People who are familiar with greek mythology will be familiar with the character who bears my given name. She was the daughter of king Minos who helped lead Theseus through the labyrinth to slay the Minotaur, later abandoned by him and rescued by the god Dionysius. The interesting thing is that before that myth came into being there were other stories that had her as a nature goddess. And although the Myths that come to us through Homer, and later through Roman writers such as Ovid, are still being rewritten in different forms today. Just look at the Percy Jackson series of Rick Riordan.
Yoga predates a written tradition. It is not possible to point to one book written by one person who 'invented' it. Like the oral traditions that predated Homer, the practices of yoga had likely been coalescing for many generations before anyone began to write any of it down. And even as people wrote bits of it down, it continued to evolve, riding the waves of cultural shift and personal invention. Most practices evolve, just as cultures do. Even a practice like football, that has the rules written meticulously is open to change through time.
What is true in a culture that keeps careful track of things in a form more precise than an oral tradition, is that it is possible to lay claim to a new idea, or practice, and to know very precisely of what that practice consists. There can be good and bad in that. If a practice is too rigid it will not be able to adapt to changing needs, and if it is too changeable it is likely to loose the core of what it is and become something else.
I think the structure of the practice of yoga is perfectly suited to be both strong and flexible. It has adapted to greater scientific understanding of human physiology, and to the potential for science to quantify physiological benefits of practice. If you read the older texts teachers tended to talk about benefits in general and rather grandiose terms, (for example in the Gheranda Samhita how the kaki mudra is the destroyer of all diseases. By the time of Krishnamacharya (one of the greatest teachers of the early part of the 20th century, born in the late 1880s, and died in the late 1980s, who trained the likes of Patthabi Jois, and Desikachar, and Indra Devi) although he was not citing specific research, he was talking rather specifically about benefits of specific postures (for example, in the Yoga Makaranda he recommended supta konasana and upavishtakonasana for menstrual pain). Today pretty much every issue of the professional association IDEA's magazine contains blurbs on research on yoga and related disciplies (e.g. in April there was something on meditation and heart disease).
If you change too much about something it becomes something else.... but what to change and why? I see a lot of interesting variations of yoga practice. We sit among an explosion of branches from branches, from branches moving out of a huge trunk, so long, its' roots are shaded in fog. Not every adaptation will survive. Not every type of practice will survive. Some will survive and expand and create their own branchings. Remember Gin Miller? Step aerobics grew out of group exercise.... it was a huge success, and has led to its own varients (though today it is not as popular as it once was, it still maintains a market share). I think anyone who has been in fitness for a while can think of something they took a class in that did not turn out to be the next big thing.
I think a reason why many teachers call themselves eclectic, or study in different forms, is that they want to bring in bits of what they find good from many traditions. Although, the reason some teachers choose to study in a very codified form like Iyangar is the precision and depth it provides, and the fact that that form was created by one of the greatest teachers of the last generation. Pilates is a good example of a discipline with specific principles, but which is seeing a lot of varients and spin offs. And there is certainly a debate about how much can be changed before t is Pilates like rather than Pilates. Well, the same thing applies to Yoga, and its spin offs. The most important thing, I think is to choose your teachers well. I study with lots of different people, but I try to pick people whose teaching I respect greatly. There is a huge financial benefit to having a program for which you can sell training, certification, and supporting products. As a consumer of such products I want to give my money, and my even more valuable time, where I will learn the most. Sometimes that is in a traditional class, and sometimes in a new variation. I took a workshop in the traditional series 1 of Patthabi Jois last year, and the year before I took a workshop of yoga designed for larger bodied people (which the teacher called 'MegaYoga'. They were both, in their own way wonderful. It is the same with my reading. On my desk right now I have the current issue of Idea Today, a copy of the Yoga Sutras, a book called Reading Buddhist Art, Light on Yoga, Investigations in Stress Control, and The Quadrivium.
So, I will continue to try to understand the tradition; its roots, and its branches. I will seek teachers for their substance, rather than their form. And I will try to make whatever buds I put out on my little branch as strong and healthy as I can.