For what it's worth, this is how my Original Blessing approach views this topic: (It is an extension of Teilhard de Chardin's philosophy, and I believe it is compatible with Polkinghorn's.)
In creating our Universe, God desired to have one (or more) of the creatures it was destined to produce to become conscious of His creative role, and render Him homage and gratitude for it. Since He may have allowed many ways life could begin and many ways for it to develop, He may have, from the very beginning, allowed for an aspect of His spirit to become a Universal Guide and Savior (Christ) whatever direction creation took in a local environment. On planet Earth, life seems to have developed through an evolutionary process that encouraged survival--often at the expense of selfishness and other properties not in line with His objective of Bearing His Image. Even after He bestowed on a primate species, Homo sapiens, the gift of Mind and Conscience so that His will could be discerned, the gift was spurned. It was then up to Jesus, as Universal Christ, to 'take up the Cross' and by rejecting the selfishness of animal instincts (which he also had as a true human), to accept his invitation to love our neighbor as ourselves. Jesus took on our human flesh to show that it was possible for us to do that, too. We can only speculate how conscious life on other planets could have developed. Their 'evolution' may not have required the degree of selfishness that ours appears to have had. Perhaps they did not need the Universal Christ to 'intervene' in their behalf. If they did, perhaps Christ would have taken on their genome. Certainly it would NOT have been the human, Jesus.