Ever since the first human being descended on the Earth, squatting has been the most natural posture to finish one's daily "business". With the advent of civilizations, human habits (discipline), shelter (housing), clothing (cotton & silk), food (farming & cooking) and several factors evolved but the seating posture for defecation remained the same i.e squatting posture.
The very fact that such a posture comes naturally even to babies in the womb and (children while playing) further proves that it is the most commonly used posture by humans.
In Yogasanas, there is a very popular posture called "Shashankasana" which provides a massaging effect for abdominal organs & stimulates the nervous action of the bowels to give a good motion. Even in squatting position, the same effect is observed. If you rotate a photograph of Shashankasana by 90 degrees, you can notice how similar it is to the squatting posture.
When the flush toilet was invented during 16th century, it caught some eyeballs but was still limited to royalty who adored it's seating posture which seemed more "dignified" (since it's posture resembled sitting on a throne). Over the next few centuries, it gradually witnessed penetration into the masses of western world (Europe & America), and by 19th century, it had become the norm for them. However, eastern world (India, Pakistan, China, Japan, Korea) chose not to switch and stuck on to doing their business in squatting posture.
Over the last few decades, bowel related diseases like hemorrhoids, appendicitis, constipation, irritable bowel syndrome have been on the rise especially in the western world due to several reasons including diet & lifestyle. That triggered a series of experiments and research studies in which scientists & doctors began to notice an interesting pattern. They noticed that the probability of such diseases was higher when one used the western toilet. Further research on this topic revealed that the seating position for western toilet was actually against human anatomy.
Here is an article written by Dr.Mercola explaining how western toilets have led to increasing Colon and Pelvic diseases:
http://articles.mercola.com/sites/articles/archive/2012/12/03/toilet-squatting-position.aspx
The following article on toxic removal & tissue cleansing actually recommends squatting position for healthy bowel movement:
http://www.yourreturn.org/Inertia/Bowel_Cleansing.htm
In the medical sciences field, a very popular Doctor & Neuroscientist named Daniel Lametti has been creating awareness about the benefits of Indian toilet. Following is a popular article written by him:
http://www.slate.com/articles/health_and_science/science/2010/08/dont_just_sit_there.html
As more Doctors in the western world started recommending Indian toilets for healthier living, several companies began to offer solutions in the form of converters & accessories which could be used to achieve the same position, effect & benefit as that of squatting posture.
For example, following are a few ads of companies which offer such solutions:
This short video clip explains all these concepts clearly (based on research at Stanford University) with the help of animation:
http://www.youtube.com/watch?v=pYcv6odWfTM
Hence, Indian toilet is not only the oldest form but also the most scientifically proven form for human anatomy which the western world has been realizing of late and embracing it gradually.
