Scientists have discovered a molecular mechanism by which a parent’s experiences can alter the genes of its children.
Several recent studies have demonstrated connections between environmental factors and inherited genetic traits – for instance, people whose parents lived through famine tend to have higher rates of diabetes and heart disease – but this latest research, published in the journal Nature, marks the first hard evidence of such a modification process at work.
Before we dive into the details, though, let’s back up a bit, and take a look at why this is such a Big Freakin’ Deal.
See, the whole concept of inheritance via experience has been – and will probably continue to be – a very hard sell to modern biologists. As you might remember from science class, the 18th-century theory of Lamarckism, which proposed that traits could be modified through an individual’s “use and disuse” of them, was blown out of the water by Darwin’s theory of evolution by natural selection, which demonstrated – through mountains of hard data – that traits are actually shaped by millions of tiny variations, and the degree to which those variations help an individual create successful offspring that carry them on.
For more than a century, the whole Lamarck debate seemed to be settled – but lately, it looks like some elements of Lamarckism may be making a surprise comeback, in a new field called epigenetics - the study of gene changes caused by chemical factors other than modifications to the DNA sequence itself:1
Epigenetic memory comes in various guises, but one important form involves histones — the proteins around which DNA is wrapped. Particular chemical modifications can be attached to histones and these modifications can then affect the expression of nearby genes, turning them on or off.
For example, in 2007, the journal Nature published data showing that exposure to extended periods of cold could cause plants to alter the molecular process by which their DNA was copied – thus “silencing” certain genes in their offspring. Then in 2009, MIT’s Technology Review discussed some animal studies with even more shocking results: apparently, a mouse’s environment can affect the memory capacity it passes on to its descendants.
But whereas those studies were mainly concerned with the effects of epigenetic alteration, this new research has gone a step further, and mapped a specific epigenetic process that turns genes on and off. A team led by Professor Martin Howard and Professor Caroline Dean at the John Innes Centre performed a mathematical analysis of experimental data, and discovered the mechanism by which plants exposed to extended cold periods produce descendants with delayed flowering:
Professor Howard produced a mathematical model of the FLC system. The model predicted that inside each individual cell, [a gene known as] FLC should be either completely activated or completely silenced, with the fraction of cells switching to the silenced state increasing with longer periods of cold.
Not only did the plants’ gene expression pattern line up with the mathematical predictions – the team’s research also showed that histone proteins were modified in a way that would alter the FLC gene, and that this alteration happened during the period of cold. This is the first true demonstration of histones’ role of epigenetic modification.
At first glance, this might not seem to have a whole lot to do with neuroscience – but in a wider context, the implications of epigenetics look pretty incredible.
For plenty of obvious reasons, modern biological science has never been big on the idea “genetic” or “ancestral” memories – recollections of specific events passed down to us from our ancestors (e.g., the Jungian collective unconscious). And yet, while epigenetic modifications don’t offer much support for that idea, they do seem to suggest that our ancestors’ experiences can affect the biological development - and thus, the minds – of future generations.
We’ve still got a long way to go before we understand all the ways in which gene expression affects brain development. But if histones can help mice pass their enriched learning capacity on to their children, the question of what humans can pass on seems, at the very least, worth investigating.
1. Just to be safe, I want to point out that, on the whole, the theory of evolution through natural selection still explains a great deal about how biological systems work, and its principles have been verified in a multitude of fields. At the risk of being over-obvious: these new discoveries don’t threaten the main trunk of evolutionary theory; they’re just pruning a few of its branches.