“Random mutation plus natural selection produces new genetic information.”
§1 The claim, as taught
Mutations are the original source of all genetic variation. Gene duplication followed by mutation can give rise to genes with new functions. Over vast spans of time, the accumulation of such changes, filtered by natural selection, accounts for the diversity of life.Representative summary of introductory-text treatments (e.g. Campbell Biology, chapters on mutation and genome evolution). PLACEHOLDER: to be replaced with exact quotations and page numbers.
§2 The strongest evidence offered
These are the examples most often cited. We present each one fairly and say what it actually shows.
Lenski's E. coli: citrate use
In the Long-Term Evolution Experiment, running since 1988, one population gained the ability to use citrate in the presence of oxygen after about 31,500 generations. The key step was a duplication that placed the existing citT transporter gene under a promoter active with oxygen.Nylon-digesting bacteria
Bacteria were found digesting byproducts of nylon manufacture, a substance that only appeared in the 20th century. Structural work showed that the enzyme (NylB) shares the fold of an existing enzyme family, and that a few substitutions raised its activity.Gene families from duplication
Genomes contain families of similar genes, such as the globins and opsins. Researchers infer that these arose by duplication followed by divergence. The pattern is observed. The history is reconstructed.Function in random sequences
An ATP-binding activity was found at a frequency of roughly 1 in 1011 in a library of random protein sequences. This is cited to show that functional sequences may be less rare than critics claim.§3 The grade: two claims hiding in one
The textbook statement combines a modest claim with a sweeping one. Graded separately, they look very different. Hover or tap a rung to see why it got its score. How the grading works →
Mutations modify, tune or break existing genes
BStrongly supportedMutations originate new protein folds and multi-part systems
DExtrapolation§4 What it would take
Here is what would move the claim up a grade. These are not impossible demands. They are the observations the claim itself implies.
- A new fold, observedShow a protein fold with no detectable similarity to existing folds arising by undirected mutation in a laboratory population.
- A multi-part system, observedShow a new function that needs several new, cooperating parts appearing step by step, where each step is selected for.
- A rate that fits the clockShow that measured mutation rates, population sizes and waiting times can produce the required innovations in the time available.
§5 Another reading of the same data
Across decades of experimental evolution, most adaptive mutations damage or remove an existing function, or adjust its regulation. Michael Behe surveyed the experimental literature and called this “the first rule of adaptive evolution”: break or blunt any gene whose loss would increase the number of offspring. The citrate result fits the pattern. A transporter the cell already had was switched on under new conditions.
Douglas Axe's mutagenesis experiments estimated that about 1 in 1077 sequences forms a working enzyme domain of around 150 residues. That figure is disputed, and other estimates are far more generous (see Claim № 4.03). But if it is anywhere close, a random search cannot find new folds in the time and population sizes available.
Read through a design lens, living things look as if they were built with a rich initial store of information and the capacity to adapt: to adjust, switch on, or give up existing functions as conditions change. The observations fit that reading at least as well as they fit the textbook one.
§6 Reasoning check
The grade weighs the evidence. This check looks at the reasoning: the step from the evidence to the conclusion. The same tests are applied to both readings. How the reasoning check works →
- Clear case
“New genetic information” covers two things: a new use for an existing gene, which has been observed (citrate), and new genes and folds, which have not. Evidence for the first is counted as evidence for the second.
- Clear case
“Over vast spans of time … accounts for the diversity of life” extends observed tuning and breaking of genes to the origin of every biological novelty, without showing that the process scales.
- PossibleIn the evidence: Lenski's E. coli: citrate use
Often reported as “a new function evolved.” What was observed was an existing transporter expressed under new conditions. Both descriptions are accurate; only the second says what kind of novelty it was.
- Possible
Behe's “first rule” generalises from laboratory and short-term studies, which favour quick gains by losing function. Whether the rule holds over longer times and larger populations is an open question, and should be tested rather than assumed.
§7 Questions to ponder
- Is gaining a new use for an existing gene the same as gaining a new gene?
- If the citrate trait took about 31,500 generations in a population of trillions, what does that suggest about the rate of more complex innovations?
- The 1 in 1011 and 1 in 1077 estimates measured different things. What would a fair comparison require?
§8 Sources
- Blount ZD, Borland CZ, Lenski RE. “Historical contingency and the evolution of a key innovation in an experimental population of Escherichia coli.” PNAS 105:7899–7906 (2008).B
- Blount ZD, Barrick JE, Davidson CJ, Lenski RE. “Genomic analysis of a key innovation in an experimental Escherichia coli population.” Nature 489:513–518 (2012).B
- Keefe AD, Szostak JW. “Functional proteins from a random-sequence library.” Nature 410:715–718 (2001).C
- Negoro S, et al. “X-ray crystallographic analysis of 6-aminohexanoate-dimer hydrolase.” J. Biol. Chem. 280:39644–39652 (2005).B
- Ohno S. Evolution by Gene Duplication. Springer (1970).C
- Behe MJ. “Experimental evolution, loss-of-function mutations, and ‘the first rule of adaptive evolution’.” Quarterly Review of Biology 85:419–445 (2010).B
- Axe DD. “Estimating the prevalence of protein sequences adopting functional enzyme folds.” J. Mol. Biol. 341:1295–1315 (2004).C
- Behe MJ. Darwin Devolves. HarperOne (2019).C
- Sanford JC. Genetic Entropy. FMS Publications, 4th ed. (2014).C
Source grades are provisional. In production each links to a full published evaluation that readers can challenge.
§9 Your notes
Mutate a working “gene”
A sentence stands in for a gene, with words as its functional parts. Each mutation changes one random letter. Turn on selection to keep only mutations that leave every word readable. See whether selection preserves meaning or builds new meaning.
| Mutations attempted | 0 |
| Words broken | 0 |
| Removed by selection | 0 |
| New real words formed | 0 |
This is an analogy, and analogies have limits. Real genes have some redundancy, and real selection acts on whole organisms. Even so, the lab shows a real distinction: keeping function is different from creating it. For real codons and amino acids, try the DNA explorer in the Probability Lab.