November 7, 2009

Archaeology in the Taguatinga Valley – The Archaeology Channel

Although I haven’t been able to catch this latest offering from TAC, this video and the previous two, first aired a few weeks back should definitely be worth setting aside some time for over this (or any other) weekend – here’s a description of the first,  Archaeology in Taguatinga Valley, from TAC’s website:

This video describes the Archaeological Scientific Salvage and Cultural Heritage Management Program of Taguatinga Valley in Brazil’s capital, Brasilia. The Goiano Institute of Pre-History and Anthropology (IGPA) from the Catholic University of Goias (UCG) conducted research on a massive water treatment project and carried out extensive public education. The work was supervised by Brazilian National Institute of Historical and Artistic Heritage (IPHAN) and funded under contract by the Company of Basic Sanitation of Brasilia (CAESB).

The next is Welcome to Chucalissa, is described as follows:

Located in Memphis, Tennessee, the Chucalissa prehistoric site represents the widespread Mississippian Culture.  Founded initially around A.D. 1000, Chucalissa village reached its peak around 1500 with the construction of large platform mounds around a central plaza.  Part of a complex society and supported by farming and natural foods, the Native American people of this site traded throughout much of the Midwest and South.  Since its rediscovery in 1940, the site has become an education center for the University of Memphis through the C. H. Nash Museum.

And finally we have Uncovering Ancient St. Louis, as explained here:

“Ancient history” didn’t happen just in famous places like Rome, Tikal and Angkor Wat.  It happened also in the heart of North America.  Modern St. Louis residents may not realize that their city once hosted a complex Native American culture, represented by a cluster of mounds, possibly an actual city rivaling Cahokia across the Mississippi River.  A small army of scientists, while uncovering thousands of prehistoric Native American archaeological sites around this fertile convergence of rivers, has some fascinating questions about what took place here.

I’ll try and add comment at a later date when I’ve had time to watch these items in full.

November 6, 2009

Current Anthropology – New Edition, First 50 Years Issue

Current Anthropology, December 2009, Volume 50 number 6 is now out, which as will be apparent from the headline, marks no less than 50 years in the field, and there are a number of essays contained therein which reflect on the past, present and future of this publication. Here’s part of editor Mark Aldenderfer’s introduction to the proceedings:

In this issue we celebrate 50 years of Current Anthropology. By no means the most long‐lived anthropology journal (that honor must go to the Journal of the Royal Anthropological Institute, which technically began its run in 1872 but whose origins can be traced to 1863), it is certainly unique. The six celebratory essays explore the history of this remarkable journal from the perspectives of past editors, beginning with Cyril Belshaw, who took over from Sol Tax, the journal’s founder, and then Adam Kuper, Richard Fox, and Ben Orlove, as well as two past presidents of the Wenner‐Gren Foundation, Sydel Silverman and Richard Fox. Barbara Metzger, who joined the journal as a copy editor in 1964 at Tax’s behest and became arguably the central figure of the journal through the terms of five editors, provides another perspective on CA’s evolution. These very personal reflections offer us insights into not only the history of the journal but also the changing nature of scholarly publishing and the ways in which CA shaped, and was shaped by, the contours of these changes.

Although Sol Tax first saw CA as a venue for reviews and news, the realities of scholarly publishing even then moved him toward a broader conception of the idea of “current” research. Over the decades, as our editors have stressed, current meant just that—publishing not just the new for the sake of newness and currency but also the best of that research. Here the journal over the decades has been tremendously successful. Although I am aware of dissatisfaction with and rejection of quantitative measures of journal impact, such measures are nevertheless one way to document the quality of a journal and its influence on a field. Using the Institute for Scientific Information’s impact factor formula as reported in their annual Journal Citation Reports (see http://tinyurl.com/ygvxffq for definitions and caveats), since 1997, CA has ranged from the first to the seventh position of all indexed anthropology journals (lower numbers are better). This is a remarkable achievement for a four‐field journal in an era of increasing specialization, and the past editors must be heartily congratulated for keeping CA timely, relevant, and important to the field across these five decades. For the sake of modesty, I will forgo comparisons with the other two major four‐field journals!

