Human exposure to wheat and milk is nearly global. However, as compared to human evolution, the introduction of milk and wheat is very recent (5000–10,000 years). Food allergies and intolerance to milk and wheat have increased during the previous four decades. The etiology of allergy illnesses, which is often defined as plurifactorial, is the consequence of an interaction between genetic predisposition and epigenetic alterations in the setting of environmental changes. Understanding of genetic and epigenetic mechanisms, as well as their role in allergies and other antigen-driven illnesses, has improved significantly in recent years. However, environmental variables are equally difficult to define and link to illness risk. 

More than a million years separate Homo habilis from today’s humanity, more than a million years to acquire ability to collect sustenance through foraging in various habitats. One million years to fine-tune and modify our genetic code; yet only 1% of that time, 10,000 years, to face the three greatest revolutions of human history: the agricultural, industrial, and post industrial revolutions. With large and quick environmental changes comes adaptation, but not time for fine-tuning. Tolerance and unfavorable dietary reactions may now constitute evidence of adaptive triumphs and failures.

Reference: https://journals.lww.com/co-allergy/Abstract/2017/12000/A_history_into_genetic_and_epigenetic_evolution_of.11.aspx