James Linzel's List: IB Biology Readings and Resources

• “The biological species concept emphasizes the species as a community of populations, reproductive isolation..., and the  ecological interactions of sympatric populations that do not belong to the same species”
• “The species is the principal unit of evolution. A sound  understanding of the biological nature of species is fundamental to writing about evolution and indeed about almost any aspect  of the philosophy of biology... I define biological species as `groups of interbreeding natural populations that are reproductively  (genetically) isolated from other such groups.' The emphasis of this definition is... on genetic relationship... This new  interpretation of species of organisms emphasizes that biological species are something very different from the natural kinds  of inanimate nature”
• The genetic version of this  perspective is, to a good approximation, the Dobzhansky-Muller model of divergence, in which genes that have been the site  of adaptive fixations within separate populations may also be the site of negative epistatic interactions in species hybrids  and cause inviability or sterility when hybridization occurs
• The most striking commonality to emerge from these studies is that these genes have extraordinarily  rapid rates of adaptive amino acid replacement. This finding makes sense, for if we suppose that some fraction of amino acid  replacements are prone to negatively epistatic interactions when placed in a hybrid background, then those genes that have  the highest rates of amino acid replacement will also tend to be those that cause these types of Dobzhansky-Muller incompatibilities
• The findings that rapid evolution of genes, including that caused by genomic conflict, can lead to the formation of reproductive  barriers notwithstanding, there remains the question of how much gene flow can be tolerated between diverging populations  if speciation is to occur
• Not even populations with many rapidly evolving genes can be expected to become reproductively isolated from other populations  if gene flow rates are high
• In Mayr's world view, new species arise under allopatry, and, after that, as divergence accrues, the geographic ranges of  related species may later come to overlap. In this way, related but divergent species may be sympatric, in contrast to most  closely related species, which are expected to have disjunct, allopatric distributions.
• although the pattern described by Mayr still largely applies, rapidly evolving gamete recognition proteins  play a strong role in reproductive isolation
• This is the apple maggot fly that has diverged into two host races (apple and hawthorne), apparently under geographic sympatry  and aided by the different fruiting times of the two hosts
• Now we learn from Guy  Bush's former student Jeffrey Feder and his colleagues (38) that the sympatric divergence that occurred within U.S. populations may have been facilitated by genetic variation that  came in by means of gene flow from largely separated populations in Mexico.
• he question of sympatric speciation has also been much discussed in the context of the highly speciose cichlid fishes from  the great African lakes: Victoria, Malawi, and Tanganyika
• it is a wonder how hundreds of species  could form within confined bodies of water within <1 million years
• But, unlike animals, and indeed most eukaryotes, prokaryotes have always presented special species-related challenges because  of the absence of regular gene exchange.
• although  LGT generally can obscure older phylogenetic histories, the subset of LGT that leads to homologous recombination is largely  limited to closely related bacteria. This finding supports a view of bacterial species that resembles, in some respects, the  biological species concept

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• A large part of the future of biology depends on interdisciplinary studies that allow easy travel across the three  dimensions
• that all living phenomena  are obedient to the laws of physics and chemistry. The other overarching principle of biology is that all living phenomena  originated and evolved by natural selection

• In addition to being strict anaerobes, ace-togens and methanogens live from H2, us-ing the simplest and arguably most ancient forms of energy metabolism ( 8). Both syn-thesize ATP by reducing CO2 with electrons from H2 to make acetate and methane, re-spectively. They use a chemical mechanism called flavin-based electron bifurcation ( 6) to generate highly reactive ferredoxins—small, ancient iron-sulfur proteins ( 5) that are as central to their energy conservation as is ATP ( 6). The shared backbone of their energy metabolism is the acetyl–coenzyme A pathway, the most primitive CO2-fixing pathway ( 8) and the one typical of sub-surface microbes ( 9). Metabolism in these anaerobes is furthermore replete with reac-tions catalyzed by transition metals such as iron, nickel, molybdenum, or tungsten, another ancient trait
• their main by-product today is adenosine triphosphate (ATP), life’s primary currency of metabolic energy
• before there was oxygen to breathe
• It is conceivable that early life harnessed energy from volcanic pyrite syn-thesis ( 2), zinc sulfide–based photosynthesis ( 3), ultraviolet radiation, or lightning, yet none of these processes powers known mi-crobial life forms.
