There is much debate on the prevalent theme and meaning of this movie. One of the hypotheses posits that the film is actually about food.
At the start of the film, the apes are shown living in clans but strictly vegetarian because they do not yet master tools that would enable them to eat anything else. They are easily intimidated and defeated by predatory creatures such as leopards. However, when the first tool is fashioned out of the bones of a carcass, the apes are instantly empowered and become the Men that dominate the food chain.
In the figurative year 2000 representing the future in general, the progression and evolution of humanity are obvious but also closely derived from the invention of the tool. On the Pan Am space shuttle, Dr. Heywood Floyd—the modern man—enjoys a meal, much like he would on a regular airplane. However, every component is sealed, liquefied, labelled, and most importantly, vegetarian.
The proposition is that the future will lead to bland, synthetic foods stripped down to their very essential nutrients and vitamins. Man, for thousands of years, dominates and exploits the food chain until its total depletion. The last things to disappear are the fruits and vegetables as these require the least energy to produce. Man is then forced to fabricate his own foods in labs, taking away any relation to the ground or to the earth. Food can now be produced on demand, regardless of any natural conditions.
Special attention was taken in this movie to make the experience of space as credible as possible. In all the movies discussed on this site, this one proposes the most resolved example of nutrition in space. Brought to Floyd on the spacecraft by the attendant on a small tray, this meal is sealed-tight and resistant to the lack of gravity. Every clearly marked “course” is consumed with a straw, resembling a line of synthetic flavoured juices. This is very similar to a TV dinner which is a commentary on modern society and its sacrifice of human interaction in favour of isolating technology. Eating, what used to be an important social activity, has often become solitary and done out of necessity.