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Category Archives: Anthropometry

Eye color, face shape and perception of trustworthiness

An old popular Galician song said:

Ollos verdes son traidores…
azules son mentireiros,
os negros e acastañados son firmes e verdadeiros.

Translated:

Green eyes are treacherous…
blue ones are deceitful,
the black and brown ones are loyal and truthful.

Just word of a silly mariner song? Intriguingly science confirms now, in a way, part of this perception (at least for blue and brown eyes).
But notice please that it is the precisely the perception what is being confirmed: people seem to perceive blue eyes in general as somewhat less trustworthy. The study says nothing about people with blue eyes being untrustworthy in fact, just that we tend to distrust them more than people with brown eyes.

Karel Kleisner et al., Trustworthy-Looking Face Meets Brown Eyes. PLoS ONE 2013. Open access → LINK [doi:10.1371/journal.pone.0053285]

Abstract

We tested whether eye color influences perception of trustworthiness.
Facial photographs of 40 female and 40 male students were rated for
perceived trustworthiness. Eye color had a significant effect, the
brown-eyed faces being perceived as more trustworthy than the blue-eyed
ones. Geometric morphometrics, however, revealed significant
correlations between eye color and face shape. Thus, face shape likewise
had a significant effect on perceived trustworthiness but only for male
faces, the effect for female faces not being significant. To determine
whether perception of trustworthiness was being influenced primarily by
eye color or by face shape, we recolored the eyes on the same male
facial photos and repeated the test procedure. Eye color now had no
effect on perceived trustworthiness. We concluded that although the
brown-eyed faces were perceived as more trustworthy than the blue-eyed
ones, it was not brown eye color per se that caused the stronger perception of trustworthiness but rather the facial features associated with brown eyes.

So the authors conclude that it is not eye color but associated face shape what drives untrustworthiness because the phenotype associated with blue eyes is more angular, less rounded, at least for males:

Figure 2. Shape changes associated with eye color and perceived trustworthiness.
Thin-plate
spline visualizations of the way face shape correlates with eye color
(a–f) and trustworthiness (g–i). Generated face shapes of blue-eyed
woman (a) and brown-eyed woman (c) compared to average female face (b).
Generated face shapes of blue-eyed man (d) and brown-eyed man (f)
compared to average male face (e). Generated face shapes of
untrustworthy-looking man (g) and trustworthy-looking (i) man compared
to average male face (h). The TPS grids of perceived trustworthiness for
women are not shown because shape analysis did not meet statistical
significance. The generated facial images (a–f) were magnified 3x for
better readability.

They claim that they found no correlation with facial shape for women but I find in the image above almost exactly the same pattern for men and women and not only what they detected: notably the blue eyed people (both genders) and the less trusted men all have in my opinion:
  • Smaller eyes
  • More serious (defiant, analytic, unsympathetic) expression
  • Proportionally broader face or at least jaws
In general the faces to the left look significantly colder, less empathic, a perception that blue eyes can only enhance.
The authors ponder if there is a phenotype linkage disequilibrium associating face and eye color, what seems plausible. But then go on speculating about sexual selection and what not. 
In this sense Razib has an interesting critical analysis questioning if selection is behind the blue eye incomplete sweep in West Eurasia or Europe. If I understand him correctly he seems to suggest, never clearly naming it, that blue eye may have been favored because of the associated skin pigmentation trait, a key adaptive value in the dark winters of Europe and very especially the northern half of it.

Update: is this a peculiarity of Central Europe or the Czech Republic?

A reader sent me an email in which it was questioned if this association is peculiar of the Czech Republic, where the study was performed, and can’t be extended for example to Britain. Examples of soft-faced blue-eyed Britons mentioned were Hugh Grant and Alec Baldwin (I’m not sure if Baldwin is such a good counter-example but Grant is for sure one such case). 

I find it a very good criticism and hope that entices debate.

See also: Causes of skin and hair color variance in Europeans remain undetermined.

