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Climate and the evolution of brachycephalization.

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AMERICAN JOURNAL OF PHYSICAL ANTHROPOLOGY 62425-437 (1983)
Climate and the Evolution of Brachycephalization
KENNETH L. BEALS, COURTLAND L. SMITH, AND
STEPHEN M. DODD
Department of Anthropology, Oregon State Uniuersity, Coruallis, Oregon
97331
KEY WORDS
Brachycephalization, Cranial index, Cephalic index,
Climate, Ecotype
ABSTRACT
Significant associations of cranial shape for 82 ethnic groups
and seven climate variables are described. Variation among current populations is partially attributed to cold adaptation throughout the Pleistocene.
Application of data files tabulated by the authors is described for a number of
problems. Temporal distribution of 115 specimens indicates a geometric trend
(CI = 76.7 - 1.96 log time x lo3). Cranial indices are summarized within
alternative taxonomic models and between climatic ecotypes. Evidence supports the hypothesis of cold adaptation among “Classic” Neandertals. Limitations of the thermodynamic model are discussed. It is probable that a decrease
of the cranial index occurs from the Middle to Upper Paleolithic. During the
Holocene, the index increases under all climatic conditions.
Adaptive significance of head shape was
first suggested in a classic study by Boas
(1911), which indicated that generational
change occurred with the cephalic index
among the children of European immigrants.
Weidenreich (1945) later described the trend
of brachycephalization among recent hominids. Suggestions as to the cause have included effects of pedomorphism, population
admixture, neurocranium balance, encephalization, stature increase, heterosis, nutritional deprivation, nomadic incursions, and
abandonment of cradling (Bielicki and Welon, 1964; Hooton, 1946; Hulse, 1971).
In 1955, Coon mentioned that brachycephaly would be advantageous in regions of
cold climates. This hypothesis is based upon
the effect of surface area:mass ratios that
underlie the rules of Allen and Bergmann.
Beak (1972) evaluated the climatic adaptation model with a worldwide sample of 339
populations. The climatic associations were
highly significant. For example, ethnic
groups exposed to winter frost have a mean
cephalic index that is 4.3 units higher than
those living within the tropics. The conclusions are independently supported by the
data of Hiernaux (1968) for Africa and by
Crognier (1981)for populations of Europe and
the Mediterranean.
0 1983 ALAN R. LISS, INC.
Such evidence suggests that a portion of
the paleontological trend toward brachycephalization may be explained by the increased occupation of cold environments
throughout the Pleistocene. The primary
purpose of the current investigation is to
evaluate the cold adaptation hypothesis empirically. “Adaptation” is used in the broad
sense of any adjustment to ecological factors.
MATERIALS AND METHODS
For several years, the authors have been
tabulating paleontological and distributional
evidence relative to surface area:mass ratios.
Our ultimate objective is to combine a computerized mapping program with rates of evolutionary change, distance analysis, and
climatic correlation to project clinal distributions into the remote past. Development of
such a research tool would then permit comparison of newly discovered hominids with
trait distributions as expected at any point
in time and space. The objective thus requires the statistical data pertaining to both
paleontological and contemporary ecological
associations.
The present study is thus part of a more
comprehensive project, and a portion of the
Received January 19, 1983; accepted August 30,1983.
426
K.L. BEALS. C.L. SMITH, AND S.M. DODD
evidence and discussion within the text originates from analyses of other related problem
areas which are in various stages of manuscript completion and with results as yet unpublished. General methodology is first
described, followed by a particular application to the brachycephalization problem.
The concept is to use computer technology
as a kind of “time machine” to construct
outline maps, plot trait predictions by latitude and longitude, draw clinal maps for any
point in time within any geographical area,
compare the predictions to known reference
points (the paleontological data already
available), and calculate the probability of
“correspondence” of a particular specimen to
the empiric expectation (given multiple
regression with time, sex, location, and climate). Such a tool would be analogous in
some respects to x2 observatiodexpectation
analysis within genetics-except that the deductive theory (i.e., Hardy-Weinberg Equilibrium, Law of Segregation) does not exist, and
the system thus depends upon the empirical
data bases.
Paleontological data are derived from a reference file with 147 specimens from 75 sites
(having a minimum antiquity of 10,000
years) and tabulated from 54 original and
secondary sources. The file contains site,
specimen number, cranial index, cranial capacity, date, sex, latitude and longitude, climatic association, taxonomic attributions,
qualification notes, and references. Data on
the cranial index are not available for the
total sample of 147. Those that do have such
reports (118) are listed in Table 1.
Head shape information among ethnic
groups derives from 339 populations as originally separated by Beak (1972)into climatic
stress zones. This sample has been increased
to 362 by addition of group means from temperate regions. A composite of 82 populations
(means of same ethnic group from different
locations) were tabulated into a climatidanthropometric file with cephalic index and 11
additional anthropometrics. Climatic correlations for each can be calculated for latitude
and longitude, climatic zone, solar radiation,
total hours of sunshine, winter water vapor
pressure, summer water vapor pressure,
mean annual precipitation, coldest month
minimum mean temperature, warmest
month maximum mean temperature, and isothermic zone. (Solar radiation is total heat
as expressed in annual kilogram calories per
square centimeter of earth surface. Water
vapor (millibars) indicates total amount of
air moisture. Isothermic zones are taken from
Schwidetzky’s [19521 arbitrary scale of isotherms-ranging from 1 [over 30°] to 6 [under 10“1 .)
