(Originally posted in May 2016. Update at bottom)
Darwin’s Finches… The Galapagos finches are one of the most famous illustrations of natural selection in action. Michael Denton explains why these birds are a double-edged sword for Darwinian theory. For more information about Michael Denton, or to purchase his new book, “Evolution: Still a Theory in Crisis.”
MORE Dr. Denton from his post on the matter (H/T Evolution News):
Darwin’s Finches Are Evidence for Evolution? Think Again
…The Galápagos finches put on display the two strict requirements that must be present in order for natural selection to work its magic. If these two factors are not present, natural selection is impotent to change any creature at all, much less create a new species.
First, the finches’ beaks are clearly adaptive. Each distinct variation gives the lucky individual a definitive leg-up in its specific environment. There is an obvious, practical reason why the differentiation is helpful to the species in question. This is absolutely essential in order for natural selection to pick between variations in species. Natural selection can only “see” those variations that are adaptive — causing one individual to live, and carry on its genes, and another to die and not leave offspring. If a variation is neutral or does not somehow increase fitness in the specific environment the creature lives in, Darwin’s mechanism cannot select it.
Second, there is a functional continuum among the finches’ beaks. That is, between a finch with a tiny beak and a finch with a large beak, there are tiny, step-by-step changes, and each change makes the creature slightly more fit in its environment. This is also essential for natural selection to work.
The problem for Darwinian theory comes in explaining evolutionary change where, unlike the case of Darwin’s finches, these requirements are absent. First, there may not be a continuum. That is, natural selection cannot make large jumps or drastic changes. There must be small steps. Secondly, each single step must be beneficial to the individual. It is not enough for the first and last versions of the adaptation to be helpful — all the intervening steps must increase fitness as well.
There are examples of creatures throughout the biological world that break one or both of these rules. Many creatures just don’t fit the natural selection story like the Galápagos finches do….
UPDATE
Natural History Museums everywhere feature Darwin’s Finches as evidence for evolution theory. How do these finches support the idea of evolution? Are the changes we observe in finch beaks due to evolution or epigenetics?
The prevailing theory for the molecular basis of evolution involves genetic mutations that ultimately generate the heritable phenotypic variation on which natural selection acts. However, epigenetic transgenerational inheritance of phenotypic variation may also play an important role in evolutionary change. A growing number of studies have demonstrated the presence of epigenetic inheritance in a variety of different organisms that can persist for hundreds of generations. The possibility that epigenetic changes can accumulate over longer periods of evolutionary time has seldom been tested empirically. This study was designed to compare epigenetic changes among several closely related species of Darwin’s finches, a well-known example of adaptive radiation. Erythrocyte DNA was obtained from five species of sympatric Darwin’s finches that vary in phylogenetic relatedness. Genome-wide alterations in genetic mutations using copy number variation (CNV) were compared with epigenetic alterations associated with differential DNA methylation regions (epimutations). Epimutations were more common than genetic CNV mutations among the five species; furthermore, the number of epimutations increased monotonically with phylogenetic distance. Interestingly, the number of genetic CNV mutations did not consistently increase with phylogenetic distance. The number, chromosomal locations, regional clustering, and lack of overlap of epimutations and genetic mutations suggest that epigenetic changes are distinct and that they correlate with the evolutionary history of Darwin’s finches. The potential functional significance of the epimutations was explored by comparing their locations on the genome to the location of evolutionarily important genes and cellular pathways in birds. Specific epimutations were associated with genes related to the bone morphogenic protein, toll receptor, and melanogenesis signaling pathways. Species-specific epimutations were significantly overrepresented in these pathways. As environmental factors are known to result in heritable changes in the epigenome, it is possible that epigenetic changes contribute to the molecular basis of the evolution of Darwin’s finches.
([no paywall] Genome Biology and Evolution, Volume 6, Issue 8, August 2014, Pages 1972–1989)
As well as this article — with a hat-tip to WINTERY KNIGHT — by Jonathan Wells. at EVOLUTION NEWS. Here is an excerpt:
- Wait a minute. Average beak size increased slightly during one drought, only to return to normal after the rains return. Then average beak size decreased slightly during another drought. A region of DNA is correlated with beak size. And somehow that tells us how finches evolved in the first place? As Winston Churchill might say, “Never in the field of science was so much based by so many on so little.”