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Posted by on January 10, 2013 in Anthropometry, Europe, pigmentation, psychology, West Eurasia

 

Frontal bulge: an almost exclusive characteristic of Homo sapiens

Even if the article is behind a paywall, the abstract is self-explanatory enough to be worth a mention:

Emiliano Bruner et al., Geometric variation of the frontal squama in the genus homo: Frontal bulging and the origin of modern human morphology. American Journal of Physical Anthropology, 2013. Pay per viewLINK [doi: 10.1002/ajpa.22202]

Abstract

The majority of studies of frontal bone morphology in paleoanthropology have analyzed the frontal squama and the browridge as a single unit, mixing information from different functional elements. Taking into account that the bulging of the frontal bone is often described as a species-specific trait of Homo sapiens, in this article we analyze variation in the midsagittal profile of the genus Homo, focusing on the frontal squama alone, using landmark-based superimpositions and principal components analysis. Our results demonstrate that anatomically modern humans are definitely separated from extinct human taxa on the basis of frontal bulging. However, there is minor overlap among these groups, indicating that it is necessary to exercise caution when using this trait alone to make taxonomic inferences on individual specimens. Early modern humans do not show differences with recent modern humans, and “transitional” individuals such as Jebel Irhoud 1, Maba, and Florisbad, show modern-like frontal squama morphology. The bulging of the frontal squama in modern humans may represent a structural consequence of more general cranial changes, or it could be a response to changes in the morphology of the underlying prefrontal brain elements. A subtle difference between Neandertals and the Afro-European Middle Pleistocene Homo sample is associated with flattening at bregma in the former group, a result that merits further investigation.

Frontal bone: the frontal squama or scales is labeled as 1
Source: Atlas of Human Anatomy.
I wonder how much this confusion between frontal squama (rising of the forehead) and browridge (facepalm!) has caused the strange theories of Trinkaus and followers?
 
 

Elephant hair density helps cooling

The low density of elephant hair has been demonstrated to help cooling:
Conor L. Myrvhold. What Is the Use of Elephant Hair? PLoS ONE 2012. Open access ··> LINK [doi:10.1371/journal.pone.0047018]

At low densities, hair has almost no effect on air flow and does not
trap an insulating air layer near the skin, but the extended hair acts
as a pin fin that increases thermal exchanges with the surrounding air.
Thus, as the hair density decreases from that of very furry animals, a
break-even point is reached where the hair function switches from an
insulator to a heat exchanger. This break-even point occurs at a density
of about 0.3 million hairs/m2 [26] for thick hair covers with creeping flow in between (recall that 1500 hairs/m2 is about the maximum density of elephants). For comparison, the hair density of the human head is about 2 million hairs/m2 (see Methods and Discussion S1).

These heat dispersal properties were already known for plants (leaf hair, cactus’ spines) but it is the first time to be demonstrated for an animal, more specifically a mammal like us. 
Figure 1. Pictures of elephant hair on the top of the back of an Asian elephant, (A) and an African elephant’s head (B).
The presence of hair on elephants was first noted by van Leeuwenhoek
[30]. Photos taken by Conor L. Myhrvold in the Woodland Park Zoo,
Seattle, Washington, from outside of the elephant enclosure, with
permission from the Zoo.
I searched online for hair density on human body (the question we all have in mind, right?) and I could only find a commercial reference (I’d appreciate a better one if you know one). Still it seems that the hair density on tights and legs (and therefore probably on most of the body) in humans is 50 hairs/cm², what translates as 0.5 million hairs/m², somewhat (but not a lot) above the threshold mentioned above.
I’d dare suspect that this means that human body hair (vellus) is for most people thermally neutral but then I wonder how it works with sweat, which is a key part of our tropical thermo-regulatory natural design. Elephants and plants do not sweat (although they do get wet on occasion), so it may well work somewhat different for them.
That seems to be an interesting challenge to explore.
 
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Posted by on November 27, 2012 in Anthropometry, biology, elephants, hair, human evolution

 

Causes of skin and hair color variance in Europeans remain undetermined

Portuguese & N. Irish

Our ability to predict pigmentation traits from genetic loci remains limited but this new paper adds some honest research on the matter:

Sophie I. Candille et al., Genome-Wide Association Studies of Quantitatively Measured Skin, Hair, and Eye Pigmentation in Four European Populations. PLoS ONE, 2012. Open access ··> LINK [doi:10.1371/journal.pone.0048294]
One of the findings is that women have darker skin shades than men in Europe (but not among peoples with dark skin from several continents, where men are darker). Another unstated but curiously counterintuitive finding is that Portuguese (from Porto) have on average the same skin tone as Polish (from Warsaw) do:

Table 1. Skin, hair, and eye pigmentation by sex and country.

However for hair and eye color, Polish have lighter shades, approaching the Irish (Dublin) extreme values, while Portuguese approach Italians (Rome) in hair color and show darker eyes on average than anybody else among the sampled populations.
Another curiosity of the survey is that Irish women show significantly lighter hair shades than Irish men, a phenomenon not appreciable elsewhere.
The authors found that, in general:

… in this European sample, pigmentation phenotypes are mainly stratified by country, whereas height is mainly stratified by sex.

