Well, Chuck , I believe it happened because there is virtual unanimity among highly-trained experts, using the reliable scientific method, that it happened.
the LORD God formed the man from the dust of the ground and breathed into his nostrils the breath of life, and the man became a living being. (Genesis 2:7, 1984 NIV)
There is such a thing as evolving within species in nature (even wolves into a variety of dogs, etc), but never any cross over of species. That is the real issue in a discussion of Darwin's ideas ---which are clearly atheistic and speculation.