Darker blood in your stools means that the bleeding is more likely in your stomach or small intestine which are higher up in the digestive tract.
Bleeding higher up in the digestive tract is often caused by bleeding ulcers. While bleeding ulcers sounds dangerous, they can be a result of taking over-the-counter medications like aspirin or ibuprofen which are known to lead to ulcers that cause digestive tract bleeding.
If you are not taking medications, there are a number of other causes and sources of the bleeding.
Bleeding lower in the digestive tract can be caused by intestinal polyps or colon polyps. Polyps are not that dangerous by themselves, but there is a possibility that polyps can develop into colon cancer. This type of cancer is much more likely in people over age 50.
People over 50 who may be experiencing bleeding during bowel movements should not hesitate to get screened for colon cancer. Although colon cancer is one of the major cancer killers, it's also very easy to cure if diagnosis is made early. By discovering and removing polyps before they turn cancerous, colon cancer can be completely prevented.
An important consideration in determining the source of the blood in the digestive tract is the color of the poop and how well the blood had become mixed in with the stool. If the blood is not well intermixed with the poop, the cause is very likely burst blood vessels, or rectal bleeding which occurs at the end of the digestive tract.
Also, if you are able to see red or blood on the toilet paper, it is likely that the bleeding had just occurred and indicated lower gastrointestinal bleeding.
If the stool is red and well intermixed with the blood, the cause of the bleeding is likely higher up in the digestive tract, and if the poop is black, that is usually an indicator that the stool had mixed with the blood a long time ago and has had time to decay inside the body.