[gumby]

Spaces between words are a relatively recent addition to scripts like the Greek or Latin alphabets, roughly 1500 years ago. Early Greek was also written boustrophedon (“like an ox plows a field”) that is, left to right, then the next line is right to left, and so on. Sometimes a point (dot) was used to break words.

Spacing is hardly standardized in languages using Latin script; French typography, especially in older books is notably different from English or German, with spacing between sentences or certain punctuation being different. Then again phrases or terms which in English or French would be multiple words are written as single “words” in German („Straßenkehrgerät“ == “Street Sweeper”). And I find Russian spacing rules disturbing.

And look at Arabic which does have spacing but in calligraphy can grossly violate the bounds of what you might consider “running text” coming from a European background.

[lynguist]

The boustrophedon has one more rule that you omitted and it’s extremely natural, – when you write from right to left you flip all the letters! My little daughter intuitively writes in this system even though no one taught her that nor did she see it somewhere. She explains that that way you know how to read longer passages that need to wrap over.