What is the exact number of races of humans, as defined by science?

 In scientific terms, the concept of human races is not well-supported. Modern biological anthropology and genetics recognize that the concept of race is a social construct rather than a meaningful biological categorization. The genetic variation among individuals is continuous, and there are no clear-cut boundaries that define distinct races.

Human genetic diversity is primarily clinal, meaning that genetic variations change gradually across geographic regions rather than forming discrete racial categories. The Human Genome Project and subsequent research have highlighted the relatively small genetic differences among human populations compared to the overall genetic similarity.

The scientific consensus is that there is only one human race—Homo sapiens. The idea of dividing humans into distinct races based on physical characteristics like skin color, facial features, or hair type has been debunked within the scientific community.

While there are observable variations in traits such as skin color, hair type, and facial features due to adaptation to different environments, these variations do not align with clear-cut racial categories. The understanding of human diversity is better described in terms of populations, ethnicities, and geographic ancestries rather than discrete races.

It's important to approach discussions of human diversity with sensitivity and an understanding of the historical and social context that has led to the use of the concept of race. Emphasizing our shared humanity and the scientific understanding of human genetic diversity can contribute to more inclusive and accurate discussions about human differences.