• suggesting that natural ion gradients in such vents ignited life’s ongoing chemical reaction.
• Ancient anaerobic niches deep in Earth’s crust often contain acetogens (bacteria) and methanogens (archaea), groups that biolo-gists have long thought to be ancient
• In the an-aerobic environments of submarine hydro-thermal vents, geochemically generated H2is the main source of chemical energy

  • Chemiosmotic gradients using protons. 
• Their synthesis is driven by environmental sources of chemical en-ergy such as H2 plus CO2 that are harnessed during conversion to more thermodynami-cally stable compounds such as methane and acetate
• chemiosmotic coupling
• ATPase is as universal among cells as the ribosome and the genetic code and was clearly one of the earliest biological innovations. Indeed, the primordial ATPase could have harnessed geochemically gen-erated gradients at an alkaline hy-drothermal vent
• The energy stored in the ion gradient is then harnessed by an enzyme [an adenos-ine triphosphatase (ATPase)] to phosphory-late ADP.
• Aceto-gens pump while transferring electrons from ferredoxin to nicotinamide adenine dinu-cleotide (NAD+); this energetically downhill (exergonic) reaction is catalyzed by a single protein comple
• Methanogens pump while transferring a methyl group from one cofactor to another at a methyltransferase complex
• Energy-releasing processes that link the two might shed new light on biology’s biggest question
• hydrothermal vents derive from reactions in Earth’s crust and thus contain large amounts of catalytic transition metals
• The process of serpentiniza-tion not only generates a strongly reducing environment; it also makes the effluent alka-line.
• The synthesis of high-energy bonds that underpin substrate-level phosphorylation can be catalyzed by metal ions alone ( 2); it does not require either proteins or mem-branes, whereas chemiosmotic synthesis of ATP requires both
• This indicates that substrate-level phosphorylation came before chemiosmosis ( 10) in early bioenergetic evo-lution and powered the evolution of genes and proteins

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• First, DNA is synthesized from RNA in metabolism, which has long served as an argument that RNA came before DNA in evolution. By the same reasoning, we infer that amino acids came before RNA in evolution, because in metabolism RNA bases are synthesized from amino acids: glycine, aspartate, glutamine, CO₂ and some C₁ units in the case of purines; aspartate, ammonia and CO₂ via carbamoyl phosphate in the case of pyrimidines (figure 2c). Amino acids are thermodynamically favoured over nucleotides and thus more likely to accumulate in larger amounts in a hydrothermal setting anyway [35,36]; similarly in metabolism, some might spill over into RNA-like bases.
• Life is the harnessing of chemical energy in such a way that the energy-harnessing device makes a copy of itself.
• (i) alkaline hydrothermal vents as the far-from-equilibrium setting,  (ii) the Wood–Ljungdahl (acetyl-CoA) pathway as the route that could have underpinned carbon assimilation for these processes,  (iii) biochemical divergence, within the naturally formed inorganic compartments at a hydrothermal mound, of geochemically  confined replicating entities with a complexity below that of free-living prokaryotes, and (iv) acetogenesis and methanogenesis  as the ancestral forms of carbon and energy metabolism in the first free-living ancestors of the eubacteria and archaebacteria,  respectively.
• (i) thioester-dependent  substrate-level phosphorylations, (ii) harnessing of naturally existing proton gradients at the vent–ocean interface via the  ATP synthase, (iii) harnessing of Na⁺ gradients generated by H⁺/Na⁺ antiporters, (iv) flavin-based bifurcation-dependent gradient generation, and finally (v) quinone-based (and Q-cycle-dependent)  proton gradient generation. Of those five transitions, the first four are posited to have taken place at the vent. Ultimately,  all of these bioenergetic processes depend, even today, upon CO₂ reduction with low-potential ferredoxin (Fd), generated either chemosynthetically or photosynthetically, suggesting a reaction  of the type ‘reduced iron → reduced carbon’ at the beginning of bioenergetic evolution.
• However, since their discovery, submarine hydrothermal vents stand out among the possible environments  for life's origin, holding particular promise for understanding the transition from geochemistry to biochemistry [8–12]
• Submarine hydrothermal vents harbour highly reactive chemical environments with far-from-equilibrium conditions, being  rich in gradients of redox, pH and temperature
• he far-from-equilibrium condition is important because it harbours the potential  for exergonic chemical reactions [14]. Concentration is important as a prerequisite for autocatalysis and for self-regulation, defining characteristics of living  systems
• The chemical disequilibrium at vents arises from the contact between their reducing, H₂-containing effluent with CO₂-containing ocean water, which is more oxidize
• Hydrogen is a reducing agent: an electron donor. Given a suitable acceptor, of which there are many [20], hydrogen is a source of energy.