As ever, the contents are behind a paywall, albeit one which in my opinion is very good value for money – as I’ve mentioned before, the cost of a digital annual subscription isn’t much different from what some journals charge for access to a single paper, and moreover the papers published in CA this year have been especially wide-ranging, informative and thought-provoking, a trend which I imagine will continue long into the future.

To access the Table of Contents, just click this link.

November 4, 2009

Long Toes & Short Ankles Help Sprinters Accelerate Faster

The Journal of Experimental Biology has published an interesting paper about some unique features in sprinters: longer toes and shorter ankle joints. The only one flaw is that their sample size is limited, they only compared 12 collegiate sprinters with 12 non-athletes of the same height. Regardless, from a physical anthropological point of view, this comparative & biophysical analysis informs us what traits help humans sprint faster.

The significance of long toes and short ankle joints can be explained from a purely physics perspective. From the start of a sprint, the only way a human can accelerate is through the transfer of energy from the force of the leg muscle to pushing on the ground. The advantage of longer toes provide maximum contact with the ground just a little bit longer than shorter toes.

Posterior Leg Muscles

The ankle joint is shorter because there is an inverse relationship between tension force and distance — think torque and angular momentum. Sprinters have a 25% shorter distance between the Achilles tendon and center of rotation of the ankle. The Achilles tendon is the common attachment of the gastrocnemius and soleus muscles into the calcaneus. When contracted, these two muscles flex the knee and plantar flex the foot. With a shorter ankle joint, these muscles shorten less for the same joint rotation. If muscles shorten less, then they shorten more slowly. This facilitates them to produce greater force that more than compensates for the reduced leverage.

When these two adaptations are combined, the authors figured that the greatest acceleration is achieved when the Achilles tendon lever arm is the shortest and the toes are longest. Comparing these anatomical features to other sprinting animals, like ostriches, greyhounds and cheetahs, they authors observed that they also have feet built for sprinting with similar features.

The authors, who are not physical anthropologists, state in press releases that they think these adaptations could have had some evolutionary backing. They raised the tired hypothetical scenario where early human ancestors, now those with longer toes and shorter ankle joints, were better able to run away from the saber tooth tiger or marauding tribe and reproduce that trait. But I disagree, while there certainly is an inherited component to the size and shape of our bones, muscles, and joints, our bodies are malleable and depending on training, our bones and muscles can change!

Furthermore, the majority of humans are not sprinters, as I understand it. In fact, most of us are good at long distance motility. Our bodies are extremely inefficient at sprinting but we’re really good at staying the course! Most of us have lots of Type I muscle fibers, slow but fatigue resistant fibers. Anyways, I don’t mean to rag them on this concept, as I mentioned they aren’t physical anthropologists and they seem to only be speculating on this last point. Either way, I believe the observation they made is interesting!

    Knight, K. (2009). SHORT HEELS GIVE ELITE SPRINTERS THE EDGE Journal of Experimental Biology, 212 (22) DOI: 10.1242/jeb.039735
    Lee, S., & Piazza, S. (2009). Built for speed: musculoskeletal structure and sprinting ability Journal of Experimental Biology, 212 (22), 3700-3707 DOI: 10.1242/jeb.031096

November 4, 2009

Four Stone Hearth 79 @ Anthropology.net

As by necessity this edition is being put together quite hurriedly, let’s get straight to the posts – I received a grand total of 3 submissions, and two of those were from one contributor, namely Eric at The Primate Diaries, which is where we’ll begin.

In Reexamining Ardipithecus ramidus in Light of Human Origins, Eric examines the way in which the recent Ardipithecus ramidus discoveries have been interpreted, in this case by Owen Lovejoy, the anthropologist who headed up much of the recent investigations.

