They were human looking constructs created by Companion genetic engineering all of which were similar in appearance. The purpose of these surrogates was to provide a vehicle through which the disabled could live their lives. Whilst the biosurrogates were genetic constructs, the virtual programming designed to transfer the identities of a human being into them was limited to the Taelons. Thus, Sparrow turned to the abilities within the Jaridian Replicants which allowed for a mind of the user along with their memories, thoughts and feelings to be moved into a biosurrogate.
Unknown to Da'an, the bioengineering program was altered by Synod leader Zo'or who instead wanted a weapon. Tampering with the programming, he was able to turn the biosurrogates into aggressive mobile weapons with similar feats as those of a Replicant. The bodies were only activated if a consciousness was transfered into them or if they recieved a sudden burst of energy which was why the constructs remained in a shielded facility. One biosurrogate was awakened when a photographer broke into the facility and started taking pictures of it. It then killed the reporter and a security guard whereupon its Jaridian inspired attack program activated as well as its full compliment of weaponry. (Episode: One Man's Castle)