The evolution of evolution

By July 26, 2018Science
[This was put together almost a decade ago, initially as a half hour public presentation for the 150th anniversary of the publication of Darwin’s Origin of Species, so could not be exhaustive in its depiction of all those who have dealt with evolution; nor could it be exhaustive with regard to the mechanisms of genetic variation, so please forgive my numerous omissions. In addition, it had to be understandable by non-specialist scientists and educated non-scientists.]

Many people seem to think that the concept of evolution began with Charles Darwin, but it didn’t. It began over two and a half thousand years ago. While many of the ‘ideas’ seem fanciful in retrospect, they all are about change in the biota over time.

Anaximander (c. 610 – c. 546 BC) was a pre-Socratic Greek philosopher, who claimed animals sprang out of the sea long ago. He put forward the idea that humans had to spend part of this transition inside the mouths of big fish to protect themselves from the Earth’s climate until they could come out into the open air and lose their scales1,2. These concepts are laughable today, but they illustrate the beginning of the Greek Miracle, where explaining nature is done without resorting to myth or religion, but with material principles. This is at the very heart of science.

Xenophanes (c. 570 – c. 475 BC) was a disciple of Anaximander, and developed the latter’s theories further. He also observed fossil fish and shells and concluded that the land where they were found had been under water at some time in the past3,4. This is something western civilisation had to re-learn two thousand years later.

Empedocles (c. 490 – c. 430 BC) established the four ultimate elements – earth, air, fire and water. This theory of the four elements became the standard dogma for the next two thousand years; and is something to which we will return. His thesis was that these four elements entered into combinations and gave rise to strange results – heads without necks, arms without shoulders etc. As these fragmentary structures met, there were seen horned heads on human bodies, bodies of oxen with human heads, and so on. But most of these products of natural forces disappeared as suddenly as they arose; only in those rare cases where the parts were suited to each other, did the complex structures last. Thus, the organic universe sprang from spontaneous aggregations of forms which suited each other5,6.

Zhuang Zhou (‘Zhuangzi’ c. 369 – 286 BC), the Chinese philosopher,mentions that life forms have an innate ability to transform and adapt to their surroundings. While he doesn’t give any evidence or provide a mechanism, his ideas about the transformation of life, from simple to more complex forms, hints at evolution7,8. Zhuangzi further mentioned that humans are also subject to this process as they are a part of nature, something that we seem to have to re-learn today, the hard way.

Lucretius (c. 99 – c. 55 BC), the Roman poet and philosopher,in his only surviving work, the epic philosophical poem entitled De Rerum Natura On the Nature of Things, gave a similar story to Empedocles8,9.

Al-Jahiz (776 – c. 868), the Arab philosopher, wrote an encyclopedia (entitled ‘The Book of Animals’) describing over 350 varieties of animal. In this he speculated on the influence of the environment on animals and used this in an attempt to explain the origins of the varieties of human skin colour (he was black). He also speculated on the struggle for existence and the structure of food chains10,11.

Ibn Miskawayh (932 – 1030), the Persian philosopher and historian, wrote that ‘Matter adopted the form of vapour which assumed the shape of water. The next stage of development was mineral life. The highest form of mineral life is coral. It is a stone which has branches like those of a tree. After mineral life develops vegetation. The development of vegetation culminates in a tree which bears the qualities of an animal. This is the date-palm which has male and female genders. The date-palm is therefore considered the highest among the trees and resembles the lowest among animals. Then is born the lowest of animals.’12,13

So, you can see that the concept of evolution, in the sense of ‘change over time’ goes back a long way and has a tradition in several different civilisations

The next person of note who mused on the topic was Pierre-Louis Moreau de Maupertuis  (1698 – 1759), who was a French mathematician, philosopher and man of letters. He produced some important works in biology and wrote the following in his Vénus Physique. “Chance, one would say, produced an innumerable multitude of individuals; a small number found themselves constructed in such a manner that the parts of the animal were able to satisfy its needs; in another infinitely greater number, there was neither fitness nor order: all of these latter have perished. Animals lacking a mouth could not live; others lacking reproductive organs could not perpetuate themselves… The species we see today are but the smallest part of what blind destiny has produced…”14,15 While this anticipates natural selection, it was an incidental part of the work and was not supported by any evidence.

