Darwin's finches highlight the unity of all life

Darwin’s finches highlight the unity of all life
The discovery of the genes that influence the beak shape in the famous Galapagos finches highlight the underlying unity of all life. Credit: Paul Krawczuk/Flickr, CC BY

When Charles Darwin visited the Galapagos Islands in October 1835, he and his ship-mates on board HMS Beagle collected specimens of birds, including finches and mockingbirds, from various islands of the archipelago.

At the time, Darwin took little interest in the quaint , making only a one-word mention of them in his diary. As painstakingly shown by Frank Sulloway and more recently by John Van Whye, it wasn't until two years later that the finches sparked Darwin's interest.

By then he had received feedback from the leading taxonomist of the time, John Gould, that the samples comprised 14 distinct species, none of which had been previously described! Gould also noted that their "principal peculiarity consisted in the bill [i.e. beak] presenting several distinct modifications of form".

So intrigued was Darwin by this variation in size and shape of beaks that in the second (1845) edition of Journal of Researches he included illustrations of the distinctive variation between species in the size and shape of their beaks. He added a comment that:

Seeing this gradation and diversity of structure in one small, intimately related group of birds, one might really fancy that from an original paucity of birds in this archipelago, one species had been taken and modified for different ends.

Unfortunately for Darwin, the closer he examined the available evidence on Galapagos finches, the more confusing the picture became. This was partly because the specimens available to him were not sufficiently labelled as to their island of collection.

Presumably, it was his doubt about the available evidence that resulted in Darwin making no mention of Galapagos finches in any edition of Origin of Species.

Why, then, do people now label them as "Darwin's finches", and why are these finches now regarded as a classical textbook example of his theory of evolution by natural selection?

Darwin’s finches highlight the unity of all life
The famously varied beak shapes of the Galapagos finches, as illustrated in the second edition of Darwin’s Journal of Researches. Credit: Wikimedia

Paragons of evolution

Despite not mentioning Galapagos finches, Darwin did make much use of evidence from other Galapagos species (especially mockingbirds) in Origin of Species.

As the influence of Origin of Species spread, so too did the evolutionary fame of the Galapagos Islands. Increasingly, other biologists were drawn into resolving the questions about finches that Darwin had left unanswered.

By the end of the 19th century, Galapagos finches were among the most studied of all birds. By the mid-20th century, there was abundant evidence that Galapagos finches had evolved to fill the range of ecological niches available in the archipelago – a classic example of evolution by adaptive radiation.

Beak size and shape were key attributes in determining adaptation to the different types of food available. In the second half of the 20th century, classic research by Princeton University's Peter and Rosemary Grant provided evidence of quite strong natural selection on beak size and shape.

Under the hood

New light has also been shed on the evolution of Darwin's finches in a paper recently published in Nature. In this latest research, the entire genomes of 120 individual birds from all Galapagos species plus two closely related species from other genera were sequenced.

The work was done by a team led by Swedish geneticist Leif Andersson, with major input from Peter and Rosemary Grant, who are still leading experts on the finches.

Comparison of sequence data enabled them to construct a comprehensive evolutionary tree based on variation across the entire finch genome. This has resulted in a revised taxonomy, increasing the number of species to 18.

The most striking feature of the genome-based tree is the evidence for matings between different populations, resulting in the occasional joining of two branches of the tree. This evidence of "horizontal" gene flow is consistent with field data on matings of finches gathered by the Grants.

A comparison of whole-genome sequence between two closely related groups of finches with contrasting beak shape (blunt versus pointed) identified at least 15 regions of chromosomes where the groups differ substantially in sequence.

Unity of life

The most striking difference between the two groups was observed in a chromosomal region containing a regulatory gene called ALX1. This gene encodes a peptide that switches other genes on and off by binding to their regulatory sequences.

Like other such genes, ALX1 is crucially involved in embryonic development. Indeed, mutations in ALX1 in humans and mice give rise to abnormal development of the head and face.

It is an extraordinary illustration of the underlying unity of all life on Earth that Leif Andersson and his colleagues have shown that the ALX1 gene also has a major effect on beak shape in finches, and that this gene has been subject to natural selection during the evolution of the Galapagos finches.

If Darwin were alive today, he would be astounded at the power of genomics tools such as those used in generating the results described in this paper. He would also be delighted to see such strong evidence not only in support of evolution but also in support of one of its major forces, .


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A gene that shaped the evolution of Darwin's finches

Journal information: Nature

This story is published courtesy of The Conversation (under Creative Commons-Attribution/No derivatives).
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Apr 03, 2015
Who'd have thought.

Apr 03, 2015
Imagine mutations occurring and remaining in ALX1.
Imagine organisms not able to repair all the various mutations occurring in ALX1.

The success or failure of repair is the fundamental driver of mutation, adaptive radiation or diversification and natural selection.

Apr 03, 2015
@foolspoo
Your comment to the rating is pending...

Apr 03, 2015
Imagine mutations occurring and remaining in ALX1.
Imagine organisms not able to repair all the various mutations occurring in ALX1.

The success or failure of repair is the fundamental driver of mutation, adaptive radiation or diversification and natural selection.


@russel

Are you ever going to any peer reviewed evidence for your views?

JVK
Apr 03, 2015
The most striking difference between the two groups was observed in a chromosomal region containing a regulatory gene called ALX1.


The different species just became different groups and a mutated gene was linked to perturbed morphology.

