Wednesday, November 30, 2011

Energetics and the evolution of human brain size

Navarette et al., 2011: Figure 2

Navarrette and colleagues refute the expensive tissue hypothesis in the current issue of Nature (subscription required). They report the results of a dissection based study of 100 mammalian species.  They did not find a negative correlation between brain size and gut mass, as would be predicted by the Expensive Tissue Hypothesis.  Instead, they DID find a negative correlation between brain size and the mass of adipose (fat) deposits. 

The authors interpret these results as supporting an alternative view of the energetics of encephalization.  They argue that increasing body fat is one strategy to protect against starvation. A different strategy involves developing a larger brain, which comes along with intelligence and the behavioral flexibility needed to secure a steady food supply.  However, fat tissue is metabolically cheap, so what explains the negative relationship between brain size and fat?  They argue that fat is expensive energetically because you have to literally carry it around!  Thus, there is an energetic cost in transporting your fat reserves wherever you go. 

The final major point is in explaining humans, which are both particularly fatty AND particularly brainy.  The authors argue that hominins are able to have the best of both worlds thanks to their unique (and energetically effecient) form of locomotion....striding bipedalism.  Bipedalism, in the end, allows us to efficiently transport our fatty selves from one patch of food to the next, and to think deep thoughts while doing so. 

Monday, November 14, 2011

Evolution of primate social behavior

Shultz et al report in a letter to Nature (requires subscription) on a phylogenetic analysis of the evolution of social stability in primates.  This is a pretty complicated phylogenetic analysis involving Bayesian estimates of evolutionary events based on the distribution of social characteristics across the phylogenetic tree.

Their main findings are consistent with a picture of primate social evolution proceeding directly from solitary individuals to large multi-male/multi-female groups sometime around 50 million years ago (mya).  Other types of social groups such as pair living and single-male/multi-female groups appear to have come about significantly later, around 16 mya. This "reversible--jump model" seems pretty non-intuitive, but is the best model for their data set. It will be interesting to see how this is received by primatologists.

Their results also support a "step-wise" acquisition of stable social groupings which starts out with loose aggregations of individuals banding together for predation defense in association with becoming diurnal. More stable social associations are a secondary occurrence that only come about later in time.

Thursday, November 10, 2011

Ancient DNA casts light on cave art

Pruvost et al., 2011: Fig 2
The prehistoric cave paintings in France were recently made even more famous in Werner Herzog's film "Cave of Forgotten Dreams".  There has been academic debate surrounding these cave paintings, which mostly depict animals.  Some have argued that the paintings have religious or symbolic meaning and are only loosely related to past biodiversity.  Others have maintained that the paintings might be a more literal documentation of the types of animals present in the environment.  However, some of the paintings depict animals, such as leopard spotted horses, that may or may not have existed in pre-domestic, wild populations. 

Enter ancient DNA studies. In a report in PNAS, Pruvost and colleagues describe the results of DNA analysis of 31 wild, pre-domestic horses from Europe.  Their findings indicate that the full range of horse coloration depicted in French cave art were present in pre-domestic horses, based on the distribution of genes linked to coat color expression.  This study suggests that prehistoric cave painters weren't making up animals...these coat coloration actually existed in horses in the wild. 

Tuesday, November 8, 2011

Climate change and endemic species

Sandel et al report in Science on a strong link between the rate of late Quaternary climate change and the geographic distribution of endemic species.

Sandel et al, Figure 1.

Thursday, November 3, 2011

New study of lumbar spinal curvature in hominins

Been et al. Figure , illustrating calculation of lordotic angle

In a new study just up on AJPA early view, Been and colleagues report on a study of lumbar spinal curvature (lumbar lordosis) in fossil hominins. Previous studies had relied on the degree of wedging of lumbar vertebrae to estimate the degree of lumbar curvature.  The new study introduces a method "based on the relationship between the lordotic curvature and the orientation of the inferior articular processes relative to vertebral bodies in the lumbar spines of living primates" (Been et al., AJPA).

The study finds that australopiths had a nearly modern-human like degree of lordosis, supporting the notion of lumbar lordosis as a morphological adaptation to habitual bipedalism.  The study also tentatively suggests locomotor differences between Neanderthals and modern humans based on degree of lumbar curvature.

