Answer: According to sources, the most probable answer to this query is that evolution happens because when life came it sought for survival. Now, this is through mutation which causes random DNA sequences leading to genotypic and phenotypic changes. Natural selection as relation to adapting to the selection forces of the environment. And when these factors is added by the niche and other large case scenario to cause major anatomical changes, speciation comes through. And that, the process of evolution. And how it is a mechanism and an intermediate interaction with the environment.
Animals have a mitochondria, a nucleus, and a cell membrane, bu they do not have chloroplasts. You can only find chloroplasts in human and plant cells, not a animal's cell. Hope it helps!