Evolution
“Nature is the source of all true knowledge. She has her own logic, her own laws; she has no effect without cause nor invention without necessity.” ~ Italian polymath Leonardo da Vinci
2.5 billion years ago, after the continents had stabilized, prokaryotic sociality provoked a major evolutionary event: an archaean host and endosymbiotic bacterium committed to everlasting partnership through irreversible specialization; thus arose single-celled eukaryotes.
The concept caught on. Within a few hundred million years, a variety of eukaryotic cell types had arisen, including plants, fungi, and metazoa: the precursor to animals. The biggest difference in lifestyle among them was diet.
“It seems that Nature has taken pleasure in varying the same mechanism in an infinity of different ways.” ~ French philosopher Denis Diderot in 1753
With quantum exactitude, plants evolved the wondrous ability to turn sunlight and water into energy, and so were autotrophic. Though heterotrophic, fungi were flexible in eating ready-made foodstuffs from other organisms, dead or alive. In contrast, proto-metazoa were particular: requiring a diet of fresh, prefabricated amino acids and vitamins.
Many unicellular organisms have a colonial form: congregating when food becomes scarce, or as a defense. Single-celled green algae exposed to unicellular predators are easy prey. Clumping makes a difference. Small cell colonies offer an ideal trade-off between security from predation and maintaining sufficient surface area for nutrient uptake.
The next evolutionary step from aggregation was labor specialization at the cellular level. Prokaryotic colonial cells are not differentiated, but cells coordinate to perform different tasks.
Multicellularity was a déjà vu to the emergence of eukaryotes. Both were spurred by cellular cooperation.
Whence animals arose. In their innocence, early worms had no idea what trouble their inheritors a billion years hence would bring to their beloved home planet. In evolutionary terms, humans would turn descent into a dirty word.
The evolution of multicellular eukaryotes was by no means a declaration of independence; quite the contrary. Eukaryotes have constant association with their prokaryotic forbearers in the form of a microbiome.
Animals are so dependent upon their microbial companions as to require their assistance in development, digestion of foodstuffs, and protection from pathogens. An animal’s microbiome is essential. In ignorant ingratitude, we call our most important friends germs.
“The human body and its symbionts can be viewed as a community of interacting cells.” ~ American microbiologist David Relman
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In understanding evolution, a microscopic point of view makes a meaningful point. Genetic elements do not compete, nor do cells. Instead, the consistent themes of evolution, beginning at the cellular level, are: adaptation, cooperation, coordination, and specialization.
Multicellular life arose by endosymbiosis: the realization of mutual advantage by union. Photosynthetic chloroplasts and mitochondria, which are the power plants in plant and animal cells, were the products of unification and specialization.
As life grew more complex, cells of all sorts were symbiotic add-ons. Greater complexity was achieved mostly through modularity. Once a structure is established, the potential exists for fractal repetition for different functionality.
“In modern complex organisms, novel adaptations result mostly from reorganization of existing structures.” ~ Russian evolutionary biologist Alexander Badyaev
Organs are macroscopic extensions of the organelles within cells. The main innovation in plants was modularity: the evolution of semi-autonomous regions embodied within the embryonic meristems of roots and shoots.
Bones
Following the violent maneuvers of tectonic plates ~1.5 billion years ago, huge quantities of minerals, including calcium carbonate (CaCO3), were washed into the oceans. This abundance provided the possibility for inhabitants to get hard.
At first, unicellular organisms employed CaCO3 to regulate mineral intake. By a half billion years later, calcium carbonate was being put to more creative purposes: strength, stability, protection, and motility. The evolutionary explosion of the Cambrian period owed largely to mineralized body parts. Shells, spines, and skeletons evolved.
For building bones, the employment of calcium carbonate ceded to calcium phosphate, which afforded greater chemical stability, especially in the acidic environments that are created after intense physical activity.
“Bone is an intriguing composite of essentially 2 materials, the flexible protein collagen and the hard mineral called apatite.” ~ physicist and physical chemist Roland Kröger
The evolved properties of bone owe to an intricate, fractal, hierarchical organization. The principal building blocks of bone at the nanometer scale are curved needle-shaped nanocrystals that form larger twisted platelets which resemble propeller blades.
“At the smallest scale, needle-shaped mineral units form platelets that organize into stacks bridging multiple collagen units.” ~ structural biologist Natalie Reznikov et al
The platelet blades continuously merge and split during bone development. Interweaving mineral and protein form continuous networks that provide superior strength.
“The combination of the 2 materials in a hierarchical manner provides bone with mechanical properties that are superior to those of its individual components alone. There are 12 levels of hierarchy in bone.” ~ Roland Kröger
Besides numerous nested structures in bone, a common feature of all of them is a slight curvature, effecting twisted geometry. The mineral crystals are curved, the protein strands (collagen) are braided, the mineralized collagen fibrils coil, and entire bones themselves have a twist, such as those seen in the curving shape of a rib.
