He DID evolve.
That evolution is a part of what made him the great leader he was.
"I am not, nor ever have been in favor of bringing about in any way the social and political equality of the white and black races. I am not nor ever have been in favor of making voters or jurors of Negroes, nor qualifying them to hold office, nor to intermarry with white people. And I will say in addition to this that there is a physical difference between the white and black races which I believe will ever forbid the two races living together on terms of social and political equality.
And inasmuch as they cannot so live, while they do remain together there must be the position of superior and inferior and I as much as any other man am in favor of having the superior position assigned to the white race. Abraham Lincoln in his fourth debate with Stephen Douglas in the campaign for the United States Senate on September 18th of 1858."
"I do but quote from one of those speeches when I declare that "I have no purpose, directly or indirectly, to interfere with the institution of slavery in the States where it exists. I believe I have no lawful right to do so, and I have no inclination to do so." Lincoln's First Inaugural Address, March 4, 1861.
"My paramount object in this struggle is to save the Union, and is not either to save or to destroy slavery. If I could save the Union without freeing any slave I would do it, and if I could save it by freeing all the slaves I would do it; and if I could save it by freeing some and leaving others alone I would also do that. What I do about slavery, and the colored race, I do because I believe it helps to save the Union; and what I forbear, I forbear because I do not believe it would help to save the Union. I shall do less whenever I shall believe what I am doing hurts the cause, and I shall do more whenever I shall believe doing more will help the cause." The Collected Works of Abraham Lincoln edited by Roy P. Basler, Volume V, "Letter to Horace Greeley" (August 22, 1862)
"Do the people of the South really entertain fears that a Republican administration would, directly, or indirectly, interfere with their slaves, or with them, about their slaves? If they do, I wish to assure you, as once a friend, and still, I hope, not an enemy, that there is no cause for such fears." The Collected Works of Abraham Lincoln edited by Roy P. Basler, Volume IV, "Letter to Alexander H. Stephens" (December 22, 1860)