When they could not determine the uses of some human organs, they were called "vestigial", or "leftover from our evolutionary past". (This led to unnecessary (but profitable!) surgeries to remove appendixes, adenoids and so on.) Later, the so-called leftovers were determined to have functions that were hitherto unknown, much to the embarrassment of scientists.
At one time, the "simple" cell was considered to be rather well understood. Then technology advanced, and science advanced with it. The "simple" cell is not so simple after all. In fact, it is astonishingly complex — and it is still not fully understood.
Arrogance naturally spills over when studying the human genome. Since it is not fully understood, showy scientists (with their faulty evolutionist worldview) tag things they do not understand as "junk DNA". The fact is, DNA is also astonishingly complex. It would be much safer for scientists to label something as "not yet understood" rather than to pretend they know all about it, call it "junk", and then get humiliated later on.
When I pointed out the astonishing complexity of just one strand of DNA and how there is no way it could have formed by chance, an ignorant fundie evolutionist said, "It must have been less complex back then". (Yes, I get told things by people who are woefully ignorant of science all the time, but have faith in evolutionism.) This short video shows some of the complexity of DNA and the information exchanged contained within.