Obviously, an EC places emphasis on the Garden of Eden as an incredibly significant area of God’s creation but not the only area and mechanism of creation.
Bro Jardine (who I’m sure did not believe in evolution) when talking about the Garden of Eden makes the following rational suggestion:
“This arena was originally a contracted territory—the Garden of Eden and its vicinity. Beyond this the Bible gives no account, but this is no reason to presume that all that was exhibited under the dominion of Adam here were the all of the whole globe, or that all that was transacted here was the origin of all that then did exist on the face of the earth or even now exists, but that it was the all and the origin of all as pertaining to a new creation yet to be revealed, as the beginning of the world to man in this relationship, as the beginning of the purposes of God to both him and his habitation in view of a higher and nobler destiny—is without dispute. And from this point of view the seven days of creation may have been but seven days—a week—to set in order this territory as the earth on which to begin those purposes. But we do not say this was the case; we merely at present suggest it.”
In fairness I draw your attention to his final words, his comments are a suggestion not a certifiable fact in his mind. However, that an early Christadelphian would even suggest Gen 2-3 being a localised special creation, the beginning of God’s revelatory purpose is interesting. Such a view might not be as palatable now. It is consistent with my understanding.
Bro Norris in 1965 (ie around the time of the Lovelock debate) while personally rejecting evolution, drew attention to the limited extent of Eden and our limited knowledge of God’s operations saying
“in the limited nature of our knowledge, even from Scripture, of what the condition of the world outside Eden may have been at that time, we find sufficient latitude for a proper calmness in the face of possibilities which do not injure our deposit of faith” 
It is obvious that while Genesis 1 is about all the earth, Genesis 2-3 is an intimate picture of a localised garden and God making a couple miraculously and revealing Himself for the first time.
 Jardine, ‘The Bible as a Law of Life and Immortality’, The Ambassador of the Coming Age (2.7.115), 1865)
 Norris, AD “Where Science and Religion meet” The Christadelphian, Volume 102page 149–150 (1965)