Question

what is the basis of Human classification

Answer 1

The term race or racial group usually refers to the concept of dividing humans into populations or groups on the basis of various sets of characteristics. The most widely used human racial categories are based on visible traits (especially skin colour, cranial or facial features and hair texture), and self-identification.
Conceptions of race, as well as specific ways of grouping races, vary by culture and over time, and are often controversial for scientific as well as social and political reasons. The controversy ultimately revolves around whether or not races are natural types or socially constructed, and the degree to which observed differences in ability and achievement, categorized on the basis of race, are a product of inherited (i.e. genetic) traits or environmental, social and cultural factors.
Some argue that although race is a valid taxonomic concept in other species, it cannot be applied to humans. Many scientists have argued that race definitions are imprecise, arbitrary, derived from custom, have many exceptions, have many gradations, and that the numbers of races delineated vary according to the culture making the racial distinctions; thus they reject the notion that any definition of race pertaining to humans can have taxonomic rigour and validity. Today most scientists study human genotypic and phenotypic variation using concepts such as "population" and " clinal gradation". Many contend that while racial categorizations may be marked by phenotypic or genotypic traits, the idea of race itself, and actual divisions of persons into races, are social constructs.
History
In ancient civilizations

Blue-eyed Central Asian ( Tocharian?) and East-Asian Buddhist monks, Bezeklik, Eastern Tarim Basin, 9th-10th century.
Given visually complex social relationships, humans presumably have always observed and speculated about the physical differences among individuals and groups. But different societies have attributed markedly different meanings to these distinctions. For example, the Ancient Egyptian sacred text called Book of Gates identifies four categories that are now conventionally labeled "Egyptians", "Asiatics", "Libyans", and "Nubians", but such distinctions tended to conflate differences as defined by physical features such as skin tone, with tribal and national identity. Classical civilizations from Rome to China tended to invest much more importance in familial or tribal affiliation than with one's physical appearance (Dikötter 1992; Goldenberg 2003). Ancient Greek and Roman authors also attempted to explain and categorize visible biological differences among peoples known to them. Such categories often also included fantastical human-like beings that were supposed to exist in far-away lands. Some Roman writers adhered to an environmental determinism in which climate could affect the appearance and character of groups (Isaac 2004). In many ancient civilizations, individuals with widely varying physical appearances became full members of a society by growing up within that society or by adopting that society's cultural norms (Snowden 1983; Lewis 1990).