chr20 · 20q13.33 · 118 nt · 2006

HAR1

HAR1A / HAR1B

What it is

HAR1 is a short region that stayed almost unchanged for hundreds of millions of years, then changed 18 times on the human line. It does not make a protein. It makes RNA in Cajal–Retzius neurons, the cells that lay down the first map of the developing cortex. Think of it as a timing cue for how the brain's outer sheet is stacked.

Why it matters

Largest acceleration signal; cortical lamination timing.

Operator load

• 01 · ΔE

  Enhancer activity

  These stretches of DNA do not code for proteins. They act as volume knobs — turning nearby brain-development genes up or down at the right moment.

• 02 · C

  Compensatory substitution

  When one letter in the sequence changes, another often changes to keep the whole switch working. Evolution rewired the circuit without breaking it.

• 03 · T

  Three-dimensional rewiring

  The genome folds in 3D. Human-specific changes can re-route which switches sit next to which genes, even if the letters look similar in a straight line.

• 06 · P

  Population spread

  Once a change is useful, it spreads. Many HAR variants rose quickly in ancestral humans and are now nearly fixed across living populations.

Pollard et al. Nature 2006 · Beniaminov et al. RNA 2008