Final answer:
Humans are about 99.9% genetically identical, with the 0.1% variation responsible for individual differences. Despite the diversity in appearance and certain genetic traits, the vast majority of our genetic makeup is remarkably similar. Small genetic differences, however, can have significant medical implications.
Step-by-step explanation:
Despite the observable variation in features such as skin color and facial structure, humans are remarkably genetically similar to each other. Studies have shown that genetically, any two humans are approximately 99.9% identical. The 0.1% of genetic material that does vary among individuals accounts for visible differences, such as height, eye color, and certain physiologically relevant characteristics like the sense of smell or resistance to certain diseases through mutations such as in the CCR5 gene.
Biological anthropologists have found that biological variation within the human species does not support the division into discrete racial categories, as there is often more variation within these groupings than between them. Allelic differences, the spread of humans across diverse environments, and cultural factors have all contributed to the wide range of physical characteristics observed in human populations.
Although these genetic differences play a role in making each one of us unique, they are relatively minor when considering our entire DNA sequence. Important to note, these genetic variations are crucial in certain medical scenarios, such as the need for a close match in HLA proteins during bone marrow transplants, further underscoring the significance of even small amounts of genetic divergence among humans.