Next from the same author is Male Chauvinist Chimps or the Meat Market of Public Opinion? in which he comments at length on the stereotypical way in which food provisioning by male chimps (and by implication humans) has been interpreted, with claims that such behaviour supposedly increases their chances of copulating with females shortly after food has been shared – as he points out in the post, when the actual data are examined and analysed over the long term, in this case 22 months, we see a different story, as neatly summed up here:

The larger story lay not in the fact that females preferred to mate with males who provisioned them, but that they were opportunistically shifting their mating strategies for their own reproductive interests. In earlier studies by Boesch at the same site it was demonstrated that 84% of undesirable advances were rejected by females (Stumpf & Boesch 2006; pdf here), promiscuous mating was reserved for the early part of estrous and that 93% of all copulations were terminated by females (Boesch et al. 2006; pdf here). Females chose who they would mate with, when they would mate with them and how long it would last.

The point made thereafter is that instead of the view that male chimps shared food with females as a short term tactic, in reality the females appear to be calling the shots by adopting long term strategies in order to discern who  would make the best father for their offspring, recalling past food sharing, in addition to overall male ranking when making their choice.

And although this wasn’t actually submitted, I’ve included it anyway – Science Got Ardi Wrong or: The Enigma of Ardipithecus [UPDATED], which again points out some of the many holes in recently publicised news articles and the like – another very pertinent article which is not to be missed.

From Ad Hominin, Ciarán submits a post to which I referred to in a previous post here, namely Did Neandertals and modern humans interbreed?, and although I commented on just one paragraph, the account of the proceedings at the recent Human Evolution 150 Years After Darwin conference in Gibraltar reveals the ongoing debate regarding how archaic H. heidelbergensis and Neanderthals should be viewed, with particular reference to Atapuerca, and whether they should even be viewed as two entirely separate species in the first place.

In a similar vein we have this from Zinjanthropus: Skepticism is good, but… from which this is the introduction:

Earlier this week, Eric Michael Johnson drew my attention to a post by psychologist Christopher Ryan at his blog Sex At Dawn.  Ryan attacks Lovejoy’s monogamous humans model by citing many different lines of evidence.

I became so distracted by the reported testes:body mass ratio of 1/160 in humans that I couldn’t stop until I had some answers.  I am a female human, but even I thought that 1 kg of testicles would be an awful lot to lug around.  So I got out my books and my calculator and did some math, wrote in, and it was fixed.  Peer review in action!

Time now to serve off in other directions, where we find a bag of posts, mixed in topicality but all similarly interesting and well worth the read.

Over at Aardvarchaeology, Martin regales us with Danes Run Entire Urn Burials Through CT Scanner, whilst Alun Salt runs censorship through the mill with Libel, Censorship and Blog Comments, and further informs us that ‘It’s Not Just Jack Who Names the Planets’, in another riveting piece.

Sticking with archaeology, here’s a post called ‘Tramp Down Babylon’ from anthropologyworks which revisits the damage done to the site in the years since the US military has occupied the site, whilst back in the UK comes some slightly better news which concerns the recent discovery of the remains of a bluestone henge that is believed to have preceded the more monumental phase which eventually led to the construction of the megalithic complex with which we are familiar today. Eternal Idol has “It’s not quite Tutankhamun’s tomb, but…” – an account of Professor Mike Parker Pearson’s recent presentation on “Bluestonehenge”, which offers a nice report on the excavations ahead of a more formal publication some time in February 2010.

Brian at Old Dirt -New Thoughts asks ‘How Much Should We Dig?, with reference to his ongoing Hamline Project all the way up there in Alaska.

Neuroanthropology chip in with The Uncultured Project, and include a link to the actual project website here.

