Book Thoughts: Pauly’s Controlling Life

In Controlling Life (1987), Philip Pauly explores how scientists have sought to manipulate life for the sake of human benefit through a biographical account of the enigmatic biologist-engineer Jacques Loeb. Pauly’s motivation is to point out that the drive for biotechnology in the 1960s was not borne from a vacuum. The lack of historical context, he argues, is due to historians not integrating such themes into the history of biology; and those that have, he claims, have made “superficial” connections to eugenics (p. 3). The result is that “scientific control of life has recurrently been conceptualized in fictional, even mythical, contexts – in terms of Faust, Frankenstein,” H. G. Wells, and Aldous Huxley” (pp. 3-4). This is surprising, given that “in a general sense, of course, control of life is coextensive with civilization,” as seen in domestication and agriculture (p. 4). The goal of Pauly’s book then is to fix this situation – to provide a “historical context” for this controlling desire – by focusing on the eccentric personality of “biologist-engineer,” Jacques Loeb (1859-1924). (Note, however, that this was published in 1987; the discipline has taken on fully these ideas.)

Today, Jacques Loeb is known for his work on artificial parthenogenesis, in which he initiated the development of sea urchin eggs by immersing them in a salt solution (rather than penetration by sperm). His work was popular and some of the public even took the experiment to mean that one of the sexes would be rendered superfluous.* Or that women should be careful about bathing in salty sea water, lest they wind up like the Virgin Mary! And foreshadowing Huxley’s Brave New World, some speculated that human life would be born in test tubes.

Loeb did not think so extremely, so to what end were his experiments? As Pauly argues, artificial parthenogenesis is better understood within the broader context of Loeb’s work: to control life. After a stint in vertebrate physiology/psychology, Loeb joined the plant physiologist Julius Sachs, extending his mentor’s botanical work on tropisms to the animal kingdom (a tropism is when an organism orients itself towards some stimulus such as light/dark or up/down (gravity); for instance, sunflowers track the sun’s movement across the sky). By manipulating such variables as light, Loeb discovered that he could control the “voluntary movements” of various animals. In one experiment, Loeb found he could cause a caterpillar to starve to death at the tip of the plant, even though food was nearby – in this instance, the “heliotropism” determined the insect’s movement, not its need to nourish itself.

How or why this happened was not of Loeb’s concern. A critical feature of Loeb’s view of science was that the search for causes was a pointless and distracting endeavor. Influenced by (and correspondent with) the anti-realist philosopher/physicist Ernst Mach, Loeb argued that “the determination of such internal conditions and the mechanisms by which they influenced action” were not central to his project (p. 40). Science’s task, according to Mach, was to “cope with the environment” and to provide concepts that allowed humans to predict and control (p. 43). In addition to Mach, Pauly points to the engineer Josef Popper-Lynkeus, who “did not consider material improvement to be the major significance of technology. For him, technology expressed a fundamental element of the human spirit, and could be justified on the same grounds as fine art: its ability to stimulate “aesthetic sensations”” (p. 44). According to Popper-Lynkeus, creations such as the undersea telegraph cables were “important not for their utility but for “purely aesthetic reasons”” (p. 44). Like Mach, Loeb thought speculation regarding causes (whether atoms or behavior) was fruitless, but argued that controlling phenomena was the point of science; like Popper-Lynkeus, Loeb did not necessarily control organisms for any utilitarian purpose, but because he could. Science was not done for the sake of knowledge, but for the sake of control. It was engineering.

Tubularia_indivisa,_hydranth_of_male_colony_(from_Allman,_1872)

A species of Tubularian from Allman, G. J., The Monograph of the Gymnoblastic or Tubularian Hydroids

Following the behavior work, Loeb brought this Machian/Popper-Lynkean engineering perspective to how tropisms influence biological growth and development. For example, by suspending a worm in water, rather than allowing it to grow upon a surface, Loeb wrote,

“I have succeeded in finding animals in which it is possible to produce at desire a head in place of a foot at the aboral end [its “foot” or anchor point], without injuring the vitality of the animal … A Tubularian has by artificial means been so altered that it terminates in a head at both its oral and aboral ends. If, for any reason, it were necessary to create any number of such bioral Tubularians, this demand could be satisfied” (quoted by Pauly, p. 50).