Monday, October 17, 2011

Robust australopith facial structure

SK 48 - P. robustus
A longstanding question in paleoanthropology concerns whether or not the robust australopithecines are a monophyletic group (a group sharing a common ancestor to the exclusion of all other critters). These hominins have massive jaws and facial structures associated with extremely powerful chewing muscles. Two species of robust australopith have been found in east Africa, and one from southern Africa. Some have argued that the robust australopiths from east and southern Africa are closely related and belong to a single genus, Paranthropus. Others have pointed out that the similarities between the eastern and southern forms largely have to do with heavy chewing, and that the observed similarities might easily have evolved in parallel in two hominins with similar diets. This scenario would imply that the robusts in east and southern Africa were instead most closely related to the non-robust (gracile) hominins living in their respective regions. 

In a recent article in PNAS, Villmoare and Kimbel take a fresh look at this debate by analyzing CT scans of several species of gracile and robust australopithecines. They focused on a feature called the anterior pillar, a ridge of bone running vertically down the side of the nose.  This feature has been argued to be a shared derived trait linking the South African hominins P. robustus (robust) and A. africanus (gracile). The anterior pillars of P. robustus and A. africanus turn out to be quite different when viewed internally. Furthermore, the internal structure of P. robustus is very similar to the structure of P. boisei, an east African robust, even though P. boisei usually lacks the visible external anterior pillar. The authors interpret these findings as additional evidence that the eastern and southern robusts are a natural group, and that the superficial resemblances between P. robustus and A. africanus are the result of parallel evolution.

Thursday, September 22, 2011

The hand of Australopithecus sediba

Kivell et al, 2011 Fig 1 (Left view = palmar, Right view = dorsal)
Kivell and colleagues report on the nearly complete hand of Malapa Hominin 2 (MH2), which has been attributed to Australopithecus sediba, a possible ancestor to genus Homo from the site of Malapa in South Africa. By nearly complete, I mean it is only missing a couple of wrist bones and the distal phalanges of the four non-thumb fingers. And everything that is preserved is in amazingly good condition. 

The biggest question about the A. sediba hand fossils is: did this species make tools?  The authors' answer is yes: A. sediba had hand morphology which would allow it to make tools. How they arrive at this conclusion is interesting. One of the major hand fossils that they compare with this hand is the OH7 Homo habilis hand from Olduvai Gorge. H. habilis (handy man) has been considered a tool-maker  since these fossils were discovered over fifty years ago in direct association with Oldowan stone tools. Kivell et al. compare the morphology of the MH2 hand with OH7 and find that MH2 has some derived features such as "reorientation of the scaphoid and capitate intercarpal articulations" (Kivell et al. 2011, pg 1416) which are lacking in OH7. Thus, they argue, these features indicate that the MH2 hand is more derived than the OH7 hand, and might be a "better potential morphotype for the basal Homo hand morphology" than OH7 (Kivell et al. 2011, pg 1416). They make this argument even though A. sediba is neither assigned to Homo nor found in association with tools. One possibility that they raise is that OH7 is not H. habilis at all, but rather belongs to P. boisei.  Could be, but what is for certain is that the MH2 hand skeleton is going to be a very interesting part of the debate surrounding manual functional morphology, locomotion, and tool use in the future. 

Tuesday, September 20, 2011

Extinct lemurs and human evolution

Paranthropus boisei (left) and Hadropithecus (right) (Dumont et al., 2011:Fig1)

In a brief letter to PNAS entitled "Thinking outside the box: A lemur's take on hominin craniodental evolution" Lorrie Godfrey and colleagues respond to a recent article by Cerling and colleagues (discussed here). The Cerling article argued, based on stable isotope data, that the robust east African australopith Paranthropus boisei was likely a grazer.  The main point of the letter is the figure, which shows carbon isotope values for tooth enamel for a variety of hominins, Old World monkeys, and subfossil lemursP. boisei clearly has really high carbon isotope ratios.  The only other primates that can compete are Theropithecus (the grass-eating gelada baboon), and Hadropithecus, a recently extinct lemur that Dumont, Ryan and Godfrey argued just five months ago was unlikely to be a hard object feeder based on skull morphology and finite element modeling.  When you look at the skulls of these guys next to one another, the similarities are really striking! This comes full circle, back to Clifford Jolly's Theropithecus model for hominin diet from 1970, which suggested that australopiths might have had a diet based largely on grass leaves and seeds, instead of the prevailing "nutcracker" ideas. As summed up by Godfrey et al.
"there are important ways in which the diets of Paranthropus and Hadropithecus likely converged. Both probably consumed large quantities of “low-quality” foods (i.e., foods that were relatively high in structural carbohydrates and poor in nutrients and required heavy repetitive trituration). Such conclusions may have important implications for the evolution of the craniodental features that these species share."
UPDATE: 9/22/2012
I failed to notice the Cerling et al. reply to the Godgrey et al. letter to PNAS. They note that Hadropithecus could attain the observed 13C ratios by consuming CAM plants (cacti and suchlike which are common in Madagascar) instead of the C4 plants (grasses, sedges, etc) suggested for P. boisei. Thus, the isotopic and morphological similarities need not suggest any mechanical similarity in the diets of the species.  It seems like it would be useful to compare Hadropithcus with isotope values of lemurs in today's Malagasy spiny forests. Thanks for Chris Kirk for pointing out the omission.
Godfrey et al.'s isotope figure