As another portion of the overall project, a
mapping program has been devised to plot
distributions. We have used it to construct an
outline map and illustrate the geographic
location of specimens included within the
analysis (Fig. 1). It is presently limited to
plotting individual points-isophenes must be
added manually.
The biological and climatic files can be
merged with the much larger set of cultural
traits computerized from the Human Relations Area Files-which includes as many as
1,170 ethnic groups and 150 variables. Such
merger permits evaluation of biological, ecological, and cultural interrelationships.
Specifically in regard to the evolution of
head shape, there is a research design conflict between the two desirable goals of maximizing both sample size and reliability. The
problem is that circumstances such as ontological age, reconstruction, postmortem deformation, uncertain dating, and measurement error cause decisions to be made
with respect to inclusion or exclusion of particular cases. There is no completely objective solution, since the reliability is a matter
of degree.
Reports on different cranial indices from
the same specimen are averaged. Dates are
taken as the midpoints of estimates. A number of specimens have had recent dating revisions. These include material from Border
Cave, Fish Hoek, Ofnet, Saldanha, Ehringsdorf, and Ngandong (Solo). Infants are not
included within the calculations. Juveniles
are included, since the index changes little
from a time shortly following birth. Omo-1,
Krapina-C, and Krapina-D are omitted from
analysis for reasons of postmortem deformation or known measurement error. Reconstructions are not eliminated, since they
should not produce a systematic bias.
Evaluation of a variety of possible exclusiodinclusion sets (such as with or without
Steinheim and Swanscombe) did not produce
differences of sufficient magnitude to negate
any general result. Notes within Table 1 are
given to indicate briefly the interpretive
limitations.
It is not possible to correlate the paleontological cases with climatic variables as specific as those which can be associated with
CI
67.5
73.0
62.8
72.3
67.0
67.4
75.5
62.4
78.8
74.2
68.8
67.9
68.8
72.0
72.3
71.4
72.6
75.5
66.8
76.0
74.6
78.3
72.0
72.6
74.0
78.0
68.6
67.4
68.3
78.9
83.7
85.5
78.9
66.1
67.3
76.8
78.4
75.5
76.5
76.0
73.6
71.3
76.5
80.0
78.4
Specimen
Sterkfonteind
Swartkrans-46
Sangiran-4
Koobi Fora 3733
Olduvai-5
Olduvai-9
Sangiran-10
Taung-1
Lantian-2
Sangiran-2
Sangiran-3
Sangiran-17
Trinil-2
Saldanha
Choukoutien-3
Choukoutien-10
Choukoutien-12
Ngandong-1
Ngandong-6
Ngandong-7
Ngandong- 10
Ngandong-11
Ngandong- 12
Steinheim
Ehringsdorf-H
Swanscornbe
Omo-1
Omo-2
Laetoli-18
Fontechevade
Krapina-C
Krapina-D
Ganovch
Kanjera-1
Kanjera-3
Gibraltar-1
Saccopastore-1
La Ferrassie-1
Le Moustier
Monte Circeo
Neandertal
SPY- 1
SPY-2
Petralona
Teshik-Tash
1200
1200
1641
1352
1552
1452
1525
1425
1220
1565
1435
1200
1350
1200
1450
1320
908
800
530
1067
855
440
780
813
900
1004
900
1225
915
1225
1030
1172
1251
1013
1135
1231
1090
1460
1450
1250
485
CC
Date
2500
2100
1900
1700
1500
1300
830
800
775
710
710
7 10
650
500
300
300
300
250
250
250
250
250
250
225
220
175
130
130
120
110
85
85
70
70
70
60
60
52
52
52
52
52
52
50
50
F
M
F
F
M
M
M
M
M
F
F
F
M
F
F
M
F
F
F
M
F
M
M
F
M
M
F
F
F
M
M
F
M
M
S
CZ2
TR
TR
TR
TR
TR
TR
TR
TR
TM
TR
TR
TR
TR
TR
TM
TM
TM
TR
TR
TR
TR
TR
TR
TM
TM
TM
TR
TR
TR
GL
GL
GL
GL
TR
TR
GL
GL
GL
GL
GL
GL
GL
GL
GL
GL
TAX3
N-HE
N
N
AA
AR
HE
HE
AR
HE
HE
AA-AR
HE
HE
HE
HE
HE
HE-N
HE
HE
HE
N-HE
N-HE
