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Radiators are cool: A response to Braga & Boeschrsquo;s published paper and reply
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Radiators are cool: A response to Braga & Boesch’s published paper and reply
Dean Falk & Timothy B. Gage
Department of Anthropology, State University of New York at Albany, Albany, New York 12222, U.S.A. E-mail: [email protected] Journal of Human Evolution (1998) 35, 307–312 Article No. hu980237
A recent volume of this journal contained an article about cranial blood flow (Braga & Boesch, 1997a), our reply to a manuscript that was identified as a final draft of that article (Falk & Gage, 1997), and a reply to our reply (Braga & Boesch, 1997b). As the result of an editorial error the draft to which we replied was not, in fact, the final draft of Braga & Boesch. It was only after it was published that we first read the Braga & Boesch (1997b) reply. Upon reading Braga & Boesch (1997a), it became clear that, unbeknownst to us, a specimen had been removed from Table 8 of the version of Braga & Boesch’s paper to which we had replied, and the relevant statistics had been changed throughout the final publication. Because the summary table and figure presented in Falk & Gage (1997) incorporated data that were deleted from the published Braga and Boesch manuscript, they are inconsistent with Braga & Boesch (1997a) and must now be corrected. Table 1 and Figure 1 of this note should therefore replace those published in our recent reply to Braga & Boesch (Falk & Gage, 1997). The specimen that was deleted is SK 847, assigned to Homo by Clarke (1985) and Falk (1986), but classified as a robust australopithecine in the version of the Braga & Boesch manuscript to which we replied. Contrary to the 1/4 frequency provided for the parietal foramen of robust australopithecines in Table 8 of Braga & Boesch (1997a: p. 434), in their reply to our reply, Braga & Boesch (1997b: p. 504) cite a frequency of 1/5, which is based on the earlier draft that 0047–2484/98/090307+06 $30.00/0
included SK 847 as a robust australopithecine. The deletion of SK 847 and alteration of statistics in Braga & Boesch (1997a) raise questions about the attributions and scoring of the six other specimens scored as australopithecines in Braga & Boesch (1997a) but not Falk (1986): SKW 11, SK 27, KNM-ER 417, KNM-ER 23000, Stw 53, and Stw 187a. In this note, we investigate whether or not Braga & Boesch’s taxonomic attributions and scoring for these specimens should be accepted at face value as we had initially assumed. In Table 8 of Braga & Boesch (1997a: p. 434), SKW 11 is listed as a robust australopithecine with a left mastoid foramen, and the authors indicate that this observation was previously unpublished. However, this specimen is fragmentary and damaged in the region of the mastoid process (Grine & Strait, 1994), which from Figure 3(d) of Grine & Strait (ibid: p. 63) appears to be too eroded to score for emissary foramina. Fred Grine (personal communication) has confirmed this observation by examining ‘‘a very nice color lateral view of the specimen. It is clear that there is no surface bone left on the mastoid! . . . There is no possibility that this region can be scored for the presence or absence of emissary foramina.’’ Another specimen that is identified as a robust australopithecine in Table 8 of Braga & Boesch, SK 27 (a juvenile, fragmentary crushed cranium), is attributed to Homo by most workers (Clarke, 1985: p. 177; Kimbel et al., 1985: p. 128; Falk, 1986). A third 1998 Academic Press
. . .
308 Table 1 I Falk ’86
II B&B ’97
III F&G (this report)
rob; gra
rob; gra
rob; gra +
Enlarged O/M Div. hypoglossal Mastoid
7/7; 1/4* 2/3; 0/3 2/8; 2/5
2/3; 0/4 4/7; 2/2
10/10; 1/6*† 2/3; 0/2 2/9; 2/3
Parietal Occipital P. condyloid
0/3; 0/5 1/5; 1/4 5/6; 1/4
1/4; 0/3 2/7; 1/2 8/8; 2/6*
1/4; 0/3 1/5; 1/2 5/6; 1/3
Questionable attributions or scoring of B&B ’97a As robusts
As graciles
— SKW 11, ER 417 KNM-ER 23000 — SK 27 SK 27
Stw 53, Stw 187a — — — Stw 53, Stw 187a
Frequencies of emissary foramina for robust (rob) and gracile (gra) australopithecines, from Table 2 of Falk (1986), Table 8 of Braga & Boesch (1997a), and Falk & Gage (this report). Data for O/M sinuses from Falk et al., 1995; ER 1805 and ER 1813, included as graciles in I, are excluded from that category in III; and scorings for parietal and mastoid emissary foramina of KNM-ER 23000 (Brown et al., 1993) are included in III. Discrepancies between column II of this table and column II of our earlier Table 1 (Falk & Gage, 1997) are due to the fact that Braga and Boesch’s scorings for SK 847 (included in robust australopithecines in the draft of their paper to which we responded) were incorporated in our earlier table. Braga & Boesch’s (1997a) scorings for other fossils were also incorporated into column III of Falk & Gage (1997), but most are now excluded from column III of this table for reasons detailed in the text. *Fisher’s exact P<0·05. †Fisher’s exact P<0·05 with Bonferroni’s correction.
