Science doesn't 'Prove' anything, if you knew anything about Science you would know this.

What mechanism stops lots of small changes adding up to a big one?

Science doesn't see any difference in Micro and Macro evolution, the latter is just the accumulation of the former over time.

At the end of trhe day Evolution is central to modern Biology as Plate Tectonics is central to Geology or GR is central to Physics. Without it nothing makes sense. Get over it.

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'The eye can only see what the mind is prepared to accept'