Monday, September 19, 2011

The foot of Australopithecus sediba

A. sediba is a recently described species of gracile australopithecine from the site of Malapa in South Africa which dates to approximately 2Ma. A recent issue of Science contains several articles which describe in detail the anatomy of several very complete specimens. These fossils are important because they are so complete, and because their discoverers have suggested that the new species may be directly ancestral to our own genus Homo.

The paper by Zipfel et al describes the foot and ankle bones, including an articulated distal tibia, talus and calcaneus preserved encased in matrix in approximately anatomical position. Other foot specimens include a very complete distal tibia as well some metatarsals. The details of the ankle joint are pretty human-like except for a very robust medial malleolus. The real kicker is the calcaneus, which is quite gracile and lacks a weight bearing lateral plantar process (LPP). These features make the calcaneus look rather like a chimpanzee's. Coupled with the robust medial malleolus, this could mean that A. sediba retained a degree of arboreal climbing competence. I feel sure that the functional implications of this morphology will be heartily debated. 

What is especially interesting is that A. afarensis resembles modern humans in these details of the calcaneus and distal tibia. A. afarensis (the species Lucy belongs to) is the gracile australopithecine cousin of A. sediba which lived over a million years earlier and is widely considered the direct ancestor of genus Homo. Regardless of whether or not A. sediba is directly ancestral to Homo or not, this mosaic ankle morphology is interesting and suggests some level of independent evolution of modern human-like pedal morphology.

Tuesday, September 13, 2011

Testing the Guns, Germs, and Steel Hypothesis

Major geographical axes of continents from Diamond's book.

One of the big ideas in Jared Diamond's popular book Guns, Germs, and Steel: the Fates of Human Societies is the notion that the primary geographical orientation of continental landmasses (either north-south or east-west) has had a major impact on the historical pace of technological diffusion. Diamond argues that technological innovations (e.g. domestication of livestock and plants) can diffuse faster to areas which similar similar ecological conditions with the source area of the innovation. If you domesticate a strain of wheat in Chicago that produces a lot of reliable food....I might want to try to grow it my back yard too.  I would will probably have better luck if I live in New York than if I live in Austin, TX, because ecological changes happen quickly as you go south across degrees of latitude. Simple accidents of geography then, Diamond suggests, have had a big influence on the pace of technological progress and ultimately wealth accumulation on different continents. 

Ramachandran and Rosenberg set out to test this idea in an article in early view on AJPA using genetic data from modern peoples. They examined microsatellite loci from several indigenous populations in the Americas and in Eurasia. If (and this is pretty huge if) technological changes have largely occurred by the migration of populations from one place to another, then there ought to be differences in the primary axes of modern genetic variation in Eurasia versus the Americas.  In other words, changing ecological conditions across degrees of latitude should have prevented migration (and associated technological diffusion), resulting in greater genetic differentiation along the north-south axis in the Americas compared to the east-west axis in Eurasia. This pattern is exactly what the authors report, which they interpret as support for Diamond's continental axis orientation hypothesis.

Anthropological Sidebar: It is interesting (at least to me) to note that these ideas in Guns, Germs, and Steel have been somewhat controversial in anthropology. Most would agree that Diamond's argument could be described as one of geographical and ecological determinism. His supporters argue that this makes GG&S the ultimate anti-racism book, taking the wind out of the sails of any racists wanting to argue that technological progress is associated with peoples innate intellectual abilities. Others would argue that ecological determinism is a cop-out which doesn't consider the role of racism and colonialism in creating the social conditions which GG&S purports to explain.

