Creationism in Crisis - A Newly-Discovered Non-Genetic Mode for Inheritance, But It's No Comfort For Creationists

Because babies acquire their first gut microbes passing through their mother’s birth canal, mothers’ microbiomes form the basis of their offspring’s.

Photo: Sarah Chai/Pexels

Hardship affects the gut microbiome across generations | UCLA

Human gut microbiome

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The old scientific debate from the early 19th century between Darwinian evolution and Lamarckian evolution all hinged on whether characteristics acquired after birth could be inherited by offspring, as Lamarck thought, or whether what we inherit from our parents is a variation (within limits) of what they inherited from their parents:

Darwinian and Lamarckian evolution are two contrasting theories of evolution that were proposed in the past. Though both sought to explain the process of biological change over time, they differ in their fundamental mechanisms and assumptions.

1. Darwinian Evolution (Theory of Natural Selection):
   • Proposed by Charles Darwin and Alfred Russel Wallace in the mid-19th century.
   • Central concept: Natural selection is the main driving force behind evolution.
   • Mechanism: Variation exists within populations, and individuals with traits better suited to the environment are more likely to survive and reproduce. Over time, these advantageous traits become more common in the population, while less favorable traits are selected against.
   • Inheritance of acquired characteristics: Darwinian evolution does not rely on the inheritance of traits acquired during an organism's lifetime. Instead, it is based on the passing down of genetic information from parents to offspring.
   • Example: Consider a population of giraffes with varying neck lengths. If the environment favors individuals with longer necks (e.g., taller trees for feeding), those with longer necks have a survival advantage and are more likely to pass on their long-necked genes to the next generation.
2. Lamarckian Evolution (Theory of Inheritance of Acquired Characteristics):
   • Proposed by Jean-Baptiste Lamarck in the early 19th century.
   • Central concept: Evolution is driven by an organism's effort to adapt to its environment and the inheritance of acquired traits.
   • Mechanism: Lamarck proposed that if an organism acquires new characteristics or traits during its lifetime due to its environment's demands, these acquired traits can be passed on to its offspring.
   • Example: Lamarck suggested that if a giraffe stretches its neck throughout its lifetime to reach higher leaves, the elongated neck acquired during its life will be passed on to its offspring, leading to the gradual evolution of longer-necked giraffes over generations.

The key difference between the two theories lies in their view on the inheritance of acquired characteristics. Darwinian evolution relies on natural selection acting on existing genetic variation, while Lamarckian evolution suggests that acquired traits during an individual's lifetime can be inherited by their offspring, driving evolutionary change. Lamarckian evolution, however, has been largely discredited by modern genetics and molecular biology, as it does not align with the principles of inheritance through genes and DNA. Instead, the modern understanding of evolution is based on the principles proposed by Darwin, which include the processes of mutation, genetic variation, and natural selection acting on heritable traits.

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That debate has now been opened up again in an unexpected way with the news that an international team of scientists led by UCLA psychologists has shown that information produced during hardship suffered by a woman during pregnancy can be passed on to her baby via its microbiome.

On the face of it, this looks a lot like a form of Lamarckian inheritance, except for the fact that it is the microorganisms, complete with their own inherited DNA that is being passed on.

But creationists, who can be relied on to grasp at anything that seems to be non-Darwinian and claim it proves Darwin was wrong (and with their fondness for the false dichotomy fallacy, so "God did it!"), can take no comfort from the fact that this appears to be a non-genetic form of inheritance and inheritance moreover of something acquired after birth. The fact is that the gut organisms the baby acquires at birth as it passes through the birth canal, will be the result of natural selection acting on the mother's microbiome.

The reason this matters is because humans, biologically, like most other vertebrates, are alliances of the genes of multiple organisms, not just the human genes in our cells but the genes in our microbiome - something predictable from the 'selfish gene' understanding of Darwinian evolution. And this matters because other researchers have shown that the composition of our microbiome influences our immune system and our brain development, at least in early childhood and maybe even in later life. A 'healthy' population of 'good' bacteria is associated with good health.

The human gut microbiome refers to the diverse community of microorganisms that inhabit the gastrointestinal tract, primarily the large intestine. It is a complex ecosystem comprising bacteria, viruses, archaea, fungi, and other microorganisms. These microbes play a crucial role in various aspects of human health, including digestion, metabolism, immune system regulation, and protection against pathogens.

