Is there a before/after edit view in OS X Photos' Editing view? [duplicate]

While in Edit mode, hold down the Control and M keys.

This will show you the original version of your photo, with no edits applied. If you want to temporarily undo the effect of the color adjustments but keep the cropping and rotation the same, hold down M by itself.

Unlike Aperture:

• It doesn’t work in “view mode”; you have to be in edit mode. (To get into edit mode via the keyboard, press Return.)
• It’s a hold, not a toggle, so you only see the original photo for as long as you have the keys held down.

For now you could toggle between CMD + Z and Revert to Original from the Image menu.

Additionally you can make the process faster by adding a keyboard shortcut:

• Go to System Preferences -> Keyboard -> Shortcuts and then select App Shortcuts
• Click the + and select Photos from the app list
• Type 'Revert to Original' in the menu title field and choose a keyboard shortcut. I used CMD + Y.

Now you can flick back and forth by pressing CMD + Y and CMD + Z