• Serpentinization takes place because most of the suboceanic crust consists of iron–magnesium silicates like olivine, in  which the redox state of the iron is Fe²⁺. Seawater penetrates the ocean floor crust, reaching depths on the order of 3–5 km below the surface. There at high pressure  and temperatures of around 150°C, water oxidizes the Fe²⁺ to Fe³⁺, the water being reduced to H₂ with the oxygen in water being retained in the rock as iron oxides
• The production of H₂ via serpentinization has probably been taking place since there was liquid water on the Earth [22], and it continues today because, relative to the amount of water on the Earth, the amount of Fe²⁺ in the crust is inexhaustible.
• This  is true for the synthesis of carboxylic acids, alcohols and ketones [28,29], amino acids and proteins [34] and total microbial cell mass [35,36].
• in the reaction of H₂ with CO₂, the equilibrium lies on the side of reduced carbon compounds, which is why acetogens can grow from the reaction
• methanogens can grow from the reaction
• For a prokaryote, the main energetic cost in the life process is amino acid and protein synthesis, which  consumes about 75 per cent of the cell's ATP budget, with RNA monomer and polymer synthesis consuming only about 12 per cent  [41].
• Hydrothermal  vents are particularly rich in chemical and thermodynamic similarities to the core energy releasing reactions of modern acetogens  and methanogens [42,43], lineages that over 40 years ago—before the discovery of either hydrothermal vents or archaebacteria—were proposed to be  the most ancient microbes, because they are anaerobic chemoautotrophs that live from the H₂–CO₂ redox couple [44].
• But the chemistry at a Hadean vent–ocean interface would have been slightly different, with abundant Fe²⁺ [30] and far more CO₂ [32,33] in the ocean.
• The walls of these compartments unite two very important properties for early chemical evolution: catalysis  and compartmentation.
• The catalysis was provided by the transition metals and transition metal sulfides themselves of the hydrothermal mound. That  is, the microcompartments have inorganic walls made of essentially the same catalysts that are commonly found in redox-active  enzymes of modern microbes
• an important similarity to modern anaerobic autotrophs, whose enzymes of core carbon and energy pathways are replete  with FeS, FeNiS and MoS (WS) centres, FeS and NiS usually being incorporated into proteins via cysteine residues
• The presence of awaruite in serpentinizing systems  thus clearly indicates that at some point during their lifespan, serpentinizing systems regularly generate extremely reducing  conditions on the order of greater than or equal to 200 mM H₂, which would be conducive to organic synthesis, as Klein & Bach [25] point out.
• However, simulated hydrothermal conditions of 300°C and high pressure readily convert nitrite into NH₃ [63], and under very mild conditions, FeS minerals can reduce N₂ to NH₃ at yields approaching 0.1 per cent [64], whereby native Fe^±0 is also an effective catalyst of N₂ reduction under hydrothermal conditions [65], recalling once again awaruite as an indicator of serpentinization
• The foregoing would provide a mixture of H₂, CO₂ and NH₃ similar to that assumed by Amend et al. [14] for synthesis of chemical constituents of cells, in an environment laden with transition metal catalysts, with abundant  hydrothermal HS^–. That is a starting point for the synthesis of compounds with high-energy bonds
• Equation (3.1) entails the thiol group of coenzyme A (CoASH) rather than CH₃SH, and it is the line reaction of the acetyl-CoA or Wood–Ljungdahl [74,75] pathway of microbial CO₂ fixation. Such favourable energetics led Shock et al. [29, p. 73] to conclude that organisms using the acetyl-CoA pathway (acetogens, methanogens and many sulfate reducers) get ‘a  free lunch that they are paid to eat’. Provided that transition metals in a hydrothermal vent could catalyse similar reactions  as in the laboratory [51], then one would have, in principle, a route for sustained geochemical synthesis of acetyl thioesters (among many other products).  That would constitute a critical/crucial link between geochemistry and biochemistry, because acetyl thioesters (acetyl-CoA)  are the most central compounds in all of metabolism, as biochemical pathway maps will attest; and apart from the Calvin cycle,  which is obviously a late evolutionary invention [76], acetyl-CoA is the direct product of all known CO₂ fixation pathways
• Acetyl thioesters are furthermore the most probable entry point of phosphate into metabolism
• acetyl-CoA is enzymatically cleaved via phosphorolysis to yield acetyl phosphate
• can phosphorylate any number of substrates, including ADP to generate ATP, with a free energy of hydrolysis (ΔG°′) of –31 kJ mol⁻¹.