Monday, September 12, 2011

Australopithecus sediba on the cover of Science

The most recent issue of Science has a series of articles on a couple of new skeletons of Australopithecus sediba.  This is a recently described species from the South African site of Malapa at about 2Ma, discovered by a team let by Lee Berger. The authors have argued that A. sediba may be a link between gracile australopithecines and our own genus Homo. I haven't gotten a chance to wade into the several articles in any depth, but for now here is a link to the summary article by Ann Gibbons on the Science website. There will be more posts on A. sediba as I get a chance to read these papers.

Thursday, September 8, 2011

Gebo on Vertical Clinging and Leaping

A tarsier: your distant cousin and fellow Haplorhine.

In an article on early view in AJPA Dan Gebo takes up the issue of vertical clinging and leaping (VCL) as it relates to the ancestral pattern of primate locomotion.  The term VCL refers to a uniquely primate way of getting around by clinging to vertical supports and then using hindlimbs to propel the body from one support to another. 

A classic paper by Napier and Walker (1967) argued that galagos, tarsiers, and some lemurs share the behavioral traits described above, in addition to related anatomical similarities. For example, these primates have short arms that aren't very useful on the ground as well as other more detailed resemblances. These similarities, they argued, suggested that the ancestral primate must have moved around by means of VCL. Lots of people didn't buy this (reviewed in Anemone, 1990). Folks argued that Napier and Walker gave short shrift to the considerable variation in supposed VCLers.  Gebo's main thrust in this new paper is the decoupling of vertical clinging on the one hand, and leaping on the other hand (puns are unintended). He argues that the ancestor of haplorhines and strepsirrhines was at least an occasional leaper, possibly cheirogaleid-like, a characterization that many others have made.  Subsequently, Gebo argues, various groups of primates evolved further adaptations for leaping and specializations for vertical support use at different times, and probably for different ecological reasons.

Thursday, September 1, 2011

New microCT method for dental dietary reconstructions

van Dam and colleagues report in P3 on new methods to determine the diet of fossil mammals, using microCT scans of fossil micromammal teeth.  The new method involves using 3D X-ray scans to calculate enamel volumes rather than traditional methods which simply measure maximum crown height.

Measurements of the overall maximum height of a tooth, called hypsodonty (literally "high tooth") indices, are probably the most common measurement used to determine the diet of extinct critters of all shapes and sizes. Mammals with abrasive diets consisting mainly of grasses tend to have higher teeth than animals which subsist on less abrasive diets, such as tree leaves. The general idea is that higher crowned teeth have a longer functional lifespan than lower-crowned teeth. Even as the chewing surface of the hypsodont tooth wears away, there is always more enamel being uncovered.  Low-crowned (bunodont) teeth become functionally obsolescent more quickly when worn heavily, because they don't have lots of extra enamel in reserve under the surface. 

Pros of new hypsodonty method: appears to work well across a broad range of tooth types, while height measurements are less homologous across dramatically different tooth shapes.

Cons of new hypsodonty method: it takes forever to get a single hypsodonty value for a single tooth, compared to the blindingly fast old fashioned way involving a couple of caliper measurements.

Thursday, August 25, 2011

More thoughts on Paleo Hanky Panky

In an article in the American Journal of Physical Anthropology, Ghirotto and Colleagues report the results of a study of mitochondrial DNA from both early modern human fossils, Neanderthals, and living Europeans. These authors argue that their study supports a model with no Neanderthal contribution to modern human mitochondrial DNA.  This clearly contradicts the results of nuclear DNA studies, which provide strong evidence for interbreeding between Neanderthals and moderns.  What gives? Either Neanderthals and moderns got it on or they didn' one of these studies must be wrong, right?  In the future I hope to have a guest post by a geneticist about why looking at different genes can give you different answers to the same question  In the meantime, I offer my thoughts on models of modern human origins. 

First, let's not frame this as a discussion between a full replacement model versus a multiregional model.  The thing about models is that, in the word of George E.P. Box....all models are wrong. That is something that even scientists tend to forget! The  whole point of such models is to frame the logical extreme positions.  I think the image below, from a 2004 article by Osborn Pearson in Evolutionary Anthropology, illustrates this nicely. Thanks to Brett Nachman for pointing out this article.