1. Composition: The gut microbiome consists of thousands of different species, with the majority being bacteria. Some of the most common bacterial phyla found in the gut include Firmicutes, Bacteroidetes, Actinobacteria, and Proteobacteria.
2. Functions: The gut microbiome performs several essential functions:
   1. Digestion and Metabolism: It helps in breaking down complex carbohydrates and fiber that the human digestive enzymes cannot process, leading to the production of short-chain fatty acids (SCFAs) that are beneficial for gut health.
   2. Nutrient Production: Some gut microbes can synthesize essential nutrients like certain vitamins (e.g., B vitamins) and help in their absorption.
   3. Immune System Regulation: The gut microbiome interacts with the immune system, helping it to distinguish between beneficial and harmful substances.
   4. Protection against Pathogens: It helps prevent the growth of harmful bacteria by occupying the gut lining and producing antimicrobial substances.
   5. Brain-Gut Axis: Emerging research suggests that the gut microbiome can influence brain function and behavior through the gut-brain axis.
3. Factors Affecting the Gut Microbiome: Several factors can impact the composition and diversity of the gut microbiome:
   1. Diet: The type of food consumed can influence the abundance of different microbial species.
   2. Age: The gut microbiome changes with age and tends to stabilize in adulthood.
   3. Medications: Antibiotics and other medications can disrupt the gut microbiome.
   4. Lifestyle: Exercise, stress, and sleep patterns can have effects on the gut microbiome.
   5. Birth Method: The mode of delivery during birth (vaginal or cesarean section) can impact the initial colonization of the infant's gut.
4. Health Implications: An imbalance in the gut microbiome, known as dysbiosis, has been linked to various health conditions, including:
   1. Gastrointestinal disorders: Irritable bowel syndrome (IBS), inflammatory bowel disease (IBD), and others.
   2. Obesity and metabolic disorders: The gut microbiome may influence weight regulation and metabolism.
   3. Immune-related disorders: Allergies, autoimmune diseases, and susceptibility to infections.
   4. Mental health: Emerging research suggests links between the gut microbiome and conditions like depression and anxiety.
5. Further Reading:
   • Qin, J., Li, Y., Cai, Z., Li, S., Zhu, J., Zhang, F., ... & Wang, J. (2012). A metagenome-wide association study of gut microbiota in type 2 diabetes. Nature, 490(7418), 55-60. doi: 10.1038/nature11450
   • Valdes, A. M., Walter, J., Segal, E., & Spector, T. D. (2018). Role of the gut microbiota in nutrition and health. BMJ, 361, k2179. doi: 10.1136/bmj.k2179
   • Cani, P. D., & de Vos, W. M. (2017). Next-generation beneficial microbes: the case of Akkermansia muciniphila. Frontiers in microbiology, 8, 1765. doi: 10.3389/fmicb.2017.01765
   • Marchesi, J. R., Adams, D. H., Fava, F., Hermes, G. D., Hirschfield, G. M., Hold, G., ... & Hart, A. (2016). The gut microbiota and host health: a new clinical frontier. Gut, 65(2), 330-339. doi: 10.1136/gutjnl-2015-309990
   • Bäckhed, F., Fraser, C. M., Ringel, Y., Sanders, M. E., Sartor, R. B., Sherman, P. M., ... & Finlay, B. B. (2012). Defining a healthy human gut microbiome: current concepts, future directions, and clinical applications. Cell Host & Microbe, 12(5), 611-622. doi: 10.1016/j.chom.2012.10.012
Remember that the field of microbiome research is continually evolving, and new findings may have emerged after my knowledge cutoff date in September 2021. To stay up-to-date with the latest research, it's best to explore recent publications and scientific journals related to the human gut microbiome.

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The research by the UCLA-led team is explained in a UCLA news release by Holy Ober:

Adversity experienced by mothers during their childhood or pregnancy is reflected in their children’s gut microbiomes.

Key takeaways:

• A UCLA-led study has shown that hardship experienced by mothers during their own childhood or during pregnancy is reflected in the composition of their 2-year-old children’s gut microbiome.
• It was previously understood that in rodents, prenatal stress affects microbiomes into adulthood, but how long after birth the effects lasted in humans was unknown.
• The changes to this community of microorganisms are likely among the ways that hardship affects a child’s socioemotional development.

Hardship experienced by mothers during their own childhood or during pregnancy is reflected in the composition of their 2-year-old children’s gut microbiomes, reports an international team of scientists led by UCLA psychologists.

The researchers found small to medium changes in the children’s microbiomes. The research is the first to document the transgenerational effects of adversity on the human gut microbiome.

A growing body of evidence links the gut microbiome to brain and immune functioning, and according to the researchers, changes to that community of microorganisms is likely among the ways that hardship affects children’s socioemotional development.

The study, which is published in Proceedings of the National Academy of Sciences, builds on previous research in rodents, which has shown that prenatal stress disrupts maternal vaginal and gut microbiomes. Because babies acquire their first gut microbes passing through their mother’s birth canal, mothers’ microbiomes form the basis of their offspring’s.

Previous research in humans has shown that shortly after birth, stress experienced by the infant while in the womb and the mother’s own psychological distress influence the infant microbiome. And while it was known that the effects of prenatal stress on rodent microbiomes persist into adulthood, scientists did not yet know how long after birth the disturbances remain in humans, or whether they affected the next generation.

The study investigated the consequences of maltreatment to mothers during their childhoods, anxiety while pregnant and their children’s exposure to stressful life events in 450 mother–child pairs in Singapore when the children were 2 years old. The researchers asked mothers to recall abuse, neglect or other maltreatment they experienced during childhood, and mothers were screened for anxiety during the second trimester of pregnancy.

Researchers also interviewed the children’s primary caregivers to learn about stressful events that the children had experienced, and their general behavior and health, during their first two years of life, and researchers collected stool samples from the children. The researchers controlled for family income, which often serves as a proxy for childhood adversity.