• A high free energy of hydrolysis of  the acyl phosphate bond and simple phosphorylytic synthesis from thoiesters make acyl phosphates good candidates for the first  universal currency of high-energy bonds [42], the precursors of ATP.
• Amino acids are thermodynamically favoured over nucleotides and thus more likely to accumulate in larger amounts in a hydrothermal  setting anyway [35,36]; similarly in metabolism, some might spill over into RNA-like bases
• Second, the RNA world as it is currently construed in the laboratory, operates with pure mixtures of usually four bases [98]. But, in the beginning there is just no way that base synthesis could have been highly specific. Any RNA world that might  have really existed must have consisted of an ill-defined mixture of bases synthesized spontaneously without the help of either  genes or pure chemicals
• Or, we can just look at the nature of the chemical modifications that are present in the 28 modified bases  common to archaebacteria and eubacteria
• Those modifications might be a chemical imprint—a molecular fossil—of the environment in which tRNA–rRNA interactions (genes  and proteins) arose that is preserved in the chemical structure of modified tRNA and rRNA bases
• But until  we get to things that evolve via variation and selection, all we have are spontaneous reactions under thermodynamic and kinetic  control
• thermodynamics is very much chemistry's deterministic version of natural selection
• But energetics and thermodynamics can  help a lot, because they place rather narrow contraints on which paths chemistry can traverse en route in evolving systems  that ultimately spawn free-living cells.
• In fact, they are often diazotrophic and as such they just live from gases: CO₂, CO, H₂, N₂ and H₂S. At the level of overall chemical similarity, core carbon and energy metabolism in methanogens and acetogens has quite a  lot in common with geochemical processes at alkaline hydrothermal vents [43], and that is probably not coincidence.
• The standard free energy of hydrolysis (ΔG°′) of acetyl phosphate is –43 kJ mol⁻¹, meaning it can phosphorylate ADP to ATP (ΔG°′ –31 kJ mol⁻¹), and by the same token it can drive phosphorylations in intermediary metabolism as well as ATP does
• The jump we just took, to genes and proteins, is a big one, but  all models for the origin of life entail such a step, and ours does too.
• the advent of ATP as the universal energy currency was an important step in  bioenergetic evolution, displacing (we posit) acetyl phosphate
• a protein that is as universal among cells as the code
• Given genes and proteins, the origin of molecular machines such as the ATPase is an admittedly impressive, but not conceptually  challenging, evolutionary step; it is a far less problematic increment than the hurdles that had to be surmounted at the origin  of the ribosome and the code [110,117].
• In an alkaline hydrothermal environment, the ATPase has immediate beneficial function. The naturally preexisting proton gradient  [9] at the interface of approximately pH 10 alkaline effluent (alkaline from serpentinization) with approximately pH 6 ocean  water (slightly acidic by virtue of high CO₂ content) provides a geochemically generated chemiosmotic potential that ‘just’ needs to be tapped, that is, converted into  chemically harnessable energy in the form of high-energy bonds, exactly what rotor–stator-type ATPases do
• The ATPase transduced  a geochemically generated ion gradient into usable chemical energy, and since the energy was free, the means to harness it  as ATP ‘just’ required a suitable protein for the job, a complicated protein [119], but a protein
• One might object that the multi-subunit rotor–stator-type ATPase is too complicated as a starting point
• But the observation from modern microbes to be accounted for, in the evolutionary sense, is that all prokaryotes harbour  the rotor–stator-type ATPase
• hence  it was probably present in the common ancestor of all cells, which in this model was not free-living but rather was confined  to the system of inorganically formed compartments within which it arose
• indicating that  the deepest, most ancient split in the prokaryotic world is that separating eubacteria from archaebacteria
• Many attributes of archaebacteria and eubacteria are so fundamentally different  that, for lack of similar chemical intermediates in the pathway or for lack of subunit composition or sequence similarity,  independent origin of the genes underlying those differences is the simplest explanation