Figure 2 from Pearon, 2004, Evolutionary Anthropology 13:145-159

The two "competing" models are on the extreme ends, and the evidence tends to be somewhere between the two. However, in this case "between the two" is shifted heavily towards the right side of the figure. The only change I made to this figure is that I drew my own box (in red) to illustrate what the current DNA evidence seems to indicate.  I would say the interbreeding was much less than 25% as Pearson's reading of the evidence allowed in 2004.  Equally important, however, is that my red box excludes 0%, because we now know with near-certainty that Neanderthal genes did make it into modern human populations.  In other words, we now have proof that a Strict Out of Africa model is wrong.  Of course, this does bring to mind the rest of the George E.P. Box quote above. 

All models are wrong. 
The practical question is: how wrong do they have to be to not be useful?

Friday, August 19, 2011

Should the species Homo sapiens be renamed?

In a letter to Nature, Julian Cribb argues that our species, Homo sapiens should be renamed.  Does the term "wise man", he asks, accurately describe a species which is
"exterminating thousands of others; releasing carbon, nitrogen and phosphorus in amounts exceeding Earth's natural cycles; devoting 50 times more resources to making weapons than to sustaining the food supply; destroying forests; degrading soil; polluting water; pillaging the oceans; and damaging the atmosphere on a planetary scale"?
Maybe not.  However, this talk of renaming the species to more accurately describe the species is just silly. This isn't 'Nam....this is taxonomy....there are rules governing the naming of species. By the very same logic we should rename the Tibetan blackbird (Turdus maximus) simply because its turds are nowhere near as large as some other vertebrate species.

Thanks to Gabrielle Russo for pointing this letter out to me. 

Friday, August 12, 2011

No Support for Expensive Tissue Hypothesis in Platyrrhines

Kari Allen and Rich Kay report in the Proceedings of the Royal Society B on a study of the relationship between dietary quality and relative brain size in platyrrhine primates (New World monkeys).  This study is relevant to human evolution because of a big idea in paleoanthropology known as the expensive tissue hypothesis (ETH, Aiello & Wheeler, 1995). The ETH predicts that dietary quality and relative brain size should be correlated.  As the picture at the top of this post shows, the idea is that low quality diets (e.g. leaves) are a constraint on primates, which have to devote lots of energy to make big guts capable of digesting these difficult foods. With so much energy invested in making a big gut, there isn't enough energy left over to make lots of another metabolically expensive tissue...brains.  The story as relates to humans is that humans had this constraint lifted at some point in their evolution, perhaps related to an increase in easy-to digest meat acquired with the help of tools.  Humans then devoted their excess energy -- no longer needed to make a big gut -- to make a big brain. 

However, Allen and Kay find no relationship between a measure of dietary quality and relative brain size in New World monkeys.  In particular Brachyteles has a very low dietary quality and a relatively large brain, going against predictions. This doesn't necessarily mean that the ETH isn't valid for humans, but it is certainly worth thinking about why the underlying relationship doesn't appear to hold for platyrrhines. 

Thursday, August 11, 2011

Participant Observation Meets Primatology: Why do chimps build sleeping nests in trees?

Fiona Stewart was interested in knowing why great apes sleep in nests at night.  There are a couple of hypotheses which have been floated regarding nest function: sleep quality, anti-predation, anti-parasite, and thermoregulation.  To test these hypotheses, Stewart went out in Fongoli, Senegal and actually slept in nests that chimps had used the night before, in self-constructed replicas, and on the ground.  She recorded data on sleep quality, the number of bug bites per hour of sleep, and recorded mean temperature at ground height and at nest height during the night. Results are published in a brief communication in AJPA

The results are very preliminary, but her sleep was less disturbed in nests, she suffered fewer insect bites, and the nests appeared to provide some insulation from the cold.  Perhaps the most telling result was in terms of sleep quality:
"All experimental nights’ sleep in this study were uncomfortable and characterized by low sleep quality (<0.50), compared with mean sleep quality recorded for captive chimpanzees (0.86) and human societies (Videan, 2006). "

