For Christians (or anyone else) who deny Darwinian evolution.

[I_am_not_mafia]

It's a continuum from light sensing to shape sensing. It could start off light on / off, and then light at different intensities. There will be multiple cells sensing sensing this, not just one cell because there needs to be redundancy in the system and you never have a complex organism relying on a single cell. So you already then have some giving different strength signals which give you a direction to the light. This means that you already have the machinery in place to react to shapes because the cells will give different patterns of output signals so it's a single step to learning to recognise and adapt to different patterns.