Genetic Population Structure Accounts for Contemporary Ecogeographic Patterns in Tropic and Subtropic-Dwelling Humans

<div><p>Contemporary human populations conform to ecogeographic predictions that animals will become more compact in cooler climates and less compact in warmer ones. However, it remains unclear to what extent this pattern reflects plastic responses to current environments or genetic differences among populations. Analyzing anthropometric surveys of 232,684 children and adults from across 80 ethnolinguistic groups in sub-Saharan Africa, Asia and the Americas, we confirm that body surface-to-volume correlates with contemporary temperature at magnitudes found in more latitudinally diverse samples (Adj. R² = 0.14-0.28). However, far more variation in body surface-to-volume is attributable to genetic population structure (Adj. R² = 0.50-0.74). Moreover, genetic population structure accounts for nearly all of the observed relationship between contemporary temperature and body surface-to-volume among children and adults. Indeed, after controlling for population structure, contemporary temperature accounts for no more than 4% of the variance in body form in these groups. This effect of genetic affinity on body form is also independent of other ecological variables, such as dominant mode of subsistence and household wealth per capita. These findings suggest that the observed fit of human body surface-to-volume with current climate in this sample reflects relatively large effects of existing genetic population structure of contemporary humans compared to plastic response to current environments.</p></div

Relationship between basal Body Mass Index among adult females and (a) maximum temperature of hottest month, (b) genetic affinity-predicted values.

<p>Relationship between basal Body Mass Index among adult females and (a) maximum temperature of hottest month, (b) genetic affinity-predicted values.</p

Estimated adult basal BMI and child basal WH for an individual of 100% ancestry from each of Tishkoff's genetic components.

<p>Niger-Kordofan is the reference category. Bars are 95% confidence intervals.</p

Coefficient of determination (Adjusted R²) of models predicting basal body mass based on climatic variables and genetic affinity (n = 80 for all except adult male populations, n = 20).

<p>^a Model based on affinity-predicted bBMI from full adult female sample due to small sample size in adult males.</p><p>All effects statistically significant at alpha = 0.05 level, except for associations with minimum temperature</p><p>Coefficient of determination (Adjusted R²) of models predicting basal body mass based on climatic variables and genetic affinity (n = 80 for all except adult male populations, n = 20).</p

Ages and associated data for 78 radiocarbon ¹⁴C AMS dates, which are shown graphically in Figure 3 (bottom to top).

<p>Dates from the same specimen or feature are grouped together (shaded or unshaded). For some sherds recovered in burials with Kiffian decorative motifs, dates based on plant temper are older than 6000 B.C.E. (dates 26–28). Other sherds found in burials and middens with Kiffian decorative motifs and dates based on plant temper are younger than 6000 B.C.E. (dates 29, 32, 34, 45, 46, 52). Although these younger ages may be aberrant (EAAG), they are concordant with dates based on other materials when found in the same midden (dates 44–54; JFS). Likewise, two direct dates on bone harpoon points (dates 64, 65) are concordant with other dated material in refuse area 5 associated with the early Holocene occupational phase 2 (dates 64, 65). An additional pair of direct dates (dates 66, 68) on bone harpoon points found in situ in paleolake sediment, however, are more than 2 kyr younger and date to the middle of the mid-Holocene occupational phase 3. Additional testing of bone harpoon points is warranted to better understand these results.</p

Faunal list at Gobero showing taxa recorded at archaeological sites (G1-3), in early and mid-Holocene middens (middens 1–4, refuse area 5), and in the Gobero area (in paleolake deposits or on deflation surfaces).

<p><i>Abbreviations</i>: +, species present; <b>x</b>, species very common.</p>1<p>As eggshell beads.</p

Radiocarbon (¹⁴C AMS) dates for human skeletons, ceramics, charcoals, middens, fauna, artifacts and sediment.

