IANAL but as an informed citizen in England I understand majority verdicts are allowed, but with the permission of the judge. You see reports of the jury sending the judge a message saying they’re stuck unless they’re allowed one, but I don’t know how much they reveal to the judge of the sticking points. The one thing that is clear is that they don’t do so in open court: there’s a very strict rule about re-hashing or investigating how jury deliberations went. Some jurors have got into trouble for doing so, and AFAIK even academic research is very difficult or even impossible.
Relevant cartoon. (Scroll down about a page to the first cartoon drawing.)
(If you don’t want to click on that:
Foreman of sequestered jury is ordering lunch for the entire jury: “Eleven hamburgers, one frank. Eleven coffees, one tea. Eleven apple pies, one chocolate cake . . .”)
The factual answer to “Why are jury decisions required to be unanimous?” is “that’s how we, as a society, have chosen to set up our judiciary system”. Which is not a question that leaves open much room for discussion.
Questions that do leave room for discussion include “why did we set up our system that way?”, and “should we have set it up this way?”. Those questions are not factual.
ISTR reading that in Saxon England, one way to avoid a trial was to get twelve of your kinsmen to swear an oath that you were innocent. The twelve-person jury with unanimous consent probably evolved from that custom.
One oddity, which I don’t know if it would still be true because it occured 40 years ago in Virginia. I was on a criminal case where one of the jurors didn’t show up for the second day of deliberations. (I don’t know why) The defendant was given the option of accepting a unanimous 11 juror decision, which she did, and we found her guilty.
This right, like many constitutional rights, may be waived. A defendant can go without any trial at all by voluntarily pleading guilty, by waiving the right to counsel, by waiving the right to indictment, etc. No reason he can’t say, “Fine, I’ll roll with 11 jurors.”
Alternates are usually dismissed before deliberations.
When I practiced criminal law, I would usually say something like this in closing argument:
Now, all 12 of you must agree that the State has met its burden. That’s not a mere formality. There is a reason we have juries of 12, and not just let the judge decide. The State must have enough evidence not just to convince one of you, or two of you, or six of you or even 10 of you. The evidence against my client has to be so strong, so convincing, that it satisfies 12 out of 12 of you. That’s how much evidence the State must bring to trial before someone is convicted of a serious crime. So if they have only enough evidence to convince 11 out of 12, they have not met their burden and you shouldn’t change your verdict just to go along iwth the others. If we didn’t need all 12 of you to be convinced, we could have juries of 3, or 6, or 11 people. But we require 12.
Somewhat off-topic, but the formula that I’ve heard frequently as a juror in California is that jurors must find the defendant guilty “beyond a reasonable doubt”. Frankly, I’ve always found the judge’s explanation of what “reasonable doubt” means to be more confusing than the simple words themselves.
Sometimes phrased as the level of confidence you would need to make a major decision in your own life. So, would you quit your job and move across the country because some jailhouse snitch told you there was a good job waiting for you there? Of course not. You’d want more evidence before you made that kind of decision.