Wednesday, August 10, 2011

Latest installment in the "hobbit" saga

LB1 (left) next to a modern human skull
Vannucci and colleagues just published the results of a study comparing a couple of brain measurements between microcephalic modern humans, normal modern humans, Homo erectusAustralopithecus and LB1 (the most complete specimen of the recently named species Homo floresiensis).   They argue that their results support the idea that LB1 is a microcephalic modern human, not a distinct species.  I am no brain expert, but I don't really think this study puts forward a slam-dunk argument.  For example, in the measurement that they focus on (cerebellar protrusion), LB1 doesn't seem to me to fit in very well with either microcephalic or normocephalic modern humans.  It is also interesting that they publish a cluster analysis based on their data which shows LB1 clustering more closely with Australopithecus than with microcephalic moderns.
Vannucci et al. 2011, PNAS.  Figures 6 (left) and 5A (right)
LB1 was shocking when first announced....a tiny hominin with an even tinier brain living on the Indonesian Island of Flores as recently as 18,000 years ago.  If this represents a species distinct from H. erectus and H. sapiens (as I would say a majority of the experts currently believe) then it is extremely interesting.  Prior to the discovery of LB1 in 2003, our understanding was that at 18,000 years ago, H. erectus should have been long since extinct, and the only living hominin species should have been modern humans.  The debate over LB1 has been between two camps: one arguing that the Flores hominins are a pathological population of modern humans (with microcephaly) and the other camp arguing that LB1 represents a non-pathological, distinct species of human ancestor that was previously unknown to science.

Bill Jungers clearly isn't buying it the conclusions of this most recent paper.  Jungers has been an outspoken proponent of the view that LB1 is non-pathological.  He makes his opinion crystal clear near the end the of this news piece in Nature.
"[Vanucci et al.] note a fascinating similarity in the cranial measurements found in Homo floresiensis and Australopithecus but ignored it in favour of making the microcephaly argument," he says. "A weird decision, but hobbit politics as usual. 

Tuesday, August 9, 2011

Hyaena turds hold many secrets

Some of the coprolites found at the site.
This post is about fossilized poop (called coprolites). Pesquero and colleagues report on an exceptionally rich assemblage of hyaena coprolites (nearly 1000 specimens) from the site of La Roma 2 in Spain. Based on their size and morphology the authors attribute the assemblage to the Late Miocene hyaenid species Lycyaena chaeretisCoprolites often preserve fossil pollen, which make them useful for paleoenvironmental reconstruction. 

A spotted hyaena eating a flamingo.

Sunday, August 7, 2011

The Savanna: Reloaded

Cerling et al report in Nature on the results of a survey of modern soil carbon isotope profiles from East Africa. They compare the modern results to a very large sample of fossil soil (paleosol) samples from the Awash valley and the Omo Turkana basins.  These two valleys in Ethiopia collectively sample approximately the last 6.5 million years of human evolution.  Their results indicate that open environments (not forests) have dominated these two valleys over much of the course of the last 6.5 million years.  This study is also part of the ongoing debate over the paleoenvironment of Aramis, the site from which Ardipithicus ramidus is best known.   Tim White and the Ardi crew argue that the Aramis site was heavily wooded and, further, that Ardi puts the coffin nail in the savanna hypothesis. Cerling et al. replied, arguing that the Aramis isotope evidence indicated more open environs than White and colleagues claimed.  This most recent paper provides evidence consistent with the interpretation that the Aramis site was pretty open, even more open than later A. afarensis sites. 

Wednesday, July 27, 2011

Speculations About Fire, Liquid Hot Magma, and Human Evolution

DISCLAIMER: this post is just for fun and does not report on mainstream paleoanthropological research. The title of the paper in the Journal of Fire Ecology is actually "Speculations About the Effects of Fire and Lava Flows on Human Evolution".  The author comes right out and says that
this paper is not a scientific presentation of hypotheses that have been extensively tested in the field. Rather, it is a playful exercise in speculation and even 'just so stories' about human evolution and fire.
And the author Michael Medler certainly does speculate.  He starts by making the observation that hominins  (east African ones at least) evolved in a region characterized by very active volcanism (indisputable). Perhaps then, he goes on, fire has shaped human adaptations over millions of years.  This is not totally outside the realm of what some actual anthropologists have said (e.g Wrangham, 2009)....more or less that fire for cooking food and warmth was really important late in human evolution as hominins spread out of the tropics.

Tuesday, July 26, 2011

Homo erectus (or georgicus) in the Caucasus at 1.85 Ma-icus

Ferring et. al 2011. PNAS 108:10432-10436. Figure 3
Ferring et al. describe the result of an archaeological test trench at Dmanisi in this PNAS article. They found a pretty standard Mode I lithic assemblage (full disclosure: I am not at all a lithics person). What is remarkable is the fact that the site appears to have been occupied as early as 1.85Ma.  This pushes back the dates for occupation of Eurasia by an erectus-like hominin far enough to rival (and even be a teensy bit older) than the earliest dates for H. erectus/ergaster in Africa. Very cool! The authors go as far as to suggest that H. erectus originated in Eurasia instead of Africa.  Could be, but in my opinion we will need lots more even earlier fossils from Eurasia to support that hypothesis.

