It is believed that the thumb piano was invented twice in Africa; one version originating on the west coast using wooden or bamboo tines around 3000 years ago, and the other version originating on the southeast coast using metal tines around 1300 years ago. It is thought that the thumb piano's invention came about due to the African tribes' need for a portable instrument, specifically a portable marimba. The ancient African marimbas were made by placing pieces of wood over a hole in the ground and hitting those pieces of wood with sticks -- not very portable! The griots (the historians/storytellers of the tribe) needed an instrument they could play while walking to entertain with songs, stories, and poems. Thus the thumb piano was born.
One characteristic that makes the thumb piano stand out from the majority of our Western musical instruments is the way that it is tuned. Most of the keyboard instruments that we know today, like the piano, are tuned with the lowest notes to the left and scale to the right for the higher notes. However, the thumb piano's lowest notes are in the middle, with the higher notes to the right and to the left both. This arrangement of the notes makes it ergonomically easier to play with the thumbs. The tuning of the thumb piano can also be easily changed by pushing the tines in or out - similarly to how a guitar can change the tuning of each individual string. Depending on which region of Africa you're in, you might hear a different tuning of the instrument.
The modern, Westernized version of the thumb piano is known as the kalimba and was made popular by Hugh Tracey, an English ethnomusicologist who moved to Africa in 1920. He spent many years traveling around Africa studying and recording the traditional music, and he took a particular interest in the thumb piano. His work documents over one hundred different types of thumb pianos! It seems as if each group of people who came across the thumb piano altered it to fit their needs and the type of materials that were available to them. In 1954, he founded his company African Musical Instruments and began building high quality thumb pianos and exporting them around the world. He changed the tuning of the instrument to fit the notes and tones that are typical of Western music, but the structure and idea behind the instrument remained the same. Tracey's studies and production of the kalimba popularized the instrument tremendously - it can be heard in the music of Earth, Wind, & Fire, Imogen Heap, Bjork, and Jens Lekman. It can also be heard on the soundtracks for Aliens and Edward Scissorhands!
You've probably realized by now that there are many different styles, types, tunings, uses, and even names for the "thumb piano." But regardless of what you call it, the thumb piano is an instrument rich in history and culture, and it sounds really neat. Check out these videos: