In the early 1800s, ‘the theory of acquired characters’ was the most widely accepted explanation of evolution. Simply put, the theory stated that characteristics that an organism developed during its lifetime, through use, disuse or environmental influence, could be inherited by its offspring.
The French naturalist Jean-Baptiste Lamarck formalised this idea in two laws in 1809, and it remained unrivalled until half a century later. In 1859, Charles Darwin proposed natural selection, which said that variations are passed from parents to offspring and that changes that confer benefits survive while the detrimental ones perish. The two ideas co-existed for a brief while until two major scientific developments challenged Lamarck’s views.
The first was German evolutionary biologist August Weismann’s demonstration that even after cutting the tails of mice continuously for over five generations, there was no inheritance of this acquired characteristic in the offspring. The second was the rediscovery of the work of Gregor-Johann Mendel, who showed that inheritance is governed by stable, particulate units (now called genes) that are passed unchanged from parents to offspring.
The integration of Mendel’s work with Darwin’s ideas laid the foundation for understanding heredity. When DNA was later identified as the genetic material, it explained how changes in DNA sequence (called mutations) are passed from parents to offspring. Traits that improve an organism’s chances of survival and reproduction are more likely to be passed on while less advantageous traits tend to be lost over time. This was called, in short, survival of the fittest.
For a long time, Lamarck’s ideas lay forgotten.
If you have it, express it
In 1956, Canadian plant geneticist Royal Alexander Brink noticed something strange in maize. Despite having two copies of the gene for rich, purple-coloured kernels, some plants produced only weak pigments. Even more curious, their offspring also showed weak pigmentation despite carrying the same genes. This suggested that something other than DNA was influencing the trait and that this mysterious influence was heritable.
Scientists soon realised that having a gene is not enough: it must also be expressed, meaning its information must be used to make proteins. This expression is regulated in various ways. One important method involves small chemical tags added to the DNA that help cells decide whether a gene should be switched on or off. This system of gene regulation without altering the DNA sequence is called epigenetics.
In 1975, scientist Arthur Riggs proposed that these chemical tags, or epigenetic marks, could be inherited. This meant organisms could potentially pass on instructions about gene activity without changing their DNA sequence. Since it’s easier to change these marks than to mutate DNA, it raised an intriguing possibility: if an environmental trigger caused a heritable epigenetic change, then Lamarck might have been partly right.
Inheritance, at least in some cases, could be due to environmental influence. The DNA itself didn’t need to change.
Over the next 50 years, sporadic reports appeared stating that this might be the case — but none were convincing enough to firmly prove that a natural environmental cue could induce a heritable epigenetic change.
Lamarck redeemed
On May 22, a landmark study published in Cell showed, for the first time, that rice plants can acquire tolerance to cold temperatures by changing the epigenetic marks on a gene called ACT1. Surprisingly, this change was induced by exposing normal rice plants to low temperatures. Even more surprisingly, the change was heritable over five generations — proof that what Lamarck suggested over two centuries ago could indeed happen, albeit in a laboratory.
The authors of the study achieved the feat by subjecting the rice plant Oryza sativa to low temperatures and using the number and quality of seeds produced as a way to assess how well the rice adapted. They observed that from the second generation onwards, seed quality improved and, importantly, the improvement was sustained across subsequent generations.
Then they sequenced the total DNA of the cold-adapted rice and compared it with a control group grown under identical conditions but without the cold exposure. Although they found multiple genetic differences, none appeared to account for the enhanced cold tolerance. They next examined differences in gene expression between the two groups and identified 12 genes whose activity varied.
To understand why these 12 genes produced different levels of protein, the researchers investigated epigenetic marks and discovered more than 12,380 differences between the two groups. One of these changes was near a gene they called ACT1. Interestingly, ACT1 was also among the 12 genes with altered expression.
What life has endured
The team then explored how this epigenetic change regulated ACT1. They found that ACT1, a gene involved in plant growth and development, is normally expressed at high levels in rice. But when exposed to cold, its expression is switched off by the addition of a methyl group, an epigenetic tag that tells the plant’s cells not to produce the protein. Without sufficient ACT1, normal rice plants struggle to survive in the cold.
The cold-adapted plants, however, didn’t add this methyl signal. As a result, they continued to produce the ACT1 protein, which supported their development under cold stress. These epigenetic marks were then passed on to their offspring, ensuring subsequent generations also expressed ACT1 and survived in cold conditions.
In the century or so since they were discarded, Lamarck’s ideas on evolution have been exhumed several times — mostly for criticism. It is perhaps poetic that nature itself had to step in to show us that he was not entirely wrong and that the environment can indeed influence heredity. The cold-adapted rice has shown us that sometimes, very rarely, inheritance is not determined by the code for life but rather by what that life has endured.
Arun Panchapakesan is an assistant professor at the Y.R. Gaitonde Centre for AIDS Research and Education, Chennai.
Published – June 18, 2025 05:30 am IST