They also found that:

Skin and eye pigmentation are correlated in Ireland. Hair and eye pigmentation are correlated in Portugal. Skin and hair pigmentation are correlated in Poland and Italy (Table S2).

What I find rather curious and suggestive of complex genetic influences affecting more than just one pigmentation trait at the same time. But which ones? And why do they seem to operate differently in different populations?
The GWAS analysis found these loci as significant:

Table 2. GWAS, replication, and combined association results for all signals with p-value<10−5 in the GWAS.

Apparently neither the SCIN nor the FLNB genes have been related with pigmentation before. Therefore the authors applied a strong test of reliability (replication in the table), correcting for geographical structure, which actually discarded all loci except the already known ones for eye color in relation to OCA2/HERC2, which were: rs1667394, rs8039195, rs1635168, rs16950987, and rs8028689.
However further analysis showed that rs1667394 is in linkage disequilibrium (LD) with rs12913832 (OCA2), which is the actual culprit of blue eyes (a well known SNP that explains some 45% of the eye color variance among Dutch).
In regard to the failure to detect markers of skin and hair color variance, they conclude that:

The fact that we did not detect reproducible associations with skin or hair color suggests that, unlike eye color, skin and hair pigmentation variation in Europe are not determined by major loci.

Furthermore, genes that have been shown to contribute to skin color variance in South Asians (rs1426654 SLC24A5, rs16891982 SLC45A2, and rs1042602 TYR) or in African-European admixed populations (rs1426654 in SLC24A5 again), fail to show any importance in intra-European variance for this trait. However rs1426654 is fixated in Northern Europeans (CEU), so it cannot show any variation.
Other SNPs (rs16891982 and r183671 in SLC45A2, which are in LD) may contribute to skin pigmentation, however the pattern mentioned (in which Italians and Portuguese are contrasted with Polish and Irish) rather reminds me of the variation for hair and eye color instead.
They also mention that rs885479 in MC1R has not provided any clear association in previous studies but that they did find some association with skin color, however they did not practice the replication test for this SNP.
In the end not much new other than some cold water but an straightforward study for the record.

See also:

 
 

Emotional care or neglect of young children decisive for brain size, intelligence

An image says more than a thousand words. And in this case the image is a brain scan… or rather two side by side:

Both brains belong to 3-years-old children

… the child with the shrunken brain was neglected and abused by its
mother, and the child with the larger and more fully developed brain was
raised in a loving, supportive home and was looked after by its mother…

This is not just about IQ or head size, which may vary at least largely because of this type of environmental causes, but about everything in life, including emotional and social intelligence and the general ability to carry on with a normal, well integrated life (or become human waste). 
The first years of life are critical for all our development and parental love, very specially that of our mothers, is probably more important than almost anything else.

Source: Medical Daily.

 
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Posted by on October 30, 2012 in Anthropometry, biology, epigenetics, mind

 

The genetic and phenotype complexity of the Oceanic language area

In this entry, rather than discussing Polynesians alone, which seem to be just the tip of the Eastern Austronesian iceberg, I’ll try to understand here the complexity of speakers of Oceanic languages, the main native language family of Island Oceania. 
Oceanic is a branch of Austronesian but for the purposes of this entry we will only mention other Austronesian peoples/languages tangentially. The focus is Oceanic because we can’t understand the parts without the whole here most probably. 

Linguistics

Oceanic languages are scattered as follows:

  Admiralties and Yapese
  St Matthias
  Western Oceanic and Meso-Melanesian (two distinct sub-families)
  Temotu
  Southeast Solomons
  Southern Oceanic
  Micronesian
  Fijian–Polynesian
Black enclosed zones are pockets of languages from other families.
(CC by kwami)

It is certainly interesting that Micronesian and Fijian-Polynesian seem to be particularly related among them. Instead the Western Oceanic and Admiralty subfamilies (both from the islands near Papua) seem to have separated early on or diverged farther for whatever other reasons (stronger substrate influence for example).

Prehistory

Lapita pot from Tonga (source)
As I cited recently, Polynesians seem to have spread from Society Islands in the 1190-1290 CE window. The genesis of the Micronesian family is not well understood… but the overall genesis of Oceanic languages seems to be at the Lapita culture, which spread through Island Melanesia (excluding Papua) and some nearby islands (notably Tonga and Samoa also Marquesas c. 300 CE(ref)).
Early Lapita culture is dated to c. 1350-750 BCE, while a Late phase is dated to c. 250 BCE, spreading to the Solomon Islands, which show no indications of the earlier period (Ricaut 2010, fig. 2).
So a simplified chronology for Oceanic expansion would be
  1. Lapita culture from near Melanesia to Vanuatu and Kanaky (New Caledonia), then to:
    1. Fiji, Samoa and Tonga since c. 900 BCE
    2. Solomon Is. c. 250 BCE
  2. Arrival to Society Islands (Tahiti, etc.) c. 300-800 CE from maybe Samoa.
  3. Main Polynesian expansion to the farthest islands (Hawaii, Rapa Nui, Aotearoa-NZ) c. 1200 CE from Society Is.

