Epigenetics
Epigenetics is the study of changes in gene expression that don't involve altering the underlying DNA sequence: modifications, chiefly DNA methylation and histone-tail changes, that determine which genes are accessible for transcription and which are silenced, shaped directly by environmental factors.
Genes function as inherited metabolism rather than fixed destiny, and that inheritance is highly malleable. Molecular genetics' Central Dogma, formulated specifically to rule out any Lamarckian inheritance of acquired characteristics, asserts that information flows only one direction: DNA to RNA to protein. Metabolic energy itself, expressed largely through the ratio of carbon dioxide to lactic acid, guides both development and evolution instead.[1]
Curiosity, esthetics, creativity, and stimulation are necessarily and deeply linked to metabolic efficiency and structural-anatomical development.
Cells have to, in some sense, perceive themselves and their environment, because their environment is an essential part of their existence, governing what they are and what they can become. To understand the nature of cellular perception, we have to look beyond existing descriptions of what cells are.
Genetic determinism vs. evolution on purpose
[edit]DNA stores molecular entities and their concentrations but not the full developmental instructions; heredity also depends on regulatory molecules, their sensors, and sensed properties that are recreated across generations independently of DNA sequence alone.[4][5] James Shapiro and Denis Noble, editors of Evolution 'On Purpose': Teleonomy in Living Systems (MIT Press, 2023), frame the same shift away from gene-as-fixed-destiny in evolutionary terms rather than developmental ones:
| Genetic determinism | Evolution on purpose |
|---|---|
| Genes control cells | Cells use genes |
| DNA as a blueprint | DNA as a read-write library used and modified by living systems |
| One-way information flow (DNA to RNA to protein) | Information flows in all directions |
| Genome controls physiology | Physiology and environment regulate genome activity |
| DNA-only inheritance | Multiple forms of inheritance |
| Fixed genome | Dynamic genome |
{{Quote|text=The capacity of living organisms to alter their own heredity is undeniable. Our current ideas about evolution have to incorporate this basic fact of life.|author=James Shapiro|source=http://libertytree.ca/quotes/James.Shapiro.Quote.9304
The genes have often been the followers rather than the leaders in evolutionary change.
— Denis Noble[6]
{{Quote|text=In the future attention undoubtedly will be centered on the genome, and with greater appreciation of its significance as a highly sensitive organ of the cell, monitoring genomic activities and correcting common errors, sensing the unusual and unexpected events, and responding to them, often by restructuring the genome.|author=Barbara McClintock|source=https://www.huffpost.com/james-a-shapiro/barbara-mcclintock_b_1223618.html
Polygenic scores for height built from genome-wide association studies were found to be substantially overestimated due to uncorrected population stratification; correcting for it sharply reduced the apparent genetic contribution to height, undercutting confidence in similar polygenic disease-prediction scores built the same way.[7]
A systematic assessment of genome-wide association study (GWAS) performance found polygenic risk scores generally weak and inconsistent predictors of individual disease risk across most common diseases, reinforcing that DNA sequence alone explains only a small fraction of who actually gets sick.[8]
Mechanisms
[edit]DNA methylation adds a methyl group to the DNA molecule, typically at CpG sites, and can silence genes (tumor-suppressor genes in cancer, for instance) through hypermethylation of their promoter regions. Histones, the proteins DNA wraps around, get modified too: acetylation tends to activate a gene, deacetylation tends to repress it, and deregulated histone acetylation shows up in both cancer and neurodegenerative disease.
Environmental stress can trigger movement of transposable elements ("jumping genes") within the genome. In the adult brain, activity-dependent expression of genes needed for neurogenesis runs through the same machinery: the stress-response gene Gadd45b, for example, gets induced by neuronal activity via dynamic DNA demethylation, promoting new neuron growth.
Case studies
[edit]Mice descended from ancestors exposed to BPA during pregnancy showed social-recognition deficits and altered postsynaptic-density gene expression three to four generations later, even though only the original generation was ever exposed. This reflects a transgenerational epigenetic effect of an estrogenic/antiandrogenic endocrine disruptor.[9]
Non-brain human cells (kidney and nerve lines) show massed-spaced learning: repeated chemical pulses activate a memory gene more strongly than one prolonged burst, paralleling neuronal spaced-learning dynamics.[10]
Identical twins
[edit]Identical twins start with the same DNA. Differences in diet, stress, or lifestyle produce different patterns of gene expression from there, leading to measurable differences in IQ and, in some cases, one twin developing a disease the other never does.
Queen bee and worker bee
[edit]Queen bees and worker bees are genetically identical but develop into entirely different castes. The deciding factor is diet during the larval stage: royal jelly triggers DNA methylation changes that activate the genes behind a queen's fully functional ovaries and larger body, while worker larvae, fed differently, never get those changes switched on.[11]
Dutch Hunger Winter
[edit]People conceived during the 1944-45 Dutch famine showed measurably different DNA methylation at the IGF2 gene six decades later, compared to their own unexposed same-sex siblings, and carried higher lifelong risk of obesity, diabetes, and heart disease as a result.[12] The effect was specific to exposure during very early gestation, underlining how much of the epigenetic pattern gets locked in during that narrow window.
