Archive for August, 2009
Charles Robert Darwin was the son of Robert and Susannah Darwin. Darwin was born at the grand family estate known as in the beautiful “town of flowers,” Shrewsbury, England. “The Mount” was built by Darwin’s father in 1797 on two and a half acres, now called the “Darwin Gardens.”
Things were run efficiently and orderly at The Mount. Susannah Darwin maintained a “perennial garden diary” to record the details of flowerings and fruiting in the kitchen garden in their pleasure gardens and glasshouses. Darwin was the fifth of six children: three older sisters Marianne, Caroline, and Susanne; one younger sister, Emily Catherine; and an older brother, Erasmus.
As a young child, Darwin was given the nickname of “Babba,” taken from his middle name Robert. As a young teenager, his brother Erasmus just called him “Bobby.” The Darwin home was loving, caring, and cultured. Susannah Darwin skillfully used family teaching moments. When Darwin brought a flower to her, he remembers her saying, “by looking at the inside of the blossom, the name of the plant [can] be discovered;” a lifetime lesson for a budding naturalist.
The fact that Charles Darwin originated the concept of natural selection is a popluar notion. However, evolutionary concepts long predated The Origin of Species. In the Historical Sketch section of the sixth edition, even Darwin discusses the contributions of forty-four authors that had previously written on the subject of evolution, including Aristotle.
Darwin recognized that Aristotle’s concepts were compatible with natural selection. On the evolution of teeth, in The Origin of Species, Darwin wrote,
“We here see the principle of natural selection shadowed forth, but how little Aristotle fully comprehended the principle, is shown by his remarks on the formation of the teeth.”
Even though Darwin did not think Aristotle ”fully comprehended” natural selection, what can be “fully comprehended” today is that the concept of natural selection pre-dated Darwin.
In the eighth essay in Science‘s series in honor of the Year of Darwin, Carl Zimmer describes one of the most critical transitions in the history of life: the origin of cells with a nucleus, which proportedly gave rise to every multicellular form of life.
The question is—what is the mechansim that leading to the inclusion of a nucleus in some types of cells while other cells have continued without a nucleus? Cells without a nucleus are known as prokaryotic cells containing a nucleus are known as eukaryotic cells.
A eukaryote is an organism whose contain complex structures enclosed within membranes. Almost all species of large organisms are eukaryotes, including animals, plants and fungi, although most species of eukaryotic protists are microorganisms. The defining membrane-bound structure that sets eukaryotic cells apart from cells is the nucleus. The presence of a nucleus gives eukaryotes their name, which comes from the Greek ευ (eu, “good”, “noble” & “true”) and κάρυον (karyon, “nut” & “kernal”).
While the mechanism how a prokaryotic cell ever evolved into a eukaryotic cell remains a mystery, Carl Zimmer is quick to point out that –
“The fossil record doesn’t tell us much: The earliest fossils that have been proposed to be eukaryotes are only about 2 billion years old, and paleontologists have not yet discovered any transitional forms.”
Darwin had noted the same problem in The Origin of Species –
“Although geological research has undoubtedly revealed the former existence of many links, bringing numerous forms of life much closer together, it does not yield the infinitely many fine gradations between past and present species required on the theory, and this is the most obvious of the many objections which may be urged against it.”
Without physical evidence, the mechanism for this critical evolutionary step remains unresolved and spectulative after 150 years.
Charles Darwin’s book On the Origin of Species by Means of Natural Selection, or the Preservation of Favoured Races in the Struggle for Life contained his first thoughts on evolution. Now, 150 years later, computer scientist Greg McInerny is turning the idea on its head, drawing diagrams showing the “evolution” of the book as new editions were published. In the editing process, certain sections became “extinct,” that is, did not make it to the next edition. Other, stronger sections avoided the editor’s chopping block to make it into the final sixth edition—a kind of survival of the sentences—and in some cases, entirely new sections of text were added.
Together with London-based visual artist Stefanie Posavec, McInerny has devised the (En)tangled Word Bank, which shows the construction and evolution of the book. In some cases, the editions varied quite a bit, says McInerny, who is based at Microsoft Research in Cambridge in the United Kingdom. “For the second edition, Charles Darwin wanted a more popular and available version,” he says, so Darwin inserted references to a creator who may have been behind the initial creation of life. In the sixth edition, he added a whole new chapter discussing the support and criticism that had surrounded the book.
This diagram represents the fifth edition. In it, the rim consists of four layers. The outer ring represents sentences; the next ring in signifies paragraphs, then subchapters and chapters follow. The central branching design represents the same divisions, with chapters at the base and sentences at the tips. The green “leaflets” show sentences that have “survived” multiple editions, and orange “leaflets” represent those that are “dying” and will be absent from the next edition. The darker the green or orange, the longer that sentence has survived through multiple editions.