• Such differences include: (i) their  membrane lipids (isoprene ethers versus fatty acid esters) [123], (ii) their cell walls (peptidoglycan versus S-layer) [124], (iii) their DNA maintenance machineries [116,125], (iv) the 31 ribosomal proteins that are present in archaebacteria but missing in eubacteria [126,127] (v) small nucleolar RNAs (homologues found in archaebacteria but not eubacteria) [128], (vi) archaebacterial versus eubacterial-type flagellae [129], (vii) their pathways for haem biosynthesis [130,131], (viii) eubacterial- versus archaebacterial-specific steps in the shikimate pathway [132,133], (ix) a eubacterial-type methylerythrol phosphate isoprene pathway versus an archaebacterial-type mevanolate isoprene pathway  [134], (x) a eubacterial-type fructose-1,6-bisphosphate aldolase and bisphosphatase system versus the archaebacterial bifunctional  aldolase-bisphosphatase [135], (xi) the typical eubacterial Embden–Meyerhoff  (EM) and Entner–Doudoroff  (ED) pathways of central carbohydrate metabolism  versus the modified EM and ED pathways of archaebacteria [136], (xii) differences in cysteine biosynthesis [137], (xiii) different unrelated enzymes initiating riboflavin (and F₄₂₀) biosynthesis [138], and (xiv) in very good agreement with figure 2b, different, unrelated, independently evolved enzymes in core pterin biosynthesis [139], to name a few examples. The pterin biosynthesis example is relevant because the cofactors H₄F, H₄MPT and MoCo, which are central to the eubacterial and archaebacterial manifestations of the Wood–Ljungdahl pathway are pterins  (figure 2d), suggesting that methyl synthesis occurred geochemically (non-enzymatically) for a prolonged period of biochemical evolution.
• First, DNA is synthesized from RNA in metabolism, which has long served as an argument that RNA came before DNA in evolution. By the same reasoning, we infer that amino acids came before RNA in evolution, because in metabolism RNA bases are synthesized from amino acids: glycine, aspartate, glutamine, CO₂ and some C₁ units in the case of purines; aspartate, ammonia and CO₂ via carbamoyl phosphate in the case of pyrimidines (figure 2c). Amino acids are thermodynamically favoured over nucleotides and thus more likely to accumulate in larger amounts in a hydrothermal setting anyway [35,36]; similarly in metabolism, some might spill over into RNA-like bases.
• the idea that chemiosmosis is a very ancient means of energy transduction might seem counterintuitive
• In modern life, all biological energy in the form of ATP comes ultimately from chemiosmotic coupling [151], the process of charge separation from the inside of the cell to the outside, and the harnessing of that electrochemical  gradient via a coupling factor, an ATPase of the rotor–stator-type
• despite these fundamental  differences, and their unfamiliarity to most of us, the bioenergetics of methanogens and acetogens nonetheless feature bona  fide chemiosmotic circuits, with coupling proteins, ion electrochemical gradients over membranes and the ATP synthase
• In simple terms, H₂ is not a strong enough electron donor to reduce CO₂ to the level of a methyl group; the electrons would have to go steeply uphill.
• There is a consistent and robust line of biochemical evolutionary reasoning that FeS  clusters, chemolithoautotrophy and anaerobes tend to reflect antiquity [44,49,160,161]. That line of reasoning is still current [73,162,163] and is reinforced by geochemical data providing evidence for the antiquity of methanogenesis [164].
• Given the foregoing, the continuous reduction of CO₂ to organics could have ultimately driven the emergence of RNA, proteins and genes within the vent pores
• protocells,
• How (and why) did these confined protocells, dependent  on natural pH gradients, begin to generate their own gradients, enabling them ultimately to leave the vents as self-sufficient,  free-living cells?
• Chemiosmotic coupling today requires an ion-tight  membrane, so that ions pumped out return mostly through the ATP synthase, driving ATP synthesis.
• We have argued that the ATPase arose before pumping mechanisms
• But with a free, geochemically provided gradient, membrane permeability could be orders of magnitude greater,  while still allowing net ATP synthesis. All that is required is that protons should pass through the ATP synthase as well  as through the lipid phase (and that they be removed by the alkaline effluent). Any improvements in the ion-tightness of the  membrane would therefore be beneficial, as they would funnel a larger proportion of protons through the ATPase.