N-HE
N-HE
N-HE
N-HE
N
N
N
N-MM
N-MM
N
N
N
N
N
N-MM
N-MM
N
N
N
N
N
N
N
(continued on next page)
026S027E
026S028E
0 0 7 s 11E
004N037E
003S035E
003S035E
007S111E
026S028E
034N109E
007SlllE
007SlllE
007SlllE
007S112E
033S018E
040N115E
040N115E
040N115E
007S112E
007S112E
007S112E
007S112E
007S112E
007S112E
049N009E
051N011E
051NOOOE
005N036E
005N036E
004S034E
046NOOOE
046N016E
046N016E
049N020E
001S035E
001S035E
036N005W
042N013E
045N001E
045N001E
041N013E
051N005E
050N005E
050N005E
040N023E
038N067E
Location
Notes and sources4
(067) (W80) (B79)
Djetis, Holloway Revision (B79) (D65) (075)
ER 3733 (B79)
“Zinjanthropus” (067) (H72-73)(B79)
“Chellean Man” (B79) (H78)
Holloway Revision (W80)(573) (075)
Adult estimate of CC (H78) (067) (B79)
(W80)(A731(H80) (P72) (075)
Holloway revision (D65)(075)
Juvenile, CC. for adult (K80) (D65) (075)
W80) (573) (T81) (D65) (075)
(K80) (075)
Revised dating (B79)(067) (P72) 6 5 4 )
Adolescent CC +2% (W80)(D65) (075)
(W80) (D65) (075)
W80) (D65) (075)
Holloway revision, Solo-1(K80)(P72) (B79) (075)
Holloway revision, s o b 5 (K80)(P72) (B79) (075)
Holloway revision, Solo-6 (K80) (P72) (B79) (075)
Solo-9 (K80)(P72) (B74)(075)
Holloway revision, Solo-10(K80)(P72) (B79) (075)
Holloway revision, Solo-11(K80) (P72)(B79) (075)
Distorted (P72) (B79)(H51) (W80B)
Dating revised (W80)(B79) (H51) (071)
Estimated CI (W80)(P72) (B79) (052) (D65)
Kibish, uncertain date (K80)(R74)
Kibish, uncertain date (K80)(R74)
(D80)
Specimen number uncertain (K80)(W80) (B79)
CI auestioned (W80)(B79)(S80)
CI questioned (W80)(B79)
(”80) (071)
Reconstructed, redated (L70) (W801 (P75)
See above (L80) (W80)(P75)
(B79) (H51) 6 8 0 )
(W80) (B79) (H51) (S80)
(B79) (580)
Sex doubtful (B79) (H51)
(B79) (H51)(580)
(B79) (H51) (S80)
(B79) (H51)
(B79) (H51)
(W80) (B79) (W80B)
Adolescent, CC +5% (H51)(W45)
“P. Transuaalensis” (067)(P72) (P73) (B79)
TABLE 1. Paleontological data of specimens’
Specimen
Ingwavuma-1
Shanidar-1
La Quina-H5
La Quina-HI8
D. Irhound-1
D. Irhound-2
Subalyuk
Tabun-1
Broken Hill-1
La Chapelle
Florisbad-1
Quafzeh-6
Fish Hoek-1
Chatelperron
Eyasi-1
G. des Enfants-4
G. des Enfants-5
G des Enfants-6
Skhiil-4
SkhGl-5
Skhiil-9
Mladec-5
Amud-l
Predmost-3
Predmost-4
Combe Capelle
Cro-Magnon
Markina Gora
Cap Blanc
Staroselye
Choukoutien-101
Choukoutien-102
Choukoutien-103
Barma Grande
Barma grande
Barma grande
Brno-l
Le Figuer
Olduvai-1
Cape Flats
Cheddar
Gamble’s Cave-4
Gamble’s Cave-5
Laugerie
1230
1600
1500
1380
1300
1740
1580
1250
1440
1590
1715
1375
1580
1554
1520
1590
1568
1600
1271
1280
1600
1420
CC
1450
1600
1345
CI
70.5
76.2
67.6
77.0
73.2
75.1
78.2
77.0
65.9
75.0
75.0
73.7
75.0
85.5
74.3
76.3
68.6
69.3
71.8
74.5
68.1
73.1
72.1
71.3
70.2
65.7
73.8
71.5
76.3
73.1
70.2
69.3
71.3
71.6
76.3
72.2
69.0
74.7
66.0
69 .O
70.4
70.8
73.7
74.9
47
47
45
45
42
42
42
41
40
40
38
37
36
34
34
32
32
32
32
32
32
31
28
26
26
25
22
21
20
20
18
18
18
17
17
17
17
17
17
15
15
15
15
15
Date
F
M
M
F
M
F
F
F
M
M
F
M
M
M
M
M
M
M
M
M
F
M
F
M
F
M
M
M
M
S
TR
TM
GL
GL
TM
TM
GL
TM
TR
GL
TR
TM
TR
GL
TR
GL
GL
GL
TM
TM
TM
GL
TM
GL
GL
GL
GL
GL
GL
GL
TM
TM
TM
GL
GL
GL
GL
GL
TR
TR
GL
TR
TR
G1
CZ2
TAX3
MM
N
N
N
N-MM
N-MM
N
N
N-MM
N
MM-N
N-MM
MM
MM
N-MM
MM
MM
MM
N-MM
N-MM
N-MM
MM
N-MM
MM
MM
MM
MM
MM
MM
MM
MM
MM
MM
MM
MM
MM
MM
MM
MM
MM
MM
MM
MM
MM
(contin ued on tiLest page)
027S032E
037N044E
046NOOOE
046NOOOE
032N009W
032N009W
048N021E
033N035E
014S028E
045N002E
029S026E
033N035E
034S019E
044N004E
004S035E
044N008E
044N008E
044N008E
033N035E
033N035E
033N035E
049N017E
033N036E
049N017E
049N017E
045N003E
045N001E
051N039E