Clearly, bones evolved not only with purpose, but with a highly coherent structure that optimizes certain properties inherent within the chemistry of the ingredients and the combination of materials. The employment of fractals in the construction of bone illustrates Nature’s fondness for novelty and labyrinthine order via modular self-similarity.
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Evolution is the ongoing process of adapting to ever-changing environments. Those organisms that cannot do so quickly enough die out. That said, adaptation can be surprisingly swift.
“Evolution can proceed so rapidly that it shapes ecological dynamics.” ~ American entomologist Marianna Szücs et al
Overfishing
“Human predators, by exploiting at high levels and targeting differently than natural predators, can generate rapid changes in both morphological and life-history traits.” ~ Canadian evolutionary ecologist Chris Darimont et al
In the last few decades of the 20th century, overfishing decimated fish stocks throughout the world. Plummeting populations from the pummeling also had a dramatic evolutionary impact.
To gain an edge on being able to survive and reproduce, fish get smaller and grow up faster. This is a common strategy for animals experiencing rapid environmental change.
For example, Atlantic silversides can cut their average size in half in just 4 generations. Such brisk changes have been documented in populations of different fish across the world. Over the past few decades, the most commercially exploited fish have got 20% smaller, and their rates of living 25% faster.
Color
“Coloration serves as a dynamic form of information.” ~ English ethologist Innes Cuthill et al
The colors of plants and animals are produced by pigments and nanostructures which reflect light is specific ways. One purpose of coloration is camouflage: conveying an illusion.
Some plants hide their tender, tasty shoots from herbivores by giving them a reddish color. Mammal herbivores cannot see red. Instead, such a shoot looks a decayed yellow: certainly not worth taking a bite of.
More dramatic are deliberately crafted displays of color by animals to achieve an effect. Over the course of a few hours, horned ghost crabs in the sea around Singapore change color to match their background. How they know to create just the right level of reflective luminance to make themselves indistinguishable from their background is a mystery.
Cephalopods have impressive control over their coloration. Some cuttlefish quickly change color and shape according to the predator they are faced with, thereby maximizing their concealment for a specific observer.
Both in look and behavior, mimic octopus perform an astonishing imitation of a predator to the predator that an octopus is trying to scare off. A mimic octopus knows what frightens its enemies. A mimic octopus also knows what its prey likes: it may imitate a potential mate to devour a deceived suitor.
“The same color pattern can be perceived differently by different receivers, and this can be exploited by organisms to resolve different challenges simultaneously.” ~ English zoologist Tim Caro et al
Some damselfish have ultraviolet (UV) face patterns which facilitate individual recognition for preserving territoriality among conspecifics, while remaining largely hidden to UV-insensitive predators. Similarly, some mantis shrimp have covert polarized patterns which are invisible to other species.
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The same question arises when considering the evolution of functional biological coloration: how could it happen? Randomness is clearly out of the question. With great diversity, different life forms exhibit colors that work in predictable ways. Specific color signaling is received in the way intended: purposeful in conveying information that achieves a desirable effect for its sender.
So often, hidden information is involved in arriving at an adaptation: some knowledge of effective interaction that inspires a particular trait. Such is the instance of plants hiding delectable shoots in plain sight. What the capacity for camouflage indicates is that there is intelligent design work being done: a force behind Nature enabling coherence for clever display. That much is obvious.
Chameleon Colors
Ever since Aristotle described them, chameleons have populated legends and myths because of their oddities: long projectile tongues, independently-movable eyes, zygodactyl feet, a glacial pace, and the striking ability of some species to rapidly shift the vivid color displays of their bodies. (A zygodactyle has 2 toes of its foot in front, and 2 in back. Some birds are zygodactyl.)
Many animals can rapidly change color: to communicate, camouflage, or regulate their temperature. Only a few can actively tune the color of their skin at will. Squid are a notable example; so too chameleons.
Chameleons have 2 layers of specialized cells called iridophores. Each layer has light-reflecting nanocrystals. The deeper layer reflects a broad range of wavelengths, albeit biased toward red.
By altering the spacing between the crystals in the upper layer, cells shift from reflecting blue light to reflecting yellow or red. This creates a skin color change from green to yellow or orange.
A chameleon may quickly switch between camouflage or an ostentatious display to attract mates or expel a rival. It does so by mentally tuning specific skin cells; an astonishing feat that defies purely physiological explanation but becomes plausible when considering the mind controlling energy waves, with correspondent physical activity.
