Fill in the blanks in the following paragraph regarding genome evolution. In your answer, separate the two missing phrases with a comma, e.g. protein, plasma membrane. Do not use abbreviations.
"Conservation of genomic sequences between humans and chickens is mainly due to … selection, whereas the conservation observed between humans and chimpanzees is mostly due to the short time available for mutations to accumulate. Even the DNA sequences at the … position of synonymous codons are nearly identical between humans and chimpanzees."