specimen that Braga & Boesch identify as a robust australopithecine, KNM-ER 417, is a very fragmentary parietal of unknown hominid species (White, 1988: pp. 466–467). Based on the above, these three specimens are excluded from our frequencies for robust australopithecines (column III in Table 1). A calvaria of A. (P.) boisei, KNM-ER 23000, had not been discovered at the time of Falk’s 1986 study. Braga & Boesch scored this specimen as having a right mastoid foramen and cite Brown et al. (1993: p. 146) as their source. However, although Brown et al. note the presence of a mastoid canaliculus in the jugular fossa (which is for passage of the auricular branch of the vagus nerve), we find no reference to a mastoid foramen. Alan Walker (personal communication) confirms that a mastoid emissary foramen was not scored as present for this specimen, and adds: ‘‘I’ve checked my casts and I don’t think there is a foramen hiding in the lambdoid suture that I might have missed originally’’. Because of this, and because the right temporal bone (KNM-ER 23000E)
appears complete (Brown et al., 1993, Figure 4B), we score the mastoid foramen as missing in this specimen. We therefore include KNM-ER 23000 in our scoring of mastoid emissary foramina for robust australopithecines, but score it differently than Braga & Boesch. Brown et al.’s (1993: p. 147) observation of parietal foramina in ER 23000 is also included in column III of Table 1. Turning to gracile australopithecines, Table 8 of Braga & Boesch includes Stw 53 in this category, although this partial cranium is regarded as Homo by most workers (Clarke, 1985; Tobias, 1988). A second specimen that Braga & Boesch attribute to A. africanus, Stw 187a from Member 4 of Sterkfontein, is more problematic. According to Philip Tobias (personal communication), this specimen comprises ‘‘the basi-occipital and the lateral occipitals fused on to it by closure of the anterior intraoccipital synchondrosis’’. Tobias further observes that Stw 187a is probably a gracile australopithecine, although ‘‘there is still
argument over whether one or two specimens in Member 4 from Sterkfontein may perhaps fall outside the range for the species A. africanus’’. Because of this uncertainty, and because Braga & Boesch’s observations of emissary foramina in this specimen have yet to be confirmed by other workers, we exclude this specimen, along with Stw 53, from column III of Table 1. On other matters, Falk (1986: p. 320) noted that Boyd’s (1930) frequency for mastoid foramina in Homo sapiens was ‘‘probably low because Boyd scored a foramen as absent if a wire would not pass through it’’. Braga & Boesch (1997a: pp. 426–427) misquoted Falk by replacing the word ‘‘absent’’ with ‘‘present’’ in this quotation, which they then used to make an erroneous argument about scoring procedures. Turning to Braga & Boesch’s (1997b) reply to Falk and Gage (1997), in addition to the inconsistency in the sample size of robust australopithecines between this and Braga & Boesch (1997a) discussed above, no mention is made in Braga & Boesch’s reply of the inconsistencies between the data sets of the paper to which they are replying (Falk & Gage, 1997) and Braga & Boesch (1997a). To summarize, five of the six specimens that were scored as australopithecines by Braga & Boesch (1997a) but not Falk (1986) are excluded from Falk & Gage’s frequencies for emissary foramina (column III of Table 1) because of questionable scoring or taxonomic attributions. Braga & Boesch’s scoring for the mastoid foramen of the sixth specimen (ER 23000) is based on mistaking the mastoid canaliculus (Brown et al., 1993: p. 146) for the mastoid foramen. Scoring of the mastoid foramen that correctly reflects Brown et al.’s observations is included in column III of Table 1. The data presented in Table 1 and Figure 1 support earlier observations of the trends regarding cranial blood flow in fossil hominids (Falk, 1986), as well as their interpretations as articulated in the radiator theory