<p>Timelines and occupation phases 1–4 are shown at the bottom. Associated chronometric data are compiled in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0002995#pone-0002995-t002" target="_blank">Table 2</a> using current atmospheric standards <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0002995#pone.0002995-Reimer1" target="_blank">[55]</a>. All of the burials that have been dated at Gobero fall within phases 2 and 3, which are shown as green to indicate favorable humid climate conditions; more arid intervals are shown as tan including occupation phases 1 and 4. Multiple dates on individual specimens or features are boxed. A dotted line separates early and mid-Holocene human burials. <i>Abbreviations</i>: <i>B.C.E.</i>, before current era (registered to calendar year zero); <i>B.P.</i>, before present (1950); <i>G1B8</i>, burial 8 on G1; <i>G1B11</i>, burial 11 on G1; <i>G3B8</i>, burial 8 on G3; <i>K</i>, Kiffian; <i>LT</i>, Late Tenerean; <i>T</i>, Tenerean.</p

Convergence of multiple ¹⁴C AMS dates based on bioapatite radiocarbon from different materials from the same individual.

<p>Convergence of multiple ¹⁴C AMS dates based on bioapatite radiocarbon from different materials from the same individual.</p

Craniometric means for human samples.

<p>Craniometric means for early and mid-Holocene skulls from Gobero and comparative samples elsewhere from northern Africa. <i>Measurement acronyms</i> (after <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0002995#pone.0002995-Dutour1" target="_blank">[18]</a>): <i>LGO</i>, glabella-occipital length; <i>BPX</i>, maximum cranial breadth; <i>LBN</i>, basion-nasion; <i>HBB</i>, basion-bregma; <i>AFR</i>, frontal arc; <i>APA</i>, parietal arc; <i>AOC</i>, occipital arc; <i>CFR</i>, frontal chord; <i>COC</i>, occipital chord; <i>HNP</i>, nasion-prosthion; <i>HNZ</i>, nasion-nasospinale; <i>BNZ</i>, nasal breadth; <i>BZY</i>, bizygomtic breadth; <i>BFW</i>, minimum frontal breadth; <i>BFX</i>, maximum frontal breadth; <i>HORC</i>, horizontal circumference above the superciliary arches. <i>Sample acronyms and abbreviations</i>: <i>Ater</i>, Aterian; <i>EMI</i>, eastern Maghreb Iberomaurusian; <i>EMC</i>, eastern Maghreb Capsian; <i>Gob-e</i>, Gobero early Holocene; <i>Gob-m</i>, Gobero mid-Holocene; <i>Maur</i>, Mauritania; <i>Mali</i>, Hassi-el-Abiod, Mali; <i>WMI</i>, western Maghreb Iberomaurusian; <i>WMC</i>, western Maghreb Capsian.</p

Early Holocene cemetery, burials and skulls.

<p>(A)-Gobero site G3 showing excavated burials (red dots). (B)-Enlarged map of the early Holocene cemetery showing the location of 17 undisturbed burials of skeletons with dark-stained bone (red dots). Five burials (red dot with outer ring) were directly dated to a narrow range of ∼7500±250 years B.C.E. (<a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0002995#pone-0002995-g002" target="_blank">Figure 2</a>; <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0002995#pone-0002995-t002" target="_blank">Table 2</a>). (C)-Skeleton (dark-stained) of an early Holocene adult male (G3B8; ∼7515 B.C.E.) buried in supine, hyperflexed posture with hands over the mouth and feet crossed. Computed-tomography cross-section (below) across the middle of the skeleton (red line) shows the tightly bundled configuration of major limb bones (within a 25 cm×12 cm rectangle) for an adult with stature approximately 2 m. (D)-Skull of early Holocene adult male (as in C) showing long, low calvarium, broad zygomatic width and relatively flat face. (E)-Skull of an early Holocene juvenile (G3B17b; ∼7630 B.C.E; estimated age 5 years) already showing long, low cranial proportions. Scale bar in C equals 13.3 cm for skeleton and 10 cm for CT scan; skull length (glabella-opisthocranion) in D and E equals 190.0 mm and 171.0 mm, respectively. <i>Abbreviations</i>: <i>f</i>, femur, <i>fi</i>, fibula; <i>h</i>, humerus; <i>r</i>, radius; <i>ti</i>, tibia; <i>ul</i>, ulna.</p