Why have wine bottles assumed the shapes we see today? As you might guess, it was largely a practical matter, a compromise between ease of manufacture (and thus cost) and the work they were expected to do.
The simplest form for early glass blowers to achieve (glass was not widely in use for wine storage until the 17th century) was roughly spherical (per above), minus the flattened bottom, which came later. Until it did, the inconvenience of such a shape might be overcome by wrapping the bottle in a woven wicker flask (called a fiasco in Italy) that could be safely carried and set upright on the basket’s wide bottom. The indentation in the foot of modern Bordeaux (square shouldered) and Burgundy (slope shouldered) bottles, called a punt, was added to provide sturdiness to bottles destined for lengthy travel overland or by ship.
Since wine made in Alsace and Germany traveled mostly on the sedate waters of the Rhine and its tributaries, this extra precaution was unnecessary there. To this day, they retain the traditional, puntless form. There were other considerations. Those square shoulders typical of Bordeaux-style containers were originally intended to serve as a trap for the sediment that accumulated when wine was aged in bottle, resting on its side, for extended periods. This practice became common with wine originating in that part of the world, typically vinted from highly-pigmented, thick-skinned red grape varieties. In Burgundy, where the more delicate Pinot Noir tended not to share these characteristics, slope-sided bottles were adequate and thus the norm.
As to the matter of the standard size of wine bottles, we might look to our own anatomy for clues, since so many standard measures have their origins in the human body itself. Examples include the foot, the span, the cubit (a length equal to the distance from the elbow to the tip of the middle finger), and the hand by which we still gauge the height of horses.
A yard of cloth was once determined by holding one corner of the fabric to the chin and drawing the material out to arm’s length. We get a leg up, order two fingers of whiskey, employ rules of thumb. We win by a neck or a head or maybe a nose.
I am reliably informed that, in early days, a hand-blown bottle comprised a volume an average glassblower could produce with a single blast of breath; only much later standardized at 750 milliliters for the most often-encountered format. How it is that this roughly correlates with the right amount of wine for two reasonable people to consume at a single sitting is anyone’s guess.
Is it mere coincidence that two lungs worth of air produce a volume just equal to two tummies worth of wine? Or is some as yet unsuspected process of natural selection at work here? Evolutionary biology may one day provide the answer. If and when it does, you’ll read it here first.