A. Morphological Criteria of Racial classification : two types 1) Morphoscopic 2) Morphometric
Human races are classified on the basis of various morphological parameters such as Skin colour, Hair colour and form, Head form, Facial features, Nose, Eyes, Stature, Dermatoglyphics etc. A brief description of these parameters is given below:
Morphoscopic
1 Pigmentation of the Skin (Skin Colour)
Prominent colours of human skin are the white, black and yellow. However, there are immense shades of the skin colour among humanity. Pigmentation is the most prominent criteria on the basis of which the three major races were differentiated which have been described as follows:
• People who have the white skin colour are called the Caucasoid (Leucoderms)
• People who have the yellow skin colour are called the Mongoloid (Canthoderms)
• People who have the black skin colour are called the Negroid (Melanodenns)
The colour of the skin is primarily due to the presence of a pigment called melanin. All shades of skin colour have this pigment; however, there are two forms of this pigment, viz., pheomelanin which is red to yellow in colour and eumelanin which is dark brown to black. Melanin is present in the outer layers
of the skin and is produced by the specialized cells known as melanocytes situated at the base of the epidermis. The dark skin colour is an adaptation to sunlight. The greater the sunlight the darker the skin colour. It has been noticed that generally the populations living around the equator have dark skins. Natural selection helps people with dark skins in the tropics where the direct sunlight exposes the people to greater amounts of ultraviolet radiation and greater amounts of melanin acts as a protective shield against the ultraviolet radiation. Thus it helps in preventing the sunburns which may cause the DNA damage. Overexposure to sunlight and sunburns may result in melanoma whose incidence is very rare in people with the dark skin but is comparatively higher in the Europeans and Americans who have the white skin.
2 Hair Colour and Form: The human hair can be categorized into three groups: Straight or Sleek (Lissotrichous), wavy (Cymatotrichous) and frizzly/woolly (Ulotrichous). The smooth hair is usually straight and may be a little flat and wavy. They can further be thin or coarse. Mongoloid race has smooth hair. There can be three forms of wavy hair: broad wavy hair has broad waves, narrow wavy hairs have strongly curved waves and curly hairs have large spirals. The European and north east African people have such types of wavy hair form. The last category is that of the woolly hair which may be closer-knit or wider knit or pepper-corn or spiral. Such type of hair form is observed in the Negroes, Melanesians and Bushman. The hair colour of the populations living in the tropical countries is black or dark brown. In case of populations of the Europe, the hair colour ranges from black to blonde and from brown to even red colour. The texture of the hair may give a smooth finish or a coarse look and the thickness of the hair may also vary. The hair is termed as fine if its thickness is up to 56 microns, it is called medium if the thickness is between 57 and 84 microns and coarse when the thickness increases beyond 84 microns. The quantity of hair can be scanty, medium or rich or luxuriant. There are groups in whom the hair growth is found all over the body whereas there are other groups in which the body hair growth is very scanty.
3 Eyes : The eyes of the Mongoloid race have fold of the skin over the inner corner of eyes. This fold of the skin and subcutaneous tissue is also called epicanthic fold or the Mongoloid fold. In most other races of the mankind, there is no such fold. Inner corner of the eye has a small bump which is usually covered by the eye fold in case of the Mongoloid race. The eye fold may look fleshy or plump because of the presence of fatty tissue in it. This epicanthic eye fold may cover a small area on the inner side of the eyelid, or cover up to the middle of the upper eyelid or may cover it completely. In some persons the eye fold may have very little amounts of fat and in them the contours of the eyeball may be seen through the eye fold. Most of us who have seen the Mongoloid people are of the opinion that they have slanted eyes. But in reality their eyes are not slanted and it is only an optical illusion. When we see such a person, we cannot see the actual inner corner of the eye which is covered with the fold but can only see the lower edge of the fold on the inner side of the eye which is located downwards and is drooping over the corner of the eye. The other corner of the eye is generally not covered with the epicanthic eye fold and therefore we can see that corner easily and hence the eyes look slanted. The Chinese and the Japanese have these prominent eyefolds. Another feature of the eye is the iris which gives the eye its distinctive colour. The iris is pigmented and opaque and contains circular and radial muscles which change the size of the pupil of the eye. The colour of the iris may be black, brown, green, blue or variations of all these colours. The Mongoloids and Negroids have iris colour between black and brown. The Caucasoids have a large range of the colour of their eyes
Morphometric
1 Head Form
The head form can be easily determined with the help of its measurements using which the Cephalic (scientific name of the head) Index often been used to classify races is calculated as follows.
