People who believe evolution as a cosmic theory, that everything, and I mean everything, is in a constantly-changing state, come to believe that about Holy Tradition as well. Clarification of what has always been true gets exchanged for changing beliefs about what is true. Thus, under this belief, Church understanding of, say, human sexuality (sex being an especially clear example) undergoes a metamorphosis, from being a thing intended to be expressed in a relationship that is for life, a relationship that may not be broken, and all expression outside that permanent relationship as being broken, aka sin, to a negotiable thing. Divorce and contraception become normative (by which I mean acceptable among practicing Orthodox Christians) as do sexual practices that abuse (wrongly use) the sexual function, and a proper compassion for people acknowledging a sin as sin becomes a false compassion for people who simply wish to practice the sin with the approval of the Church, economia becomes license to do so, and the stern teachings of the standard we ought to be held to gets replaced by “pastoral care” that does not really call us to uphold those standards. The attitude winds up being applied to “homosexual” relationships and other modern attitudes both toward the marital act, and to the sexes in general. And that’s just one example of how evolutionism creeps into the Church; the very idea of evolution has made it plausible.
Theology is another one. I don’t have the time, but the idea of a deathless world into which a fully-formed man commits sin and causes death to enter the world gets thrown out the window, too. It comes to be treated as a mere allegory and not as an event taking place in history. The conception shared by pretty much all the fathers gets suborned.
Liturgical change becomes normative. Legitimate issues, like prayers for an empire that has ceased to exist, or doors that are no longer locked, morph into playing a guitar or singing modern songs during Liturgy that attempt to praise God in the modern manner creep in. And step by step, we become Swift Eagle Justice (or whatever).
The consensus of the fathers, the vast mass of assumptions they agreed upon, gets replaced by the confusion of the fathers, the notion that they agreed on nothing, except maybe the Creed, and that appeals to consensus are just appeals to indivduals who disagreed. All understandings, once generally taken for granted, become a matter of personal opinion. We become just another bunch of Protestants.