Q: What do you think about the unicorn?
A: We still do not know exactly what animal it is. There is no animal with a single horn like it of course. It still is very likely that it is only a pictorial representation of an animal with two horns, where the other horn is behind the one horn we see from one side. The animal looks more like an antelope than like a bull, this has been commented on. The first problem is in identifying the animal, about which there are several theories.
Secondly, since it is invariably present with this ritualistic device which I have identified as a filtering device, it shows that the unicorn also had a religious connotation in the Indus Valley, like the Golden Calf of the Near East. Whether it was itself worshiped is a matter of doubt. It could be associated with God, or some fertility cult. Note that it is always the bull, not the cow. In this sense the Hindu veneration of the cow seems to be different from the Harappan veneration of the bull. I have never seen a cow being represented on any of the seals, except when it is a bull mating a cow, but never a cow by itself. Therefore it could be some kind of a fertility sign, or a sign of one of their Gods.
Or, most likely, it could be the totem sign of one of the largest or most powerful ruling elites of the Harappan polity. With very few exceptions the filter device which you find before the unicorn is not placed before other animals. There are some exceptions, but they are rare. For the moment, the unicorn seems to be a very tantalizing symbol about which anything firm is yet to be found out.
Q: Kenoyer and others don't believe that it represents a two-horned animal because the craft level was high enough that they could easily have shown two horns if they wanted to. What about the thought that it was some sort of composite symbol, an integrative clan symbol?
A: Yes, I think S.R. Rao has also said it is a composite of a camel, a horse, and so on, although the camel and horse are never found in the Indus Valley. You cannot have a composite without the constituent animals being found there. But it could very well be a representation of what was already a mythological animal in the Indus polity, there being no real representation. We have other such animals, three-headed and two-headed animals. These were only mythological animals and the unicorn could very well have been one of them.
Q: If it was a symbol of the ruling class, why did it vanish so entirely from later Indian mythology?
A: It is difficult to say. One theory could be that it was closely associated with the rulership of Harappa and became the first casualty; when the ruling elite was destroyed the myth of unicorn went along with it. This is one possibility. The other is, taking the soma parallel further, who is most associated with soma in the RgVeda? Indra. What is most associated with the filter symbol in the unicorn seal, the unicorn. Could the unicorn be the prototype of Indra? One clue is the most common simile describing the soma drink in the RgVeda is the bull. It is very difficult to understand why a drink would remind you of a bull. A drink is a liquid, a bull is a very strong animal. Could this again be a reflection of the bull-filter device combination on the Indus seals?
Another possibility is that Indra himself displaced Varuna. The original soma drinker was Varuna, Indra is a late-comer or Varuna was a pre-Aryan god. Could the Indrasoma combination of the RgVeda be a combination of proto-Varuna, proto-soma combination in the Indus Valley. These are speculations.