309
(RT) (Falk, 1990a,b). This may be verified by comparing these data with those provided earlier (Falk, 1986; Falk, 1990a,b; Falk et al., 1995). Braga & Boesch (1997a, 1997b) assert that the only reasonable test of the RT is to determine whether or not gracile australopithecines can be statistically shown to have been characterized by a cranial radiator network of veins not seen in robust australopithecines. As detailed in Falk & Gage (1997), this is a strawman hypothesis because it contradicts the published data and discussion pertaining to the RT (Falk, 1986; Falk, 1990a,b; Falk 1992; Falk et al., 1995; Falk & Gage, 1997). On the other hand, Braga & Boesch ironically ignore the statistically significant difference in frequencies of enlarged occipital/marginal sinuses that not only distinguishes the cranial plumbing of robust and gracile australopithecines, but also constitutes a crucial basis for the RT. An important but controversial assumption upon which the RT was initially formulated (Falk, 1990a,b), was the hypothetical existence of a vast network of tiny emissary veins that serve to selectively cool the brain of hyperthermic humans. As detailed in Falk & Gage (1997), the RT has recently received dramatic support from numerous physiological and anatomical studies (e.g., Zenker & Kubik, 1996) that have confirmed the existence of an extensive cranial radiator in humans. In keeping with their inaccurate interpretation of the RT, these new data are minimized by Braga & Boesch because they are ‘‘only for humans’’ (1997b: p. 505). Put simply, the human cranial radiator came from somewhere, and the RT traces its progressive evolution from the significantly different cranial plumbing systems of robust and gracile australopithecines, to the increasing numbers of emissary veins in the descendants of gracile australopithecines that eventually resulted in the complex radiator of Homo sapiens.
310
. . .
The data presented in Table 1 and Figure 1 also have implications for interpreting Braga & Boesch’s (1997a) findings that the incidence of condylar canals was significantly higher in robust than in gracile australopithecines, which is related to their central suggestion that the volume of blood flowing through the condylar veins of robust australopithecines was relatively great and tied functionally to higher encephalization in that species relative to its ancestor (Braga & Boesch, 1997a: p. 444). Braga & Boesch’s frequencies of 8/8 and 2/6 for condylar canals of robust and gracile australopithecines respectively are significantly different (Table 1) only if one includes highly questionable specimens in their samples. Removal of SK 27, Stw 53, and Stw 187a from their samples reduces the frequencies to 7/7 and 2/4, which do not differ significantly. It remains to be seen what effects accurate sample compositions would have on Braga & Boesch’s other analyses and conclusions. Acknowledgements We thank Fred Grine for thoughtful communications about SKW 11, Alan Walker and Barbara Brown for information about KNM-ER 23000, and Phillip Tobias and Ron Clarke for their input about Stw 187a. We also gratefully acknowledge enthusiastic discussion from graduate students enrolled
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in our seminar entitled ‘‘Publishing and Other Aspects of Professionalism’’: Audrey Choh, Barbara Meilinger, Shawn Phillips, John Redmond, Martin Solano, and Dan White. References Berry, A. C. & Berry, R. J. (1967). Epigenetic variation in the human cranium. J. Anat. 101, 361–379. Boyd, G. I. (1930). The emissary foramina of the cranium in man and the anthropoids. J. Anat. 65, 108–121. Braga, J. & Boesch, C. (1997a). Further data about venous channels in South African Plio-Pleistocene hominids. J. hum. Evol. 33, 423–447. Braga, J. & Boesch, C. (1997b). The ‘‘radiator’’ bias. A reply to Falk & Gage. J. hum. Evol. 33, 503–506. Brown, B., Walker, A., Ward, C. V. & Leakey, R. E. (1993). New Australopithecus boisei calvaria from East Lake Turkana, Kenya. Am. J. phys. Anthrop. 