Erasmus Darwin (1731 – 1802) was an English physician, natural philosopher, physiologist, inventor and poet, and significantly, the grandfather of Charles Darwin. His most important scientific work is Zoönomia, from 1796, which contains the following passage:

“Would it be too bold to imagine that all warm-blooded animals have arisen from one living filament, which the great First Cause endued with animality, with the power of acquiring new parts, attended with new propensities, directed by irritations, sensations, volitions and associations, and thus possessing the faculty of continuing to improve by its own inherent activity, and of delivering down these improvements by generation to its posterity”. This, in effect, states that animals develop new traits over their lifetime and pass these on to their offspring16. This is the inheritance of acquired characteristics.

Jean-Baptiste Pierre Antoine de Monet, Chevalier de la Marck (usually simply called Lamarck, 1744 – 1829) was a French soldier, naturalist and academic. His contribution was, above all his predecessors, to present the first truly cohesive theory of evolution. On 11 May 1800, he presented a lecture at the Natural History Museum in Paris in which he first outlined his developing theory. It was explained in detail in his magnum opus Zoological Philosophy which was published in 1809, the same year Darwin was born. In it he stated “Variations in the environment induce changes in the needs, habits and mode of life of living beings….these changes give rise to modifications or developments in their organs and the shape of their parts” and “The law of nature by which new individuals receive all that has been acquired in organisation during the lifetime of their parents is so true, so striking, so much attested by the facts, that there is no observer who has been unable to convince himself of its reality”. As you can see, he was anything but modest. This quote essentially encapsulates the first part of Lamarck’s theory of inheritance of acquired characteristics.

If Lamarck had stopped there, he perhaps would be seen as an esteemed precursor to Darwin, but he didn’t. He was a geological uniformitarian and espoused steady-state non-directional geological processes, but at the same time, he advocated that organisms underwent increasing perfection over time. The incongruity of these two views was not lost on him and to overcome the problem of the simplest of organisms still being present on the planet, he hypothesised that new simple forms arose constantly by spontaneous generation from chemical precursors17,18,19. On top of this, he rejected Lavoisier’s ‘new chemistry’ of chemical elements and clung onto the old earth-air-fire-water quartet of Empedocles.

Charles Robert Darwin (1809 – 1882) was born in Shrewsbury, Shropshire, the fifth of six children of wealthy society doctor and financier Robert Darwin, and Susannah Darwin (née Wedgwood). With his brother Erasmus, he attended the University of Edinburgh to study medicine, but found lectures dull and surgery distressing, and therefore neglected his studies. This, of course, annoyed his father, who sent him to Cambridge, for a Bachelor of Arts degree as the first step towards becoming an Anglican parson.

While at Cambridge, his cousin William Darwin Fox introduced him to the popular craze for beetle collecting, and he also became a close friend of botany professor John Stevens Henslow. Despite such hobbies, in his final examination in January 1831 Darwin did well, coming tenth out of a pass list of 178. After graduation, he joined Adam Sedgwick’s geology course and went mapping with him, in the summer, in Wales. Afterward, he returned home to find a letter from Henslow suggesting he could be a suitable gentleman naturalist and companion for a self-funded place with captain Robert FitzRoy, on HMS Beagle, which was to chart the coastline of South America. His father objected to the planned two-year voyage, regarding it as a waste of time, but was persuaded by his brother-in-law, Josiah Wedgwood, to agree to his son’s participation.

When the Beagle returned on 2 October 1836, Darwin was already a scientific celebrity because in December 1835, Henslow had given selected naturalists a pamphlet compiled from Darwin’s geological letters. In mid-July 1837 Darwin started his “B” notebook on Transmutation of Species, and on page 36 wrote “I think” above the first ever diagram of an evolutionary tree. By January 1839, Darwin had the framework of his theory of natural selection as his “prime hobby”. For more than a decade this work was in the background to his main occupation, which was the publication of the scientific results of the Beagle voyage

By early 1842, Darwin had an outline of his theory, and by July of 1844 he had expanded his “sketch” into a 230-page “Essay”, to be expanded with his research results if he died prematurely. In 1847, Joseph Hooker read the “Essay” and sent notes that provided Darwin with the calm critical feedback that he needed. After digressing into other topics of investigation, most notably barnacles, Darwin returned to his theory in 1854.