Phenotype (‘race’)

A classical and unavoidable element in the ethnographic division of the region is phenotype, appearance (i.e. ‘race’). Since the first European arrival to the area the division between black Melanesians and white Polynesians (very relative as we will see now) has been part of all our conceptualizations of the region. 
Conscious of that and wanting to get a better impression I collected from the Internet what I estimate may be representative faces from the Oceanic linguistic zone and nearby areas (other Austronesians and Melanesians) and put them on a map:

Click to expand

A relatively homogeneous Polynesian phenotype can be identified and one can imagine that it stems from the area of Samoa-Tonga, considering the previous prehistorical review. But otherwise the diversity, gradations and abundance of local uniqueness seems quite impressive.
Based on other cases, one would imagine also that phenotype differences would be coincidental with genetic ones. However this is not too easy to discern, partly because Polynesians have strong founder effects that blur the matter, partly because there is no obvious strict dividing line between the various phenotypes and partly because of the insistence of some in considering Lapita as a Polynesian phenomenon, when it is obviously an Oceanic one, including and emphasizing the Melanesian side of the diverse Oceanic landscape, of which the Polynesian-Micronesian branch is just one element (famous and extended but not the core). 
Genetics
The main Y-DNA lineage among Polynesians is C2a1 (P33), not found outside Polynesia senso stricto but reaching there frequencies of 63-90% (excepted Tonga where it’s only 33%). This is a clear founder effect in this population.

C subclades in SE Asia and Oceania
(from Karafet 2010, annotated with ISOGG nomenclature)
C2a1 is clearly derived from a Melanesian superset C2a (M208) still found as C2a(xC2a1) at low frequencies in Samoa (8%) and Tahiti (4%) but also in Vanuatu (2%) and coastal Papua (13%). C2a establishes a probably genetic link of Polynesians with Lapita culture and Melanesian peoples in general.
An earlier pylogenetic stage is C2 (M38), which is probably in the region since the very first colonization process some 50 thousand years ago (or maybe even earlier). C2(xC2a) is most common in Wallacea (East Indonesia, East Timor), where it reaches maybe figures of 33% on average. It is however also found in highland Papua (13%) and Vanuatu (20%) but as it is most doubtful that C2a evolved as recently as Lapita times, we should really focus on C2a as such rather than the wider C2, which only seems to confuse the matter.
The lack of C2(xC2a) in most of the Oceanic languages’ area clearly indicates that the expansion (and subsequent founder effects) did not begin in Wallacea but in  Melanesia, at least in what regards to C sublineages.
The other major Polynesian haplogroup is O3a2 (P201), which would seem to have originated in Philippines and maybe arrived there via Micronesia:

O3 subclades in SE Asia and Oceania
(from Karafet 2010, annotated with ISOGG nomenclature)

Melanesian populations also sport some lineages that are not common among other Oceanic-speaker peoples, notably K, M and S. However they are irregularly shared with Wallacea (Eastern Indonesia, East Timor). Like C2 these lineages coalesced in the region soon after colonization by Homo sapiens.
In the motherly side of things genetic, the absolutely dominant mtDNA lineage among Polynesians (the so-called Polynesian motif) is B4a1a1, which ultimately stems from East or rather SE Asia. However it probably arrived to the region (again) via Melanesia, albeit maybe somewhat tangentially.

From Friedlander 2007 (fig. 4)

Spatial frequency distribution of haplogroup B4a* and B4a1a1 in Island Southeast Asia and the western Pacific, created using the Kriging algorithm of the Surfer package of haplogroups. Figure 4b presents the detailed distribution for Northern Island Melanesia. Data details are provided in table S3.

The matrilineal Polynesian motif does offer a possible pattern of settlement, maybe related specifically to Late Lapita, that could allow us to understand the possible origin of the phenotype differences between Melanesians and Polynesians, as could do the Y-DNA lineage O3a2. However there are lots of remnants of quite strictly Melanesian Early Lapita, as is evident by the (Y-DNA) C2a lineages retained so strongly among Polynesians within their own founder effects, whose importance we cannot afford to dismiss.

