Why are all these lines showing up on my model

[Haley_Barnes]

[pascal (Pascal Golay)]

Hi Haley - please run SystemInfo in Rhino and post the results here.

-Pascal

[John_Brock]

My guess is you are running an AMD Radeon gpu in your older Mac.
In Preferences/Settings > OpenGL, uncheck the option to use “gpu tessellation”.

Any better?