91, 137–159. Clarke, R. J. (1985). Australopithecus and early Homo in Southern Africa. In (E. Delson, Ed.) Ancestors: The Hard Evidence, pp. 171–177. New York: Alan R. Liss. Falk, D. (1986). Evolution of cranial blood drainage in hominids: enlarged occipital/marginal sinuses and emissary foramina. Am. J. phys. Anthrop. 70, 311–324. Falk, D. (1990a). Brain evolution in Homo: the ‘‘radiator’’ theory. Behav. Brain Sci. 13, 333–344. Falk, D. (1990b). Evolution of a venous ‘‘radiator’’ for cooling the cortex: ‘‘prime releaser’’ of brain evolution in Homo. Behav. Brain Sci. 13, 368–381. Falk, D. (1992). Braindance: New Discoveries About Human Origins and Brain Evolution. New York: Henry Holt. Falk, D. & Gage, T. B. (1997). Flushing the radiator? A reply to Braga & Boesch. J. hum. Evol. 33, 495–502. Falk, D., Gage, T. B., Dudek, B. & Olson, T. R. (1995). Did more than one species of hominid
Figure 1. Frequencies of enlarged O/M sinuses and emissary foramina in African pongids, humans, and gracile and robust australopithecines. Data for O/M sinuses (Table 1) from Falk (1986) and Falk (1995). Ranges for emissary foramina for apes and humans refer only to reports that used the methods of Berry & Berry (1967). Ranges for Homo are from Hauser & De Stefano (1989) and do not specify ages (ibid: 21); comparable ranges for Pan t. (labeled Pan), and Gorilla have been determined by calculating frequencies from combined juvenile and adult data of Braga & Boesch (1997a: Table 9). The range for enlarged O/M sinuses in Homo is 1·5–28% (Tobias & Falk, 1988). The ranges for Pan t. (I), Gorilla (II) and Homo (III) for five emissary foramina are: Divided hypoglossal canal, I (39–66%), II (82–98%), III (0–30%); Mastoid foramen, I (30–56%), II (no data), III (79–98%); Parietal foramen, I (1–18%), II (9–42%), III (37–83%); Occipital foramen, I (0–1%), II (0–12%), III (2–5%; from Boyd, 1930; Falk, 1986 and Hauser & De Stefano, 1989); Posterior condyloid canal, I (58–87%), II (79–92%), III (11—89%). Abbreviations: bo, bonobo frequency from Braga & Boesch (ibid); GB, Gorilla frequency from Boyd (1930); GF, Gorilla frequency from Falk (1986); PB, Pan frequency from Boyd (1930); PF, Pan frequency from Falk (1986); X, frequency for robust australopithecines; O, frequency for gracile australopithecines; BB, from Braga & Boesch (1997a; Table 1: II of this report); FG, from Falk & Gage, this report (Table 1: III).
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coexist before 3·0 Ma? Evidence from blood and teeth. J. hum. Evol. 29, 591–600. Grine, F. E. & Strait, D. S. (1994). New hominid fossils from Member 1 ‘‘Hanging Remnant’’, Swartkrans Formation, South Africa. J. hum. Evol. 26, 57–75. Hauser, G. & De Stefano, G. F. (1989). Epigenetic Variants of the Human Skull. Stuttgart: Schweizerbart. Kimbel, W. H., White, T. D. & Johanson, D. C. (1985). Craniodental morphology of the hominids from Hadar and Laetoli: Evidence of ‘‘Paranthropus’’ and Homo in the mid-Pliocene of Eastern Africa? In (E. Delson, Ed.) Ancestors: The Hard Evidence, pp. 120–137. New York: Alan R. Liss. Tobias, P. V. (1988). Numerous apparently synapomorphic features in Australopithecus robustus, Austra-
lopithecus boisei and Homo habilis: Support for the Skelton–McHenry–Drawhorn hypothesis. In (F. E. Grine, Ed.) Evolutionary History of the ‘‘Robust’’ Australopithecines, pp. 293–308. New York: Aldine de Gruyter. Tobias, P. V. & Falk, D. (1988). Evidence for a dual pattern of cranial venous sinuses on the endocranial cast of Taung (Australopithecus africanus). Am. J. phys. Anthropol. 76, 309–312. White, T. D. (1988). The comparative biology of ‘‘robust’’ Australopithecus: Clues from context. In (F. E. Grine, Ed.) Evolutionary History of the ‘‘Robust’’ Australopithecines, pp. 449–483. New York: Aldine de Gruyter. Zenker, W. & Kubik, S. (1996). Brain cooling in humans—anatomical considerations. Anat. Embryol. 193, 1–13.