- Cephalic Index (C.I.) = (Head Breadth/Head Length) x 100
Thus, if the head length is 25 cm and head breadth is 18 cm in a human male,
- Cephalic Index = (18/25) x 100 = 72
With a Cephalic Index of 72 this male falls in the category of dolichocephalic which means he has a long and narrow head. Table 1 shows various categories of the head form along with the range of the Cephalic Index, separately for the male and female.
| Category | Range of the Cephalic Index | Range of the Cephalic Index |
| Male | Female | |
| Dolichocephalic | 71.0-75.9 | 72.0-76.9 |
| Mesocephalic | 76-80.9 | 77.0-81.9 |
| Brachycephalic | 81.0-85.4 | 82.0-86.4 |
Various races of the mankind have different forms of heads.The dolichocephals are long and narrow heads whereas the brachycephals are short and broad heads. Dolichocephaly is rare in the Mongoloids whereas brachycephaly is relatively rare in the Negroes. The Caucasoids seem to have all types of head
shapes.
2 Facial Features
The facial features are the most prominent of all the characteristics which come to our notice immediately. We identify people on the basis of the facial features and most often every where there is a need of identity and the photograph of the face is required. The shape of the face may be broad, narrow, square or oval. The shape of the face can be calculated with the help of two anthropometric measurements of the face, viz., the Morphological Facial Length and Bizygomatic Breadth. The Morphological Facial Length is the straight distance between the landmarks nasion (where the upper end of internasal suture meets the frontal bone) and gnathion (lowest point on the mandible in the midsagittal plane). The Bizygomatic Breadth is the maximum distance across the zygomatic arches of the face beyond the eyes. The Morphological Facial Index is represented as follows:
- Morphological Facial Index = (Morphological Facial Length/Bizygomatic Breadth) x 100
The human face when viewed from the side or in profile view may show various degrees of prognathism (protrusion of the jaws). When the jaws are in vertical line of the face as seen in the side view, this is called orthognathism. The mouth and lips perform functions of eating food and speech. The lips in case of man are exposed to outside unlike animals who do not have them like the humans. The mucous membrane is exposed to the outside in humans and the degree with which it is turned outside is called lip eversion. The maximum lip eversion has been seen along with thick lips in case of the Negroes. The minimum lip eversion occurs in the Caucasoids.
3 Nose
The portion of the nose which is bony has a root which lies between the eyes. The portion of the nose projecting downwardsfrom root is bony and cartilaginous and is called the bridge. The Lowest most part of the nose is the tip and the sides of nose are called alare which cover the nostrils. The roots of the nose are sharp edged and projecting in case of the Caucasians. The East Asian people have nasal roots which are very low and if viewed from the side one can perhaps see the other eyeball across the nasal root. The Africans exhibit a smooth curve from one side to another. The nasal bridge seen from the side may be straight and pointed or curved forward like a hump. The bridge is often wider than the root. The alare may vary in size. Combined together the root, bridge and the tip of the nose make innumerable shapes of the nose and thus representing a huge variety among different races. The shape of the nose can be estimated by using an index of the Nasal Breadth and Nasal Height as follows:
- Nasal Index (N.I.) = (Nasal Breadth/Nasal Height) * 100
The scientists have tried to give explanation for the shape of the nose in terms of the ecological adaptations. The lowly projecting nose of the people of Central Asia has been considered as an adaptation to cold environment. Coon et al. (1950) suggested that any projection of the body in a cold climate would lose body heat much faster than any other part of the body. The ears and noses by virtue of their large surface areas have this disadvantage and races well adapted to these climates would show less protruding body parts. Very large protruding human noses have been found in tropical areas. However, the exact mechanisms of adaptations of the shape of nose to environment are still eluding.
4 Stature
The human stature has become a symbol of social prestige and during childhood almost all of you must have envied the tallest boys and the girls and longed to be like them. Not only has the variation in stature existed across different groups but also within a group as well. Children in a family also differ in size.
Although there seems to be social bias in favour of taller individuals yet it is not very clearly known whether taller height has some biological advantage.
