Genes & the Inheritance of Memories Across Generations | Dr. Oded Rechavi

KEYPOINTS

• 01

  Whether acquired traits can be inherited has a troubled history

  Rechavi, who studies inheritance in worms, traces the idea's bad reputation to the early 1900s. Paul Kammerer claimed that midwife toads trained to breed in water developed dark mating pads (nuptial pads) and passed them to their offspring. The specimens turned out to have been injected with ink, and the scandal tainted the field for decades.

• 02

  The 'memory transfer' experiments of the 1960s–80s collapsed

  American psychologist James McConnell trained flatworms (planaria) to avoid shocks, then reported that worms regrown from cut-off tails kept the memory, and that untrained worms fed ground-up trained ones learned faster. Similar brain-transfer experiments followed in goldfish and rodents. Nobody could replicate the results reliably and the field ended in what Rechavi calls a catastrophe, though the idea of a memory in molecular form remains appealing.

• 03

  Two barriers should stop experience from reaching the next generation

  The first is the Weismann barrier, proposed by August Weismann in the 19th century and called the 'second law of biology': only germ cells (sperm and eggs) carry information forward, and they are kept separate from the body's other cells. The second is epigenetic reprogramming: about 90% of the chemical marks on DNA are wiped clean in sperm, eggs and the early embryo. Rechavi says 'epigenetics' is a heavily misused word, even by scientists.

• 04

  In mammals there is evidence of effects across generations, but the mechanisms are unclear

  Children of women who were starved during pregnancy in famines in the Netherlands, China and Russia showed differences in birth weight, glucose sensitivity and risk of some neurological diseases. Rechavi stresses that for most such effects the mechanism is still unknown, and that in mammals no system has been found that amplifies inherited RNA.

• 05

  C. elegans worms pass small RNAs to their offspring

  This tiny worm always has 959 cells, 302 of them neurons, each with a known name. Andrew Fire and Craig Mello won the 2006 Nobel Prize for showing that double-stranded RNA silences matching genes (RNA interference). Worms have no T or B cells and fight viruses with these small RNAs.

• 06

  Without amplification, inherited RNA would dilute away within a few generations

  Each worm has about 250 offspring, so after four generations any molecule from the original parent would be diluted about four-billionfold. An enzyme called RNA-dependent RNA polymerase recopies the small RNAs in every generation, which keeps them from running out. Effects typically last three to five generations, and his lab found 'MOTEK' genes that act as a clock setting how long the inheritance lasts.

• 07

  Specific learned memories probably can't be inherited, but simpler states might be

  Rechavi doubts that arbitrary memories stored in brain wiring, such as this conversation, could pass to children: even identical twins wire their brains differently. Simpler changes might pass on, for example a learned aversion that works by removing the receptor for one odor, which a single RNA could in principle control. That hasn't been shown convincingly in worms.

• 08

  Germ cells can change behavior through the body

  Germ cells secrete signals that shape the rest of the body and brain. Huberman describes his dog regaining his old personality on testosterone therapy. In mammals, small RNA changes in germ cells could alter very early development or the placenta and cascade into later metabolic problems.