Radiators are cool: A response to Braga & Boesch’s published paper and reply
Dean Falk & Timothy B. Gage
Department of Anthropology, State University of New York at Albany, Albany, New York 12222, U.S.A. E-mail: [email protected] Journal of Human Evolution (1998) 35, 307–312 Article No. hu980237
A recent volume of this journal contained an article about cranial blood flow (Braga & Boesch, 1997a), our reply to a manuscript that was identified as a final draft of that article (Falk & Gage, 1997), and a reply to our reply (Braga & Boesch, 1997b). As the result of an editorial error the draft to which we replied was not, in fact, the final draft of Braga & Boesch. It was only after it was published that we first read the Braga & Boesch (1997b) reply. Upon reading Braga & Boesch (1997a), it became clear that, unbeknownst to us, a specimen had been removed from Table 8 of the version of Braga & Boesch’s paper to which we had replied, and the relevant statistics had been changed throughout the final publication. Because the summary table and figure presented in Falk & Gage (1997) incorporated data that were deleted from the published Braga and Boesch manuscript, they are inconsistent with Braga & Boesch (1997a) and must now be corrected. Table 1 and Figure 1 of this note should therefore replace those published in our recent reply to Braga & Boesch (Falk & Gage, 1997). The specimen that was deleted is SK 847, assigned to Homo by Clarke (1985) and Falk (1986), but classified as a robust australopithecine in the version of the Braga & Boesch manuscript to which we replied. Contrary to the 1/4 frequency provided for the parietal foramen of robust australopithecines in Table 8 of Braga & Boesch (1997a: p. 434), in their reply to our reply, Braga & Boesch (1997b: p. 504) cite a frequency of 1/5, which is based on the earlier draft that 0047–2484/98/090307+06 $30.00/0
included SK 847 as a robust australopithecine. The deletion of SK 847 and alteration of statistics in Braga & Boesch (1997a) raise questions about the attributions and scoring of the six other specimens scored as australopithecines in Braga & Boesch (1997a) but not Falk (1986): SKW 11, SK 27, KNM-ER 417, KNM-ER 23000, Stw 53, and Stw 187a. In this note, we investigate whether or not Braga & Boesch’s taxonomic attributions and scoring for these specimens should be accepted at face value as we had initially assumed. In Table 8 of Braga & Boesch (1997a: p. 434), SKW 11 is listed as a robust australopithecine with a left mastoid foramen, and the authors indicate that this observation was previously unpublished. However, this specimen is fragmentary and damaged in the region of the mastoid process (Grine & Strait, 1994), which from Figure 3(d) of Grine & Strait (ibid: p. 63) appears to be too eroded to score for emissary foramina. Fred Grine (personal communication) has confirmed this observation by examining ‘‘a very nice color lateral view of the specimen. It is clear that there is no surface bone left on the mastoid! . . . There is no possibility that this region can be scored for the presence or absence of emissary foramina.’’ Another specimen that is identified as a robust australopithecine in Table 8 of Braga & Boesch, SK 27 (a juvenile, fragmentary crushed cranium), is attributed to Homo by most workers (Clarke, 1985: p. 177; Kimbel et al., 1985: p. 128; Falk, 1986). A third 1998 Academic Press
. . .
308 Table 1 I Falk ’86
II B&B ’97
III F&G (this report)
rob; gra
rob; gra
rob; gra +
Enlarged O/M Div. hypoglossal Mastoid
7/7; 1/4* 2/3; 0/3 2/8; 2/5
2/3; 0/4 4/7; 2/2
10/10; 1/6*† 2/3; 0/2 2/9; 2/3
Parietal Occipital P. condyloid
0/3; 0/5 1/5; 1/4 5/6; 1/4
1/4; 0/3 2/7; 1/2 8/8; 2/6*
1/4; 0/3 1/5; 1/2 5/6; 1/3
Questionable attributions or scoring of B&B ’97a As robusts
As graciles
— SKW 11, ER 417 KNM-ER 23000 — SK 27 SK 27
Stw 53, Stw 187a — — — Stw 53, Stw 187a
Frequencies of emissary foramina for robust (rob) and gracile (gra) australopithecines, from Table 2 of Falk (1986), Table 8 of Braga & Boesch (1997a), and Falk & Gage (this report). Data for O/M sinuses from Falk et al., 1995; ER 1805 and ER 1813, included as graciles in I, are excluded from that category in III; and scorings for parietal and mastoid emissary foramina of KNM-ER 23000 (Brown et al., 1993) are included in III. Discrepancies between column II of this table and column II of our earlier Table 1 (Falk & Gage, 1997) are due to the fact that Braga and Boesch’s scorings for SK 847 (included in robust australopithecines in the draft of their paper to which we responded) were incorporated in our earlier table. Braga & Boesch’s (1997a) scorings for other fossils were also incorporated into column III of Falk & Gage (1997), but most are now excluded from column III of this table for reasons detailed in the text. *Fisher’s exact P<0·05. †Fisher’s exact P<0·05 with Bonferroni’s correction.
