October 22, 2023
Humans are born with the ability to digest lactose, this is necessary for survival through infancy. -3
The Story
Evolutionary theory proposes that humans emerged millions of years ago, transitioning to bipedal movement after an earlier arboreal existence. Much later, it is inferred that some human populations developed the ability to digest dairy into adulthood through a germline mutation that occurred roughly 2,000 to 20,000 years ago, likely in regions near modern-day Turkey. -1 This narrative assumes the domestication of animals such as cows, goats, and sheep drove this mutation up in frequency. -1 It further suggests that sustained exposure to dairy products created selective pressure, leading to a random mutation that enabled continued lactase production into adulthood. The story is good but does the evidence support it?
Evolution depends on beneficial mutations
The central claim of modern evolutionary theory is that new biological features arise through natural selection acting on beneficial germline mutations. These mutations, passed through reproduction, are said to generate the functional changes necessary to transform simple organisms into more complex ones over time.
At the Theory of Evolutions core, it depends on two things:
- Mutations producing net functional gains
- Those gains accumulating to build new biological systems
The question is not whether mutations occur, they certainly do. The question is whether observed mutations demonstrate this kind of constructive power to prove lactose persistence.
What We Actually Observe in Biology
Biology operates through highly coordinated systems, especially at the protein level. Proteins are built from genetic code and must fold into precise three-dimensional shapes to function. Even small changes in the underlying sequence can disrupt that structure.
Research consistently shows that mutations which alter protein structure most often:
- reduce stability of the folded protein
- impair function
- disrupt interactions with other proteins
- result in degradative or dysfunctional outcomes
Proteins work in teams
Proteins do not work in isolation, they function in networks. A change in one component can create cascading effects across the system.
This is why mutations are commonly associated with disease, including cancers, congenital disorders, and developmental abnormalities. Rather than constructing new systems, mutations frequently degrade or dysregulate existing ones.
https://biosignaling.biomedcentral.com/articles/10.1186/s12964-020-00642-6
The challenge is not simply forming a new protein, but forming one that:
- integrates into existing systems
- improves overall function
- leads to physiological morphology
These constraints are extremely narrow and specific.
The Key Distinction: Observed vs. Inferred
We can observe mutations and measure their effects in real time.
What we do not observe is the step-by-step emergence of new, complex biological systems through a series of mutations producing consistent functional gains. These are assumptions– not observations.
What we do observe in the present is that such mutations that might lead to physiological changes actually lead to harm and disease– not benefit.
Lactose Tolerance
“After the weaning period is over, lactase production usually declines, although the mechanisms and evolutionary reasons for this downregulation are not fully understood. However, some humans continue to express lactase throughout adult life, and are thus able to digest the lactose found in fresh milk.” Gerbault P, Liebert A, Itan Y, Powell A, Currat M, Burger J, Swallow DM, Thomas MG. “Evolution of lactase persistence: an example of human niche construction.”
Adult lactose tolerance is another commonly cited example of a beneficial mutation.
After weaning, this ability typically declines, though some individuals retain it into adulthood.
What the evidence reveals:
- The underlying system (lactase production) already exists in all humans
- The variation reflects differences in regulation, not the creation of a new function
- The historical origin of this variation is inferred, not directly observed
- Fossil DNA is too incomplete to confirm specific mutation events -4
Thus, what is observed is variation within an existing system, not the emergence of a new one- that is assumed.
Levinthal’s Paradox
The problem of protein folding, that which Evolution hinges, is one of the most important problems of molecular biology. This central problem (Leventhal’s paradox) is that the protein is first synthesized as a linear molecule that must reach its native conformation in a short time (on the order of seconds or less). The protein can only perform its functions in this (often single) conformation. The problem, however, is that the number of possible conformational states is exponentially large for a long protein molecule. Despite almost 30 years of attempts to resolve this paradox, a solution has not yet been found.
What Lactose Tolerance Reveals
- Existing biological systems are modified
- Changes affect regulation, not core design
- Outcomes are often context-dependent and involve trade-offs
They do not demonstrate the creation of new biological structures or systems.
The Core Argument
Mutations are real and observable. Their effects are measurable.
But what we consistently observe is that mutations:
- alter existing systems
- frequently disrupt or degrade function
- and only rarely produce limited, context-dependent advantages
What is not directly observed is the accumulation of mutations producing new, integrated biological systems with sustained functional gains.
That broader claim rests on inference.
Conclusion
Examples like LRP5 and lactose tolerance are often presented as clear evidence of beneficial mutation driving evolution but this claim is an inference, not an observation.
A closer analysis shows:
- the function already persists and has for thousands of years
- mutations might modify regulation, but not create a new systems
- the outcomes involve trade-offs rather than clear improvements
- historical claims about their origin is inferred, not observed
At minimum, these examples do not demonstrate the kind of constructive, system-building power required by the broader evolutionary claim. They demonstrate variation within existing biological frameworks, not the creation of fundamentally new ones.
1- https://www.npr.org/sections/thesalt/2012/12/27/168144785/an-evolutionary-whodunit-how-did-humans-develop-lactose-tolerance168144785/an-evolutionary-whodunit-how-did-humans-develop-lactose-tolerance.
2- Misselwitz B, Butter M, Verbeke K, Fox MR. Update on lactose malabsorption and intolerance: pathogenesis, diagnosis and clinical management. Gut. 2019 Nov;68(11):2080-2091. doi: 10.1136/gutjnl-2019-318404. Epub 2019 Aug 19. PMID: 31427404; PMCID: PMC6839734. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6839734/
3- Gerbault P, Liebert A, Itan Y, Powell A, Currat M, Burger J, Swallow DM, Thomas MG. Evolution of lactase persistence: an example of human niche construction. Philos Trans R Soc Lond B Biol Sci. 2011 Mar 27;366(1566):863-77. doi: 10.1098/rstb.2010.0268. PMID: 21320900; PMCID: PMC3048992. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3048992/#:~:text=After%20the%20weaning%20period%20is,lactose%20found%20in%20fresh%20milk
4 – Mélanie Pruvost, Reinhard Schwarz, Virginia Bessa Correia, +5 “Freshly excavated fossil bones are best for amplification of ancient DNA” Jan, 2007, 104 (3) 739-744; https://doi.org/10.1073/pnas.0610257104
5- https://dpi.wi.gov/sites/default/files/imce/community-nutrition/pdf/cacfp_special_dietary_needs.pdf
6- Erickson, Jim “Most ‘silent’ genetic mutations are harmful, not neutral, a finding with broad implications” University of Michigan News, June, 2022, https://news.umich.edu/study-most-silent-genetic-mutations-are-harmful-not-neutral-a-finding-with-broad-implications/
