We encountered a group of monstrous ants which appeared to confirm Mackay's theories of mutation due to extended exposure to radiation.”— Anne Palmer
Mackay was a Vault 101 scientist in 2241.
Mackay formulated a theory on mutations which states a proportional relation between the time an animal is exposed to radiation and the size of the animal. If the animal is exposed to long-term radiation, the larger that animal will grow. When Anne Palmer writes her official report to the Overseer, she expresses her belief that evidence existed to prove this theory.
During their survey, her team encountered giant ants, a battle ensued in which they drove off the attacking insects. Those that were killed were collected and sent back to Vault 101 as the physical proof of Mackay's theory. Evidence of this expedition can be found on the Overseer's terminal.
Mackay is mentioned only in Fallout 3.