specimen that Braga & Boesch identify as a robust australopithecine, KNM-ER 417, is a very fragmentary parietal of unknown hominid species (White, 1988: pp. 466–467). Based on the above, these three specimens are excluded from our frequencies for robust australopithecines (column III in Table 1). A calvaria of A. (P.) boisei, KNM-ER 23000, had not been discovered at the time of Falk’s 1986 study. Braga & Boesch scored this specimen as having a right mastoid foramen and cite Brown et al. (1993: p. 146) as their source. However, although Brown et al. note the presence of a mastoid canaliculus in the jugular fossa (which is for passage of the auricular branch of the vagus nerve), we find no reference to a mastoid foramen. Alan Walker (personal communication) confirms that a mastoid emissary foramen was not scored as present for this specimen, and adds: ‘‘I’ve checked my casts and I don’t think there is a foramen hiding in the lambdoid suture that I might have missed originally’’. Because of this, and because the right temporal bone (KNM-ER 23000E)
appears complete (Brown et al., 1993, Figure 4B), we score the mastoid foramen as missing in this specimen. We therefore include KNM-ER 23000 in our scoring of mastoid emissary foramina for robust australopithecines, but score it differently than Braga & Boesch. Brown et al.’s (1993: p. 147) observation of parietal foramina in ER 23000 is also included in column III of Table 1. Turning to gracile australopithecines, Table 8 of Braga & Boesch includes Stw 53 in this category, although this partial cranium is regarded as Homo by most workers (Clarke, 1985; Tobias, 1988). A second specimen that Braga & Boesch attribute to A. africanus, Stw 187a from Member 4 of Sterkfontein, is more problematic. According to Philip Tobias (personal communication), this specimen comprises ‘‘the basi-occipital and the lateral occipitals fused on to it by closure of the anterior intraoccipital synchondrosis’’. Tobias further observes that Stw 187a is probably a gracile australopithecine, although ‘‘there is still
argument over whether one or two specimens in Member 4 from Sterkfontein may perhaps fall outside the range for the species A. africanus’’. Because of this uncertainty, and because Braga & Boesch’s observations of emissary foramina in this specimen have yet to be confirmed by other workers, we exclude this specimen, along with Stw 53, from column III of Table 1. On other matters, Falk (1986: p. 320) noted that Boyd’s (1930) frequency for mastoid foramina in Homo sapiens was ‘‘probably low because Boyd scored a foramen as absent if a wire would not pass through it’’. Braga & Boesch (1997a: pp. 426–427) misquoted Falk by replacing the word ‘‘absent’’ with ‘‘present’’ in this quotation, which they then used to make an erroneous argument about scoring procedures. Turning to Braga & Boesch’s (1997b) reply to Falk and Gage (1997), in addition to the inconsistency in the sample size of robust australopithecines between this and Braga & Boesch (1997a) discussed above, no mention is made in Braga & Boesch’s reply of the inconsistencies between the data sets of the paper to which they are replying (Falk & Gage, 1997) and Braga & Boesch (1997a). To summarize, five of the six specimens that were scored as australopithecines by Braga & Boesch (1997a) but not Falk (1986) are excluded from Falk & Gage’s frequencies for emissary foramina (column III of Table 1) because of questionable scoring or taxonomic attributions. Braga & Boesch’s scoring for the mastoid foramen of the sixth specimen (ER 23000) is based on mistaking the mastoid canaliculus (Brown et al., 1993: p. 146) for the mastoid foramen. Scoring of the mastoid foramen that correctly reflects Brown et al.’s observations is included in column III of Table 1. The data presented in Table 1 and Figure 1 support earlier observations of the trends regarding cranial blood flow in fossil hominids (Falk, 1986), as well as their interpretations as articulated in the radiator theory
