View Full Version : The Genetic Origins of the Philippine Negritos

Sunday, June 12th, 2016, 08:23 AM
By Keiichi Omoto, Current Anthropology, Vol. 22, No. 4. (Aug., 1981), pp. 421-422.

Department of Anthropology, Faculty of Science, University of
Tokyo, Runkyo-ku, Tokyo 113, Japan. 27 I 81

The genetic origins of the Negritos of the western Pacific have been the subject of controversy among anthropologists. The question has not been properly answered up to now because genetic data have been almost nonexistent.

Since 1976, we have been carrying out population-genetic studies of the Philippine Negritos. The research consists of a series of field studies and laboratory work carried out in Japan on blood samples obtained
from various Negrito and non-Negrito populations in the Philippines. Thus far, we have been able to obtain more than 600 blood samples from the Negritos of west-central Luzon (Aeta) and those of northeastern Mindanao Mamanwa).

Field surveys of the Negritos of northeastern Luzon (Agta) and those
of Palawan Island (Batak) are schedule8 for 1981. In view of the rapidly changing habitat conditions of the Negritos in the Philippines, we consider it of the utmost importance to complete this study as early as possible.

Investigations of genetic markers of red-cell antigens, redcell enzymes, serum proteins, and HLA antigens have shown a rather high level of genetic variability (average heterozygosity) in the Negrito populations; several unusual genetic variants of high frequency have been discovered, some of which are unique (Omoto et al. 1978, Matsumoto et al. 1797, Horai
et al. 1981). In this short communication, some tentative conclusions
inferred from these data are presented.

Figure 1 is a dendrogram comparing the Negritos (Aeta) with eight other populations on the basis of genetic distances computed by Cavalli-Sforza and Edwards's method. Allelefrequency data for 17 polymorphic loci-ABO, MNS, Rh, Fy, Di, Jk, K, Hp, Tf, Gc, ACP, PGM-I, PGD, AK, ADA, GPT, ESD-were used. The data for the other populations were compiled mostly from various published reports.

It is clear that the Negritos are genetically more closely related to the Asian-
Pacific group than to the African group. Unfortunately, the published data on the African Pygmies are insufficient for this comparison, although the Pygmies have been shown to have close affinities to forest Negroes (Cavalli-Sforza et al. 1969).

Therefore, we may conclude that the African Pygmies and the Asian Negritos have different origins and that similarities at the phenotypic level such as short stature, dark skin colour, and kinky hair are probably the reflection of adaptation to similar environmental conditions. It is not known, however, whether Permission to reprint items in this section may be obtained only
from their authors.

We have thus far detected by electrophoresis at least three private polymorphisms: two red-cell enzyme variants and a serum-protein variant (table 1). ("Private polymorphism" is defined here as the occurrence at polymorphic frequency [greater than 1x1 of a unique or very unusual allele in a small, more or less isolated group, such as a tribal group or an island
population.) ESD3Nand GclN are both peculiar to the Aeta, the average allele frequency of each being approximately 0.10.

They are absent in the Mamanwa and the non-Negrito Philippine populations with the exception of Ifugao (Mountain Province, northern Luzon) and Tagalog (Manila), where the GclN allele was detected at a low frequency, probably due to ancient gene flow from the Negritos to these populations.

On the other hand, CA 13N has a remarkably high frequency (greater than 20%) among the Mamanwa, although it occurs also in the adjacent non-Negrito Manobo at a much lower one (ca. 2%).

It is absent in the Aeta. Peptide and amino-acid analyses showed that this variant is identical to CAlaQus1n,which is known to have a wide distribution in the western Pacific in low but appreciable frequencies (Omoto 1980, Omoto et al. 1981).

These results suggest that ESD3Nand GclNrepresent relatively recent mutations, possibly similar in age, while CA13Nis derived from a much earlier mutation. On the basis of neutral mutation random genetic drift theory, the age of ESD3Nand GclN has been estimated at roughly 10,000-30,000 years.

That CA13N does not occur in the Aeta suggests that the Aeta and the
Mamanwa, though usually referred to as Negritos, have different origins in terms of migration to the Philippines.

