Recent “natural selection,” i.e. adaptive evolution, leading to longer bills (beaks) in the Parus major (bird)

One of the arguments by creationists is “how can there have been evolution in the past, if we see no evolution today?” However, multiple careful studies –– especially with the advent of next-generation DNA-sequencing becoming so common –– are now showing evolution occurring today. The attached report is an example.

To demonstrate evolutionary adaptation [DNA mutational or epigenetic alterations in response to environmental “pressures”] in wild populations, one must identify a trait (phenotype) that is under selection, understand the genetic basis of that phenotype along with effects on “fitness of the species”, and detect potential drivers of selection. In the present study the “trait” is “beak length” and the “driver of selection” is “bird-feeders in the gardens of many humans.”

The best-known demonstrations of (one or a small number of) genes underlying evolution through natural selection usually involve strong selection (“hard sweeps”) on genetic variants that may be recently derived, with a major effect on variation in preselected phenotypes. However, most quantitative traits are polygenic [involving large numbers of genes], and, for these traits, selection is likely to act on many preexisting genetic variants having small-effect.

Detecting so-called polygenic selection is challenging because selection acts on multiple loci simultaneously, and selection coefficients are likely to be small. Most attempts to detect polygenic selection have focused on gene sets rather than individual genetic loci. Furthermore, even if population genomic analyses identify genes under selection, these analyses are rarely combined with detailed ecological and behavioral data, and, as a result, linking all three components of the genotype-phenotype-fitness continuum remains a big challenge. In the [attached] study, authors combined fine-scale ecological and genomic data to study adaptive evolution in the bird, the great tit (Parus major), a widespread and abundant passerine bird and well-known ecological model system with excellent genomic resources. To do so, authors analyzed genomic variation within and among three long-term study populations from the United Kingdom (N = 949 birds) and the Netherlands (N = 254 birds) and Veluwe (N = 1812 birds).

Authors found that genomic regions under differential selection contained candidate genes for bill (beak) morphology and used genetic architecture analyses to confirm that these genes, especially the collagen gene COL4A5, explained variation in bill length. COL4A5 variability is associated with reproductive success, which, combined with spatio-temporal patterns of bill length, suggested ongoing selection for longer bills in the United Kingdom. Authors discovered that bill length and COL4A5 variation were associated with use of bird-feeders, suggesting that longer bills may have evolved in the United Kingdom during the past century, as a response to domesticated feeding by humans. Evolution is therefore alive and well and is happening all the time; one simply needs to study any organism over a sufficiently long number of generations in order to find these adaptive changes in the DNA or chromatin that improves the animal’s survival to the current environment.

Science 20 Oct 2o17; 358: 365–368

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