Why do this? Because he could! In a February 26, 1890 letter to Ernst Mach, Loeb wrote:

“The idea is now hovering before me that man himself can act as a creator even in living nature, forming it eventually according to his will. Man can at least succeed in a technology of living substance. Biologists label that the production of monstrosities; railroads, telegraphs, and the rest of the achievements of the technology of inanimate nature are accordingly monstrosities. In any case they are not produced by nature; man has never encountered them” (quoted by Pauly, pp. 50-51).

Not only does Loeb express the desire to control, but as Pauly emphasizes throughout the book, Loeb is not concerned with the distinction between what is natural and what is artificial or monstrous. As with biotechnology, or what Loeb calls the “technology of living substance,” the point is to create entities that do not exist in nature so as to make life do what humans want life to do. Here is Pauly’s excellent summary:

“The core of the Loebian standpoint was the belief that biology could be formulated, not as a natural science, but as an engineering science. More broadly, it meant that nature was fading away. As biologists’ power over organisms increased, their experience with them as “natural” objects declined. And as the extent of possible manipulation and construction expanded, the original organization and normal processes of organisms no longer seemed scientifically privileged; nature was merely one state among an indefinite number of possibilities, and a state that could be scientifically boring. This transformation … was a generalization from biologists’ practice as they saw the extent of artificialization taking place in laboratories. Nature was disappearing, not as a result of argument, but through trivialization; not through disproof, but displacement. The natural became merely one among any results of the activity of biological invention” (p. 199).

For Loeb, whether artificial parthenogenesis or manipulation of tropisms created unnatural organisms or behaviors was irrelevant; what mattered was that it allowed scientists better access to controlling biological phenomena for whatever purpose.

Importantly, Loeb did not hold onto the Machian view forever; in fact, in 1915, Loeb publicly repudiated his former views, perhaps to take on a new debate where Mach must be left behind, that of mechanism vs. vitalism – was the causes of life explainable by physics and chemistry or was there something unique to biological life? This debate is far too expansive to cover here, so I will simply restate Loeb’s apparent reasoning: While Loeb rejects Mach’s stance regarding science’s purpose (Loeb now thinks it is about understanding, not control), he retains a Machian distaste for speculation, much of which is vitalist.** Vitalists held that there was something special in biology that produced life; in contrast, Loeb thought life could (eventually) be explained entirely through physico-chemical mechanisms simply because organisms were physico-chemical machines. To do this, Loeb mostly abandoned biology for physical chemistry; in addition to his ontological reductionism which he had always held, Loeb absorbed it into his theoretical work, reducing life phenomena to those of chemistry. For example, in a debate about “colloids,” which some held to be the substance that made biology unique and was not explainable by the chemistry of the day, Loeb showed that chemistry was indeed up to this task. This style of thought and work continued until his death in 1924.

With all this talk of a “Loebian” or “engineering ideal,” what of its influence? Pauly argues that because of his unstable career and low number of graduate students, Loeb was never able to create a school of thought. However, Pauly claims that his engineering ideal did influence a small number of significant figures: H. J. Muller, J. B. Watson, B. F. Skinner, and Gregory Pincus. Not coincidentally, the geneticist Muller had wanted to be an engineer, but was influenced by the work of Loeb; by 1911, age 21, Muller’s “major scientific goal was to control evolution” by “producing mutations by physico-chemical means;” he eventually did produce thousands of mutations in a single experiment by exposing flies to X-rays. Why?*** By controlling mutations, Muller wrote,

“We would hold the key to unthinkable sources of concentrated energy that would render possible any achievement with inanimate things. Mutation and transmutation [of elements] – the two keystones of our rainbow bridges to power!” (quoted, p. 179).

Muller thought a lot about eugenics, but did not care for how it was practiced at the time: either “positively” (encouraging the genetically superior to reproduce together) or “negatively” (preventing the genetically inferior from breeding, frequently through forced sterilization). Instead, Muller imagined a “creative” eugenics reminiscent of Loeb’s parthenogenesis work, in which scientists separated reproduction from sex; he wrote a book advocating this called Out of the Night, a major influence on Aldous Huxley’s Brave New World. A related real-world development was the invention of oral contraceptives, done by Gregory Pincus, who, like Muller, cited Loeb as an influence.

