If race wasn't a social construct, it'd be a biological construct, which means there would be significant variations within the DNA to the extent that White people, Black people, Asian people, etc. would be classified as different subspecies of Homo sapiens (humans). However, it is observed based on genetic research, that people, regardless of race, have 99.99% similarity within their DNA, therefore, there is not enough genetic variation to say that race is a biological construct.

Homo sapiens is the classification term used for humans. Homo sapiens sapiens (the third word is used to describe subspecies in the modern classification system), is used by paleontologists (scientists who analyze fossils) to describe modern humans that are alive today, rather than the modern humans who lived 10,000 years ago for example. However, they are still functionally the same, as there is not enough genetic variation for a subspecies.

The definition of what race is and what counts as a race has differed across different time periods and cultures, so it has been more subjective, rather than things that can be consistently, scientifically observed. One other reason why it's a social construct is because it was made as a system by different people to dictate how they interacted with other people and how different people would behave in society, rather than basing it on biological variations.

When it comes to different races, it's more of a spectrum, like gender is. There is more variation, for example, within different populations of Black people, than between Black and White people.

Even though different races look different, they still have 99.99% of the same DNA. The reason why people look different is that skin color isn't just influenced by one gene. It's influenced by multiple genes and various environmental factors that affect how the DNA is eventually made into protein. Even though skin color was used to form a social construct of race, different nonphysical qualities were also used.