There is a different of only one amino acid in one chain of the hemoglobin of human and gorillas. what might have caused this difference?

The difference of one amino acid in the hemoglobin chain between humans and gorillas is likely due to a mutation in the DNA sequence that encodes for that specific protein. Such mutations can occur randomly over evolutionary time and may be influenced by factors such as genetic drift, natural selection, or environmental pressures. This small variation can have implications for the protein's function, but it is often the result of the gradual accumulation of genetic changes over millions of years of evolution.