During the course of evolution the tallest animals became the focus of extinction. The larger individual has greater calorie needs during the growing period as well as during its life time. In the past when food was scarce, animals with smaller bodies would have been at a biological advantage. The natural selection
may act against individuals who have a genetic potential for larger body size, especially in times of scarcity of food. Many studies have shown that immigrants to the United States from other countries increased in their height. Historically speaking, the human populations have been increasing in stature over the past one hundred and fifty years. The Europeans, especially the Dutch are one of the tallest populations with an average stature of more than six feet whereas the Pygmies of the Congo basin have the shortest stature which is around four feet. Availability of food in the past seems to have played a significant role in the development of stature.
B. SEROLOGICAL AND GENETIC CRITERIA OF RACIAL CLASSIFICATION
Racial classification is also made on the basis of certain serological and genetic criteria. Such types of traits include ABO, MN and Rh blood group systems, ABH secretion system, PTC (Phenylthiothiocarbamide) tasting ability and other genetic markers. A brief description of each is given:
1 ABO Blood Group System
The phenomenon of the occurrence of two or more clearly different classes of the phenotypes with appreciable (>1%) frequencies in the same population is referred to as polymorphism. Different blood group systems, serum protein and red cell enzyme polymorphisms, haemoglobin variants and numerous other genetic traits are examples of the genetic polymorphisms.
The blood groups are valuable anthropological characters, since most of them occur in different proportions in different parts of the world. One of the most widely used blood group system for studying variation among various ethnic groups is the ABO system. The membrane of the red blood cells (erythrocytes) of human beings has a large variety of blood group antigens (agglutinogens) and in the ABO system the antigens involved are known as A and B. An antigen is basically a molecule which would initiate the production of the corresponding antibodies (agglutinins) in the immune system which in turn would neutralize (agglutinate) the antigen which is acknowledged by the body as something foreign and potentially dangerous. The term ANTIGEN has been derived from the
fact that it is AAT/body GAAerator.
The blood groups are characterized by the antigens which the red blood cells carry on their membranes. If in a person the red blood cells have A antigens on their surface, the blood group of that individual will be referred to as A; if one carries the B antigens, the blood group is referred to as B, if one carries both A and B antigens then the blood group is referred to as AB and if there is no antigen present on the red blood cells, the blood group is known as O. The plasma or serum of different individuals contains naturally occurring ABO blood group antibodies, except AB blood group persons as given in
| Blood group | Antigen (agglutinogen) on RBCs | Antibody (agglutinin) in plasma |
| A | A | anti-B |
| B | B | anti-A |
| AB | A and B | none |
| O | None | anti-A and anti-B |
The frequencies of the ABO blood groups can also help in tracing the origin of the racial groups. Thus, for example, it has been found that one of the colonies of the Gypsies in Hungary had ABO blood group frequencies similar to those of the Hindus of North India rather than those of the Hungarians. The linguists found commonality in the language between the Gypsies of Hungary and the Hindus of North India and suggested that the former might have migrated from India to Hungary around 500 years back. There have been numerous such instances where on the basis of blood group frequencies, information about the migration of the population groups has been generated.
2 MN Blood Group System
In the MN blood group system, there are three distinct blood group types (phenotypes) viz., M, N and MN, controlled by two codominant autosomal alleles – MNM and MNN. The red blood cell membranes therefore can carry two different types of antigens (agglutinogens) namely M and N on their surfaces,
either singularly (in homozygotes) or both (in heterozygote).The persons carrying M antigen on the surface of their red blood cells are called type M, those carrying N antigen are called type N and those carrying both the antigens are called MN. The naturally occurring corresponding antibodies (agglutinins) are very rare in the MN blood group system. It means that, unlike the ABO blood group system, in the MN blood group system, no naturally occurring anti-M and anti-N antibodies are present in the serum of the individuals. The M blood group, frequency has been reported highest in the Eskimos (83.5%), followed by the Mexican Indians (61.2%). At the lowest end of the frequencies of the M type are the Australian aborigines and Papuans. On the other hand, the N blood group shows the highest frequency in the Australian aborigines and Papuans (67.4% and 69%, respectively) whereas the Eskimos and the Mexican Indians show the lowest frequencies (0.8% and 3.1%, respectively).The Papua New Guinea and Australian islands are separated from each other but there is strong resemblance among the inhabitants of these two islands who share a similar picture of the distribution of the MN blood groups. It is worthwhile to explore the reasons for this affinity in the blood group frequencies between the Papuans and the Australian aborigines. One of the striking similarities in the MN blood groups is between the American Negroes and the Pygmies of the Africa.
