Optimality
Many biomechanics have been honed to a peak of perfection, whether it be bacteria homing in on a food source via Brownian motion or a shark swimming straight to its prey by measuring electrical micro-fluxes that vary by a mere millionth of a volt.
Dandelions
Wind-dispersed plants evolved ingenious ways to lift their seeds. ~ Japanese biologist Naomi Nakayama et al
The flower of a dandelion turns into a mass of seeds known as a dandelion clock. Each seed is suspended from a parachute-like stalk which is easily released by a puff of wind.
The parachute is a bunch of bristles called a pappus. Each pappus carries ~100 filaments, each filament attached to a central point. The pappus provides aerodynamic drag, slowing the descent of each seed. A seed aloft may be wafted kilometers from its origin.
As a pappus falls air flows between the bristles to create a low-pressure vortex. This vortex travels above the pappus yet not attached to it: an invisible but faithful familiar that generates lift and prolongs the seed’s descent.
The key to sustaining lift lies not in the pappus bristles, but in the spaces between them. The bristles together occupy just under 10% of the pappus’s area and yet create 4 times the drag that would be generated by a solid disc of the same radius. Air currents entrained by each bristle interact with pockets of air held by its neighbors, creating maximal drag for minimal expenditure of mass. A pappus’s porosity – the air that it lets pass – determines the shape and dynamics of the low-pressure vortex which keeps a parachute aloft.
Only a precise combination of size, mass, shape, and pappus porosity could generate an optimal vortex ring. As air is appreciably viscous at the scale in which the pappus operates, size is significant. The tiniest insects do not fly with solid wings but swim through the air using paddles. The dandelion parachute is as effective an aerofoil as those in larger seeds that disperse from taller plants, such as the winged seeds of the maple.
Manta Rays
Manta rays glide through the ocean with their mouths open, filter feeding copious quantities of zooplankton. Parallel lobes in their mouths with tiny gaps between them let mantas eat plankton while releasing the seawater.
Water entering a manta mouth flows between the cartilaginous lobes, forming vortices before swooshing out. Instead of getting sucked into these vortices, plankton ricochet off the lobes, back toward the manta’s esophagus to be swallowed. The biological implementation is ideal. Because incoming particles are pushed away from the lobes via fluid dynamics, these filters remain clean and manta rays can continuously feed.
If there’s no clogging, they don’t have to shut their mouth and try to clean off all these little particles. ~ American marine zoologist Misty Paig-Tran
Deep-Sea Fish Sight
This is unheard of in vertebrate vision. ~ Finnish sensory biologist Kristian Donner
As an energy efficiency, crickets and cave fish lost their sight generations after their forebears moved into pitch-black caverns. Deep-sea fish took a different tack.
The last glimmer of sunlight is gone at 1,000 meters. Below that are faint flashes of bioluminescence from bacteria, shrimp, octopi, and fish. With the opportunity to communicate and hunt, at least 3 different branches of deep-sea fish independently evolved elaborate arrays of opsins that pick up the specific spectra that ambiently appear, affording color vision through ingenious receptor cell design and unique sensory processing.
Rod opsin photopigments are tuned to different wavelengths of light, allowing color vision in the dark. ~ Czech evolutionary zoologist Zuzana Musilova et al
Cells
Cells are in many ways optimized for processing materials and interacting with the environment; so too many organisms in their construction and operation.
Through exquisite adaptation, microbes perfected metabolism to near the optimality afforded by physical chemistry, with the slight trade-off of being able to adjust to alternative nutritional conditions. This efficiency goes a long way in explaining the diversity, versatility, and staying power of the littlest life. In shedding all inessentials while wisely retaining contingency tools, viruses took economy to an extreme.
In a chemically chaotic environment, an E. coli bacterium feels its way to a food source using surface receptors fore and aft, relying upon a mental heuristic with a reliability in decision-making so fine that it couldn’t perform much better if it considered every single molecule in the neighborhood.
Optimality also abounds in eukaryotic cells. The ribosome, for instance, has maximal self-production efficiency, both in the number of proteins and their composition. Ideally, ribosomal proteins should be ~3 times smaller than an average cellular protein, and they should all be roughly similar in size – just as they are.