Darwin’s book was half written when, on 18 June 1858, he received a paper from Alfred Russell Wallace describing natural selection. Shocked, Darwin sent it on to Charles Lyell, as Wallace had requested, and, though Wallace had not asked for publication, Darwin suggested he would send it to any journal that Wallace chose. Darwin’s family was in a panic, as children in the village were dying of scarlet fever, and he put matters in the hands of Lyell and Hooker. They decided on a joint presentation at the Linnaean Society, and on 1 July read the paper ‘On the Tendency of Species to form Varieties; and on the Perpetuation of Varieties and Species by Natural Means of Selection’. Darwin’s baby son had died of scarlet fever three days earlier and he was too distraught to attend the meeting.

Darwin’s book, On the Origin of Species by Means of Natural Selection, or The Preservation of Favoured Races in the Struggle for Life, proved unexpectedly popular, with the entire stock of 1,250 copies oversubscribed when it went on sale on 24 November 185920,21,22. In it, Darwin set out “one long argument” of detailed observations, inferences and consideration of anticipated objections. His only allusion to human evolution was the understatement that “light will be thrown on the origin of man and his history”. His theory is simply stated in the introduction:

“As many more individuals of each species are born than can possibly survive; and as, consequently, there is a frequently recurring struggle for existence, it follows that any being, if it vary however slightly in any manner profitable to itself, under the complex and sometimes varying conditions of life, will have a better chance of surviving, and thus be naturally selected. From the strong principle of inheritance, any selected variety will tend to propagate its new and modified form.”23

Gregor Johann Mendel (1822 – 1884) was an Austrian Augustinian priest and scientist. Between 1856 and 1863 Mendel cultivated and tested some 29,000 pea plants and showed that the inheritance of traits was discrete and followed particular mathematical relationships, which were later named after him (‘Mendelian genetics’). When Mendel’s paper was published in 1866 in the obscure Proceedings of the Natural History Society of Brünn, it had little impact and was cited about three times over the next thirty-five years. His paper was criticised at the time, but is now considered a seminal work. It was not until much later that the importance of his ideas was realised. In 1900, his work was rediscovered by Hugo de Vries and Carl Correns. Mendel’s results were quickly replicated, and genetic linkages quickly worked out. It had immediate impact and became accepted rapidly24,25,26.

The modern evolutionary synthesisis a union of ideas from several biological specialties and forms an overarching account of evolution. This synthesis has been generally accepted by most working biologists. It was produced between 1936 and 1947, and the development of population genetics (1918–1932) by Sewall Wright, J.B.S. Haldane and R.A. Fisher provided the stimulus. This showed that Mendelian genetics was consistent with natural selection. The synthesis is still, to a large extent, the current paradigm in evolutionary biology. Julian Huxley invented the term, when he produced his book, Evolution: The Modern Synthesis (1942)27.

Deoxyribonucleic acid (DNA) was first isolated as a compound from pus in surgical bandages in 1869 by the Swiss chemist Friedrich Miescher, only three years after Mendel’s work was published. In 1928, Frederick Griffith discovered that traits of the “smooth” form of the Pneumococcus bacterium could be transferred to the “rough” form by mixing killed “smooth” bacteria with the live “rough” form. This indicated that DNA carried genetic information. DNA’s role in heredity was confirmed in 1952, when Alfred Hershey and Martha Chase, in their famous experiment, showed that DNA is the genetic material of the T2 bacteriophage (a virus which infects bacteria). The following year James Watson and Francis Crick published their double helix structure for the DNA molecule, based on X-Ray diffraction images taken, and crystallographic parameters worked out by Rosalind Franklin.

Evolution is defined as the change in the properties of populations of organisms that transcend the lifetime of a single individual and there are two major mechanisms which drive it. These are genetic drift and natural selection. Genetic drift is a multifarious process which produces changes in the frequency of traits in a population, while Natural Selection is Darwin’s process causing heritable traits that are beneficial for survival and hence reproduction to become more common in a population28,29.