045N001E
046N034E
040N115E
040N115E
040N115E
044N008E
044N008E
044N008E
049N017E
045N004E
003S035E
035S018E
051N003W
001S036E
001S036E
045N001W
Location
Notes and sources4
Border cave, date revised (067) (P72) (P75)
(W80)(K70)(B79) (075)
Sex doubtful, adult (B79) (H51)
Child (B79) (H51)
(067) (W80) (P72) (B79)
(067) W80) (P72) (B79)
Child (7-9 years) (A76)
(W80)(B79) (M74) (H51)
“Rhodesian Man” (067) (P72) (B74)
(B79) (H51)(580)
(067) (P72) (B79) (P75)
Jebel Kafzeh (W80) (V75)
(067XP72 (P75)
(P72)
Sex doubtful (067)
Grimaldi (F78) (NND)
(F78) (NND)
(F78) (NND)
(B79)(P72) (H51)(M74) (075)
(H51) (B79) (P72) (M74) (075)
(M74)(P72) (H51)(B79) (075)
Lautsch, (W80) (B79) (071)
Record cranial volume, (W80)(B70)(075)
(B79) (NND)
(B79) (NND)
(p72) (B79)
(P72)(B79) (D65)
Kostenki (A76) (071)
Maedalenian. absolute date uncertain W45) (071)
Chiid, CI estimated for adult (A76)
Upper cave (W38)(W80)(B79)
Upper cave (W80) (879) (W38)(075)
Upper cave (W80) (B79)(W38)(075)
Grimaldi, date uncertain (NND)
Grimaldi, posthumous deformation (K80) (NND)
Grimaldi, Mentone (K80) (NND)
(W80)(P72) (B79)
Child (B80)
Low CI due to postmortum distortion (P74) (067)
TABLE 1. Paleontological data of specimens (continued)’
b@
N
tr
0
U
tr
m
P
F
v,
Lr
m
x
em
(Y,
74.9
75.1
74.6
70.0
73.8
72.0
72.6
73.4
80.5
77.7
88.9
86.2
77.0
83.3
78.7
75.7
72.7
76.8
78.9
70.5
73.7
78.2
65.8
67.0
72.4
68.6
77.4
72.5
Laugerie
Liu Kwang-1
Obercassel
Obercassel
Springbok-1
Chancelade
Keilor-1
Talgai-1
Ofnet “2.1”
Ofnet “2.11”
Ofnet “3.1”
Ofnet “4.1”
Ofnet “5.11”
Ofnet “8.1”
Ofnet “11.1”
Ofnet “13.1”
Ofnet “14.1”
Ofnet “15.1”
Ofnet “18.1”
Ofnet “21.1”
Ofnet “24.1”
Ofnet “25.1”
Cohuna
Kow Swamp-1
Kow Swamp-5
Kow Swamp-14
Tze Yane-1
Wadjak-T
11
10
10
10
10
10
10
1260
1210
1550
Location
045N001W
024N109E
015N007E
051N007E
025S029E
045N001E
038S145E
027S150E
049NO 10E
049N010E
049N010E
049N010E
049N010E
049N010E
049N010E
049N010E
049N010E
049N010E
049N010E
049N010E
049N010E
049N010E
036S144E
036S144E
036S144E
036S144E
030N105E
008S112E
S
F
F
F
F
M
F
F
F
F
M
F
M
M
M
F
~~
F
M
M
M
M
F
;: y
11
11
11
11
11
11
11
11
11
11
15
15
15
15
15
14
13
12
11
M
M
M
GL
GL
GL
GL
GL
GL
GL
GL
GL
GL
G1
GL
GL
TR
TR
TR
TR
TM
TR
G1
TM
GL
GL
TR
GL
TR
TR
GL
CZ2
MM
MM
MM
MM
MM
MM
MM
MM
MM
MM
MM
MM
MM
MM
MM
MM
MM
MM
MM
MM
MM
MM
MM
MM
MM
MM
MM
MM
TAX3
Notes and sources4
(N79) (NND)
(N79) (NND)
(N79) (NND)
(N79)(NND)
(N79)(NND)
(P72) (075)
(T81) (075)
(T81) (075)
(T81) (075)
(P72) (W58) (075)
(P72) (B79) (W45B) (D65) (075)
L. Basse (F78) (NND)
Liukiang (075) (P72)
(F78) (NND) (B79)
(F78) (NND) (B79)
May be later burial (067) (P72)
(P72)
(W45B) (075)
Adolescent, CC +5%(W45B)
Ofnet redated from Mesolithic-Newell-79 (N79)
(NND)
ID numbers from Neumann catalogue (N79) (NND)
(N79) (NND)
(N79)(NND)
(N79) (NND)
TABLE 1. Paleontological data of specimens (continued)’
Date
1500
420
1540
1530
1593
1370
1480
1500
CC
‘The 118 specimens are abstracted from the 147 listed in HOMDAT, which include the cranial index. The specimens are in chronological order. Columns include
specimen and site, cranial index (CI), cranial capacity (CC), estimate of date ( X 1,000), presumed sex (S), location, climatic zone (CZ), taxonomic code (TAX), and
notes and principle sources. A complete file may be obtained by writing. The authors are grateful for attention to errors or omissions.
*Climatic codes: TR, tropical; TM, temperate; GL, glacial.
3Taxonomic codes: AA, A. africanus; AR, A. robustus; HH, H habilis; HE, H. erectus; N, Neandertal, Neandertaloid, archaic H. sapiens; MM, early modern, H.
saoiens.
