What Role do Physical Traits Play in Singing?

The discussion about castrati and their supposed physical advantage made me think. There is one issue about singing ability that has worried me for some time now - I don't believe it is addressed by many teachers, and I would really like to hear your opinion: How (un)important a role do physical traits play in the act of singing?
I recall your comment that all of the great singers from the past who were trained in this school of singing were singers from Nordic countries - where people are usually tall, with a large bone structure. I don't mean necessarily that everyone from Sweden or Germany is able to sing Wagner, but they certainly have a physical advantage to produce voices suited for this kind of repertoire (you can't find Heldentenors in Latin America, for instance, unless they have German ascendance). What about people from ethnic groups that do not play such an important role in opera history (people with indian ascendance, like me, who tend to be short, with a smaller bone structure), are we less able to sing because of our physical traits? Do smaller people have less resonance space or breath capacity, therefore are in physical disadvantage for singing? I know this is a very dumb question, and I know it sounds kind of eugenic, but personally it bothers me a lot. Could you please tell me your opinion on the subject?
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This is a great question. I think the physical make-up of a person has an influence on the result of their singing but is not a determining factor of whether they can sing or not. I think of voices as an instrument. And like other instruments they can come in different sizes. Take the family of string instruments as an example. You have the violin, viola, cello, and bass. They are essentially the same instrument, played the same way, more or less. Their function is determined by the same principles, just like all voices function by the same principles. The only difference is the size of the instrument. This changes the resultant tone relative to the difference in the physical structure. But there is also a sameness, a similar quality between the different instruments that we can recognize. This is a fundamental truth that applies to voices as well. You mention Helden voices compared to singers with smaller physical structures from Latin countries. To me it is a pretty logical relationship. This doesn't mean we will never see an exception, but the tendency makes sense. This also doesn't mean that the smaller instrument cannot be used with intensity. It just means that when it is, it probably will still not be appropriate for the more dramatic expression of the Helden category. There are times for dramatic expression in Rossini and Donizetti and the like. Just as there are plenty of opportunities for lyrical expression in Wagner and that type. So for me singing is singing, and it should include the ability to sing with sweetness and lyricism as well as dramatic intensity, regardless of the size of the instrument. The natural characteristics will determine where in the spectrum of vocal music the individual voice will be suited. But having the physical structure of a smaller instrument doesn't mean that it is less capable of singing. It is just capable of singing to a lesser degree of intensity. Just as a voice of a larger physical dimension is more capable of singing, it just naturally has a higher degree and may have difficulty singing at a lower degree of intensity. So one should not sing things for which it is not well suited and stick to what it is suited for. (This does not mean larger voices always sing loud and smaller voices always sing quiet) Just as a larger instrument is not well suited to the lighter music and can in some cases find it taxing to sing. It would be rare to have a cello play violin music, although perhaps it could do it. It is common to warn singers against singing repertoire that is too big for them, as we would find with a light voice trying to sing dramatic music. But I feel it is just as risky to have larger voices singing music that is too light for their instrument. This is not to say that singers should never explore rep outside their fach, or that they aren't capable of it. Once someone has developed their skill in coordinating the instrument they are capable of exploring a much wider range of rep. But for the developing singer that has a larger instrument it can create just as much of a problem trying to sing music that is too light for them as a young lyric voice can by singing things that are too big. It is all about learning to listen to what the voice and the body are telling us by their behavior. We need to watch out that we don't ask for things that impair the natural behavior of the individual voice. And as we all know, each voice has its own characteristics and qualities that we need to recognize.