The final entry comes from the New York Times, who in common with Kambiz in a previous post here, announce Claude Lévi-Strauss Dies at 100, from which this is taken:

A powerful thinker, Mr. Lévi-Strauss was an avatar of “structuralism,” a school of thought in which universal “structures” were believed to underlie all human activity, giving shape to seemingly disparate cultures and creations. His work was a profound influence even on his critics, of whom there were many. There has been no comparable successor to him in France. And his writing — a mixture of the pedantic and the poetic, full of daring juxtapositions, intricate argument and elaborate metaphors — resembles little that had come before in anthropology.

So that’s it for this time round – the next Four Stone Hearth, the 80th no less, is due out on Wednesday November 18th – no host is as yet slated, so if you fancy having a go at hosting on your own blog or site, just follow this link where instructions on how to do so can easily be found. Thanks for reading this somewhat brief edition, which I hope wasn’t too perfunctory, but limited battery life in a cafetería was a strong natural selector on this occasion.

Science Got Ardi Wrong or: The Enigma of Ardipithecus [UPDATED]

November 3, 2009

Claude Lévi-Strauss Has Died

Claude Lévi-Strauss died two days ago. He was 100 years old.

I shouldn’t have to write about his impact to the field of anthropology, in summary it was profound. He authored many texts. He set forth structuralism, a mode of thought by which we can compare relationships between social systems. His contributions to studying cultures and anthropology were deep and he will be missed.

Claude Lévi-Strauss

November 1, 2009

Four Stone Hearth 79 – Call for Submissions

Despite an ongoing bout of intermittent Interweblessness, I’m hoping to get the next Four Stone Hearth up and running as normal; Martin R seems to be away from his desk at the moment, so if anyone would like to submit anything for this coming Wednesday, please mail me by Tuesday at tim(oneword)jonzi AT gmail DOT com and I’ll do my best to ensure that all suitable submissions are duly included. Thanks.

Following on from the most recent post by Kambiz, readers, or in this case listeners might be interested in tuning into BBC Radio 4 tomorrow at 21.00 London time, when the first of a two-part documentary ‘Aping Evolution’ is due to air, in which Professor Steve Jones will apparently be challenging evolutionary psychology, described thus:

Evolutionary psychology seeks to explain human behaviour from the hunter-gatherers or our nearest relatives, the chimpanzee, and has some seductively simple theories. One argument is that we have Stone Age brains in 21st-century skulls, from which we can account for everything from the violence that men show to their stepchildren to why racism exists. Is evolutionary psychology a truly useful addition to the canon of ideas to come out of Darwinian evolution or a just-so science that can be adjusted to suit the researchers’ prejudices?

Another quick reading link which might be of interest is this from Science Daily: ‘Moonlighting’ Molecules Discovered; Researchers Uncover New Kink In Gene Control’, and from which this is a snippet:

“Everyone knows that transcription factors bind to DNA and everyone knows that they bind in a sequence-specific manner,” says Heng Zhu, Ph.D., an assistant professor in pharmacology and molecular sciences and a member of the High Throughput Biology Center. “But you only find what you look for, so we looked beyond and discovered proteins that essentially moonlight as transcription factors.”

The team suspects that many more proteins encoded by the human genome might also be moonlighting to control genes, which brings researchers to the paradox that less complex organisms, such as plants, appear to have more transcription factors than humans. “Maybe most of our genes are doing double, triple or quadruple the work,” says Zhu. “This may be a widespread phenomenon in humans and the key to how we can be so complex without significantly more genes than organisms like plants.”

Reading through the rest of the article, it seems there could be some very far-reaching implications, especially in the ongoing debate as to why despite our apparent genetic proximity to the chimpanzee for example, we are so radically different.