309
(RT) (Falk, 1990a,b). This may be verified by comparing these data with those provided earlier (Falk, 1986; Falk, 1990a,b; Falk et al., 1995). Braga & Boesch (1997a, 1997b) assert that the only reasonable test of the RT is to determine whether or not gracile australopithecines can be statistically shown to have been characterized by a cranial radiator network of veins not seen in robust australopithecines. As detailed in Falk & Gage (1997), this is a strawman hypothesis because it contradicts the published data and discussion pertaining to the RT (Falk, 1986; Falk, 1990a,b; Falk 1992; Falk et al., 1995; Falk & Gage, 1997). On the other hand, Braga & Boesch ironically ignore the statistically significant difference in frequencies of enlarged occipital/marginal sinuses that not only distinguishes the cranial plumbing of robust and gracile australopithecines, but also constitutes a crucial basis for the RT. An important but controversial assumption upon which the RT was initially formulated (Falk, 1990a,b), was the hypothetical existence of a vast network of tiny emissary veins that serve to selectively cool the brain of hyperthermic humans. As detailed in Falk & Gage (1997), the RT has recently received dramatic support from numerous physiological and anatomical studies (e.g., Zenker & Kubik, 1996) that have confirmed the existence of an extensive cranial radiator in humans. In keeping with their inaccurate interpretation of the RT, these new data are minimized by Braga & Boesch because they are ‘‘only for humans’’ (1997b: p. 505). Put simply, the human cranial radiator came from somewhere, and the RT traces its progressive evolution from the significantly different cranial plumbing systems of robust and gracile australopithecines, to the increasing numbers of emissary veins in the descendants of gracile australopithecines that eventually resulted in the complex radiator of Homo sapiens.
310
. . .
The data presented in Table 1 and Figure 1 also have implications for interpreting Braga & Boesch’s (1997a) findings that the incidence of condylar canals was significantly higher in robust than in gracile australopithecines, which is related to their central suggestion that the volume of blood flowing through the condylar veins of robust australopithecines was relatively great and tied functionally to higher encephalization in that species relative to its ancestor (Braga & Boesch, 1997a: p. 444). Braga & Boesch’s frequencies of 8/8 and 2/6 for condylar canals of robust and gracile australopithecines respectively are significantly different (Table 1) only if one includes highly questionable specimens in their samples. Removal of SK 27, Stw 53, and Stw 187a from their samples reduces the frequencies to 7/7 and 2/4, which do not differ significantly. It remains to be seen what effects accurate sample compositions would have on Braga & Boesch’s other analyses and conclusions. Acknowledgements We thank Fred Grine for thoughtful communications about SKW 11, Alan Walker and Barbara Brown for information about KNM-ER 23000, and Phillip Tobias and Ron Clarke for their input about Stw 187a. We also gratefully acknowledge enthusiastic discussion from graduate students enrolled
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in our seminar entitled ‘‘Publishing and Other Aspects of Professionalism’’: Audrey Choh, Barbara Meilinger, Shawn Phillips, John Redmond, Martin Solano, and Dan White. References Berry, A. C. & Berry, R. J. (1967). Epigenetic variation in the human cranium. J. Anat. 101, 361–379. Boyd, G. I. (1930). The emissary foramina of the cranium in man and the anthropoids. J. Anat. 65, 108–121. Braga, J. & Boesch, C. (1997a). Further data about venous channels in South African Plio-Pleistocene hominids. J. hum. Evol. 33, 423–447. Braga, J. & Boesch, C. (1997b). The ‘‘radiator’’ bias. A reply to Falk & Gage. J. hum. Evol. 33, 503–506. Brown, B., Walker, A., Ward, C. V. & Leakey, R. E. (1993). New Australopithecus boisei calvaria from East Lake Turkana, Kenya. Am. J. phys. Anthrop. 