• Hence if there  were any genetic component to early membranes, we would predict that coupling would steadily improve, which is to say that  organic membranes would tend to become less permeable to small ions over time. On the face of it, that seems a reasonable  statement, but it leads to an unexpected problem
• Soon, a Donnan equilibrium is established,  in which the electrical charge across the membrane balances the concentration gradient, annulling the proton-motive force.
• In such an open system, the pH gradient is  maintained not by pumping, but by the continuous circulation of hydrothermal fluids and ocean waters, continually juxtaposing  phases in redox and pH disequilibrium
• far from being a problem, leakiness is actually a necessity.
• Transfer of protons into an impermeable  cell will result in a Donnan equilibrium that opposes further transfer unless counterions are also transferred, or unless  the proton can be pumped out again
• The solution is surprisingly simple: a Na⁺/H⁺ antiporter, an otherwise unassuming protein that would hardly be a prime suspect for evolutionary heroics, except in alkaline  hydrothermal vents.
• In a world of genes and proteins, a Na⁺/H⁺ antiporter is far easier to invent than an ATPase. It is a single protein, and an ancient one that is also a component of  both Ech and Complex I
• Electron transfer from ferredoxin to NAD⁺ drives the extrusion of Na⁺ via Rn
• So there is clear proliferation benefit for the invention, by  chance mutation, of proteins that can pump, and that benefit exists at regions of the vent where flux is impaired. This is  likely the initial selective advantage of pumping.

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• Like most other mammals, monkeys that lived 30 million to 60 million years ago had just two opsin genes encoding the photopigment proteins that tune cone photoreceptor cells in the retina to absorb light in a range of wavelengths
• Later, a region of the allele duplicated and inserted, creating a third opsin gene and solidifying the transition from a landscape of blues and either reds or greens (it’s not certain which opsin came first) into the rich color spectrum that humans and many other primates see today.
• just three amino acid substitutions account for the 30 nm difference in peak absorption between the modern-day red and green cones in humans, with each change shifting the photopigment’s color spectrum by 5 nm to 15 nm.¹
• A single nucleotide change can change your color vision.” (See illustration below.) Yet, despite this simplicity, the evolutionary circumstances that allowed our primate ancestors to adopt trichromacy
• In 1983, Nathans and Hogness published the amino acid sequence of bovine rhodopsin, and a year later they published the human rhodopsin sequence.²
• Rhodopsin, expressed in rod photoreceptor cells, enables animals to see in dim light. To understand color vision, Nathans and his colleagues had to track down the three opsins embedded in the cell membranes of the three varieties of cones, which absorb short (blue), medium (green), or long (red) wavelengths of light. Fortunately, despite about a billion years of divergence between them, rhodopsin and the cone opsin genes shared enough sequence homology for the known sequence to serve as a probe for the unknown genes.
• Two of them—the red and the green—reside on the X chromosome and are 96 percent similar in their amino acid sequence
• “It has been thought for some time that a major theme of evolution is duplication followed by divergence.”
• With just one X chromosome, all males are dichromats, but because females carry two Xs, they can carry two different alleles for the X-linked opsin gene, granting such heterozygotes trichromatic vision.⁴
• So how do cone cells, which carry an organism’s full genome and thus the genes for all three opsins, limit the expression of two of them?
• Three amino acid substitutions in the red opsin protein account for the spectral tuning of the green opsin. At position 180, swapping serine for alanine produces a 6 nm shift of the absorption spectrum; tyrosine to phenylalanine at position 277 provides a 9 nm shift; and changing a threonine to an alanine at position 285 confers another 15 nm shift in maximum absorption. Together these three changes produce the 30 nm gap between the maximum absorption of the red and green opsins.
• Importantly, the opsin gene duplication on the X chromosome did not include the enhancer, resulting in a single enhancer being responsible for turning on both genes.
• Both studies suggest the possibility that the primate brain was primed to accept the new stimulus offered by a third cone opsin—no major rewiring required
• Mammalian ancestors presumably lost some of these opsin genes along the evolutionary way
• “Or it could be the brain is primed to figure this out and gives you color vision. I don’t think we know.”
• But demonstrating the existence of such benefits has proven difficult.
• Digging deeper into the data, however, Melin uncovered a subtler effect. “Where we see the difference is in accuracy,” she says. “Trichromats are making way fewer mistakes, but foraging at a more leisurely pace.”

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