 

November 1, 2009

Robin McKie Of The Observer Reviews 3 Books On Human Evolution

Ciarán Brewster, a.k.a. adhominin, just tweeted about three book reviews. The reviews, written by Robin McKie of The Observer, cover recent books on cooking and human evolution which were written by some pretty big names in anthropology:

  • Catching Fire: How Cooking Made Us Human by Richard Wrangham
    Wrangham’s thesis is that the advent of cooking reduced our energy demands of actually chewing, we do have a smaller muscles of mastication, jaws and teeth. This shift diverted the energy we would be spending on the act of eating, along with eating more easily digestable nutrients, to developing massive brains. Something I didn’t know and learned in the reviews is that people who eat only on uncooked meat or veggies will slowly starve, sucks for those on the raw food diet.
  • The Well-Dressed Ape: A Natural History of Myself by Hannah Holmes
    Holmes addresses the fact that human females are the only primates with enlarged breasts and discusses theories on why. She says that the large breasts allow more feeding time for infants, which kept the babies more compliant and less likely to cry, which would otherwise attract predators. Our relatively hairless skin also evolved as a direct function of predator pressure, early human ancestors needed greater surface area to cool off our skin with sweat as they ran from predators in the savannah.
  • The Humans Who Went Extinct: Why Neanderthals died out and we survived by Clive Finlayson
    Finlayson discusses why and possibly how Neandertals were so easily replaced by modern humans. He argues that the harsh landscape of early Africa, about 100,000 years ago, when modern humans emerged forced them to learn new technologies and lifestyles that were, “more inventive and intelligent as they struggled for survival. European Neanderthals, untutored in the school of hard knocks, were no match for our ancestors when they met.”

These books seem to be entertaining, you should check them out if you haven’t already. Also, if you’re on Twitter and looking to follow some active anthropology minded folks, I’ve compiled what I believe to be a pretty comprehensive list of anthropology Twitterers. Check that out too, and follow it… If I’m missing anyone please let me know on Twitter or via this post’s comment thread.

October 30, 2009

A Cave Shut by Closed Minds? La Carihuela Neanderthals vs. the Junta

Carihuela y las ventanas

 

Back in August of this year, two words I frequently encountered when trying to visit sites of interest in Andalucía, southern Spain, were“Cerrado” (closed) and “No”, which as a tourist you take in your stride, leg it to the nearest hostelry and reconsider the rest of the day from the perspective of its slightly less interesting alternatives. As an eminent archaeologist working on what is potentially one of the more important sites in Spanish archaeology, with the prospect of confirming the latest known Neanderthals to have lived anywhere in the world, you might hope for more positive words from those tasked with permitting your work to go ahead unhindered. But as we see from the sorry tale unfolding below, this is not always the case, especially where the cave of La Carihuela is concerned.

Martin Cagliani at Mundo Neandertal points us towards this story, in which Spanish archaeologists are complaining that the local Junta (legislative assembly) of Andalucía will not allow the re-excavation of the Mousterian layers in the cave which it closed in 1996, (although work seems to have been conducted at least as late as 1998 by Carrión, linked PDF, Fig.2) where it is claimed there are Neanderthal remains dating to around 21,500 years bp, located within the cave of La Carihuela, about 45 km from Granada. If confirmed, this would make these Neanderthals far younger even than those whose artefactual traces have been found at Gorham’s Cave on Gibraltar dating to around 24,500 bp, at the same time perhaps taking the species’ existence right up to the Last Glacial Maximum.

The news article referred to is in Spanish, and is reported at Público.es, from which I’ll roughly translate some of the more pertinent points, while there’s also a freely accessible paper (PDF) on the subject of pollen sequences in the cave, as well as a description of its layout, the stratigraphic sequences within the galleries,  published in 2006, to which I’ll briefly refer throughout.

The report begins by describing how the cave might be the site of the very last Neanderthals tthat once walked this planet, because following the discovery of a male (Neanderthal) skull back in the 1950s, in the vicinity of Mousterian stone tools, it was realised shortly thereafter that according to pollen analyses, the layer from which the fossil had been retrieved might date to as late as 21,500 years bp.