Leif Andersson and his colleagues have shown that the ALX1 gene also has a major effect on beak shape in finches, and that this gene has been subject to natural selection during the evolution of the Galapagos finches.


Everything currently known to serious scientists about how ecological variation is linked to ecological adaptations shows that the epigenetic landscape is linked to the physical landscape of DNA via RNA-directed DNA methylation and RNA-mediated amino acid substitutions that stabilize the organized genomes of species from microbes to man.

See for an accurate representation of biologically-based cause and effect in birds:
http://www.scienc...14001869

JVK
Apr 03, 2015
It makes more sense to classify the birds as a single species of ground finch with ecologically driven variations, Zink says.

http://discoverma...-neutral

Ecological variation is the raw material by which natural selection can drive evolutionary divergence [1–4]. http://rspb.royal...81.short

JVK
Apr 03, 2015
The notion has gained some currency that the only worthwhile biology is molecular biology. All else is "bird watching" or "butterfly collecting." Bird watching and butterfly collecting are occupations manifestly unworthy of serious scientists!" (p. 443)

http://icb.oxford...citation

The biologically uninformed claim:
...the finch populations remain behaviorally and morphologically distinct and, according to Grant, are on their way to becoming separate species. http://discoverma...-neutral

How much longer do these "bird-watchers" think it will take for the conserved molecular mechanisms of RNA-directed DNA methylation and RNA-mediated amino acid substitutions to cause a new species to evolve?

Or, like other pseudoscientists, are they waiting for them to mutate and become different species?

Apr 04, 2015
This was partly because the specimens available to him were not sufficiently labelled as to their island of collection.


This is not quite true. Darwin gave his bird specimens to John Gould (a professional ornithologist) to classify and it was he who suggested the correlation between beaks and islands but Darwin had not labelled his birds properly.

There were, however, three other collections made on the same trip which were labelled by island, that of Capitan of the Beagle Robert Fitzroy and Fitzroy's shipboard servant, Harry Fuller as well as Darwin's servant Syms Covington. They only collected skins but they were properly correlated with Islands.

In the end, by comparing skins with birds, only two of Darwin's Finches could not be correlated with islands.

[See 'Charles Darwin: Voyaging' by Janet Brown; Wikipedia]
http://en.wikiped..._finches

JVK
Apr 04, 2015
This was partly because the specimens available to him were not sufficiently labelled as to their island of collection.


Obviously, that does not matter at all given what has been learned about the conserved molecular mechanisms of biologically-based cause and effect that link Darwin's "conditions of life' to biodiversity without the pseudoscientific nonsense about mutations and natural selection.

Why did you mention it?

Apr 04, 2015
@Vietvet

The question:
Is life without DNA repair possible?
brings over seventy million search return results.

The first few thousand are mostly peer reviewed.
If I flood all threads with peer reviewed links you will ask who will read this?

Your world or world view will not change even if the fundamental driver of evolution changes from mutation to repair.

You simply do not care.

My claim can be refuted by pointing out a single exception.
If you find life without repair by all means post this.


Your role here as vigilante enforcing the integrity of comments and articles is not appreciated. You have been called 'sheriff' That is hint enough.

JVK
Apr 04, 2015
Your world or world view will not change even if the fundamental driver of evolution changes from mutation to repair.


His ridiculous antagonism shows up in every discussion that might otherwise lead to examination of what is currently known about biologically-based cause and effect.

My claim can be refuted by pointing out a single exception.


My model can be supported by everything that's been published by serious scientists during the past two decades.

See the latest: MicroRNA control of protein expression noise http://www.scienc...abstract

Reported as: MicroRNAs silence the noisy genome http://www.scienc...41.short

"...ascribed intrinsic noise reduction to enhanced transcription that presumably compensates for the mRNA degradation (which maintains a given expression level). Recent reports on the "circular" nature of gene expression—namely, that mRNA degradation..."

Apr 04, 2015
@russell: The question if DNA repair is important is unrelated to the question about evolutionary mechanisms. You don't give references on the latter. In fact, your failure is so blatant that at this point I am unsure if you know what a reference is. If you don't, you can ask for clarification here.

Moving on: Part of evolutionary variation is mutation, which is what repair tries to undo. Perhaps you are confusing failure of repair, so the mutation goes through, with mutation?

JVK
Apr 04, 2015
From 2012: http://www.abc.ne...7620.htm
"The concordance of the findings of a scientific study and an ancient myth is a striking example of how traditional ecological knowledge can inform and enhance scientific research."

From 2013: Ecological variation is the raw material by which natural selection can drive evolutionary divergence [1–4].

The differences in amino acid composition among different tissues can lead to large differences in trophic discrimination [38]. http://rspb.royal...81.short

From 2014: "...learning about evolution is not the primary function of the decision, but rather to use it as a building block for students to learn more about their ecology." http://www.educat...olution/

Does anyone remember when theorists stopped touting the pseudoscientific nonsense about mutations and evolution?

Apr 06, 2015
@TLOM

DNA repair is at best semi-conservative.
DNA replication is at best semi-conservative.

Mutations do not 'go through' when repair and replication are semi-conservative.
The repair and replication are viewed as 'successful'.

Saying all successes are semi-conservative is a fancy way to say no repair or replication is perfect.

The prior sequences and sequences after repair or replication remains unchanged at the cost of altered gene expression.

Repair does not "undo" anything.

https://adapaproj...+that%3F

The book has references.
http://yalepress....00085402

Enjoy.

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