Its origins date back to populations of immigrants from the Caribbean islands that immigrated to Panama during the 19th and 20th centuries. Many of these immigrants were brought in to help with the construction of the Panama Canal, and they included West Indians from Jamaica, Trinidad, Martinique & Barbados to name a few. More than 25,000 immigrants came to Panama from the islands and workers from Barbados, Jamaica, and Martinique made up 2/3 of the canal labor team. The majority of the descendants of these populations live on the Atlantic coast in Colon and other cities and towns.
Now ends the fact-based research. The following ideas are from my personal experience during Carnavales 2005 in Panama. I went to Cuanga (a small town up the Atlantic Coast) and Portobelo, each for two days and "learned" to Congo dance. So, this is what I got from my personal experience, mind you, some of this I had to translate from Spanish and I hope I got it all right accurately:
Congo is an upbeat Afro-Caribbean dance that has drummers, singers, and dancers. Usually, an elder woman leads the singing, and it is call and response type songs. Then the drums come in. They're bongo drums (that's all I know to call them) and there didn't seem to be a set number. Only men can drum (one of my friends informed me). We all gathered in a circle and the song leader would begin singing. Everyon else would join in and the drums too. There are usually men already in the circle, called "Pajaritos" or little birds. I was told that during the slave times these were the look outs. They whistled or gave a signal if the master was coming since dancing was forbidden. They are usually dressed in an interesting way- one guy was in a very colorful red and yellow outfit that looked like a Court Jester costume. The other guy had various objects pinned to his clothing- sticks, bottles, whatever. They served as kind of referees in the circle and they had whistles. Then a woman would enter the circle and dance, taking small steps kinda like shuffling her feet and moving her hips and she would move around the circle. The key was to move just the hips and feet mostly and keep the rest of the body pretty still. Also, her hands/arms are usually up to guard her face. Sometimes the women would balance a plate on their head while they were doing it, just to show how skilled they were. A man would enter and he usually had his arms spread eagle, and he made like big movements around the circle and did small kicks and bows toward the woman. Now, the whole point is for the man to try to get close to the woman and kiss her. So the woman can let him get close, but not too close, hence her hands are up near her face. Everyone is doing turns and spins. So you are kinda dancing with the person, but you don't get too personal. So the men would bow or dip towards you, and you can spin around and dodge them. Its very cute and fun to do. I loved it.
Every dances as well. Children as young as five or school age would have their own circles while I was in Portobelo. The adults and teens were still the bulk of the singers and drummers, but the circle and dancing was only for the kids.
Also, if an elder woman comes in the circle, everyone clears out and lets her dance. Then a man or two comes in and tries to dance with her. Its like a respect thing.
The pajaritos will blow their whistle if its time for you to get out of the circle or if you get kissed and "lose" (I got the whistle blown on me cause my friends didn't explain the whole point of the dance beforehand).