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SUNDAY SCIENCE: CAN YOU INHERIT MEMORIES FROM YOUR ANCESTORS?  
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Hannah Critchlow
June 17, 2024
The Guardian
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_ The science of epigenetics suggests we can pass on trauma – but
trust and compassion too _

, Illustration: Elia Barbieri/The Guardian

 

Since the sequencing of the human genome in 2003, genetics has become
one of the key frameworks for how we all think about ourselves. From
fretting about our health to debating how schools can accommodate
non-neurotypical pupils, we reach for the idea that genes deliver
answers to intimate questions about people’s outcomes and
identities.

Recent research backs this up, showing that complex traits such as
temperament, longevity, resilience to mental ill-health and even
ideological leanings are all, to some extent, “hardwired”.
Environment matters too for these qualities, of course. Our education
and life experiences interact with genetic factors to create a
fantastically complex matrix of influence.

But what if the question of genetic inheritance were even more
nuanced? What if the old polarised debate about the competing
influences of nature and nurture was due a 21st-century upgrade?

Scientists working in the emerging field of epigenetics have
discovered the mechanism that allows lived experience and acquired
knowledge to be passed on within one generation, by altering the shape
of a particular gene. This means that an individual’s life
experience doesn’t die with them but endures in genetic form.
The impact of the starvation your Dutch grandmother suffered during
the second world war, for example, or the trauma inflicted on your
grandfather when he fled his home as a refugee, might go on to shape
your parents’ brains, their behaviours and eventually yours.

Much of the early epigenetic work was performed in model organisms,
including mice. My favourite study is one that left the neuroscience
community reeling when it was published in Nature Neuroscience, in
2014 [[link removed]]. Carried out by Prof
Kerry Ressler at Emory University, Georgia, the study’s findings
neatly dissect the way in which a person’s behaviours are affected
by ancestral experience.

The study made use of mice’s love of cherries. Typically, when a
waft of sweet cherry scent reaches a mouse’s nose, a signal is sent
to the nucleus accumbens, causing this pleasure zone to light up and
motivate the mouse to scurry around in search of the treat. The
scientists exposed a group of mice first to a cherry-like smell and
then immediately to a mild electric shock. The mice quickly learned to
freeze in anticipation every time they smelled cherries. They had
pups, and their pups were left to lead happy lives without electric
shocks, though with no access to cherries. The pups grew up and had
offspring of their own.

At this point, the scientists took up the experiment again. Could the
acquired association of a shock with the sweet smell possibly have
been transmitted to the third generation? It had. The grandpups were
highly fearful of and more sensitive to the smell of cherries. How had
this happened? The team discovered that the DNA in the grandfather
mouse’s sperm had changed shape. This in turn changed the way the
neuronal circuit was laid down in his pups and their pups, rerouting
some nerve cells from the nose away from the pleasure and reward
circuits and connecting them to the amygdala, which is involved in
fear. The gene for this olfactory receptor had been demethylated
(chemically tagged), so that the circuits for detecting it were
enhanced. Through a combination of these changes, the traumatic
memories cascaded across generations to ensure the pups would acquire
the hard-won wisdom that cherries might smell delicious, but were bad
news.

The study’s authors wanted to rule out the possibility that learning
by imitation might have played a part. So they took some of the
mice’s descendants and fostered them out. They also took the sperm
from the original traumatised mice, used IVF to conceive more pups and
raised them away from their biological parents. The fostered pups and
those that had been conceived via IVF _still _had increased
sensitivity and different neural circuitry for the perception of that
particular scent. Just to clinch things, pups of mice that had not
experienced the traumatic linking of cherries with shocks did not show
these changes even if they were fostered by parents who had.

The most exciting thing of all occurred when the researchers set out
to investigate whether this effect could be reversed so that the mice
could heal and other descendants be spared this biological trauma.
They took the grandparents and re-exposed them to the smell, this time
without any accompanying shocks. After a certain amount of repetition
of the pain-free experience, the mice stopped being afraid of the
smell. Anatomically, their neural circuits reverted to their original
format [[link removed]]. Crucially, the
traumatic memory was no longer passed on
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brain structure of new generations.

Could the same thing hold true for humans? Studies on Holocaust
survivors and their children
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Prof Rachel Yehuda at the Icahn School of Medicine at Mount Sinai
Medical School, New York, revealed that the effects of parental trauma
can indeed be passed on in this way. Her first study showed that
participants carried changes to a gene linked to levels of cortisol,
which is involved in the stress response. In 2021, Yehuda and her
team carried out more work
[[link removed]] to find expression
changes in genes linked to immune-system function. These changes
weaken the barrier of white blood cells, which allows the immune
system to get improperly involved in the central nervous system. This
interference has been linked to depression, anxiety, psychosis and
autism. Since then, Ressler and Yehuda
[[link removed]] have collaborated, with
others, [[link removed]] to reveal
epigenetic tags in PTSD afflicted war zone-exposed combatants. They
are hoping this information could aid PTSD diagnosis or even
pre-emptively screen for individuals who might be more prone to
developing the condition before they enter the battlefield.

In all times and across all cultures, people have paid their dues to
their ancestors and pondered the legacy they will leave for their
descendants. Few of us believe any more that biology is necessarily
destiny or that our bloodline determines who we are. And yet, the more
we learn about how our body and mind work together to shape our
experience, the more we can see that our life story is woven into our
biology. It’s not just our body that keeps the score but our very
genes.

Might this new understanding increase our capacity for self-awareness
and empathy? If we can grasp the potential impact of our ancestors’
experiences on our own behaviour, might we be more understanding of
others, who are also carrying the inherited weight of experience?

We are, as far as we know, the only animals capable of “cathedral
thinking”, working on projects over many generations for the
benefit of those who come after. It’s an idealistic way to think
about legacy, but without it we will struggle to tackle complex
multigenerational challenges such as the climate and ecological
emergencies. Our knowledge of epigenetics and its potential to
massively speed up evolutionary adaptation could support us to do
everything we can to be the ancestors our descendants need. Conflict,
neglect and trauma induce unpredictable and far-reaching changes. But
so do trust, curiosity and compassion. Doing the right thing
today could indeed cascade across generations.

_DR. HANNAH CRITCHLOW is a neuroscientist and author of The Science
of Fate
[[link removed]] and Joined-Up
Thinking
[[link removed]] (Hodder)._

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__

The University of Chicago’s New Climate Initiative – Brave
Research Program or Potentially Dangerous Foray into Solar
Geoengineering
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Jessica McKenzie
Bulletin of the Atomic Scientists
June 20, 2024

* Science
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* biology
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* genetics
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* nature vs. nurture
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* epigenitics
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* human genome
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