Monday, July 25, 2011

Paranthropus boisei: Cow-Man of the Pleistocene?

The elusive cow-man
Lots of anthropological research focuses on figuring out what our ancestors ate. One long-standing question concerns the diet of robust australopithicines, a group of three species of early hominin that most researchers place together in the genus Paranthropus. These three species share a suite of adaptations of the teeth, jaws and cranium which all relate to extremely powerful chewing. The consensus among researchers has been that Paranthropus species ate a diet of hard objects (e.g. nuts or hard fruits), or perhaps a difficult-to-process diet of tubers and other undergrouund plant storage organs.  

A new carbon isotope study reported in this article in PNAS by Cerling and colleagues argues that P. boisei subsisted on C4 vegetation like grass and sedges, not on hard objects (hence the cow photo). This is consistent a previous study of dental microwear by Ungar et al. of which found no evidence for hard object feeding in P. boisei.  This result is surprising, as several dental microwear studies of the southern African robust hominin P. robustus are consistent with hard object feeding in this species, and carbon isotopes for robustus show much more C3 plant use (C3 vegetation comes from bushes and trees, including fruit). Thus, it appears that there may have been considerable dietary diversity within this genus, with P. boisei having diverged from a more "traditional" primate diet to focus on grazing. 

Sunday, July 24, 2011

Neanderthal/Human Hanky Panky

The Neanderthal in the mirror
A recent paper published in Molecular Biology and Evolution shows the presence of an x-linked haplotype in about 9% of all non-African populations. This would appear to be very strong evidence for significant interbreeding between Neanderthals and non-African populations. 

It is interesting how this plays out in discussions of human origins by non-specialists.  This blog post discusses what the author views as potentially racist interpretations of a related article.  Apparently some people are saying that because non-Africans had access to this additional (Neanderthal) gene pool it might have somehow made them more "evolutionarily advanced".  This is ridiculous. Remember, there weren't any Neanderthals (as far as we know) in Africa, hence it would have been pretty hard for African populations to mate with them, unless we are counting sexting. Clearly any claim that mating with Neanderthals makes you smarter/better/more evolved is just a post-hoc "what-if" claim that has no basis in the actual research.

The origin of malaria

Plasmodium infected red blood cell
If you have taken an introductory Anthropology course you have probably heard about malaria. It is a devastating killer disease in the tropics caused by an infection of the Plasmodium falciparum parasite which infects human blood cells.  We talk about it in intro anthro courses because of the relationship between malaria and another devastating disease, sickle cell anemia.  Sickle cell anemia is a genetic disorder caused by having two copies of the recessive gene which causes it. However, individuals which are merely carriers for the disease (having only one copy of the bad gene) don't get the anemia, and actually have increased resistance to malaria.  Its a classic case of a balanced polymorphism, and it explains why sickle cell anemia is prevalent in parts of the world where malaria is endemic.

In this article in PNAS, Prugnolle et al. discuss the possible origins of malaria, based a survey of the diversity of malarial parasites in several different monkey species in Central Africa.  They detected P. falciparum (the human killer) for the first time in monkeys.  This strain appears to be specific to non-human primates.  This opens up the possibility for a monkey source for human malaria, instead of the gorilla source which had been suggested by other workers.  This study is part of a fascinating recent revolution in primatology, involving the study of parasites from a genetic perspective.  I will take up that topic in a future post. 

Friday, July 22, 2011

What a big nose you have Mr. Neanderthal....but why?

Todd Rae and colleagues argue that the Neanderthal face was not adapted for extreme cold in this article in the Journal of Human Evolution.

The paper tackles two major assumptions about the paranasal sinuses: (1) big paranasal sinuses are good for surviving really cold weather and (2) that Neanderthals had really big paranasal sinuses. 

The authors conducted a study of 2D and 3D X-rays on a sample of humans, other primates, and rodents.  They showed that arctic critters actually exhibit smaller paranasal sinuses, not larger ones.  Furthermore, when you correct for the size of the cranium, the sinuses of Neanderthals weren't any bigger than those of humans living in temperate latitudes. 

