lack
          exact duplication even with similarly affected close
          relatives. Cranial developmental pathologies are immensely
          variable in final expression, genetic or not.

          Demanding exact duplication for proof of pathology is an
          impossible standard and far too restrictive to provide proof
          of speciation. The standard should instead be to show that
          LB1 falls outside modern microcephalic variation rather than
          single case comparisons with the burden of proof on the
          dramatic shift in paradigm that speciation presents. LB1
          and the other cranial fragments do not yet begin to meet
          that necessary standard.

          Nor do the dental expressions, all of which supposed
          variation from modern human characters are actually present
          in current regional populations from that area in
          significant numbers. Even if not the majority expressions,
          several of them are relatively common there and all are
          present.

          Proposing microcephalic erectus is really pointless, until
          the supporters of speciation do a comprehensive comparison
          to complete sets of modern micro and nanocephalic examples
          rather than the onesy-twosy micro-set comparisons done to
          date.

          The German stuff is not proof; it is offered as disproof
          which is a different matter. The burden of proof remains on
          the proposal of speciation as a complete and integrated
          concept, which it is not at this point. Disproof can come
          in at any point and apply significantly and fatally to any
          aspect of the proposal without beginning to have to meet the
          standard of proof necessary to establish a proposal of this
          magnitude. This cannot be established by fiat regardless of
          who makes such a proclamation or how intensely critics of
          the proposal are castigated for whatever reason and in this
          case we have seen nearly every possible example of that,
          whether regarding moral, ethical, legal or professional
          competancy standards.

          There are significant enough reservations from a number of
          competant professionals, including a very large portion of
          those who have directly handled the bones, including nearly
          all of those who did so independantly of the initial
          publishers, that as a civilian I see all kinds of red flags
          all over this. Clarification is not helped at all by
          intense accusations of professional incompetance and
          ulterior motives directed at such critics.

          Those critics remain incompletely answered at best on every
          issue, not the least of which are a number of issues
          regarding pathology.

          Speciation as a conclusion is very much premature;
          speculation on what kind of ancestry may have lead to such
          speciation is even more so.

          Dale

          --- In palanthsci@yahoogroups.com, Mikey Brass <mike@a...>
          wrote:
          >
          > Ralph Holloway wrote:
          >
          > > For whatever it is worth, the Weber et al stuff proves
          nothing. None of
          > > the so-called 19 microcephalics studied by Weber et al
          have the shape of
          > > LB1. Microcephalics do not have large cerebral lobes
          over-riding small
          > > cerebellar lobes, and that is what LB1 has.
          >
          > To plagerise from Jaime Headden, what about a late
          microcephalic Homo
          > erectus?
          >
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