4Reference codes: A73, Aigner and Laughlin, 1973; A76, Alexeyev, 1976; B35, Von Bonin, 1935; B50, Briggs, 1950; B70, Brain, 1970; B79, Brace, Nelson, Korn and
Brace, 1979; B80, Billy, 1980; D62, Dart, 1962; D65, Day, 1965; D80, Day, Leakey, and Magori, 1980; F78, Frayer, 1978; H51, Howell, 1951; H72, Holloway, 1972;
H73. Hollowav. 1973: H78. Hollowav. 1978: H80. Hollowav. 1980: H81. Hollowav. 1981: H80. Howells. 1980: J66. Jacob. 1966: 573. Jacob. 1973: K70. Kelso. 1970:
K80, Kenned;,’ 1980; L70, Leakey, 7970; L72, Leakey, MLngai and Walker, 19?2; L73, Leakey, 1973; L74; Leakey, 1974; L75, Lestrel, 1975; ‘M62, McKern and
Kozlik, 1962; M74, Mann and Trinkaus, 1974; NND, Neumann, no date; “79, Newell, 1979; 052, Oakley, 1952; 067, Oakley and Campbell, 1967; 071, Oakley,
Campbell and Molleson, 1971; 075, Oakley, Campbell and Molleson, 1975; P72, Phenice and Sauer, 1972; P73, Parenti, 1973; P74, Protsch, 1974; P75, Protsch, 1975;
R74, Rightmire, 1974; S54, Singer, 1954; S77, Sigmon, 1977; S80, Smith, 1980; T71, Tobias, 1971; T81, Thorne and Wolpoff, 1981; V49, Vallois, 1949; V75, Vallois
and Vandermeersch, 1975; W39, Weidenreich, 1939; W45, Weidenreich, 1945; W45B, Weidenreich, 1945B; W58, Woo, 1958; W71, Wolpoff, 1971; W80, Wolpoff, 1980;
W80B, Wolpoff, 1980B.
CI
Specimen
m
m
30W
Fig. 1. Illustration of computerized mapping (HOMPLOT). Desired scale
and region are specified by input of SWNE coordinates. Customized maps
and data analysis may be drawn from existing files (HOMDAT = 147 specimens, 8 variables; CLIMDAT = 82 populations, 11 anthropometric and 10
climatic variables; CRANDAT = 122 populations, cranial capacity data; CULMAP = 1,150 cultures, 150 variables. Inquiries should be directed to the
50s
authors. The map plots locations of cranial index reports for Pleistocene
speciments. Data points may be labeled or numbered. “Choukou” illustrates
label character length limitation. Plotting accuracy is limited to nearest
degree (note Cape Flats). Any datum associated with points can be plotted
(i.e., “35S, 18E”). Isophenes must currently be drawn manually. Options
include color differentiation, paper gloss, and grid overlay.
U
0
U
U
r
F
431
CLIMATE AND BRACHYCEPHALIZATION
living groups. We have classified the specimens as reflecting a general adaptation
among their immediate ancestors toward
tropical, temperate, or glacial conditions.
“Tropical” is considered as the normal absence of winter frost, and includes both dry
heat and wet heat. “Temperate” refers to
regions having winter frost, but a moderate
mean temperature. “Glacial” includes both
wet cold and dry cold.
The world mean cephalic index for 362 populations is 78.5 units. This value, however,
overestimates the actual amount of phylogenetic change, since it is well known that the
cephalic index averages 1 to 2 units higher
than the cranial index. While it is possible
that variation with frontoparietal musculature may be a factor, Krantz (1980) argues
that the observed higher values for the cephalic index are the result of geometric effect-removal of approximately equal surface
tissue produces a disproportionate length/
breadth ratio with a n oval object. To more
accurately compare the paleontological record to contemporary populations, we have
reduced the world mean for the cephalic index by 1.5 units, which gives a n average of
77 units for the cranial index.
It is desirable to organize the data by taxonomic category as well as time. The ubiquitous problem is a lack of consensus for a
number of specimens-largely those that are
morphologically intermediate. It is a problem that affects all of the statistical interpretations, since each possible arrangement
produces a difference in the sample size, descriptive statistics, probabilities of significance, and rates of change.
As a practical matter, we have evaluated
the data with two taxonomic models. The
first is “gradualistic” in the sense that the
attributions correlate almost exactly with
time. The second is based upon the most common alternative attribution of disputed specimens. For example, the material from Solo
(Ngandong 1, 6, 7, 10, 11, 12) is included as
Neandertal in the former model and as Homo
erectus in the latter. Details are given in
Table 1. Within the text H. erectus, Neandertal, and early modern H. sapiens refer to the
gradualistic list.
RESULTS
Previous work (Beak, 1972) has already
demonstrated that head shape has a significant relationship to zones of climatic stress.
Weather is a multivariate phenomenon, how-
ever, and it may be that some other climatic
element could be more appropriately applied
to the fossil record. Correlations were therefore calculated between the cephalic index
and the nine variables previously described.
Results are summarized in Table 2.
Climatic zone has the virtue of being the
simplest variable to classify throughout the
past. It may be noted that it also has the
highest correlation with the cephalic index,
explaining approximately 21% of the variance itself.
In Figure 3, contemporary groups are compared to the fossil record, with a humidity
factor (wetnessldryness) distinguished for the
former. Differences between wetldry heat and
wetldry cold are significant. However, these
zones were originally based upon annual precipitation, and such moisture by itself seems
to have no effect. The apparent anomaly was
investigated by correlating climatic zone
with vapor pressure-arbitrarily assigning 15 for dry heat through dry cold, respectively.
As cold increases, vapor pressure decreases
(r = -0.41 in winter and -0.56 in summer).
Annual precipitation and vapor pressure
have different meteorological causes. However, by simultaneously classifying temperature and precipitation, climatic zone incidentally correlates with vapor pressure as
well.
