Ever since an atman started its cosmic sojourn it does not act like a Karta doer. An atman always remains passive and let manifest human form do all the work.
The cosmic journey of an atman starts when Brahman, God Almighty explodes self with a big bang. This results in all atmans scattering all over cosmos at unimaginable speeds. In the melee, hurtling atmans gathered impurities similar as a rolling ball gathers moss. To cleanse self of dross impurities within starts cosmic journey of atman, the consciousness within!
Life evolves in cosmic system directly governed by inscrutable laws of karma, as we sow so shall we reap nothing less or more. Karma gets necessitated so that atman within can purify itself. In absence of karma life simply could not evolve in cosmic system everything would decay and die.
By decay and die we mean all atmans would remain inert, endlessly rotating all over cosmos doing nothing. Of its own no atman can purify itself. To regain its lost original pure prime pristine primordial form an atman needs a medium, a body to work out its karma.
No sooner life supporting planets like mother earth evolved, atmans become free to manifest life forms and starts evolution of life on mother earth.
Both evolution and karma were integral to an atman gaining absolute purity in its cosmic sojourn.