What is alpaca ?
it is  a domesticated species of South American camelid.
Since when have they been domesticated?
im not sure but they  are similar to llamas
Can they be eaten by humans?
Alpaca
The alpaca ("Vicugna pacos") is a species of South American camelid. It is similar to, and often confused with, the llama. However, alpacas are often noticeably smaller than llamas. The two animals are closely related and can successfully cross-breed. Alpacas and llamas are also closely related to the vicuña, which is believed to be the alpaca's wild ancestor, and to the guanaco. 
There are two breeds of alpaca: the Suri alpaca and the Huacaya alpaca.
Alpacas are
Chilihueque
Chilihueque or Hueque is a South American camelid variety or species that existed in central and south-central Chile in Pre-Hispanic and colonial times. There are two main hypotheses on their status among South American camelids: the first one suggests that they are locally domesticated guanacos and the second that they are a variety of llamas brought from the north into south-central Chile. The alpaca has also been suggested as a possible identity.
According to Juan Ignacio Molina, the Dutch captain Joris van Spilbergen observed the use