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Chameleons have extraordinarily long tongues that strike at prey with astonishing speed; a complex trait shared with frogs.
Frog Strike
“For frogs, the forces acting on the tongue during impact and retraction can even be beyond the body weight of the animals.” ~ German biomechanist Thomas Kleinteich & Ukrainian entomologist Stanislav Gorb
A frog uses its whip-like tongue to swiftly snag prey, faster than you can blink your eyes. Its tongue can pull up to 1.4 times the frog’s body weight.
(A frog tongue strike takes only 20 milliseconds. Human eyes blink in 1/10th of a second: 5 times slower.)
Unlike the human tongue, which is attached at the back of the mouth, frog tongues are attached at the front. This lets frogs easily slip caught prey down their throats.
A frog’s tongue hits with a force 5 times that of gravity, yet the food sticks as the frog swiftly snaps its bungee cord back. The secret is the saliva, abetted by a cleverly designed tongue.
Unlike other animals, a frog’s salivary glands are not inside the mouth, where saliva drips onto the tongue. Instead, a frog tongue itself secretes saliva.
A frog’s super-soft tongue curls around a prey upon contact, then deforms as it is pulled back toward the mouth. The tongue continuously stores the intense applied physical forces in its stretchy tissue, dissipating the recoil shock via internal damping.
“The frog tongue acts more like a car’s shock absorber than a pressure-sensitive adhesive; its viscoelastic nature enables rapidly applied forces to be dissipated in the tongue tissue.” ~ American mechanical engineer Alexis Noel et al
The tongue is just one aspect of a frog’s food delivery system. Special saliva is the other.
Frog spit has 3 distinct phases, superbly designed for the instant task at hand. The saliva is watery when it first hits its insect prey, filling all the victim’s crevices.
In preparing for retraction, the saliva suddenly becomes sticky and thicker than honey, gripping the insect for the rocket ride back. Once the tongue is retracted, the saliva thins again, allowing the captured bug to be sheared off in the mouth.
In all phases, saliva thickness remains constant. Only its consistency varies. A shear-thinning liquid, frog spit makes its wondrous conversions via quantum effects. What triggers the viscosity transforms is not known, but they appear as a byproduct of the tongue’s extension.
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Organisms evolve for an array of reasons: to better exploit resources, to improve breeding odds, to optimize efficiency, or to overcome an onslaught from predation or poison. The desire to live drives life and evolution. While adaptations may at times involve many changes, sometimes they are quite specific.
Killifish
Killifish are a hardy freshwater fish that often live in ephemeral waters: estuaries, wetlands, and vernal ponds that may mostly evaporate for a spell. Killifish eggs may survive weeks without water.
There are over 1,270 species of this once-abundant fish, found throughout the Americas, and to a lesser extent in much of the world. Alas, the pollution that people produce can do in even the stoutest swimmers. Many millions of Atlantic killifish on the east coast of the United States lost their lives to a continuing chemical onslaught by human industry.
Yet some of these slippery slivers of silver survived the pollutants that plague American waterways. Genetic analysis revealed that several populations managed mutations which allowed them to withstand 8,000 times the levels of toxicity that might murder a lesser fish.
Though the genetic changes among surviving killifish were generally convergent, each population rapidly adapted to mounting toxicity in their own way. There was no other significant alteration in these killifish; only the ability to live in what would otherwise be toxic waters.
“Atlantic killifish populations have rapidly adapted to normally lethal levels of pollution in urban estuaries. Distinct molecular variants contribute to adaptive pathway modification among tolerant populations.” ~ American evolutionary geneticist Noah Reid et al
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There are countless examples of adaptation under duress. The only reasonable conclusion that might be drawn from these is that evolution can be purposeful: a concept cogently encapsulated in the word adaptation.
Blind Cave Fish
The Mexican tetra is a small, hardy, freshwater fish, native to rivers in Texas and eastern Mexico. Those that live in caves have lost their sight. Being able to see is energetically expensive. Nature favors economy.
The Mexican tetra went blind without any genetic mutation. Instead, the genes responsible for developing eyes and sight were silenced via methylation, an epigenetic technique. This is an explicitly directed, exquisitely thrifty adaptation.
“Epigenetic processes can play an important role in adaptive evolution.” ~ American developmental biologist Brent Weinstein et al
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Various evolutionary factors may affect the fortunes of populations, including mating selection, which might alter the proportions of certain traits. But trait dominance does not lead to exclusivity. Instead, diversity typically persists. This is a strategy of Nature that provides a survival edge when changed conditions render a dominant trait disadvantageous.
Guppy Love
Male guppies display dazzling variations in their colorations. Female guppies have strong mating preferences based upon male color pattern. This seems a formula for particular patterns to dominate the guppy world. Yet male guppies with rare color patterns persist and do even better than males with more popular patterns; presumably because they are less likely to be preyed upon by predators, who prefer to target the familiar.