In psychology, J. B. Watson and B. F. Skinner extended Loebian ideals of controlling behavior to the mind (including humans). “By arguing that control was knowledge, he [Watson] broke down the barriers between the aims of pure psychology and those of behavioral technology. In this sense behaviorism was a model Loebian science, organized around the desire “to get the life phenomena under our control”” (p. 174). Pauly claims that Watson’s Behavorist Manifesto shared a positivistic methodology with Loeb’s early work, emphasizing external/environmental control of organisms; for example, he treats the reflex as a given phenomenon, rather than as something to be analyzed and understood. B. F. Skinner, an English major whose only scientific readings before graduate school happened to be the writings of Jacques Loeb, elaborated upon Watson’s behaviorism; after all, operant conditioning is all about controlling the psychology of organisms. Thus, Loeb managed to influence indirectly a handful of important scientists that contributed especially to the control of life.

Loeb’s indirect influence perhaps remains today, as themes reminiscent of his early work persist. For instance, the (relative) disregard for the natural/artificial distinction is evident in modern experimental biology (though debated). But more importantly, while “Loebism” never took over the biological sciences, important areas of the discipline are dedicated to controlling life, most especially biotechnology, genetic engineering, and experimental evolution. Ironically though, much of this is possible because scientists rejected the anti-metaphysical stance (for lack of better words) of the younger Loeb; instead of avoiding the search for causes, biochemistry and molecular biology have sought out the roots of what makes life function. Modern biotechnology would not work without the extreme reductionism that allowed for the discovery of DNA structure and its replication process. However, Pauly does show that the ideology of biotechnology is not at all new and that biologists over 100 years ago sought the same thing as some modern biologists do: controlling life.

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* Today, it would render males superfluous, but at the time, Loeb thought males were X0 and females XX, meaning that development without sperm would create males, not females.

** This new position is also seen in Loeb’s views on evolution. Early in his life, he avoided the topic due to it being full of speculation not amenable to experiment (such as Weismann’s determinants or Haeckel’s historical program); however, with his move to the United States and the later rise of the acute anti-Semitism/racism of World War I, Loeb “perceived that the evolutionary biology he disliked as being used to support racism, national chauvinism, and militarism. In order to oppose these political positions … it was imperative to develop an authoritative alternative to an evolutionism that was no longer necessarily progressive” (p. 142). For a brief period, Loeb engages the public on these issues.

*** Ironically, Muller received similar criticism as Loeb did from the same figure, T. H. Morgan, who wondered what was the point of these highly artificial organisms. How did they help us understand genetics, evolution, and development?

“Experimental Evolution Amongst Plants” (1895)

Tl;dr: This post features my (thus far) favorite quote that I have found when doing historical work on experimental evolution. In his speech/article, Liberty Hyde Bailey argued that the truth of evolution had already been demonstrated… centuries ago as well as in the present day, not by the academic elite, but by those involved in the cultivation of fruits, vegetables, and flowers. For Bailey, the domestication of plants and animals was a form of experimental evolution.

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The Historical Importance of Modularity

I am currently sitting in on a graduate philosophy of biology seminar and the theme of this semester’s seminar is evo-devo and we recently discussed the concept of modularity. I’m also sitting in on a history of biology course and we have talked a little about the early 19th century French scientist, Georges Cuvier. While attending the seminar, I was delighted to make a historical link between the two! (And oddly enough, one of the works we read in the seminar was a chapter from a book on modularity co-authored by Gunther Wagner which opens with the same link I had made.)

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Ants and Their Castes in the Spencer-Weismann Controversy

Wikipedia: Meat eater ant feeding on honey

Ant (Wikipedia)

Ants are evolutionarily weird and are quickly rising in my favorite organisms list.  The same evolutionary principles apply to ants as they apply to us, of course, but because ants are haplodiploid, live in large colonies, and have a caste system, biologists have to apply the same principles differently – it isn’t exactly intuitive. Ants (and other insects such as bees and termites) are frequently the subjects of hot debate when it comes to kin selection, but their role in evolutionary disputes is over a century old. Charles Darwin discussed them in The Origin of Species, but they were later the center of the controversy between Herbert Spencer and August Weismann.

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Wait. What? Herbert Spencer was a Lamarckian?

While reading Peter J. Bowler’s The Eclipse of Darwinism, I was surprised to find out that the “social Darwinist”* Herbert Spencer was actually more Lamarckian than Darwinian. He apparently expressed Lamarckian views prior to the 1859 publication of The Origin of Species, and while he accepted Darwinian explanations and the theory of natural selection, Spencer believed Lamarckism – defined (here) as the inheritance of acquired characteristics through use/disuse – was the more important of the two theories. In fact, in his article, “The Inadequacy of Natural Selection,” Spencer states quite strongly that “either there has been inheritance of acquired characters, or there has been no evolution” (621).