Excavations began in earnest during the late 1970s, and by the early 1990s, a team of 30 researchers were working there, putting it on a par with Atapuerca, near Burgos in the north,  for the amount of effort invested in the site. But in 1996, following what is described as an arbitrary decision by local authorities, this work came to a sudden halt, and despite repeated requests from the archaeological community to reopen the cave, the Junta has remained obstinately silent on the case, allegedly not even picking up the phone to engage in the debate, according to D. Gerardo Vega Toscano. Profesor Titular, Dpto. de Prehistoria. UCM, Madrid.

He remarks that the scientists in this case are effectively at the mercy of the politicians, who basically don’t give two hoots whether the cave is the last refuge of the Neanderthals, or simply a hole in the ground.

One wonders from reading this whether the Junta is a fit and appropriate body to hold sway over such affairs, and moreover where the Spanish Ministry of Culture stands in this – surely it should be they who decide the scientific importance and appropriate funding levels required by such sites, and I find it hard to believe that no-one from the Ministry has seen fit to intervene.

Vega Toscano is for his part unconvinced of the very late date of 21,500 bp proposed for the remains, which he cites as absurd, opining instead that a date of 28,000 years bp is a more realistic proposition – it should be noted here that the estimate based on the pollen samples uses 28,440 bp and 21,430 bp as its parameters, with the real date presumably falling somewhere in between the two. The oldest known actual remains of Neanderthals are from Zafarraya, occupied between 31,000-27,000 bp, and the remains at La Carihuela should provide secure dates assuming that the specimens are in good enough condition.

Gorham’s Cave on Gibraltar is also known as a late Neanderthal refuge, with a most recent date of 24,500 bp ascribed there to Mousterian artefacts, while in Portugal at Lagar Velho, what appear to be the remains of a hybrid Neanderthal child are also put at 24,500 bp, so there seems no reason why a similar date shouldn’t apply at La Carihuela, and maybe 21,500 years bp, or a millennium or two beforehand, in the overall context isn’t completely out of the question. The fact that Mousterian technologies appear to have continued to be employed right up to the very end is interesting in itself, suggesting a lack of contact between archaic and anatomically modern populations – whether further investigations within Carihuela will reveal late-surviving Neanderthals were using bone or antler implements in addition to their own Mousterian tool-kits remains to be seen, but seems doubtful.

Contrary to the opinions of Vega Toscano, there is however support for the much later Neanderthal survival dates, as the article goes on to report the opinions of José Carrión, Professor of Botany at the University of Murcia, who remarks that 21,000 years bp marks the start of the Glacial Maximum, when temperatures plunged ever deeper for the following 3,000 years, a situation he believes could have tipped Neanderthals over the edge, coinciding with the extinction of fauna such as the mastodon and sabre-toothed tiger. (Although Neanderthals had previously survived through at least 2 previous ice ages, they had done so in the absence of competition from AMH, and as far as I’m aware, no major faunal extinctions had taken place in the earlier glaciations either, or at least not to the extent that Neanderthal prey animals disappeared from the menu).

Carrión further makes the point that apart from pollen dating, the bones from La Carihuela can be dated, and so might yet reveal themselves to be younger than the Gorham’s Cave presence – whether the fossil skull mentioned earlier has been dated isn’t stated here, and whether it continues to languish unexamined in a Granada museum, isn’t clear. Other researchers have dismissed the idea that climate alone could have accounted for the demise of the Neanderthals, preferring instead to cite a multitude of inter-related factors.

Keep reading →

October 29, 2009

Grandma Plays Favourites: X-Chromosome Relatedness and Sex-specific Childhood Mortality – Proceedings of the Royal Society B

As this paper is freely accessible for the next 7 days, I’m posting it here in the hope that as many readers as possible will have time to readgrandmother hypothesis primate diaries it through. Molly Fox et al turn their thoughts to the question of why women are able to live for many years after they able to conceive offspring, a phenomenon seemingly at odds with the idea that members of a species tend to die off once their reproductive days are over.

