"If we had 12 fingers, I wonder whether the Bill of Rights … would have been 12 amendments long"

So tweets Neil deGrasse Tyson. This is a plausible hypothesis, and might often explain why there are ten of this or twenty of that or a hundred of something else. But:

The hypothesis turns out not to be particularly likely as to the Bill of Rights—there actually were 12 amendments originally proposed by the First Congress; it's just that the first two weren't ratified right away (one never was, and the other was ratified only 200 years later, and became the Twenty-Seventh Amendment):

THE Conventions of a number of the States, having at the time of their adopting the Constitution, expressed a desire, in order to prevent misconstruction or abuse of its powers, that further declaratory and restrictive clauses should be added: And as extending the ground of public confidence in the Government, will best ensure the beneficent ends of its institution.

RESOLVED by the Senate and House of Representatives of the United States of America, in Congress assembled, two thirds of both Houses concurring, that the following Articles be proposed to the Legislatures of the several States, as amendments to the Constitution of the United States, all, or any of which Articles, when ratified by three fourths of the said Legislatures, to be valid to all intents and purposes, as part of the said Constitution; viz.

ARTICLES in addition to, and Amendment of the Constitution of the United States of America, proposed by Congress, and ratified by the Legislatures of the several States, pursuant to the fifth Article of the original Constitution.

Article the first… After the first enumeration required by the first article of the Constitution, there shall be one Representative for every thirty thousand, until the number shall amount to one hundred, after which the proportion shall be so regulated by Congress, that there shall be not less than one hundred Representatives, nor less than one Representative for every forty thousand persons, until the number of Representatives shall amount to two hundred; after which the proportion shall be so regulated by Congress, that there shall not be less than two hundred Representatives, nor more than one Representative for every fifty thousand persons.

Article the second… No law, varying the compensation for the services of the Senators and Representatives, shall take effect, until an election of Representatives shall have intervened.

Article the third… Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances.

Article the fourth… A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed….

Thanks to my brother Sasha for the pointer.

UPDATE: What was originally item two in this post has been moved to a separate post, because it was just so good.