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“Spandrels” before “spandrels” were cool

In 1979, Stephen Jay Gould and Richard Lewontin famously attacked what they called the “Adaptationist Program.” They accused evolutionary biologists and sociobiologists of concocting “just-so stories” in which scientists would claim a particular trait, an adaptation, was a result of natural selection without rigorously testing their hypotheses. If they did test the claim and it turned out the claim was false, the scientist would create another just-so story, rarely questioning whether the trait was an adaptation or possibly a byproduct or fixed by non-adaptive processes. Most readers are familiar with this argument, so I won’t expand any further.

Upon reading material for my history major paper, I came across some arguments by the biologists T.H. Morgan and William Bateson that seemed oddly familiar…

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How to test for selection (Adaptive Recursion III)

ResearchBlogging.orgBefore my unintended break from blogging, I had started writing about the work by Stolz, Feder, and Velez on bioluminescent color in the Jamaican click beetle, Poryphorus plagiophthalamus (here and here). In this organism are two sets of bioluminescent organs – a dorsal pair and a single ventral organ. Not only can the two sets of organs differ in color within an organism, but – and this is what makes the species special – the colors can be polymorphic within the species. By that I mean within a population, one can find green and yellow-green dorsal organs in addition to yellow-green, yellow, and orange ventral organs. Variation of bioluminescent color within the population is apparently unheard of, even within the rest of the Poryphorus genus. The polymorphism of bioluminescent color provides a simple system for evolutionary and ecological study (as I point out in my first post about the species).

Fig 1: (A) Paired dorsal light organs of P. plagiophthalamus. (B) Allele colors in dorsal organs: green (dGR) and yellow–green (dYG). (C) Ventral light organ of a yellow bioluminescing beetle. (D) Allele colors in ventral organ: green (vYG), yellow (vYE), and orange (vOR). From Stolz et al. (2003).

Instead of outlining the entire series of studies like I had intended, I want to extract two larger themes out of the papers – how biologists test for selection on DNA sequences and how the different color alleles in the beetles arose (and I promise, this is a really cool system of allele origination!).

I ask the first question because the authors employ several tests to detect selection and when writing about these studies for a mini-review in my evolution course, I stumbled in this area. I resolved to figure this out for personal education purposes and because I have yet to find a good source that explains these tests in a readily understandable way, I decided to blog about it. For this reason, if I make any mistakes, please point them out! I am writing about this topic to teach myself something I didn’t learn in any of my classes!

I also want to note that readers probably won’t come out understanding evolution in Jamaican click beetles after reading this post. I look at the selection tests out of order and I don’t discuss in much detail the resulting selective scenario the authors propose. (The post about allele origination will be chock-full of click beetle biology, however!)

The three tests I examine are the QTL sign test, the McDonald-Kreitman test, and substitution rate ratios.

QTL Sign Test

(Apparently) developed by Allen Orr, the QTL sign test helps detect whether selection may or may not have acted upon quantitative traits at the molecular level. QTL means “quantitative trait locus” – basically a gene whose alleles affect the phenotype in a quantifiable way and is not necessarily an on/off system. Additionally, a quantitative trait is frequently affected by multiple loci (or polygenic). A quantitative (and not on/off) trait such as weight is not controlled by a single gene – there is no “gene for weight”; instead, weight is a culmination of multiple genes that happen to act upon weight.

Scientists first pick a quantitative trait to examine based on how strong of a difference there is between two phenotypes, R. After QTL mapping in which the affecting loci/nucleotides are found, the QTLs can be given a plus or minus sign for positive or negative effects, respectively; a higher (plus) or lower (minus) weight, for example. When the distribution of plus/minus loci is determined, a statistical test can be performed to infer the likelihood of that given distribution appearing by chance, or in this case, how likely the difference in phenotypes (R) is to have evolved neutrally (Figure 1; left, shows what a neutral distribution could look like). If the found probability is less than 0.05, the null hypothesis (neutral evolution) can be safely rejected. Selection probably played some role.

Stolz et al. use a QTL sign test to find whether or not diversifying selection is acting on the bioluminescence of the dorsal and ventral organs. Luciferase in the click beetles is a great example of a QTL: the detected mutations do not turn luciferase on or off, but instead shift the produced light’s wavelength by several nanometers up (plus) or down (minus).

A difference between a typical QTL analysis and the analysis performed on click beetles is that we are looking at point mutations within a single gene, rather than multiple loci. Stolz et al. thus call their analysis a QTN test – a quantitative trait nucleotide test – but the same principles of QTL apply: bioluminescent color is affected by multiple mutations, not just a single one, and they each have quantitative effects.