The ‘Grandmother Hypothesis’ is described and expanded upon thus in the linked paper:

With menopause occurring around age 50, women survive several decades longer than their gametes (Dorland et al. 1998; Hawkes 2003). Why should women have such conservative life histories that they save up enough energy for 25 years of reproductive retirement? Human females represent a particular conundrum in evolutionary studies: after menopause they are unable to reproduce and have no obvious way to increase their genetic contribution to future generations. As this is the basis for natural selection, many researchers have sought to explain how post-menopausal longevity is adaptive in women.

Among evolutionary biologists, the ‘grandmother hypothesis’ is the most widely recognized explanation for human female post-reproductive longevity. It suggests that vigorous, skilled, elderly women are able to contribute to their grandchildren’s survivorship through nutritional provisioning (Hawkes et al. 1998; Hawkes 2003). According to Hamilton’s relatedness coefficients (Hamilton 1966), grandmothers share a quarter of their DNA with grandchildren, and so a woman can increase her genetic contribution to subsequent generations by keeping her grandchildren alive and healthy. Supporters of this model often refer to the Hadza, a modern foraging society in Tanzania, where grandmothers are more effective than children at extracting tubers from the dry ground. While a mother is breastfeeding an infant, and thus unable to forage enough to provide for weaned children, the grandmother provides food for the older siblings (Hawkes 2003; Hawkes & Jones 2005).

The authors further suggest that this may be a behavioural and survival trait that can trace its roots back to the early Pleistocene, 1.7m-1.9m years bp (described in the paper as the Plio-Pleistocence boundary, recently re-dated to 2.6m years bp), when global cooling caused the expansion of African tuber-friendly grasslands, prompting ancient hominids to include a great many more tubers in their diet. From these origins, where grandmothers are suggested to have been important contributors of nutrition to two generations of descendants, researchers such as Soffer and Adovasio have taken the theory further, suggesting that grandmothers contributed a much greater role in child-rearing than simply providing nutritional foodstuffs.

The interesting aspect of this paper is how the authors suggest simply having a grandmother isn’t equally beneficial to grandchildren of either gender, with clear differences suggesting that in some instances having a maternal grandmother can be better for boys than a paternal grandmother, whilst a grand-daughter with a maternal grandmother appears to benefit most of all, as indicated here:

Tests of the grandmother hypothesis have been carried out on modern and historical populations. Most of the data correlate grandchild survivorship with grandmother survival and/or proximity, and it is often reported that only maternal grandmothers (MGMs) are found to have a positive effect on grandchild survivorship (Sear et al. 2002; Voland & Beise 2002). Studies that have not distinguished between MGMs and paternal grandmothers (PGMs) have found no correlation between grandmother’s presence and grandchild survivorship (Hill & Hurtado 1991; Lahdenperä et al. 2004). To date, only two previous studies known to the authors have distinguished between boys and girls when investigating the effect of both grandmothers.

A study of a Japanese population found that the presence of a PGM had a negative effect on boys and a positive effect on girls, while the presence of an MGM had a positive effect on children of both sexes, especially on boys (Jamison et al. 2002). They point to cultural features of the society as a possible mechanism for these findings. A study of an Ethiopian population reported the sex-specific information, but it was not analysed in the paper (Gibson & Mace 2005). More tests of the grandmother hypothesis are summarized in Sear & Mace (2007).

