To Y Not #31894:
Of course you know this, but, I only recently came to have basic insight into Paṭicca Samuppāda process.
Not knowing four noble truths IS cause for beginning less sansarā. We never removed viññana because we never knew four truths. Because we never removed viññana, there was always abhisaṅkhāra, which lead to Bhavā until now.
But, Now that we are fortunate enough to born in this buddha sasana, I hope that may all of us be able to become at least sottapana anugami and maximum of us become anāgāmi in this life itself.
May Dhamma spread wide and far.