Because cells can make ribosomal RNA much faster than proteins, the more RNA that a ribosome has, the more rapidly a ribosome may be produced. Ribosomes are stuffed with as much RNA as possible to maximize the rate at which more ribosomes may be made.
Mitochondria – the power plants within cells – are about as efficient as they can be in producing energy. Inefficiencies are attributed solely to the limits of chemical reactions between the various elements employed.
The number of mitochondria within a cell are also optimized. The more mitochondria, the greater the rate of ATP production, and thereby the faster the response to meet physiological needs. But there are energy and material costs to having excess mitochondria, so their production is tightly regulated.
The nucleus manages 99.75% of the DNA found within a eukaryotic cell. The mitochondria have the other 0.25%. In evolutionary time, mitochondria kept most of the DNA needed for their operation, while relinquishing the inessential to the nucleus. This is a most efficient distribution, as are the management practices of these organelles in employing their DNA.
The mitochondria organelle contains a small chromosome with only 37 genes, but these genes are absolutely essential for metabolism. In order for ATP to be produced properly in a cell, a few hundred other genes encoded in the nucleus must interact directly with the 37 mitochondrial genes. ~ American evolutionary geneticist Felipe Barreto
Photosynthesis
Photosynthesis is an efficient process, albeit not in absolute terms of converting available sunlight into usable chemical energy. The different photosynthesis pathways illustrate that ecological trade-offs define what optimality really means.
There are 3 metabolic pathways for carbon fixation in photosynthesis: C3, C4, and CAM. The C3 pathway consumes 18 ATP molecules to synthesize 1 glucose molecule, whereas the later-evolved C4 pathway requires 20 ATP. Despite lower ATP efficiency, C4 is an evolutionary advancement, adapted to locales with high levels of light, where the reduced ATP efficiency is more than offset by soaking up more light. The ability of C4 plants to thrive despite a restricted water supply maximizes the ability to use available light. C3 plants cannot tolerate the heat or aridity that C4 plants can. Whereas C3 is well-suited for cool, wet environments, C4 plants do well in hot, sunny climes.
C4 independently arose at least 62 times in 18 different plant families. Many evolutionary pathways were available, but these many distinct plants converged to the same chemical reaction series 7–6 million years ago, all adapting to a more arid climate.
CAM ATP usage is comparable to C4, but the CAM pathway is further optimized for minimal water usage, allowing CAM plants to live in scorching, dry environments. Like C4, CAM convergently evolved many times in the over 40 plant families which employ it. ~7% of plant species use CAM, including ancient ones which updated their photosynthetic technique.
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Convergent evolution is often indicative of adaptation toward optimal solutions given certain trade-offs, whether at the quantum, molecular, or ambient scale (or a combination thereof).
Cell differentiation, such as embryonic development, unfolds with a precision that is practically perfect. The intricate interplay of complexity in the growth process of any organism, egenetically steered while incorporating environmental inputs, unfolds with atomic precision.
Cell competition – the sensing and elimination of less fit ‘loser’ cells by neighbouring ‘winner’ cells – optimizes tissue and organ development. A tissue dynamically adjusts cell competition strategies to preserve fitness as its architectural complexity increases during morphogenesis. ~ American cytologist Elaine Fuchs et al
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Mental processing tolerates considerable noise in determining a signal, using a canny averaging of signals to determine what’s going on. Sense receptors are redundant for that purpose, as well as being fault-tolerant to partial failure, which happens regularly with interim spot downtime during receptor cell replacement.
Olfaction works by granule cells molecularly locking onto smelly molecules, requiring frequent granule cell replacement. Numerous olfactory sense cells connect to a single periglomerular neuron. Smell works by detecting vibrational wavefronts emanating from the captured molecules, not via molecular structure per se. This technique yields superior reception to the possible alternate of molecular lock-and-key.
