BIOLOGY OF HUMAN VARIATION& PHYSICAL ADAPTATION

BIOLOGY OF HUMAN VARIATION& PHYSICAL ADAPTATION

1. BIOLOGY OF HUMAN VARIATION& PHYSICAL ADAPTATION CATEGORIZATION OF THE LIVING RACES Variation Any difference between cells, individual organisms, or groups of organisms of any species caused either by genetic differences (genotypic variation) or by the effect of environmental factors on the expression of the genetic potentials (phenotypic variation). Phenotypic variance in populations tend to occur as a continuous variable over extended distances and more within than between populations, even when isolated by geographical (ocean/desert/ mountains) and /or social barriers. Race - breeding population whose members share a number of distinctive genetic characteristics that distinguishes them from members of other breeding population. Major races reflect obvious genetic differences most marked on continental basis . Studies of the development of the human cranium from the period of Homo erectus can provide valuable information for the comparison of modern living races and between the fossils that reveal the course of human evolution.

2. Cranial capacity is the measurement of the cubic capacity of the braincase. It provides an indication of brain growth at different periods of hominid evolution (Harrison et al., 1990) Large headed populations are referred to as Macrocephalic Small headed populations are Microcephalic Skin color- this is notably one of the racial differences and is of considerable sociological importance. Tropical environments are characterized by heavy pigmentation while in the temperate regions, the populations are light skinned because the sun rays are filtered by the greater depth of the atmosphere. Eye and Hair colour- this is another obvious racial characteristic. Populations in the Northern and Western Europe have light (blue) eye colour. Medium pigmentation (green eye) may also be seen but in most of the worlds population the dark brown eye colour is dominant. Human hair varies considerably in it’s shape

3. Relative length of the limbs- subspecies also vary in this aspect. Those who live in the open savannah countries commonly have longer limbs than those who evolved earlier in the forest environment. Sub-saharan Africa has long limbs described as macrobrachion , this helps to dissipate heat while the artic hunter with a bulky body conserves heat. Pelvimetric parameters- this varies considerably and have been applied in obstetrics and evolutionary biology of bipedalism. There is racial and sexual dimorphism in the pelvic index. The shape of the pelvis is android in males and gynaecoid or platypeloid in females. The skeletal material of the negroes are denser and stronger than that of the caucasoids while the Asians tend to have lighter, less compact skeletons than the caucasoids (Harrison et al., 1990).

4. Dermatoglyphics - this has shown significant differences in the inheritance of finger print patterns. High percentage of arches have been observed in Pygmies while the finger tips of Caucasoids usually have loops. The Mongoloids have a higher percentage of whorls than the Negroes or Caucasoids . Theories of Modern Hominid Evolution are: 1. Separate but parallel evolution from pre-sapiens ancestor. 2. Living races are local varieties of a single Homo sapiens sapiens genetic stock. 3. Separate evolution from distinct Neanderthal populations with substantial modification by intermittent migration and admixture. More evolved stock with better local survival value would spread out over habitable areas of the globe.

5. Africa – Negroid of sub-Saharan Africa – heavily pigmented dark-brown or black skin, hair, eyes, helical/spiral head hair (frizzy or peppercorn hair i.e Ulotricous ), thick everted lips, broad low-bridge noses, some prognathism , lightly developed calf muscle, relatively long forearm and leg, narrower pelvis, dolicocephalic, high surface area : volume ratio (small or linear). Allen and Bergmann’s Rule.

6. Europe + North Africa, Near and Middle East, India, Western Soviet. Caucasoids – Light pigmentation of skin/hair/eyes (Blue eyes, Blonde). Wavy or straight hair , narrow lips and nose (high bridge/aquiline), physique tends to be greater especially northerly, mostly dolicocephalic. Asia – East and Central. Mongoloids of East Asia (China, Mongolia)– Brachycephalic, broad faced, short statured, yellow skin, black straight hair (lissotrichous), dark brown eyes with epicanthic fold, low bridge noses, prominent cheek bones. Japanese tend to be more dolicocephalic. Negritoes of South East Asia – Phillipines , Indonesia, Malaysia, Andaman Island. Resemble Pygmy Negroes superficially. Dark skinned, moderately prognathous with dark curly or wooly hair.

7. Australia and Pacific – Hominids have been in Africa and Eurasia most of evolutionary history but entered Australasia < 50,000 y.a . Australian Aborigines or Australoids - moderately pigmented skin, hair and eyes, marked supra-orbital bony thickening, receding forehead, marked prognathism with large teeth, dolicocephalic, platyrrhine with depressed nasal root, wavy head hair and plenty facial and body hair, linear physique and slightly muscled arms and legs.