Thursday, July 21, 2011

The Evolution of Grandparents

 Rachel Caspari discusses the evolution of grandparents in this interesting Scientific American article. 

Using dental techniques for estimating age based on the degree of tooth wear and dental eruption sequences, Caspari and colleagues calculated a simple ratio of old individuals (>30 years) to young individuals (<30 years). They discovered that the number of old individuals increased slowly from australopithicines onward, but the number skyrocketed upward in modern humans of the Upper Paleolithic. Caspari argues that increased numbers of oldsters, possibly as a result of some cultural shift, started a positive feedback loop which led to increasing cultural complexity in modern humans during the Upper Paleolithic.  In other words, learning the complex behaviors characteristic of modern humans becomes possible when you have your wise old granny and grandpa to teach you. 

Thanks to Mimi Myrtille for bringing this article to my attention in a Facebook Post. 

Wednesday, July 20, 2011

Where did modern humans come from?

Most everyone agrees the general answer to that question is "Africa" but recently there has been some debate as to where in Africa the earliest modern humans (H. sapiens) came from. In a previous post I discussed an argument that the source population might have been of North African origin.  The paper arguing for a North African origin was actually a response to this paper by Henn and colleages, who conducted a genetic analysis of living hunter gatherers.  Their results indicate that Southern African hunter gatherer populations have greater genetic diversity than hunter-gatherers in other parts of Africa, thus these populations are inferred to be older. I am slightly uncomfortable with this conclusion, because I don't understand how the authors can rule out the existence of more ancient modern human populations in other parts of Africa which have not survived to the present day.  But, on second thought, wouldn't that same argument apply to any argument based on modern human genetic diversity?

Both the North African and Southern African arguments are in conflict with the most commonly accepted notion that modern humans evolved in East Africa.  An East African origin is supported by the fact that Ethiopia is home to the oldest fossil evidence of modern humans from Omo Kibish (McDougall et al., 2005, news story), as well as the slightly younger fossils from Herto in the Middle Awash.

Tuesday, July 19, 2011

Did Neanderthals Bury Their Dead?

Image © Emmanuel Roudier, 2008
Sandgathe et al. take up this question in an article in early view in the Journal of Human Evolution entitled "The Roc de Marsal Neandertal child: A reassessment of its status as a deliberate burial".  The child from Roc de Marsal has been considered by many to be a deliberate burial. Sangathe and colleagues question the child's status as a burial on several grounds: the position of the body (on its stomach with partially flexed legs), the lack of distinctive burial objects (grave goods), among others.  They even argue that the hole the child was buried in was a natural depression, not a (cave)man-made grave pit.  I find their arguments fairly convincing....which makes me think critically about how quickly we are willing to attribute modern-human like behaviors to ancient human ancestors.

Monday, July 18, 2011

"Boxing" Hypothesis for the Origins of Bipedalism

Add this to the list of published ideas about the selective advantages of bipedalism.

In a PLOS One article Carrier reports that human subjects deliver more powerful punches from a bipedal (orthograde) posture than from a quadrupedal (pronograde) posture.  This might suggest that forelimb fighting among males competing for females is a selective pressure for bipedalism.

Maybe we can call it the Rocky Hypothesis?

Sunday, July 17, 2011

Geographic variation in Neanderthal diets

Zaatari et al. report (in an early view article in the Journal of Human Evolution) on the diets of a large sample of Neanderthals from across their geographic range, inferred using molar microwear texture analysis.  Results support previous studies indicating Neanderthals ate lots of meat...but the analysis revealed significant variability in the amount of plant foods incorporated in the diet.  I find this interesting for several reasons, including the current "Paleo Diet" craze I have been hearing about lately.  Even Neanderthals, a temporally and geographically restricted group, had significant variability in their diet....imagine the amount of variability in the much more ecologically diverse groups of modern human foragers the paleo-diet folks are trying to mimic. Which paleodiets should I try to follow?  The highly carnivorous ones? or the mostly vegetarian ones?

Saturday, July 16, 2011

Modern Human source population in North Africa?

This article in early view on the PNAS website by J-J Hublin and Richard Klein argues that North African human cultures making Aterian Middle Stone Age tool industry might have been the source population for modern humans.

This area is near-and-dear to me because I was on a dig there in the summer of 2009, the year the team discovered a modern human skull.  This skull, nicknamed Bouchra, was recently featured in a special on the National Geographic Channel.