In the infancy of the jury trial, there were no witnesses. The jury was self-informing. Members of the jury were drawn from the community. It was expected that they would know, either firsthand or on the basis of what they had heard, the true facts of any disputed incident, and they were gathered together to say what those facts were. Ronald Allen and Joseph Miller, in their insightful paper, see the ideal of the self-informing jury as very much alive today. Allen and Miller tell us that jurors ideally should experience firsthand the factual information needed to arrive at rational verdicts. In their ideal world, jurors compelled to rely on others' accounts would enter the heads of witnesses to distinguish what was actually observed from what was added, lost, or distorted in the recounting process. According to this model, witnesses should educate jurors on relevant facts within their knowledge, and jurors should assimilate the facts presented by the various witnesses to determine both what happened and the implications of those events given the applicable law.
Lempert, Richard O. "Experts, Stories, and Information." Northwestern University Law Review 87 (1993): 1169-1181.