(continued from my previous post)
Let's look at the technology. An early type of horoscope was the "astrologer's board", a fixed zodiac on which gems could be moved around, each symbolizing a different planet. This would suggest a whole-sign system, if houses were used, at all. Apparently the earliest known astrologer's board is from 2100 to 2200 BP, prior to our major textual sources.
http://www.cbsnews.com/news/worlds-olde ... discovered. It would be easiest to use such a board, I imagine, either with no houses or whole-sign houses.
We often find the Hellenists using houses sparingly, even though they give one or more thematic schema. Delineations for which we today might use houses, to them were often determined through planetary relationship or "lots" (Arabian parts.) It is almost as though astrologers initially developed some house-free techniques, subsequent to thinking, "OK, now that we've settled on houses, what do we do with them?"
Here I will display my ignorance, in the hope that someone will help me out, but I actually do not find whole signs to be a very realistic way of dividing up a horoscope-- which is fundamentally a stylized representation of the earth in the cosmos.
I have yet to get my head around how the whole signs system fits the problem that different signs take different amounts of time to rise, depending upon latitude and time of year, which the ancients were well aware of.

Regardless of whether degrees represent time or distance, rising sign times do not squish neatly into 30-degree segments.
[I am still puzzled by a horoscope divided into two equal hemispheres, upper and lower, because day and night balance each other with 12 precise hours a piece only at the equinoxes; a problem for any house system.

If someone can explain how this works with uniform 30-degree signs I would greatly appreciate it.]
I am also puzzled by why the emerging sun is shown under the horizon (significantly so, for a late degree rising) when the ascendant supposedly represents the sun's position at dawn; thus positioning much of the first house into what seemingly ought to be the 12th house. Similarly, I don't get why the MC should wind up far from the 10th house in a high-latitude birth at certain times of year, when supposedly it relates to the 10th house.
(But Larxene, I think this explains how you could get a first house planet either by day or night, depending upon whether it was above or below the ascendant.)
To me, there is a real unhinging of "hinges", "cardines", angles, &c. from houses in both equal houses and whole signs systems, which is why I wonder if several systems were designed separately and then superimposed. I do understand the "logic" of explaining weak and strong houses as far as it goes, but
why it should seem logical to anybody escapes me. (However, you can map it very well onto daily weather patterns in the Egyptian summer, if anybody is interested.)
The ancients had several means for estimating the ascendant, which could then be relatively easily mapped onto the rest of the horoscope in an equal house system. I think at one point Valens says, that one can find the ASC, and count 90 degrees from it to get your MC, in addition to more sophisticated methods.
But neither equal house system really gets at the above problems of the impact of time and latitude on the horoscope, which quadrant systems seem designed to solve.
Porphyry houses make sense, because it is simple enough to walk outside (assuming a flat plane,) identify the points of sunrise, sunset, and the MC simply by looking at the sky, dividing the quadrants by 3, and extrapolating into the lower hemisphere.
It does seem as though whole signs were the "default" house system initially, but that with time, more refinement took place. However, this did not happen in any unified step-by step fashion.
History is a lot messier than tidy schemes for systematization, as Ptolemy clearly realized.