Is Io a pre-European tradition?

From time to time, I am asked whether I believe Io to be a pre-European tradition or not. Here are my thoughts:

• I am open to the idea that the Io tradition does have a history prior to the arrival of the European to Aotearoa-New Zealand. Given the multiplicity of atua in the traditional Māori pantheon, it is likely that someone, somewhere was inspired enough to conceive of one, overall and superior atua. 
• My question, however, is this: can we be finally conclusive and definitive about it? Is it possible to finally prove that Io is pre-European? In my view, I don't think so. As I say, I am open to the possibility. I am just doubtful whether we can prove the Io tradition to be pre-European - it could be, it might not be.
• I have found that evidence asserting Io as a pre-European tradition is unconvincing and occasionally disappointing. For example, Michael Shirres (who I met and knew) relied solely on the work and evidence of my granduncle Māori Marsden in his book He Tangata. He does provide examples of Io literature from other iwi traditions but none point directly to a pre-European history for Io. He relies solely upon Uncle Māori’s assertion that it is and no other corroborating evidence is provided. (See note below as to what I think Uncle Māori's real interest was.)
• It’s also notable to discover that references to Io begin to appear in the written record later in the 19th century rather than earlier. For example, Io does not appear in the numerous whakapapa books of authorities such as Te Rangikāheke of Te Arawa and Mātene Te Whiwhi of Ngāti Toa. Whakapapa dictated by my tupuna Te Ahukaramū of Ngāti Raukawa in 1856 does not include Io, however, whakapapa written by his grandson Kipa Roera in 1915 does include Io. I do not think it correct to assert that because Kipa includes Io in his whakapapa that his grandfather knew Io too. As I say, it is possible that Te Ahukaramū did know Io but it is difficult to conclusively say he did.
• There is also the explanation offered by some (often very reputable people such as Pei Te Hurinui) that Io was never shared publicly and was known only by those initiated in the tradition. It is asserted that Io was a secret cult and this accounts for the absence of Io in whakapapa books written in the early 19th century. This is possible. The problem with this, however, is that just as we can say that Io was secret, was not written down and this accounts for the absence of Io in the written record, we can also equally say that because we have no written evidence we can not conclusively say that Io is pre-European.
• The other problem is the lack of evidence from other parts of Polynesia. There is very little literature found in Te Moananui-a-Kiwa that is akin to Io in the same way that we can find similarities throughout Polynesia for Tāne, Hine, Ranginui, Papa and particularly Tangaroa. Additionally, if there is a Polynesian claim for a supreme being it is more likely for Tangaroa, for obvious reasons.
• Hence, in my view, it is difficult to be finally conclusive on the pre-European provenance for Io. As I say, I am open to the possibility. I just think it is difficult for us to prove it today.
• I also ask, does it matter anyway? Does it really matter that we can prove Io to be pre-European? For me, I think, in the end, no. What is more important (and more interesting) is the meaning, value and significance of the Io tradition rather than its history, as interesting as this might be. I find now that it is more important to ask, what does the tradition hold for us today and going forward?
• I suggest that it is this question that lies at the heart of Māori Marsden’s enthusiasm for the Io tradition. He wrote about it on various occasions and I was present at a number of wānanga where he spoke about Io (he gave me some Io whakapapa too and the Ngā Puhi version of Tāne's ascent). As I say, I suspect that his real interest in Io was not because of its historical provenance but rather because of the value he saw in the tradition for young Māori like myself. Uncle Māori, as a Minister, was more interested in the spiritual welfare of his people than their history (although he knew a lot about this too!) and this led him to think about the value of the tradition rather than its history. 
• I believe that the preoccupation with proving a pre-European history for Io really comes from a lack of confidence in our Māoritanga. At least, this was my experience - for I look back now and see that my concern to discover proof for pre-European Io was really about 'feeling authentic', trying to get in touch with some true or real experience and knowledge of Māoritanga. In doing so, I idealised the past and overlooked the richness of the present. When I began to ask myself what mātauranga Māori was all about anyway - when I began to look into the meaning and significance of the Io tradition - I found that my anxiety to 'prove' the authenticity of the Io tradition diminished.
• As I spent more time exploring what the tradition actually represents - its core wisdom - I began to see that it is not Christianity dressed up in Māori symbols and ideas, as some would have it. I see the Io tradition as a profound meditation on the nature of life and existence based upon the idea that there is one source for all things and to which all things return in a perennial and unending cycle. I also see that it contains ideas of growth and maturation, that the world is birthed from Io and is equivalent to Io, an idea that contrasts with the Old Testament idea that the world was 'created' by God, is a manifestation of God's creative power and is not, therefore, equivalent to God.
• We see, therefore, that there are similarities and differences between the Io and Christian traditions.  However, they are not exactly the same. I believe, also, that interest in the Io tradition grew in our iwi communities in the face of the rise of Christianity. There was an intensification of interest in the Io tradition, there were even attempts to build bridges between the Io tradition and Christian. This is found in Kipa Roera's whakapapa books (in my possession) as well as in the letters of Rev Paora Temuera of Ōtaki to Eric Ramsden.