Your pelvis controls so much of the motion and is such a connection point for you body that the slightest changes in its position can cause massive impact on the rest of your body. Due to our seated position for a lot of our lives the powerful hip flexors (psoas, illiacus, rectus femoris) adapt to become short due to their constant shortened position with sitting. Psoas attaches to the lumbar spine and if it becomes overly short will pull the lumbar spine into a further lordotic curve causing the pelvis to follow it and rotate in the anterior direction. Iliacus also plays a roll in this with its attachment to the pelvis.
The result of this anterior tilt to your pelvis is a chain of reactions that can cause you to have pain and problems throughout your lower back and your upper legs. Your spinal erector muscles get put into a shortened position and haver to take the brunt of an extra load and the insertion point of your hamstrings now moves higher. This is where the "tight" vs. "taut" argument comes into play. Most people have heard the story of how if your hamstrings are tight it is a main cause of low back pain and that we need to get your hamstrings loosened up. While this could be a cause I argue it is rarely the issue. We have more athletes and athletic people coming in with tight hamstrings and what is the first thing we want to do with them or they want done? STRETCH the hamstrings. This is all well and good but if the hamstrings are already pulled into a taught position all the stretching in the world won't help them.
When we sit or ischial tuberosity (insertion of the hamstrings) moves superior from it's natural position and pulls the hamstrings into a minor stretch. This then translates to standing up if we are extremely tight in the anterior hip. Nothing changes in position of the pelvis, just the position of our body. Our body is an amazing adapter to whatever position or stress we constantly put it into.
How to help fix it below:
Now, there is all the bad new so how the heck do we fix it or what should we look at? The first major change is trying to stop sitting so much. Secondly is we need to get that anterior hip to loosen up and get psoas and illiacus to loosen up and let go. Please see that post here if you'd like ideas for that. If we can correct these things we are well on our way to letting the pelvis set back into correct posture and taking the extra stress off our back and hamstrings.
One other simple but extremely effective option is to work on your posture by setting your pelvis in its correct spot by simply contracting your butt. By using this powerful muscle it will pull your pelvis back into a posterior position and be where it needs to be. The changes in the kinetic chain will be immediate.

In the picture on the right we would expect to see improvement from the red line to the blue line with a simple contraction of his gluten to help reset his pelvis into a neutral position.
The basic take away is don't always assume tight hamstrings are due to them actually being shortened and "tight". Look at how they sit with their pelvis and if they are anteriorly rotated and the hamstrings are "taut" because of this. Look big picture on this one.
Fix it early, fix it often.
JL