How the ratio shifted from ancestral to modern diets
Omega-3 and omega-6 are both essential polyunsaturated fats, but they compete for the same enzymes and give rise to signalling molecules with broadly different tendencies. Estimates of ancestral human diets suggest a relatively balanced intake, on the order of 1:1 to about 1:4 omega-3 to omega-6. Modern Western diets, heavy in refined seed oils, are commonly estimated at roughly 1:15 to 1:25, a large shift toward omega-6.
Because the two families share desaturase and elongase enzymes, a high omega-6 intake can crowd out the conversion of plant omega-3 (ALA) into EPA and DHA, which is one reason the balance, not just absolute amounts, draws attention.
What the ratio does and does not establish
The idea that a high omega-6 to omega-3 ratio tilts the body toward a more inflammatory signalling tone is biologically plausible and widely discussed. However, the clinical importance of the ratio itself is debated: some researchers argue that simply increasing omega-3 intake matters more than chasing a specific ratio, and that omega-6 fats are not straightforwardly harmful. The evidence is mixed rather than settled.
This is general educational information, not dietary or medical advice. Consult a qualified professional before making major changes to fat intake or starting supplements.