3 RH Blood Group System
Experiments were conducted in which the blood of the monkey Macacus rhesus was transfused into the rabbits and guinea-pigs to immunize them to produce antibodies. The resulting antibodies agglutinated not only the monkey red cells but also the red cells of about 85% of the individuals of the White race in spite of the fact that they had different ABO blood group types. Such individuals possessed an Rh factor (antigen) and hence were designated as Rh positive whereas the remaining 15% who did not show any agglutinating reaction with the rabbit anti-rhesus serum were designated as Rh negative.
There are mainly three factors (antigens) of the Rh blood group system, viz., C, D, and E, and out of these the factor D (antigen D) is the most powerful and elicits the greatest agglutinating reaction. The other two factors (C and E) give very weak agglutinating reactions and hence can be ignored for the clinical (transfusion) purposes but anthropologically they are extremely useful.
The Rh blood group system is controlled by three closely linked loci and they can be present in an individual either of the two alleles viz., C or c; D or
d; E or e at these loci. An Rh gene complex could therefore be assembled in eight different ways: CDe, cDE,cde, cDe, cdE, Cde, CDE and CdE. Seven
of these assemblages could be identified in the alleles already known; the eighth, CdE, remained to be found. The Rh negative refers to all those assemblages/ gene complexes which contain d instead of D. So, out of the possible eight gene complexes mentioned above, the four – CdE, Cde, cdE and cde lead to a Rh negative blood. The cde is the most commonly found Rh negative gene complex and has a frequency of about 20 – 50% in the Europeans and Asians , about 20% in some African populations and about 10% in the American Indians. This complex is rare in rest of the world. The Cde gene complex has been observed in about 13% of the Australians and about 7% of South African populations. Of the remaining Rh negative gene complexes, cdE has been found in very small proportions while CdE has not been detected in any world population. The most abundantly found Rh gene complex is the CDe for which the Asians and Melanasians have the highest frequency (range 75 – 80%), followed by the Europeans (around 50%) while in the African populations, this Rh complex, if found, has the lowest frequency (around 10%).
4 ABH Secretion System
The ABH antigens present on the red cell surface (in alcohol soluble form) can also exist in a water soluble form in the body fluids. Thus some individuals may demonstrate the presence of the blood group factors corresponding to their own ABO blood group status in their body fluids such as the saliva, urine,
gastric juices and mucous secretions. Such persons are known as the ‘ secretors’ . The others who do not secrete in their body fluids any blood group factor corresponding to their ABO blood group status are known as the ‘non-secretors’. The ability to secrete the A, B or H substances in the saliva is inherited as a Mendelian dominant character. There are two genes (alleles) responsible for the control and inheritance of the ABH secretion, viz., a dominant secretor gene Se and a recessive non-secretor gene se. These are not linked to the ABO blood group genes.
Studies have shown a high frequency of the secretors in the New York Whites (85%) and German Whites (78%) whereas the incidence of the trait was found to be comparatively lower in the American Negroes (61%).The secretor locus Se is withdrawn and renamed FUT 2 (fucosyl transferase 2) The alleles Se and se are renamed FUT 2SEC and FUT2QO, respectively and the secretors and non-secretors are renamed FUT 2 SEC and FUT 2 NON SEC, respectively
5 PTC Tasting Ability
A chemical substance known as phenylthiocarbamide (PTC) has a very bitter taste for most people, but there are some others who cannot taste this substance.
Thus people can be divided into two categories on the basis of their ability to taste PTC; the tasters and non-tasters. The trait is controlled by a pair of autosomal genes (alleles) – the dominant taster allele T and the recessive non-taster allele t. The ability to taste PTC is dependent on the presence of the
dominant gene (I). The world populations have shown different frequencies of the PTC tasters. The American Indians and African Negroes have more than 95% of the population as the tasters of PTC while the Australian aborigines have the lowest frequency of the tasters (27 – 50%). An experiment on the
chimpanzees revealed that about 74% of them were PTC tasters thus showing similarity to the humans in their frequency of this genetic trait which may be taken as an evolutionary affinity to the humans.
