He usually tried to separate his emotions from the problem, and at these times he promoted freedom and colonization out of the nation. Jefferson wants to indicate that American nature is equal or superior to Old World nature. In comparison, he describes Africans as innately inferior in many ways. This comparison extends to other aspects of nature. Jefferson provides a table of animal weights, and compares them to Old World animals.
American animals are bigger.
This is also interesting to me because it is not all that subtle. He appeals to reason in all matters. He wishes for political solidarity to reflect that present in nature. His arguments are provided in a matter of fact fashion, despite their extreme subjectivity and qualitative nature. This contrasts nicely with the appeal to emotional descriptions present in his discussion of Virginia's natural landforms.