Moving Through Fluids
Physics sets effective constraints for biological evolution. The physics of fluid flow determine the operational range of swimming. ~ German biophysicists Johannes Baumgart & Benjamin Friedrich
Whether fish, turtle, bird, or cetacean, the selfsame efficiencies of animals in swimming can be characterized by a simple scaling law with 2 limits. The 1st limit is encountered at slower speeds, where the bulk of fluid resistance comes from skin friction, as water wants to adhere to an animal’s body. At faster speeds the 2nd limit appears, as resistance largely comes from pressure in front of and around the body.
Animal evolutionary biomechanics address these limits.
All swimming animals essentially reach the hydrodynamic limits of performance. There are general principles at work here. ~ Indian scientist Lakshminarayanan Mahadevan
Swimming and flying animals are optimally adapted for cruising through their environments, producing thrust via quite different propulsors: wings for flying and, in fish, caudal fins for swimming.
Since drag can never be completely eliminated, perfect efficiency is not possible. But animals have evolved to a narrow range of highly efficient parameters. ~ English naturalist Chris Packham
Turning
The act of turning while simultaneously moving forward creates a centrifugal force that is directed away from the centre of curvature of the turn. Newtonian mechanics dictates that the magnitude of the centrifugal force is proportional to (a) the curvature (the reciprocal of the radius of the turn), and (b) the square of the speed. Hence, the sharper the turn, and the higher the speed, the greater the danger of losing control. ~ Indian-born Australian biologists Mandyam Srinivasan & Mandiyam Mahadeeswara
The craft of flying presents many challenges, including takeoffs, turns, and landing. Turning during flight is especially tricky: requiring exquisite coordination to ensure that the resulting centrifugal force does not disrupt the intended turning trajectory. The centrifugal force depends upon the flight speed and turn curvature. To limit centrifugal force to a manageable level and prevent sideslips, sharp turns necessitate lower speeds.
Bees, bats, and birds all naturally optimize their flight to achieve the fastest possible turns given the mechanics imposed by gravity. Bats and hummingbirds are especially impressive in their pinpoint turns during flight. How intention translates into physical movement is itself astonishing, let alone maximizing performance from a physics standpoint.
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There is a larger-scale optimality in life which can only be appreciated at the ecosystem scale. With rare exception, the skill of predators is never quite enough to wipe out their prey. This apparent suboptimality is ideal in maintaining a delicate balance that sustains all parties involved, and so avoids the self-organized criticality of extinction. There have been exceptions, which makes the history of life unpredictably fascinating. (The self-engineered mass extinction event mankind is presently engaged in at full tilt illustrates the fantastic idiocy of a creature that arrogantly considers itself supreme. For a connoisseur of melodrama, the irony is delicious.)
Many traits are evolved refinements from baser originations. The refinement process is not necessarily toward biodynamic perfection. It may instead be toward something sensible but suboptimal, as trade-offs are involved. Evolution driven by perception is exemplary.
Evolution by Perception
As life is an ecological exercise evolution often proceeds upon perception. This creates opportunities for deception.
Perception is often aimed at satisfying desire. When choices are available, individual preference plays a part.
In that multiple preferences are often entwined, Nature may produce tantalizing approximations which are not wholly satisfactory. The craft of evolutionary enticement is often an exercise in compromise.
Organisms perceive stimuli relatively rather than quantitatively. This leads to simple preferences when a single factor is involved. But a confluence of factors commonly leads to compromise based upon prioritized preference.
Nectar
Bats that pollinate plants want lots of sugary nectar. The plants they visit give them limited quantities of watery nectars: 20% sugar content versus the 60% preferred.
The ultimate reason is an overabundance of bats. There is a fierce competition for a limited amount of nectar.
The proximate cause is bats’ own preference in trade-off. A bat prefers more nectar even if it is less sugary, so that is what plants deliver. And, following the inexorable law of show business, a plant leaves them wanting for more. Thus pollination proceeds.
Multiple dimensions can interact and cause nonrational decisions, where you are given 2 options and you actually take the lesser one. ~ American neurobiologist York Winter
Iridescence
When mating season comes around, the heads of male Iberian emerald lizards turn turquoise. This honest signal of health seems a risky adaptation, as the vibrant hue might attract birds of prey from above as well as willing females below.
