Why did biological inspiration for object-oriented programming stop at cell-to-cell communication? What about levels below (organelles) and above (tissues, organs)?
It didn't actually, but in this case the computer allows things cleaner than biology. We could have gone a lot farther in making the interior of an object a real object space rather than what we did. Years later we did try that, and it is a good idea.
Also, take a look at the article I wrote for Scientific American in September 1984 "Software" that talks about organizations of active objects as "tissue programming"