91, 137–159. Clarke, R. J. (1985). Australopithecus and early Homo in Southern Africa. In (E. Delson, Ed.) Ancestors: The Hard Evidence, pp. 171–177. New York: Alan R. Liss. Falk, D. (1986). Evolution of cranial blood drainage in hominids: enlarged occipital/marginal sinuses and emissary foramina. Am. J. phys. Anthrop. 70, 311–324. Falk, D. (1990a). Brain evolution in Homo: the ‘‘radiator’’ theory. Behav. Brain Sci. 13, 333–344. Falk, D. (1990b). Evolution of a venous ‘‘radiator’’ for cooling the cortex: ‘‘prime releaser’’ of brain evolution in Homo. Behav. Brain Sci. 13, 368–381. Falk, D. (1992). Braindance: New Discoveries About Human Origins and Brain Evolution. New York: Henry Holt. Falk, D. & Gage, T. B. (1997). Flushing the radiator? A reply to Braga & Boesch. J. hum. Evol. 33, 495–502. Falk, D., Gage, T. B., Dudek, B. & Olson, T. R. (1995). Did more than one species of hominid
Figure 1. Frequencies of enlarged O/M sinuses and emissary foramina in African pongids, humans, and gracile and robust australopithecines. Data for O/M sinuses (Table 1) from Falk (1986) and Falk (1995). Ranges for emissary foramina for apes and humans refer only to reports that used the methods of Berry & Berry (1967). Ranges for Homo are from Hauser & De Stefano (1989) and do not specify ages (ibid: 21); comparable ranges for Pan t. (labeled Pan), and Gorilla have been determined by calculating frequencies from combined juvenile and adult data of Braga & Boesch (1997a: Table 9). The range for enlarged O/M sinuses in Homo is 1·5–28% (Tobias & Falk, 1988). The ranges for Pan t. (I), Gorilla (II) and Homo (III) for five emissary foramina are: Divided hypoglossal canal, I (39–66%), II (82–98%), III (0–30%); Mastoid foramen, I (30–56%), II (no data), III (79–98%); Parietal foramen, I (1–18%), II (9–42%), III (37–83%); Occipital foramen, I (0–1%), II (0–12%), III (2–5%; from Boyd, 1930; Falk, 1986 and Hauser & De Stefano, 1989); Posterior condyloid canal, I (58–87%), II (79–92%), III (11—89%). Abbreviations: bo, bonobo frequency from Braga & Boesch (ibid); GB, Gorilla frequency from Boyd (1930); GF, Gorilla frequency from Falk (1986); PB, Pan frequency from Boyd (1930); PF, Pan frequency from Falk (1986); X, frequency for robust australopithecines; O, frequency for gracile australopithecines; BB, from Braga & Boesch (1997a; Table 1: II of this report); FG, from Falk & Gage, this report (Table 1: III).
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coexist before 3·0 Ma? Evidence from blood and teeth. J. hum. Evol. 29, 591–600. Grine, F. E. & Strait, D. S. (1994). New hominid fossils from Member 1 ‘‘Hanging Remnant’’, Swartkrans Formation, South Africa. J. hum. Evol. 26, 57–75. Hauser, G. & De Stefano, G. F. (1989). Epigenetic Variants of the Human Skull. Stuttgart: Schweizerbart. Kimbel, W. H., White, T. D. & Johanson, D. C. (1985). Craniodental morphology of the hominids from Hadar and Laetoli: Evidence of ‘‘Paranthropus’’ and Homo in the mid-Pliocene of Eastern Africa? In (E. Delson, Ed.) Ancestors: The Hard Evidence, pp. 120–137. New York: Alan R. Liss. Tobias, P. V. (1988). Numerous apparently synapomorphic features in Australopithecus robustus, Austra-
lopithecus boisei and Homo habilis: Support for the Skelton–McHenry–Drawhorn hypothesis. In (F. E. Grine, Ed.) Evolutionary History of the ‘‘Robust’’ Australopithecines, pp. 293–308. New York: Aldine de Gruyter. Tobias, P. V. & Falk, D. (1988). Evidence for a dual pattern of cranial venous sinuses on the endocranial cast of Taung (Australopithecus africanus). Am. J. phys. Anthropol. 76, 309–312. White, T. D. (1988). The comparative biology of ‘‘robust’’ Australopithecus: Clues from context. In (F. E. Grine, Ed.) Evolutionary History of the ‘‘Robust’’ Australopithecines, pp. 449–483. New York: Aldine de Gruyter. Zenker, W. & Kubik, S. (1996). Brain cooling in humans—anatomical considerations. Anat. Embryol. 193, 1–13.