There is a skew to this blue. The lizard’s head is iridescent: reflecting light differently depending upon the angle from which it is seen. Iridescence is caused by microscopic structures that scatter light, rather than by pigments, which absorb and reflect certain wavelengths.
The fine layers of chitin in butterfly wings, which give them their sheen, do so through iridescence. Iridescent green in swallowtail and gossamer-winged butterflies is achieved via microscopic chitin gyroids: an intricate geometric design of oppositely congruent labyrinths which are a mathematically optimal way to fold space.
In animals, reds and yellows are commonly the result of pigments. But blues are mostly structural. In lizards, blue comes from geometric arrangements of guanine in their scales.
Structural coloration does not always result in iridescence, but it does with Iberian emerald lizards; lucky for them. Whereas females from afar catch a vivid turquoise visage, raptors above see a dull green that blends in. The specific iridescence in emerald lizards gives them what they want and need.
Nature puts iridescence to distinct purposes. For emerald lizards it abets camouflage while permitting an honest social signal. In the case of butterflies and some other animals, iridescence can create a startling shine that gives pause to potential predators. Shifting colors create confusion that hinder a predator’s ability to pinpoint location. Either effect gives glittering prey more time to escape.
Peacock Spiders
Male peacock spiders compete to attract mates via elaborate dance displays that show off their stunningly colorful abdomens. Males evolved both brilliant colors and a deep velvety black that provides maximal contrast.
Super black locally eliminates white specular highlights, reference points used to calibrate color perception, making nearby colors appear so bright they’re practically glowing. ~ American evolutionary biologist Dakota McCoy
The ultrablack effect is achieved by nanometric bumps which more thoroughly absorb light than smooth textures. These nanostructures bounce light around and diffract it in a way that evades the view of an onlooker. And the bumps are microlenses which angle entering light so that the light traverses a longer path and spends more time interacting with light-absorbing black melanin pigment than it would on a flat surface.
The luxe look of peacock spiders resembles birds of paradise, which convergently evolved similar nanostructures for their ultrablack feathers. Anti-reflective microlenses independently evolved for flower petals, tropical shade plant leaves, light-sensitive nodules on sea star arms, and ommatidia in moth eyes.
Stingers
If you felt the pain right away, you would react and swat the insect away before it finished injecting its venom. ~ Indian American mechanical engineer Bharat Bhushan
Insect stings are memorable experiences, as they are meant to be by their givers. To deliver the maximal message, stingers are ingeniously engineered, with a soft tip that stiffens close to an insect’s abdomen.
Wasps and bees don’t want to create too much pain to start with. The softer tip makes it less likely that you’ll notice the initial insertion. ~ Bharat Bhushan
Stingers are ~7 times more elastic at the tip than at the base. The gradient in hardness and rigidity along the length of the stinger helps it penetrate as deep as possible while maintaining its integrity.
The stingers of wasps and bees differ in some ways. For one, wasp stingers are curved, whereas bee stingers are straight. But they have much in common.
The stingers of both have 2 serrated lancets that project from the end of the stinger. The lancets move back and forth to pierce the skin – a massaging motion that loosens the skin to open it up. A channel between the 2 lancets delivers venom.
Stingers have a clever design to optimize the mechanical properties without being too heavy. ~ Bharat Bhushan
The stinger cuticle is a laminated microstructure. Stingers have ideally placed hollow spaces to reduce weight while maintaining the strength necessary to penetrate thick skin.
The stingers really are elegantly designed and mechanically durable. ~ Bharat Bhushan
Stinging is also accomplished with precision. Bees and wasps sting at the most efficient angle for penetration: 10° for a wasp and 6° for a bee. These sting angles indicate why wasp stingers are curved and bee stingers straight.
Similar considerations were at work in the designs of spider fangs and scorpion stingers, which have distinct engineering characteristics that deliver utmost impact.
Shore Crabs
Common British shore crabs in the same species (Carcinus maenas) carefully camouflage themselves using distinct stratagems. Whereas crabs in mudflats look like mud, those in rock pools rely on disruptive coloration: high-contrast patterns which break up body outline appearance.