The authors continue by proposing the following:

The grandmother hypothesis is based on the fact that women are genetically related to their grandchildren, and we should not overlook the nature of that genetic relatedness. Grandsons and granddaughters differ in the proportion of their X-chromosomes shared with MGMs and PGMs (figure 1). According to our proposed X-linked grandmother hypothesis, if grandmothers invest in grandchildren because of their genetic relatedness with them, then their adaptive incentive to invest may vary in a way that mirrors this variation in genetic relatedness. As a consequence, grandmothers’ differential investment in grandchildren could cause differential survivorship of those grandchildren…

…Although the X-chromosome contains only about 4.4 per cent of our DNA, with its estimated 1529 genes, it contains perhaps approximately 8 per cent of all human genes (Pennisi 2003; NIH 2007; Parang et al. 2008; NCBI 2009a). The dramatic differences in X-relatedness between grandmothers and grandchildren confound the Hamiltonian concept that grandchildren are 25 per cent genetically related to each grandparent. If approximately 92 per cent of our genes are autosomes, then a grandmother shares one-quarter of that, or approximately 23 per cent of her total genes with a grandchild, plus X-relatedness.1

If a grandmother shares no X-chromosome with a grandchild, then their overall genetic relatedness is approximately 23 per cent, and if they share an entire X-chromosome, then it would be approximately 31 per cent. Therefore, MGMs and grandchildren are likely to share 25 per cent of their genomes, while PGM and granddaughter may share a total of approximately 31 per cent of their genes, with a likelihood of 27 per cent inheritance, while a PGM and grandson may share only approximately 23 per cent.

We can only wonder whether these conclusions were borne out in ancient communities and whether it was realised that there was closer bonding and greater survival amongst children with certain alloparental configurations, or whether child-care was undertaken on a more ad hoc basis, whereby other surrogate mothers who were still of reproductive age were also co-opted into rearing off-spring when the need arose. Moreover, infant mortality was probably high and seemingly arbitrary, especially where actions of predators, illness and infections were concerned, in which case the grandmother effect would have been diminished, except in those cases where an older person such as a grandmother would have had greater experience in recognising symptoms and knowing of potential remedies, something which presumably could also have applied also to grandfathers.

I’m not sure at what age humans living in the early and later stages of the Pleistocene would have become grandparents, but my guess would be quite young, possibly by age 30-35, though whether females would also have become unable to conceive by that age I don’t know; but it seems there could have been some overlap, during which time a grandmother could herself have still given birth to children, unless a menopausal clock kicked in soon after their own off-spring had given birth, which seems unlikely. If we still assume an age of 50 for menopause however, by the time she reached 50, a Pleistocene woman could easily find herself in the role of great-grandmother, though whether humans in significant numbers reached that ripe old age back then, again seems unlikely.

Keep reading →

October 28, 2009

Four Stone Hearth Volume #78 @ _Paddy K_

Today marks the half-way point between the most recent edition of Four Stone Hearth and the next, so here’s a quick recap on the 78th edition, as hosted by Paddy K – if by some chance you haven’t been able to read the various entries, please be sure to do so, as there is a very good range of posts covering stuff like the contested origins of Neanderthals in Europe, who as we learn in a presentation from TED probably had fair skins, and on to thick-skinned Creationists who appear not only to have entirely missed the gist of the Ardipithecus implications, but as far as I can tell, apparently show not the slightest interest in the other animals and plant-life, or the landscapes they inhabited 4.4 million years ago, let alone how the sites under investigation came into existence and were preserved in the first place.

One destination almost certainly not on the must-see wish-lists of said Creationists would likely be the seedier side of the British Museum’s less known rooms, where a goodly collection of controversial art and artefacts have accumulated over the years, including an intriguing 11,000 year-old carving in calcite of a couple locked in embrace, from the desert of Judaea, as I recall. Zahi Hawass is heard darkly muttering beneath the brim of his slightly odd hat, whilst elsewhere we see a vision of the future that was old hat before we even got there. There’s plenty more in this issue to make it worth setting aside about an hour to read the lot, so many thanks to Paddy K for continuing what has been a very good series of 4SH blog carnivals, despite the hazardous nature of his cycling activities around the streets of Stockholm.

The next edition, the 79th no less, will be held here at Anthropology.net on Wednesday November 4th – I think my email address for submissions should be somewhere onsite, or if in doubt, maybe get them to me via Martin R; details here at Four Stone Hearth.