In the same way that Issac Newton discovered the laws of gravity, Charles Dawin embarked on a mission to discover the natural laws of evolution. A central question is – why did Darwin change and retract by up to 30% between editions? Was it because, unlike Newton, Darwin abandoned use of the scientific method?
On the Beagle voyage, Darwin recorded events in a series of notebooks. Darwin was on the Galapagos Islands from September 16 through October 20, 1835 and recorded these events in a red field notebook now entitled EH1.17 on pages 18B through 50B. Darwin’s notebooks are available on-line at http://darwin-online.org.uk/content/.
The data Darwin documented on the finches in the Galapagos Islands is remarkable in that Darwin refers to “beaks” only once on page 34B (see illustration, line 5) and to “finches” only once on page 43B –
“Small Finc[h] picking from same piece after alights on back”
Not only will the notebook not win a prize for scientific excellence for studying finch beaks, neither will Darwin’s collection of finches from the different islands because the birds from the different islands were mixed together. Darwin never documented any sequential change in beak sizes in the birds collected from the different islands, and acknowledged in his autobiography -
“Unfortunately most of the specimens of the finch tribe were mingled together.”
The current whereabouts of Darwin’s EH1.17 notebook is unknown. The notebook was part of the Darwin Collection at Down House and was microfilmed by Cambridge University Library (and sold by Micromethods) in 1969. The notebook has since been missing and was presumably stolen around 1983, or shortly before, and is now registered as stolen property.
While further investigation of the notebook is no longer possible, Darwin’s evidence for the evolution of the finch beak was simply a re-construction based on the emerging theory of evolution by John Gould back in England long after Darwin set-sail from the Galapagos Island in October 1835.
Now, reference to Darwin’s finches should be for historical purposes, and not as evidence for evolution.
“I can see no difficulty in natural selection preserving and continually accumulating variations.”
“An extraordinary amount of modification implies an unusually large and long continued amount of variability, which has continually been accumulated by natural selection for the benefit of the species.”
As natural selection acts continuously, the process is to continus without limits. Darwin explains –
“What limit can be put to this power, acting during long ages and rigidly scrutinising the whole constitution, structure, and habits of each creature, favouring the good and rejecting the bad? I can see no limit to this power, in slowly and beautifully adapting each form to the most complex relations of life.”
Contrary to Darwin’s premise on the continuous action of natural selection without limits, however in an article in the journal Evolution,* the North American freshwater fish Centrarchidae diversity has been found to be constrained.
“The decline in fitness with increasing distance from an adaptive peak can constrain morphological divergence between sister lineages… These findings indicate that piscivory has curtailed the diversification of feeding morphology in the centrarchids”
Evidence from this freshwater fish fails to demonstrate that natural selection acts continuously without limits as hypothesized by Darwin.
* Evolution 63, 1557 (2009)
“No other work of mine was begun is so deductive a spirit as this; for the whole theory was thought out on the west coast of S. America before I had seen a true coral reef.”
Darwin’s theory was “thought out”—even before Darwin had seen the evidence. This is Darwin’s “I Think” approach. Darwin was caught swinging on the pendulum between the scientific method and logic, a popular trend in certain nineteenth century circles.
At the time, use of inductive reasoning was being challenged by the popular British philosopher – John Stuart Mill. Mill promoted the use of deductive reasoning over the scientific method. In ascribing to Aristotelian logic, Darwin argues –
“How odd it is that anyone should not see that all observations must be for or against some view if it is to be of any service!”
Darwin continues –
“In fact the a priori reasoning is so entirely satisfactory to me that if the facts won’t fit, why so much the worse for the facts, in my feeling.”
Ironically, the facts were irrelevant to Darwin. The major problem with deductive reasoning is that the conclusions can be misleading, inconclusive, and even erroneous. Darwin even concedes in The Origin of Species –
“For I am well aware that scarcely a single point (evidence) is discussed in this volume on which facts cannot be adduced, often apparently leading to conclusions (hypothesis) directly opposite to those at which I have arrived.”
Darwin did not use the scientific method, a fact he acknowledged. Two years before the publication of The Origin of Species, in writing to a friend, Darwin succinctly states –
Newton applied the scientifc method. Discovery of the natural laws of gravity and motion by Newton over the centuries have been steadfast and practical. By contrast, in abandoning the scientific method with speculations, Darwin developed a theory that continues to be widely contested.
Do you think Darwin would have developed a different theory using the scientific method?