While natural selection directs evolution, genetic drift supplies the raw material. It takes many different forms, from simple transcription errors (mutations) of one letter (e.g. G for A; Guanine for Adenine), to the duplication of entire genes, up to the duplication of entire genomes (polyploidy). Add to this the occurrence of horizontal gene transfer and endosymbiosis and you get more than enough raw material upon which natural selection can work30,31.

Endosymbiosis is the merging of two organisms to form a single new organism. It sounds hard to believe, but it has happened before and gave rise to all the multicelled organisms on the planet – including all plants and animals. Chloroplasts undertake photosynthesis and Mitochondria generate most of the cell’s supply of Adenosine Triphosphate (ATP) which is a source of chemical energy. In 1883, Andreas Schimper observed that chloroplast subdivision was like that of free living Cyanobacteria (blue-green ‘algae’), and he suggested that green plants (cells of which contain chloroplasts) had arisen from a symbiotic union of two organisms.

Subsequently, it has been found that Mitochondria have their own DNA, which differs from that of the cell nucleus and is similar to that in the Proteobacteria. Similarly, Chloroplasts also have their own DNA, and that is similar to the DNA of Cyanobacteria. These organelles also have innermost surrounding walls which are most like bacterial membranes. In addition, their internal structure and biochemistry are similar to bacteria. It seems clear that these organelles were bacteria which have been incorporated in the cells symbiotically.

Lateral (or Horizontal) gene transfer is any process in which an organism incorporates genetic material from another organism without being the offspring of that organism. There is a growing awareness that horizontal gene transfer is a very significant phenomenon, and amongst single-celled organisms it is perhaps the dominant form of genetic transfer. It was first noticed in Japan in 1959 with the transfer of antibiotic resistance between different species of bacteria. It occurs in bacteria by cell-to-cell contact or by viral infection. There is also some evidence that Mitochondria and Chloroplasts have transferred some genetic material to the nuclear DNA of the eukaryotic cell.32,33

Polyploidy occurs in cells and organisms when there are more than two homologous sets of chromosomes. Many organisms are normally diploid meaning they have only two sets of chromosomes – one set inherited from each parent. Polyploidy is the duplication of the entire set of chromosomes within an organism. It may be due to abnormal cell division and occurs in some animals, such as goldfish, salmon and salamanders, but is especially common among ferns and flowering plants, including both wild and cultivated species. Polyploidy is known to have resulted in many new species.

Examples of polyploidy in animals are more common in the ‘lower’ forms such as flatworms, leeches and brine shrimp. Polyploid animals are often sterile, so they often reproduce by parthenogenesis (i.e. without fertilisation by a male). Polyploidy is pervasive in plants and some estimates suggest that 30-80% of living plant species are polyploid, and many lineages show evidence of ancient polyploidy in their genomes. Huge explosions in flowering plant diversity appear to have coincided with the timing of ancient genome duplications in many groups.34,35

Gene duplication is any duplication of a region of DNA that contains a gene; it may occur as an error in homologous recombination. Duplications can be, and often are, marginally or severely detrimental. For instance, duplications of oncogenes are a common cause of many types of cancer. This is the case with the P70-S6 Kinase 1 gene, duplication of which leads to breast cancer. Despite these commonly being detrimental, they are not always so, and are considered to play a major role in speciation.36

Finally, I bumped into an interesting fact while researching this article. Charles Darwin’s last publication was written just two weeks before he died and was on a minute bivalve (a clam) which was attached to the leg of a water beetle. The specimen was sent to him by amateur naturalist, Walter Drawbridge Crick, whose grandson, Francis Crick, was one of the discoverers of the structure of DNA, the molecule that evolves.37

As Darwin said in his book: “There is grandeur in this view of life, with its several powers, having been originally breathed into a few forms or into one; and that, whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been, and are being, evolved.”23

It is an unalloyed pleasure to study them.



One Comment

  • Jim says:

    This is a really good summary of the history of the concept of evolution. It is something to which all students, particularly biologists and geologists, should be exposed.

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