It also may be noted that Schwidetsky’s
(1952) scale of isotherms (temperature only)
predicts the index virtually as well as
climatic zone. It has a correlation of -0.45
compared to -0.39 for coldest month temperature and -0.14 for warmest month temperature. Again, however, the %uccess” of the
scale is enhanced by its intercorrelation with
TABLE 2. Correlations and probabilities of significant
difference between climatic variables and mean cephalic
index among ethnic groups‘
Climatic zone
Isothermic zone
Winter temperature
Solar radiation
Winter water vapor
Hours of sunshine
Summer water vapor
Summer
temperature
Annual precipitation
r
Fr
P
0.46
-0.45
-0.39
-0.39
-0.29
-0.22
-0.22
-0.14
0.09
0.09
0.09
0.09
0.10
0.11
0.11
0.001
0.001
0.001
0.001
0.005
0.023
0.021
0.104
0.03
0.16
0.399
0.11
‘N = 82 composite means (subgroups, i.e., Australians and
Eskimo, in different locations averaged). Vapor pressure is in
millibars (IO’dynes cm’). Solar radiation is in kcal cm’ earth
surface. Variables are elaborated in text.
K.L. BEALS, C.L. SMITH, AND S.M. DODD
432
.
.-m
.-m
?
x
.
a
u0
.
r
a
s
c
W
c
0
D
0
d
CI
0
Ln
0.
0
0
0
0
0
In
0
.
0
0
0
0
0
e
0
e
0
0
0
0
0
0
Ln
0
*a
0
0
c
L
.n
Ln
0
0
0
In
433
CLIMATE AND BRACHYCEPHALIZATION
vapor pressure (r = -0.68 in winter and
-0.73 in summer).
Our interpretation of cephalic index among
living groups is that winter conditions are
more important than those of the summer.
Temperature is more important than humidity. Temperature and vapor pressure have
interactive effects so that general climatic
classifications correlate more highly with the
index than do the individual variables.
Turning to the Pleistocene, the mean hominid cranial index has increased 9 units. Figure 2 plots the distribution through time.
The trend is general-not simply confined
to the recent past. It is, however, geometric.
A log transform of individual dates yields a n
intercept of 76.6 at 10,000 B.P., compared to
77 as the observed current mean (CI = 76.7
- 1.96 log time x lo3). The log of absolute
date for the 115 samples gives a correlation
of -0.28 back through time, with a significance of 0.001. A slow rate of increase is
observed while hominids occupied only tropical environments, but it accelerated dramatically with a n adaptation to the rigors of
winter.
The appearance of hominids in cold is relatively recent. The earliest specimen (for
which we have a n estimate of the index) from
a nontropical location is Lantian, with a n
approximate date of 775,000 B.P. Even this
should be considered as a marginal case of
mixed broadleaved forest-grassland ecology,
and semitropical to temperate climate. If we
take 500,000 years of time for adjustment to
any substantial amount of winter stress, this
is still less than one eighth of hominid existence. If the hypothesis is correct, however,
we should expect this relatively short period
of time to have a disproportionate effect upon
the total amount of change. It has been noted
already that the rate of change was indeed
extremely slow prior to the occupation of cold
environments.
Table 3 provides a summary by taxon, independently of time. A comparison of the
means with the percentage of samples from
temperate and cold environments within the
hominid file is shown below.
-
Taxon
A ustralopithecusl
H. habilis
H. erectus
NeandertaV
Neandertaloid
Early modern
H. sapiens
x CI
Temperate1
Cold
67.5 _+ 2.2
0%
71.2 k 1.0
73.8 k 0.6
35%
70%
73.9 5 0.6
73%
The percentages are not meant to be taken
as a measurement of the actual geographical
TABLE 3. Summary of cranial indices among
hominids from climatic zones
Gradualist
model
N
X
r
H. erectus
Tropical
Temperate
Glacial
Total
Neandertal
Tropical
Temperate
Glacial
Total
Early modern H.
sapiens
Tropical
Temperate
Glacial
Total
9
5
70.0
73.5
14
71.2
13
12
16
41
14
5
37
56
-
Alternate
model
N
X
r
3.9
15
5
1
21
71.5
73.5
80.0
72.4
70.9
73.9
76.2
73.8
4.4
2.6
3.2
4.1
1
5
15
21
68.3
75.6
75.9
75.5
71.4
72.7
75.0
73.9
2.9
3.5
5.i
4.7
-
3.9
3.0
_
20
12
37
69
4.3
3.0
4.3
2.2
3.1
3.2
70.5
72.6
75.0
73.3
3.2
2.7
5.1
4.7
distribution, since they reflect more intensive field work in certain areas, i.e., Europe.
The mean of the index is, however, partially
determined by the particular frequency of
samples that happen to come from different
ecological zones.
Among contemporary populations, the
large amount of heterographic information
on the cephalic index derives from the historical circumstance of the trait being regarded
as nonadaptive and hence indicative of racial
affinity. In actuality, the trait has become
one of the most extensively documented examples of climatic adaptation known. It has
no taxonomic (racial) utility beyond the secondary correlation of particular groups (such
as Africans and Europeans) being inhabitants of particular climatic regions.
A similar circumstance is apparent from
the fossil record. Variation between tropical
and glacial ecotypes exceeds variation between taxa. For example, the difference between tropical and glacial Neandertals is 5.1
units, whereas the difference between all
Neandertals and early modern H. sapiens is
only 1.2 units.
The hypothesis in question predicts that
means within taxa will systematically increase in accordance with decreasing temperature. Including modern populations, there
are seven possible trials, and the means are
shown below.