C. Other Genetic Markers
a. Haemoglobin
Haemoglobin (Fib), also known as blood globin or blood protein, is a ferroprotein comprised of globin and haem molecules and occurs in three different normal forms in man viz., Hb A Hb A2 and Hb F. The normal hemoglobin A (Hb A) is comprised of two chains of the alpha globin polypeptides and two chains
of the beta globin polypeptides. In the fetus, instead of the two beta globin chains two gamma globin chains are present, resulting in the formation of foetal haemoglobin F (Hb F). An example of an abnormal haemoglobin variant of the beta chain, designated as sickle cell haemoglobin S (Hb S), present in abnormal red cells of the shape of a sickle which resulted in sickle cell anaemia, has been discovered. It was later on found that many populations in Africa had sickle cell haemoglobin.The persons with HBb S were found protected against the malaria and hence the frequency of such persons was found quite high (10 – 40%) in some African populations. It was further noticed that the heterozygote ( Hb AS) individuals were more resistant to the malaria than the homozygote (Hb SS) individuals. A large number of other haemoglobin variants, mostly of the beta chain, have been reported in the world populations and represent the structural examples of the human haemoglobinopathies. In the Indian populations, the most frequently encountered haemoblobin variants include Hb AS, Hb AD and Hb AE, among others.
b. Thalassaemia
The thalassaemia, often called the Cooley’s anaemia, represent an another type of the hereditary human haemoglobinopathies in which the rate of synthesis of one of the globin chain (alpha or beta) is altered. It results in severe haemolytic disease in which the red cells are destroyed and is quite prevalent in the countries around the Mediterranean Sea. In the areas of the world where malaria is endemic, thalassaemia is quite high which raises the issue about its possible heterozygote advantage to the carrier under the malarial conditions.
c. Glucose – 6 – phosphate dehydrogenase (G6PD) deficiency
Glucose-6-phosphate dehydrogenase is an enzyme in the human red cells (erythrocytes) which catalyzes the oxidation of glucose-6-phosphate to 6- phosphogluconate in the glucose metabolism. Some individuals are deficient in this enzyme and hence are called the G6PD deficiency disease patients. This
disease is found in the Mediterranean area (Sardinia, Greece and Israel), Africa (East and West Africa, Congo) and India. In the tropical countries with high incidence of the falciparum malaria, the G6PD deficiency individuals are found in good numbers. A large number of the variants with the deciency of the G6PD enzyme activity have been detected in different world populations. It has been hypothesized that patients with the G6PD deficiency are better protected against malaria. The G6PD deficiency is inherited as an X-linked genetic trait.
d. Haptoglobin
Haptoglobin is a glycoprotein globin present in the human serum that combines with the free haemoglobin from the lysed red cells and thereby preventing its excretion by the kidneys. Human haptoglobin is polymorphic with three phenotypes viz., HP 1, HP 1,2 and HP 2, detectable by the biochemical technique of gel electrophoresis. These are controlled by a pair of codominant autosomal alleles HP1 and HP2. In some African populations living in the malarial areas, the serum haptoglobins are totally absent (phenotype HP 0) and the condition is called ahaptoglobinaemia or hypohaptoglobinaemia. Such type of cases has not been found in the European populations. The frequency of HP*1 allele is very high in populations of the African continent, suggesting some selective advantage.
8 Dermatoglyphics
The dermatoglyphics (derma means skin and glyphics means to carve) is the study of the patterns of the ridges on the hands, fingers and soles. These ridges
provide roughness and are useful for a strong grip. One thing important about the dermatoglyphic patterns is that these do not change with age and are unique in a way that no two individuals have same dermatolgyphic patterns. This characteristic of the finger prints has made them unique for personal identification to the extent that they act as a person’s signature and are almost fool proof evidence against suspects in a crime from where these evidences are collected.
The dermatoglyphic patterns prove useful in classifying different populations. A triradius is a centre of the delta shaped (deltoid) junction of three regions each containing curved streams of parallel ridges i.e. a three ridge system. Depending on the number of triradii present, the patterns of the ridges on the
human finger tip are mainly classified into the following types.
- Whorl (W): it possesses two triradii. A triradius is a point from where ridges in three directions seem to emerge.
- Loop Radial (Lr): it possesses one triradius and the loop opens towards the radial (thumb) side.
- Loop Ulnar (Lu): it also possesses one triradius and the loop opens towards the ulnar side.
- Arch (A): it is pattern which does not have any triradius