How did European scientists and writers in the nineteenth century attempt to make sense of the differences in the appearance and behavior they observed between themselves and non-Europeans?

The Europeans scientists and writers century based the differences in appearance and behavior they observed between themselves and non-Europeans mostly on biological factors.

Explanation:

According to several studies conducted on the human behavior and how it is different from society to society, it is concluded that the differences are based on biological factors that an individual is exposed to. But biological factor alone is not responsible, the environmental factors also come into play. Following biological factors, a particular behavior can be present in the said gene but it would be incorrect to say that the gene controls the behavior. Genes simply facilitate the traits passed on from parent to offspring but the environmental factors act as the stimulus to bring the behavior into action.

Same is followed for the difference in the appearance. Genes from the father and the mother to their offspring are responsible for their appearance. For example, the child of a mother with brown eyes is most likely to have the same color of eyes as the mother. The environment plays less role in this case as compared to the behavior.