Other mtDNA lineages like Q1 or M27 are of relevance in Melanesian populations. Q1 did make its way into some Polynesian populations but as minority lineage only.

Update (Oct 31):


Terry in the comments sections grunts a lot but now and then provides useful complementary data, for example this Y-DNA map of the region from Kayser 2006:


Kayser 2006 – fig. 1
Frequency distribution of (A, B) NRY and (C, D) mtDNA haplogroups found in Polynesia with a genetic origin in (A, C) Asia or (B, D) Melanesia.


As is apparent since Kayser’s publication (if not before), the Melanesian patrilineages are much more common (actually dominant) among Polynesians than the matrilineages from the same origin, what is attributable to a founder effect related to the Lapita culture.
Another interesting reference is this Y-DNA map of Papua (New Guinea) and some nearby islands (from Mona 2007):

Mona 2007 FIG. 2.—Y-chromosome haplogroups and their frequencies in populations from the Bird’s Head region and elsewhere in New Guinea. Data from other populations of New Guinea were used from previous studies (Kayser et al. 2003, 2006). Size of the pie charts is according to sample size of the groups. Abbreviations are as in supplementary table S1, Supplementary Material online.

Both maps and/or the data in the relevant papers provide key information on possible origins for the C2a-M208 patrilineal founder effect, so important in general in the Oceanic peoples and specially the Polynesian branch. The exact origin cannot be pinpointed without further research (or maybe not at all) but it’s clear that C2a-M208 only exists from Papua (New Guinea) to the East, so it must have a Melanesian origin be it Papuan or from the nearby islands.

Bibliography

  • François-Xavier Ricaut et al., Ancient Solomon Islands mtDNA: assessing Holocene settlement and the impact of European contact. Journal of Archaeological Science, 2010 ··> LINK (PDF).
  • Jonathan S. Friedlaender et al., Melanesian mtDNA Complexity. PLoS ONE, 2007 ··> LINK (open access).
  • Tatiana Karafet et al., Major East-West Division Underlies Y Chromosome Stratification Across Indonesia. MBE 2010 ··> LINK (free access).
  • Michael Knapp et al., Complete mitochondrial DNA genome sequences from the first New Zealanders. PNAS 2012 ··> LINK (open access).
  • Manfred Kayser et al., Melanesian and Asian Origins of Polynesians: mtDNA and Y Chromosome Gradients Across the Pacific. MBE 2006 ··> LINK (free access).
  • Stephano Mona et al., Patterns of Y-Chromosome Diversity Intersect with the Trans-New Guinea Hypothesis. MBE 2007 ··> LINK (free access).

_________________________________________________________________________________
Note: updates after first posted version in maroon color.

 

Candidate genes for facial morphology

Figure 4
candidate SNPs
click to expand
So far, in people of European ancestry from Germany, Netherlands, North America and Australia:
Fan Liu et al., A Genome-Wide Association Study Identifies Five Loci Influencing Facial Morphology in Europeans. PLoS Genetics 2012. Open access ··> LINK [doi:10.1371/journal.pgen.1002932]

Abstract

Inter-individual variation in facial shape is one of the most noticeable phenotypes in humans, and it is clearly under genetic regulation; however, almost nothing is known about the genetic basis of normal human facial morphology. We therefore conducted a genome-wide association study for facial shape phenotypes in multiple discovery and replication cohorts, considering almost ten thousand individuals of European descent from several countries. Phenotyping of facial shape features was based on landmark data obtained from three-dimensional head magnetic resonance images (MRIs) and two-dimensional portrait images. We identified five independent genetic loci associated with different facial phenotypes, suggesting the involvement of five candidate genes—PRDM16, PAX3, TP63, C5orf50, and COL17A1—in the determination of the human face. Three of them have been implicated previously in vertebrate craniofacial development and disease, and the remaining two genes potentially represent novel players in the molecular networks governing facial development. Our finding at PAX3 influencing the position of the nasion replicates a recent GWAS of facial features. In addition to the reported GWA findings, we established links between common DNA variants previously associated with NSCL/P at 2p21, 8q24, 13q31, and 17q22 and normal facial-shape variations based on a candidate gene approach. Overall our study implies that DNA variants in genes essential for craniofacial development contribute with relatively small effect size to the spectrum of normal variation in human facial morphology. This observation has important consequences for future studies aiming to identify more genes involved in the human facial morphology, as well as for potential applications of DNA prediction of facial shape such as in future forensic applications.

 
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Posted by on September 14, 2012 in Anthropometry, human genetics