Article: According to the 2000 edition of a popular physical anthropology textbook, forensic anthropologists are overwhelmingly in support of the idea of the basic biological reality of human races. Forensic physical anthropologist and professor George W. Gill has said that the idea that race is only skin deep "is simply not true, as any experienced forensic anthropologist will affirm" and "Many morphological features tend to follow geographic boundaries coinciding often with climatic zones. This is not surprising since the selective forces of climate are probably the primary forces of nature that have shaped human races with regard not only to skin color and hair form but also the underlying bony structures of the nose, cheekbones, etc. (For example, more prominent noses humidify air better.)" While he can see good arguments for both sides, the complete denial of the opposing evidence "seems to stem largely from socio-political motivation and not science at all". He also states that many biological anthropologists see races as real yet "not one introductory textbook of physical anthropology even presents that perspective as a possibility. In a case as flagrant as this, we are not dealing with science but rather with blatant, politically motivated censorship".

Now answer this question: What does Gill think the complete denial of opposing evidence stems from?
socio-political motivation