H. erectus
Neandertal
Early modern
H. sapiens
Contemporary
ethnic groups
Tropical
Temperate
Glacial
70.0
70.9
71.4
73.3
73.9
72.7
76.2
75.0
75.5
78.9
80.0
-
434
00
K.L. BEALS, C.L. SMITH, AND S.M. DODD
I
LOWER
PLEl STOCENE
I
H. ERECTUS
- -
I
NEANDERTAL
I
I
EARLY MODERN
ETHNOGRAPHIC
PRESENT
Fig. 3. Means of cranial index for hominids from tropical, temperate, and glacial climates. Ethnographic data
is subdivided into humid and dry thermal stress zones
(N = 362 group means).
General exceptions to the theory do not
exist, and the probability of such a n occurrence by accident alone is 0.008 (0.ij7). In
Figure 3, the relative difference between taxa
is illustrated for the gradualist model.
The individual taxonomic means are, of
course, dependent upon the specific specimens which are included. The alternative
model lists the data (see Table 3) by attribution of disputed forms to a n alternative classification. A primary difference is the number
of specimens included as Neandertals (N =
21 rather than 41). It is apparent, however,
that the overall pattern of climatic adaptation remains the same; there are again no
exceptions. The results cannot be explained
as the arbitrary effect of a particular phylogenetic model.
It is true that variations in time between
ecotypes within taxa influence the difference
between means. For example, the cases classified as temperate H. erectus are collectively
much younger than those from the tropics. It
is also apparent from Figure 3 that other
factors in addition to climate are required to
explain the evolutionary change. There exists during the Pleistocene a slight increase
of cranial index even among tropical ecotypes. It is obvious that a theory that accounts for a n increase as being due to
adaptation to winter cold cannot explain such
an observation when winter cold is not
present.
We may nonetheless evaluate the effect of
the consequence of climate in addition to
whatever the nonclimatic factors are through
time. This may be done by comparison of the
regression of specimens unexposed to winter
frost to each separate observation among
those whose immediate ancestors were exposed. Such a procedure also permits the ambiguity with taxonomy to be eliminated since
it is simply a test of time and climate only. A
sign test further reduces any effect on the
CLIMATE AND BRACHYCEPHALIZATION
parametric summaries that result from measurement error-existing to some unknown
extent in regard to fragmentary or reconstructed remains.
The cranial index regression for tropical
forms only is -0.70128 log age (in thousands
B.P.) f 0.76, with a n intercept of 71.99 at
10,000 B.P. If we take the null hypothesis
that the unknown factors associated with
time can explain the observations within
temperate and cold regions, then we expect
a n equal number of signs above and below
the regression. Our observations yield 61
cases above the tropical regression, but only
12 below, with a probability less than 0.0001.
By comparing each trial to the prediction,
it is then possible to adjust for collective temporal difference between ecotypes within
taxa. Results are summarized below, in
which the values represent the mean additive magnitude of the index when compared
to tropical contemporaries.
435
likewise has a known mechanism of selection
that will result in differential reproductionnamely death by exposure. Such deaths include any life crisis in which heat radiation
is a contributory factor, such as increased
physiological stress in cases of traumatic
injury.
Variations in the cephalic index of modern
populations are at least partially a consequence of adaptation to cold during the Pleistocene. Ecotypic differences within taxa exist
both dependently and independently of time,
and with time independently of taxon.
The historically important assumption that
head shape was a nonadaptive trait (and
hence indicative of racial affinity) is no longer
tenable. Furthermore, there is no reason to
believe the trait serves any better for taxonomic diagnosis. To illustrate, the difference
between Neandertals and H. erectus is 2.6
units (gradualist model) and 3.1 units (alternate model), while the ecotypic means vary
as much as 7.6 and 8.5 units.
Complicating any taxonomic utility is the
Temuerate
Glacial
substantial “natural” variation. For example, the difference between Skhiil 5 and
H. erectus
4.40
Neandertals
4.17
6.94
S k h d 9 is 6.4-equivalent to the average
Early modern
1.80
4.70
change between the Lower Pleistocene and
H. sapiens
Upper Paleolithic-with a time span in excess of 2 million years. At Ofnet, specimens
The relative differences between climatic vary by 8.4 units within centimeters in space,
regions among early modern H. supiens is and identical time and climate.
approximately the same as between current
The implication is that if head shape is
ethnic groups. Glacial Neandertals, living included among the traits used for taxonomic
under arduous winter conditions, show a n assessment, some adjustment for the effect of
even higher relative magnitude.
climate must be made. It is further suspected
Significance of difference between means that any trait that plays a role in surface
was calculated by t test, comparing tropical area:mass ratios will require a similar apspecimens to those from both temperate and proach.
glacial conditions. Data for H. erectus do folCranial capacity, for instance, is almost
low the expected direction; yet, the probabil- universally used for taxonomic comparison
ities are not significant (p = 10% for the and assessment. The distribution, however,
gradualist model and = 20% for the alter- mirrors the adaptive pattern of the cranial
nate). While it is probable that differentia- index. The modern ethnic group data show a
tion by climatic ecotype began a t such a n sex-combined increase from 1293 to 1300 to
early date, the small sample size precludes a 1362 to 1385 to 1425 cm3 from dry heat
definite answer.
through dry cold zones, respectively. These
Results are significant for Neandertal spec- are ecotypic rather than taxonomic associaimens and early modern H. supiens. The tions, and are of substantial magnitude. Cligradualist model yields probability levels less mate affects size as well as shape; if one
than 0.005, the alternate, less than 0.001.
compares values from one taxon to another,
the ecotypic and taxonomic variation is conDISCUSSION
founded. A given mean may, for example, be
A partial explanation for the relation be- significantly greater for no reason other than
tween climate and the architecture of the containing a higher proportion of specimens
human cranium is found in the physical prin- from colder thermodynamic environments.
ciples of heat radiation and by the distribuA number of specimens represent populational evidence through time and space. It tions exposed to periglacial conditions. Mul-
436
K.L. BEALS, C.L. SMITH. AND S.M. DODD
tivariate analysis among current groups
living under comparable stress has been performed, although results are as yet unpublished. Briefly, extreme cold is typified by
moderate stature, moderate nasal index,
round cranium, large cranial volume, small
brain size relative to weight, large brain size
relative to stature, and lateral body build.
