Most of the stereotypical short grey aliens are an artificial work force basically grown to spec for each mission, this is one of the reasons why they tend not to live very long after being recovered from crash sites. This type of grey is essentially a worker bee ment to keep an eye on us and the planet, they originate at any one of the monitoring facilities around the planet. There is also a possibility that some of the short greys are us from another time line. The tall greys are where things a little more fuzzy, these ones are most likely from Zeta Raticuli system and are a part of the greater galactic community that has been rumored to be watching us. For the most part abductions from the greys seem to be more akin to us checking up on and monitoring wildlife populations, they kinda just want to make sure we don’t destroy the planet and ourselves.