Ibeji

In Yoruba culture twins are believed to be sacred at birth and protected by the deities called Ibeji.The Ibeji and all twins are considered one soul contained in two bodies; inextricably linked in life through destiny. If one twin dies an Ere Ibeji (a small wooden figure) is made so ensure that the departed's soul remains as strong as the living's. 


Read more about this belief at:
http://www.randafricanart.com/Yoruba_Customs_and_Beliefs_Pertaining_to_Twins.html
http://santeriachurch.org/the-orishas/ibeji/