It's not a binary thing, and it's why mortality is measured with LD50 (lethal dose for 50% of exposed subjects). The actual distribution is a curve spanning a s

It's not a binary thing, and it's why mortality is measured with LD50 (lethal dose for 50% of exposed subjects). The actual distribution is a curve spanning a spectrum of venom resistance. The snake eliminates more mice with lesser resistance than mice with greater resistance, and over time, the mice with higher resistance have more offspring. This is more of an adaptation driven change than a random mutation driven one.