Stolz et al. looked at the divergence between the dGR and vYE alleles, assuming these two alleles to be the ancestral and least-derived states of the loci (for reasons not explained here). The difference between phenotypes (R), wavelength in this case, is 31 nanometers. Nine fixed non-synonymous substitutions contribute to this difference and the nine nucleotides in vYE increase wavelength (and are assigned ‘plus’ status) (Figure 1; right). The probability of finding nine plus mutations and zero minus mutations was 0.039 – low enough to reject the null hypothesis of neutral evolution. This finding provides evidence that selection is acting on bioluminescent color.

Figure 1: On the left is an example of a neutral distribution of plus and minus nucleotides - there is no detectable directional selection. On the right is a recreation of the data from Stolz et al. (2003) with nine plus mutations of varying strengths. The number line only indicates the order of the nucleotides in the gene; it has no implications of genetic distance.

McDonald-Kreitman Test

A well-known way to detect selection at the molecular level is the McDonald-Kreitman (M-K) test. The test compares the ratios of synonymous and non-synonymous fixed differences between species and polymorphic differences within a species. This may sound a bit complicated at first, but it makes sense – let me explain.

A synonymous (s) site is where a base substitution has no effect on the translated codon (hence synonymous; same amino acid = same “word”), and a non-synonymous (n) site is where the translated codon does change. A polymorphic (P) site is one which shows variation within the species whereas a fixed (D) site shows no variation within the species but is different compared to a related species.

This is how the M-K test works to detect selection: under neutral evolution, selection is not acting and thus differences should only be attributable to the mutation rate. Furthermore, because they are only affected by the mutation rate, the ratios of non-synonymous to synonymous differences (n/s) should be equal between fixed (Dn/Ds) and polymorphic (Pn/Ps) categories. Additionally, the ratio between fixed and polymorphic (D/P) sites should be equal between synonymous and non-synonymous categories. Basically, all ratios should divide to 1 (Table 1) and any divergence from 1 indicates selection may be acting. If D > P or n>s, then directional selection is presumed to be acting upon the sequence.

Table 1: An example of neutrality in a McDonald-Kreitman test; all ratios divide to 1.
Fixed (D) Polymorphic (P)
Synonymous (s) 13 4
Non-synonymous (n) 13 4

As with the QTL sign test, the McDonald-Kreitman test used on the beetles is slightly different – instead of testing between species differences, they tested the differences between the ventral and dorsal loci. (These loci have diverged for over a million years and can presumably be treated as “different species.”)

Let us first look at a region of luciferase that does not affect color (non-color region). (Table 2).

Table 2: McDonald-Kreitman test for the non-color region of luciferase.
Fixed (D)
Synonymous (s) 13
Non-synonymous (n) 16
The non-color region of luciferase shows a similar table to Table 1. This 2×2 contingency table has a p-value of 0.845, an indication of neutrality.

The ratios of synonymous/non-synonymous in both fixed and polymorphic columns are either the same or close to being the same (Dn/Ds ≈ Pn/Ps). The “fixed” ratio confirms the site is selectively neutral – the non-synonymous sites are being fixed at the same rate as synonymous sites. Furthermore, Ds/Ps ≈ Dn/Pn.

Now let’s look at the coding region of luciferase (Table 3).

Table 3: McDonald-Kreitman test for the color region of luciferase.
Fixed (D) Polymorphic (P)
Synonymous (s) 1 6
Non-synonymous (n) 16 6
There is an excess in Dn and a deficit of Ds in the color region. P-value = 0.011.

There is an excess of fixed non-synonymous sites which indicates the presence of selection. However, Stolz et al. note that Ds is low compared to the rest of the numbers in the table (and in Table 2) which they claim is “atypical of directional selection” (emphasis mine). They exclude codon bias as a possible explanation and also note that this “paucity” of silent fixations is abnormal within the Poryphorus genus. They conclude that intergenic recombination may have cleared any differences between the two loci (reducing both Ds and Dn) and rapid selection subsequently increased Dn. (Don’t worry; intergenic recombination will make a lot more sense in a later post.)

Thus, much like the QTL sign test, the McDonald-Kreitman test looks for divergence from the neutral model in the distribution of base substitutions, inferring the presence of selection if the divergence is strong enough.