These are examples of traits that should also
be expected to show ecotypic variation evolving through the fossil record and also those
that are especially indicative of the extent of
cold adaptation among fossil forms.
Such adaptation has been most widely discussed in reference to Neandertals (e.g.,
Howell, 1957). Head form data support the
independent affirmative conclusions of Trinkaus (1981) with regard to postcranial remains. Glacial Neandertals fit the roundheaded model that is expected under such
conditions. It is true that their average cranial index is less than the means of populations of the present living under extreme cold
(Fig.3). However, if we make the comparison
with specimens that were contemporary, the
difference is striking; Glacial and Tropical
Neandertals vary more than the average difference between A ustralopithecus and early
modern H. sapiens.
The climatic model succeeds in two major
ways: It explains the general variation
tween groups, and it explains why a
trend toward brachycephalization occurred
throughout the Pleistocene. As is often the
case, however, the apparent failure of a theory is more interesting than its success.
There are two apparent and perplexing failures. As may be seen in Figure 3, the index
seems to decrease between Temperate/Glacia1 Neandertals and early modern H. supiens. Secondly, the index increases even
among forms and populations unexposed to
winter frost.
The first case bears upon the longstanding
debate on the “Neandertal problem” (i.e.,
Howells, 19761, particularly with respect to
extinction, migration, or gene flow coincident with the origin of the Upper Paleolithic.
We plotted the available information on the
assumption that the observed decrease was
not significant. Using all cases from Europe
and southwest Asia between 15,000 and
75,000 B.P., the overall slope is 0.04971, with
a correlation through time of 0.21 and a probability of 0.052. The level of significance is
so close to the arbitrary 5% level that we
cannot reject the statistical probability of a
decrease.
There are, nonetheless, multiple interpretations of the evidence. Some of these include
a possible effect from the postglacial warming trend, insulation from extreme cold by
improved technology, sampling inadequacy,
and gene flow (or replacement event) from
the tropics. Further work with multivariate
analysis may resolve the problem.
The second apparent failure concerns the
fact that the index increases even when adaptation to cold cannot be a plausible explanation. The extremely slow rate of increase
within the tropics for 2 million years could
conceivably be some combination of sample
size, dating, or measurement error; yet we
must accept the rapid increase within the
same type of heat stress for the recent past
as genuine-as it is based upon thousands of
individual observations and dozens of ethnic
groups.
The basic problem is that the index increases not only under conditions of cold (as
expected), it also increases under conditions
of severe heat (when unexpected). Our interpretation is that a climatic explanation cannot be the sole adaptive factor. It may not
even be the most important. Whatever such
additional processes may be, circumstantial
evidence indicates that their effect would
have to be exponential-with small significance until about 15,000 years ago. Such circumstantial speculation immediately suggests a connection with isolation breakdown.
Convincing evidence requires, however, the
demonstration that isolation breakdown not
only changes the distribution of the variance,
but also the mean of the trait over time.
ACKNOWLEDGMENTS
The authors are indebted to David Frayer
and Gerry Brush for assistance in the preparation of the files. Evaluation of data was
supported by unsponsored research funds
from the Oregon State University Computer
Center. Dave Fuhrer and Bob McNaughton
aided in the creation of the mapping
program.
LITERATURE CITED
Beals, KL (1972) Head form and climatic stress. Am. J.
Phys. Anthropol. 37r85-92.
Bielicki, T, and Welon, Z (1964)The operation of natural
selection on head form in an East European population. Homo I5r22-30.
Boas, F (1911) Changes in Bodily Form of Descendants
of Immigrants. Washington: U.S. Government Printing Office.
Coon, CS (1955) Some problems of human variability
and natural selection in climate and culture. Am. Nat.
89:257-279.
CLIMATE AND BRACHYCEPHALIZATION
Crognier, E (1981) Climate and anthropometric variations in Europe and the Mediterranean area. Ann.
Hum. Biol. 8:99-107.
Hiernaux, J (1968) La Diversit6 humaine en Afrique
Sub-Saharienne. Bruxelles: Universitk Libre de
Bruxelles.
Hooton, EA (1946) Up From the Ape. New York:
Macmillian.
Howell, FC (1957)Evolutionary significance of variation
and varieties of Neanderthal man. Quart. Rev. Biol.
37:330-347.
Howells, WW (1976)Explaining modern man: Evolution-
437
ist versus migrationist. J. Hum. Evol. 5:477-495.
Hulse, FS (1971) The Human Species. 2nd Ed. New York:
Random House.
Krantz, GS (1980)Climatic races and descent groups. N.
Quincy, Massachusetts: Christopher.
Schwidetzky, I (1952) Selektions Theorie und Rassenbildung beim Menschen. Experientia 8:85-98.
Trinkaus, E (1981) Neanderthal limb proportions and
cold adaptation. Aspects Hum. Evol. 21:187-224.
Weidenreich, F (1945)The brachycephalization of recent
mankind. SW. J. Anthropol. 1:l-54.
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