The crabs are highly variable in colour and pattern, and are often extremely difficult to see. Rock pool individuals have high levels of disruption. This is an effective way to disguise the body’s outline in the complex rock pool backgrounds where matching the colour of the environment is often not possible. In contrast, mudflat crabs closely match the mud in terms of colour, brightness, and pattern but lack high-contrast disruptive markings that might give them away in the uniform mudflat environment. ~ Martin Stevens
Such specific camouflage is exemplary of adaptation as a teleological exercise, conducted by localized coherence.
Mimicry
Imitation is the sincerest form of flattery. ~ English cleric Charles Caleb Colton
Mimicry is the evolutionary development of deceit. 2 cowbird species illustrate its potential power.
Cowbirds
The screaming cowbird is a brood parasite whose fledglings look and sound like baywings, its primary host. This precise mimicry is rewarded with negligible rejection by deceived baywing mothers.
Meantime, shiny cowbirds dump their eggs in the nests of many other birds, including baywings. Unlike their close cousin, shiny cowbird hatchlings match neither the appearance nor the begging call of their hosts. Their mortality from host rejection is 83%.
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Mimicry confers various advantages. Foremost is safety.
Cagey Vines
Mimicry in animals is rather common, whereas documented cases in plants are rare. ~ Chilean botanists Ernesto Gianoli & Fernando Carrasco-Urra
The tropical woody vine Boquila trifoliolata mimics the leaves of the trees it climbs onto, including size, shape, color, orientation, petiole length, and tip spininess. All told, the vine can mimic 9 different leaf features of any of 12 different host species. A single vine can alter its leaves to specifically match the different trees it is on. This offers considerable protection against herbivory. How B. trifoliolata manages such sophisticated mimicry is mysterious.
Batesian Mimicry
In 1848, English entomologist Henry Walter Bates went to the Amazon on an expedition to study life there. His was the first scientific account of animal mimicry, particularly the type that bears his name: Batesian mimicry, which is phenotypic imitation by a palatable species of another that is noxious.
Bates found numerous examples of innocuous butterflies with wing patterns that mimicked species unpalatable to would-be predators. He called them “mockers.”
Longwings, the Batesian butterflies, speciated by mating preferences for specific patterns. The gene for wing color is inherited along with the mating choice. Different species are still able to interbreed but choose not to.
Such speciation is a 2-step process. 1st, populations isolate behaviorally: choosing not to mate based upon cosmetic genetic expressions, such as a wing pattern in the case of longwing butterflies. Once separation is well-established, more extensive genetic modifications occur, sometimes rapidly, to optimize the new species to its situation.
The hoverfly is stingless. Its coloration mimics wasps and bees that carry the potential for a painful prick. This gives the hoverfly adequate protection without incurring the cost of carrying a stinger.
Mimicry need only be as precise as the key signals that the target audience relies upon for recognition. Typically, coloration is critical.
Flies that mimic wasps or bees do so only to the degree that it confers sufficient protection. Because birds prefer snacking on larger flies than smaller one, larger mimics are better imitators. The little flies simply aren’t under enough pressure to evolve perfect disguises. Mockers work the essentials into their act while letting the rest slide.
Wasps kill large numbers of other insects. Many wasp mimics evolved to avoid being eaten by predatory wasps rather than by educated vertebrate predators. ~ German entomologist Michael Boppré et al
The essentials change if the mimicked model becomes scarce or disappears entirely. Venomous coral snakes disappeared from an area in North Carolina around 1960. The local harmless kingsnakes that mimicked coral snakes quickly adapted to become a more precise imitation of their model, so that potential predators would not make the mistake of thinking them fake. Scarcity in the real thing incited better precision in the fakes.
Only the most precise mimics are favored as their model becomes increasingly rare. ~ American zoologist Christopher Akcali & American biologist David Pfennig
Müllerian Mimicry
In the late 19th century, German biologist Fritz Müller emigrated to southern Brazil and studied the forest there. He observed what came to be called Müllerian mimicry: poisonous species that shared a common predator, mimicking each other’s warning signals. The species involved are not necessarily closely related.
