On a cold February day in 1860, twin boys were born to Mary Jane Gaull. The first she named George. The second, born about one hour later, she named John after her father. The birth registration does not list the father's name but if Scottish naming convention was followed, George was likely named after his paternal grandfather.
The next year, in 1861, a census was taken in Scotland. John Gaull (pictured to the left in a 1928 photo) can be found living with his mother and her parents, John Gaull and Mary Christie, on the family farm in Whitehaugh, Chapel-of-Garioch, a small Aberdeenshire village. George on the other hand was living several miles away in Inverurie, listed as a "boarder" with the family of James and Isabella Hoey. What brought about this circumstance is unknown. George seems to have gone through life using only the Irvine surname whereas his twin brother, John continued to use the Gaull surname that he was registered with at birth.
By 1881, George had moved away from Aberdeenshire to Airdrie, just west of Glasgow where he boarded with Mrs. Janet Watt, a widow, at 48 High Street. George married Mrs. Watt's daughter Isabel in December 1883.
There has been a lot of research on the connection between twins - feeling each other's pain, sharing the same thoughts, etc. There is no evidence that I've found that George and John had much interaction, no family stories about them and no family photos of the two of them together. But - each named a son after the other. John named his son George Irvine Gaull and George named his son, John Gaull Irvine. It seems clear that they knew of their close fraternal relationship and as fitting tribute, they honoured it through the naming of their sons.