Today’s Wonder of the Day was inspired by Michael. Michael Wonders, “What is a social security number?” Thanks for WONDERing with us, Michael!

As a human being, there are a few physical identifiers that make you unique. For example, your DNA and your fingerprints are unlike anyone else's in the world. Beyond a doubt, they identify you as you.

If you're an American, there's another unique identifier that follows you around your whole life. It's a set of nine digits known as your Social Security Number (SSN), and your SSN is different from everyone else's.

Social Security is a U.S. government program that got its start with the Social Security Act of 1935 (originally known as the Economic Security Act). After necessary procedures and infrastructure were developed, Social Security taxes and benefit payments began in January 1937.

Social Security is a relatively-simple concept. As you work throughout your lifetime, you and your employer pay taxes into the Social Security system. The government then uses that money to pay benefits to eligible recipients. Experts estimate that about 167 million workers pay into the system to provide payments for about 59 million recipients.

Today, those recipients include older Americans who have reached retirement age, people who are disabled, survivors of workers who have died, and the dependents of those beneficiaries. While many people often think of Social Security as nothing more than a retirement program, it actually extends benefits to a much broader group of recipients.

Moreover, the government never intended Social Security to be the only source of a person's retirement income. To live comfortably, financial advisors recommend that you should also have other sources of income, such as private savings and investment accounts.

Early in the development of the Social Security program, the people in charge of keeping track of records realized that a unique identifier was needed to keep track of both tax and benefit payments for every worker. Names and addresses were either not unique enough or changed too frequently.

The nine-digit Social Security Number was developed in 1936 for record-keeping purposes. This number has since evolved into a general identifier used throughout the public and private sector for many different identification purposes.

To date, the Social Security Administration has issued over 450 million original Social Security Numbers. Nearly every legal resident of the United States has one, and most of us get one as soon as we're born.

The format of the Social Security Number is AAA-BB-CCCC, where AAA is an area number, BB is a group number, and CCCC is a serial number. The area number generally corresponds to either the state or zip code where you were born.

The group number breaks down the area numbers into smaller blocks for easier administration. The serial numbers finalize the creation of a unique identification number for each individual. Although a Social Security Number provides some basic information about where a person first applied, it doesn't reveal how old a person is or where they currently reside.

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