Definition
Epigenetics refers to lasting changes in how genes are expressed that arise from experience and environment — without any change to the DNA sequence itself. The genetic text stays identical; what shifts is which passages get read, how often, and how loudly.
Sapolsky uses epigenetics to dismantle the fantasy of genes as a fixed, sealed blueprint. Early-life experiences — maternal care, nutrition, stress — can leave durable chemical marks on the genome that change behavior far into adulthood. The genome is not a script handed down unchanged; it is annotated by life.
Why it matters
How it works
The main mechanisms are DNA methylation — chemical tags attached to the DNA that tend to quiet a gene — and modification of the histone proteins that DNA wraps around, which loosens or tightens access to it. Environmental signals, including hormones released during stress, drive enzymes to add or remove these marks. The result is a gene that is functionally dialed up or down, sometimes for life.