Müllerian mimicry need not involve look-alikes. It may be any sense that a predator employs to select its prey. Many snakes share the same auditory warning signals.
Tiger Moths
Bats hunt at night via echolocation. Tiger moths are one target. Some of these night-flying moths retain secondary metabolites from eating plants that are baneful to bats. A moth can’t advertise its inedibility to a sightless nocturnal predator by coloration as diurnal insects do. So tiger moths emit warning clicks that tell a bat that they are unpalatable.
Once a bat eats a single toxic tiger moth, that moth is off the menu. Even tiger moth species that are perfectly edible click themselves out of harm’s way.
An edible tiger moth (Bertholdia trigona) has another technique to evade becoming bat fodder: jamming a bat’s sonar with an especially dense series of clicks.
Mimic Octopus
All octopi can change color and texture. Many blend in with the décor, appearing as a rock or the look of the sea floor. One stands out for a display of even greater sophistication.
The mimic octopus puts on quite a show in the southeast Asian tropic seas. It impersonates other animals, displaying its mimicry situationally.
If attacked by a damselfish, the octopus turns into a banded sea snake, which is a damselfish predator. It does this by displaying yellow and black bands, burying 6 of its 8 legs, and waving the other 2 in opposite directions.
The octopus has been seen to mimic venomous sole, lionfish, sea snakes, jellyfish, and sea anemones, both in look and behavior. It may also masquerade as a flounder: pulling its arms in to imitate the flat fish’s shape, then waving them to replicate a flounder swimming. The mimic octopus’ repertoire extends as far as its cunning, which is considerable.
Defensive imitation is not the mimic’s only trick. It may imitate the apparent mate of a crab, thus snuggling up to a snack.
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As the mimic octopus illustrates, safety is not the only reason to mimic. Freeloading is a fine reason for imitative inducement.
The flowers of some species replicate the scent of others that pollinators favor, to attract attention without providing the payoff of nectar. Other flowers mimic the female of a certain insect to compel males to it. Various orchids employ this trick.
Large Blue Butterfly
Caterpillars of the large blue butterfly practice chemical and auditory mimicry. They feed on thyme or marjoram flowers after hatching, which primes them for the next act.
After molting, a caterpillar drops off the plant to the ground. There it secretes sweetness that attracts red ants. Suckered by sugar, the ants take the larva back their nest.
The ants feed on larval secretions by milking it: stroking the caterpillar with their antenna to have it produce a small drop of honeydew. Having pacified its caretakers, the caterpillar goes into hibernation inside an ant tunnel.
In due course the caterpillar reemerges. It seeks out the nesting chamber, where it spends up to 3 weeks feasting on red ant eggs and larvae. It can do so by secreting a hormone that tells the ants that it is one of them.
The caterpillar also mimics the sound that a queen ant makes, ensuring itself a steady food supply. By this queenly deception ants will even kill their own larvae and feed the caterpillar if food is scarce.
Having matured off the largesse of its inadvertent patrons, the caterpillar hangs itself from the roof of the nest by its legs and builds a chrysalis around itself. The large blue butterfly lives up to 9 months as a caterpillar prior to its pupal stage.
After another 3 weeks, an adult butterfly emerges. The butterfly leaves the nest to find a mate, with but a few weeks left to live.
Courting Cockroach Counterfeit
A male German cockroach in courtship offers dinner to a prospective mate: he raises his wings, exposing a pantry of deliciousness produced by the male’s tergal glands.
A female mounts a male and feeds on these nuptial secretions. This puts her in position for the male’s sexed solicitude.
Baby German cockroaches caught on. They evolved to vamp what every male cockroach is looking for. A gentle tap with an antenna scented with a knockoff version of femme fertile perfume and a male lets a little counterfeit on board for a free meal.
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Humans innately imitate in social settings. Conscious-ly not doing so is stressful. Waiters who repeat customer orders word for word, or subtly mimic a patron’s body language, earn higher tips than those that paraphrase or forgo gestural mirroring.
The evolution of mimicry and polymorphisms depends on how receivers acquire information. ~ English zoologists Rose Thorogood & Nicholas Davies