Substitution Rate Ratios

Similar to the M-K test, substitution rate ratios look at the difference between synonymous and non-synonymous substitutions between two sequences, but it doesn’t bother to examine fixed and polymorphic differences. In this way, the test is simpler.

The test comes down to two ratios: the number of synonymous substitutions per synonymous site (dS) and the number of non-synonymous substitutions per non-synonymous site (dN). If dN = dS, then the sequences are undergoing neutral evolution (similar to the reasoning in the M-K test). If dN/dS > 1, positive selection; if dN/dS < 1, purifying selection. (dN/dS is often denoted as ω.)

In the color region of luciferase, dN = 0.0217 and dS = 0.0062 (errors omitted). Thus, dN/dS = 3.49. In the non-color region, dN = 0.0023 and dS = 0.058; dN/dS = 0.040. The two dN/dS ratios were significantly different (P = 0.0013). Because dN/dS in the color region is much higher than 1, positive selection is inferred to be acting. (Stolz et al. make no mention of why the non-color region has such a low dN/dS ratio, however. The value indicates purifying selection is rather strong here, so while the non-color region may not be important in determining bioluminescent color, I would presume it codes for an essential structural component of luciferase.)

Other Indirect Tests

The three tests discussed here by no means exhaust the ways one can test for selection. Not only are there other statistical tests one can employ, but there are other indirect ways of detecting selection in a genetic sequence. For example, a reduction of local nucleotide diversity may indicate a selective sweep. As selection drives an allele towards fixation, selection further removes diversity in the surrounding sequence due to hitchhiking. This pattern was found in the ventral orange allele in the Jamaican click beetle: nucleotide diversity in vOR was 0.00046 and in vYE, vOR’s presumed ancestor, diversity was 0.00129. While this isn’t particularly rigorous, it serves as another piece of evidence that selection is acting upon luciferase in the Jamaican click beetles.

This post serves as a (hopefully) basic overview of how molecular biologists can test for selection on DNA sequences. There are many other tests and there are a host of problems associated with each one that I haven’t even begun to explore. I can never stress enough that I am not an expert in this area – I am only providing my understanding of the material in hopes of being corrected by those who know more than me as a way to teach myself evolutionary concepts and, if correct, hopefully teach others in a similar boat as mine.

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Orr HA (1998). Testing natural selection vs. genetic drift in phenotypic evolution using quantitative trait locus data. Genetics, 149 (4), 2099-104 PMID: 9691061

Stolz U, Velez S, Wood KV, Wood M, & Feder JL (2003). Darwinian natural selection for orange bioluminescent color in a Jamaican click beetle. Proceedings of the National Academy of Sciences of the United States of America, 100 (25), 14955-9 PMID: 14623957

Source I used to understand selection tests: Genetics of Populations by Philip Hedrick (Google Books)

On the Rotatability of Evolutionary Branches, or On Life’s Little Joke, or On Why We Ain’t Special

“It is obvious to common sense that some organisms are higher than others – that a dog is higher than his fleas, or a fish higher than a jellyfish.” – Julian Huxley, in Evolutionary Humanism

It may be common sense, but common sense isn’t always right.

The most rampant misconceptions of how evolution works all coincide with how we humans perceive ourselves. Many believe we are the ultimate goal of evolution, that our existence is inevitable, and that we are superior to all other species – we are perched at the top of the ladder: the Ascent of Man.

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Solving the “adaptive recursion” in Jamaican click beetles (I)

One of evolutionary biology’s old and ongoing problems is demystifying the link between genotypic and phenotypic changes. Scientists frequently know the changes in one of the two categories, but they infrequently know how a single change affects both. One great example we do know is the mutation that causes sickle cell anemia, but such knowledge can be rare, especially for more complex traits. While evo-devo aims to solve this problem, one of the more interesting criticisms of the field is its reliance on model organisms in the laboratory. Model organisms like zebrafish have been deliberately bred to exhibit as little genetic variation as possible – they all develop the same! When discussing evolution through studies of zebrafish, this feature – minimal genetic variation – hinders that very discussion. One has to go out to the field to see how evolution works.

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Of Lobsters, Sticklebacks, and Google Chrome

The following is the last take-home essay for my developmental class. This essay is about the concept of modularity and how it is being used in biology today. It’s fairly basic stuff and if you are reading this blog, you probably know most of it already! I do hope you find the comparison to Google Chrome convincing though.

(This time we were urged to write in a more popular form so the writing is at a bit lower level and we didn’t have to source anything. I guess you can take what I say here with a grain of salt then. :P)

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