The following summarizes the results of research focused on the delineation and explanation of responses in the human skeleton and dentition to the shift from hunting and gathering to corn agriculture on the Georgia coast. This region is particularly appropriate for such study because

(1) there is a large series of skeletal and dental remains representative of both a preagricultural adaptation (2200 B.c.-A.D. 1150) and a mixed agricultural and hunting-gathering adaptation (A.D. 1150-1550) ;

(2) evidence of continuous in situ cultural development from at least 2200 B.C.to A.D. 1550 implies genetic continuity for at least 3,500 years prior to European contact; and (3) the economic regime is documented by a large body of archaeological and ethnohistoric data.

Two expectations were tested. First, skeletal and dental health was expected to decline. I t is the consensus that the adoption of agriculture in the post-Pleistocene world led to a more sedentary lifeway supporting larger numbers of people and consequently a higher frequency of infectious disease
(Buikstra and Cook 1978, Lallo, Armelagos, and Rose 1978).

Therefore, the number of nonspecific skeletal infections (periosteal reactions) was expected to increase, reflecting an increase in infectious disease in general. The decline in dental health was expected to be particularly apparent in the increased expression of carious lesions, a product of a high-carbohydrate diet.

Second, given the highly plastic nature of skeletal tissue, an alteration of size of the cranial and postcranial skeleton was anticipated. Carlson has shown that the shift to softer prepared foodstuffs led to an alteration in the growth and development of the masticatory apparatus, with a consequent reduction in the size of the face, jaws, and teeth, in a series of prehistoric Nubian crania (summarized in Carlson and Van Gerven 1979).

With respect to the postcranial skeleton, a number of investigators have demonstrated that a lifeway based on hunting and gathering appears to involve more functional demand on the body than one in which agriculture is the primary mode of subsistence; studies have shown a higher frequency of degenerative joint disease (osteoarthritis) in hunter-gatherers than in agricultors.

To test these expectations, a large series of skeletons and dentitions from the Georgia coast were examined. The remains from 33 prehistoric mortuary localities, including 269 individuals representative of a preagricultural hunting-andgathering lifeway and 342 individuals representative of an agricultural lifeway, were studied. Standard techniques of observation were employed. Presence-absence of three pathological conditions-dental caries, periosteal reactions, and degenerative joint disease-was recorded.

Cranial dimensions were used to investigate possible size changes in the masticatory apparatus (ex., attachment sites for masseter and temporalis muscles) in , - particular and the cranial vault (e.g., length, breadth, and height) in general. Tooth size was approximated by length and breadth of the posterior dentition (premolars and molars) and breadth of the anterior dentition (incisors and canines) of the maxilla and mandible. Additionally, area (product of length and breadth) was calculated for the posterior dentition.

Postcranial dimensions were analyzed to allow estimation of the size of each postcranial skeletal element and calculation of stature (based on maximum length of tibia and femur) and postcranial indices (humeral robusticity and midshaft; tibia1 robusticity and midshaft; femoral robusticity, midshaft, and platymeric).

The data fit the model well. There is a marked increase in the frequency of both periosteal reactions and dental caries, reflecting a decline in skeletal and dental health respectively.

There is a decrease in the frequency of pathology related to mechanical stress-degenerative joint disease-and a change in two skeletal indices that reflect degree of functional demand -decrease in the female femoral robusticity index and increase in the male platymeric index. As expected, there are reductions in size of the face and jaws as well as the dentition, and most measures of postcranial skeletal size show marked reduction.

Analysis of these data by sex reveals several trends. The two sexes show equal increases in postcranial skeletal infections and equal decreases in the occurrence of degenerative joint disease, but males of both periods are more affected by the latter than females. Females show far more increase in frequency of dental caries and more decrease in size of the cranial and postcranial skeletons than males.

Tooth-size reduction is restricted to females. The ethnohistoric literature indicates that males did all of the hunting and females were responsible for agriculture-related activity, including field preparation, planting, harvesting, and food preparation.

This observation, coupled with the skeletal and dental changes, suggests that the behavioral alterations associated with the shift to an agricultural lifeway affected the females to a greater extent than the males. Additional factors need be considered in the explanation of reduction in dental and skeletal size, in particular.

Source: This research was initiated through the generous support of the
Edward John Noble Foundation and the American Museum of
Natural History; it was completed under a Smithsonian Institution
Predoctoral Fellowship. A detailed treatment will be provided in a
forthcoming monograph (Larsen 1981).

Sunday, June 12th, 2016, 12:25 PM
Try Human Biology, Volume 85, Numbers 1-3, February - June 2013.

Monday, June 13th, 2016, 02:19 AM
I read somewhere that some of these Negritos had a significant and detectible Denisovan ancestry while others did not.