= Paternal high-fat diet
[edit]Paternal microplastic exposure alters sperm small noncoding RNAs and predisposes female offspring on high-fat diet to metabolic disease.[13]= In mice, two weeks of a high-fat diet (60% kcal from fat) in fathers before mating, without obesity in the fathers themselves, impairs glucose tolerance in offspring through sperm small non-coding RNAs, including mitochondrial transfer RNAs upregulated as a compensatory response to paternal mitochondrial dysfunction.[14] Earlier work showed sperm tsRNAs from high-fat-diet fathers transmit acquired metabolic traits across generations without DNA-sequence change.[15] Epidemiological data link high paternal BMI to similar metabolic problems in human sons.
Multigenerational small-RNA memory in C. elegans
[edit]In C. elegans, a small RNA (P11) produced by the bacterium Pseudomonas aeruginosa PA14 triggers learned pathogen avoidance that passes down to four generations of naive offspring who never encountered the bacteria themselves, by silencing a specific neuronal gene.[16] Separately, small regulatory RNAs called piRNAs can establish gene-silencing "memory" that persists over 20 generations once established, becoming independent of the original trigger but still requiring the worm's RNA-interference/chromatin machinery to stay switched on.[17] Claims of inheritance lasting "up to 14 generations" circulating outside the primary literature appear to conflate or round these two separate findings (4 generations for pathogen-avoidance, 20+ for piRNA silencing); the real range spans both ends depending on the specific mechanism studied.
Parental stress
[edit]In mice, a stressed father can pass an altered stress response on to offspring through epigenetic changes carried in sperm, without any change to the DNA sequence itself.
Parental stress memory in plants
[edit]In soybean, offspring of parents exposed to combined drought and herbivory inherit stress-adaptive traits: higher seed protein and nitrogen, more defensive trichomes, and altered pest preference, without DNA-sequence change, at a cost of reduced yield and more empty pods.[18]
See also
[edit]References
[edit]- ↑ "Genes, Carbon Dioxide and Adaptation.," Ray Peat article
- ↑ "Genes, Carbon Dioxide and Adaptation.," Ray Peat article
- ↑ Ray Peat, "Cellular Judgments" (Tissue Firmness and Elasticity), newsletter, 1998.
- ↑ Jose AM. "Heritable information in development and disease," J R Soc Interface. 2020;17(171):20200154. doi:10.1098/rsif.2020.0154.
- ↑ Jose AM. "The folly of maintaining a genome-centric view of heredity," BioEssays. 2019;41(12):1900254. doi:10.1002/bies.201900254.
- ↑ Denis Noble, in Peter A. Corning et al. (eds.), Evolution 'On Purpose': Teleonomy in Living Systems, MIT Press, 2023.
- ↑ Sohail M, Maier RM, et al. "Polygenic adaptation on height is overestimated due to uncorrected stratification in genome-wide association studies," eLife. 2019. doi:10.7554/eLife.39702.
- ↑ Patron J, Serra-Cayuela A, Han B, et al. "Assessing the performance of genome-wide association studies for predicting disease risk," PLoS One. 2019. doi:10.1371/journal.pone.0220215.
- ↑ Wolstenholme JT, Drobná Z, Henriksen AD, et al. "Transgenerational bisphenol A causes deficits in social recognition and alters postsynaptic density genes in mice," Endocrinology. 2019;160(8):1854-1867. doi:10.1210/en.2019-00196. PMID 31188430.
- ↑ Kukushkin NV, et al. "Learning in non-brain human cells," Nat Commun. 2024. doi:10.1038/s41467-024-53922-x.
- ↑ Kucharski R et al., "Nutritional control of reproductive status in honeybees via DNA methylation," Science (New York, N.Y.), 2008
- ↑ Heijmans BT et al., "Persistent epigenetic differences associated with prenatal exposure to famine in humans," Proceedings of the National Academy of Sciences of the United States of America, 2008
- ↑ Park C, et al. "Paternal microplastic exposure and offspring metabolism," J Endocr Soc. 2025. doi:10.1210/jendso/bvaf214.
- ↑ Teperino R, et al. "Diet-induced paternal obesity impairs offspring metabolism through sperm tsRNAs," Nature. 2024.
- ↑ Chen Q, et al. "Sperm tsRNAs contribute to intergenerational inheritance of an acquired metabolic disorder," Science. 2016;351(6271):397-400. PMID 26721680.
- ↑ Moore RS, Kaletsky R, Murphy CT. "A natural bacterial pathogen of C. elegans uses a small RNA to induce transgenerational inheritance of learned avoidance," Cell. 2019;177(7):1827-1841.
- ↑ Houri-Zeevi L, et al. "piRNAs Can Trigger a Multigenerational Epigenetic Memory in the Germline of C. elegans," Cell. 2012;150(1):88-99.
- ↑ Gautam N, Kariyat RR. "Compensation of physiological traits under simulated drought and herbivory has functional consequences for fitness in soybean," Environ Exp Bot. 2024.