Children whose mothers reported more anxiety in pregnancy had microbiomes in which the species of microorganisms had populations of similar sizes, a metric biologists call “evenness,” which had not been found before. Typically, the populations of the various species that make up the gut’s microflora are “lumpier,” with some species being abundant and others less common. In the study sample, however, those differences were less prominent, and populations were of similar sizes.

The gut microbes of children who experienced stressful life events after birth also had less genetic diversity, meaning that the microbes living in each child’s gut were more closely related to each other than such microbes usually are.

However, while more experiences of adversity were correlated with less microbial genetic diversity in each child, the amount of adversity did not seem to affect how similar children’s gut microbiomes were to each other. There was still variation among the children.

There are lot of questions around whether more diversity or evenness is better or worse when the gut microbiome is developing during childhood, so we don’t know if more is better at 2 years old. But many of the species we found to be related to adversity are known to interact with the immune system in some way, suggesting that maybe the way the gut microbiome interacts with the immune system is different after adversity. There’s a lot that we need to explore in the future.

Francesca Querdasi, lead author.
Department of Psychology
University of California Los Angeles, Los Angeles, CA, USA.

The microbiome gets a lot of attention and is very exciting, but it really is just one piece of the large and complicated puzzle of human health. Our study is part of a growing body of research showing the effects of early exposure and transgenerational experience on the microbiome. When we understand how experiences of hardship can influence the gut microbiome, we can then try to manipulate diet, supplements and lifestyle to make positive impacts on an individual’s gut microbiome and broader developmental trajectory.

Assistant Professor Bridget Callaghan, senior author. Department of Psychology,
University of California Los Angeles, Los Angeles, CA, USA

The researchers also found some kinds of behavior and mental health problems associated with an abundance of certain species in the gut microbiome. Although none of those species were the same ones related to adversity in this study, the authors noted that some have been associated with adversity in past studies and may perform similar functions as the species that are related to adversity.

The brain–gut microbiome connection develops rapidly during the first two to three years of life, and it is likely that the changes due to adversity demonstrated in the new study have some influence on children’s socioemotional development.

A nascent area of study called nutritional psychiatry, which researches how changes to diet could affect mental health, is developing as scientists learn more about the brain–gut microbiome connection.

Although the main article is behind a paywall, the team's abstract and their assessment of its significance is available open access:

Significance

This study draws on a large longitudinal cohort to demonstrate that adversity experienced prenatally or during early childhood, as well as adversity experienced by the mother during her childhood, impacts the gut microbiome of second-generation children at 2 y old. Notably, some of the microbiome profiles linked to these types of adversity, especially at higher taxonomic levels, were similar to those associated with the child’s current and future socioemotional functioning. Additionally, microbes uniquely associated with adversity exposures or socioemotional functioning have similar immune-related functions within the gut, highlighting the need for further research into how generational adversity affects the gut microbiome’s functional potential.


Abstract

Adversity exposures in the prenatal and postnatal period are associated with an increased risk for psychopathology, which can be perpetuated across generations. Nonhuman animal research highlights the gut microbiome as a putative biological mechanism underlying such generational risks. In a sample of 450 mother–child dyads living in Singapore, we examined associations between three distinct adversity exposures experienced across two generations—maternal childhood maltreatment, maternal prenatal anxiety, and second-generation children’s exposure to stressful life events—and the gut microbiome composition of second-generation children at 2 y of age. We found distinct differences in gut microbiome profiles linked to each adversity exposure, as well as some nonaffected microbiome features (e.g., beta diversity). Remarkably, some of the microbial taxa associated with concurrent and prospective child socioemotional functioning shared overlapping putative functions with those affected by adversity, suggesting that the intergenerational transmission of adversity may have a lasting impact on children’s mental health via alterations to gut microbiome functions. Our findings open up a new avenue of research into the underlying mechanisms of intergenerational transmission of mental health risks and the potential of the gut microbiome as a target for intervention.

Querdasi, F, R.; Enders, C.; Karnani, N.; Broekman, B.; et al. (2023)
Multigenerational adversity impacts on human gut microbiome composition and socioemotional functioning in early childhood
Proceedings of the National Academy of Sciences; 120(30) e2213768120; DOI: 10.1073/pnas.2213768120

Copyright: © 2023 The authors.
Published by PNAS. Open access.
Reprinted under a Creative Commons Attribution 4.0 International license (CC BY 4.0)

Looked at in totality, the alliance of genes a baby inherits from its mother are not only the result of the assortative process of natural selection acting on the human genes she and her partner will have inherited, but that of the assortative process of natural selection the mother's microbiome will have inherited.

So, although this research is interesting in that it reveals a different mechanism for passing genetic information, and thus the phenotypic expression of that genetic information, from one generation to the next, is fully consistent with a neo-Darwinian explanation for genetic inheritance and genetic evolution, including alliances of genes from different biological entities, just as the 'selfish' gene explanation predicts.

And what it isn't of course, is evidence that Darwin was fundamentally wrong. In fact, he was more right than even he appreciated due to the general lack of knowledge in his day of DNA, genetics and genetic inheritance.

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