Rare males have more matings and leave more offspring than those supposedly favored by females. This rare-male effect is the process in which the evolutionary fitness of a trait rises as its relative abundance decreases.
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Whatever competition occurs behaviorally, it does not diminish genetic diversity. While certain traits may dominate, mating selection does not winnow the gene pool, nor eliminate trait rarity.
Staying Fit
“It seems intuitive that animals would need to increase their exercise capacity or physical fitness to cope with increased activity level.” ~ evolutionary physiologist Jeff Yap
For our muscles to stay in shape, we must exercise them. Rodents face a similar situation.
Even wild mice readily run on an exercise wheel. As with humans, rodent workouts are rewarded by a desirable dopamine deposit into their system; what people commonly call a “runner’s high.” Hence, though exercising is taxing, Nature provides an intrinsic incentive.
Migratory geese may fly thousands of kilometers at a stretch. To get themselves fit, geese simply sit on the water and stuff themselves with food. Yet in doing so, they develop stronger hearts and bigger flight muscles.
In a wide variety of animals, seasonal signals prompt various alterations, including those related to fitness. Migratory birds undergo innumerable genetic changes that are stimulated solely by the changing hours of daylight.
Bear muscles do not waste away despite months of inactivity. Before hibernating, bears’ bodies spontaneously release muscle-protecting compounds into their blood.
In needing to exercise to keep fit, rodents and humans are exceptions in the animal kingdom. Evolutionary trade-offs prompted this. Our ancestors lived unpredictable lives, particularly regarding food supplies. Hence our body’s ability to add fat more readily than any other animal.
Muscle mass is energetically expensive. Each kilogram of muscle adds 10–15 kilocalories a day to our resting metabolism. 40% of average human body mass is muscle.
“Most of us are spending 20% of our basic energy budget taking care of muscle mass.” ~ American paleoanthropologist Daniel Lieberman
Our physiology evolved to let weight and fitness fluctuate depending upon food availability. Rodents face similar environmental conditions, and so have a selfsame set of traits related to musculature.
So, we see that muscularity is ultimately a matter of energy, not physicality. That muscles may tone themselves is evidence that our bodies are sustained by an energetic force, species-specific in its dynamic characteristics.
Saltation
“Natural selection acts only by taking advantage of slight successive variations; she can never take a great and sudden leap, but must advance by short and sure, though slow steps. If it could be demonstrated not by numerous, successive, slight modifications, my theory would absolutely break down.” ~ Charles Darwin
“Reproductive isolation, which typically develops over hundreds of generations, can be established in only 3.” ~ Swedish evolutionary geneticist Leif Andersson et al
A sudden leap in specific evolutionary development is termed saltation. Saltation dispels Darwin’s gradualist “natural selection” hypothesis of evolution. Most saliently, saltation shows the creative flair of Nature in conjuring diversity. Many flowering plants, including the multiplicity of orchids, are the product of saltation.
Saltational Scents
Pheromones are distinctive blends of chemical compounds that are typically species-specific. Many organisms employ pheromones as signals to attract mates or other conspecifics, or for defensive or nefarious intent.
Altogether, there is an extraordinary diversity of blended scents, but with remarkable convergence of blends across very different life forms. Certain combinations are especially effective and organisms zero in on them, irrespective of evolutionary descent.
“The high species specificity of pheromones suggests that there should be strong selection against small modifications in these signals, and thus gradual evolution of pheromones through small changes in chemical components is unlikely. Instead, it seems more likely that pheromone evolution occurs via sudden major shifts in pheromone constituents.” ~ Australian biologists Matthew Symonds & Mark Elgar
In examining the pheromones of bark beetles and fruit flies, Symonds and Elgar found “closely-related species are just as different as more distantly-related species. This ardently argues against the idea of minor shifts in pheromone evolution.”
In drawing their inescapable conclusion of saltation, Symonds and Elgar wondered “how this mechanism of evolution actually works.”
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For the littlest ones, evolution is a matter of self-selection. Microbes carve their own evolutionary path by managing their own genetics. Viruses, archaea, and bacteria frequently decide how to adapt themselves to environmental conditions via self-generated genetic modifications. One way they do so is by sharing genetic concepts among themselves: a process called horizontal gene transfer. These ready-made adaptations, which microbes selectively employ, can facilitate the rapid evolution of populations. Thus, resistance quickly arises in populations of pathogens subjected to antibiotics.
At the organism level, adaptation visibly appears via bodily change. Physiological changes are often the tip of the iceberg to functional transformations, including behaviors.
The threat of being killed for food has long been recognized as a key ecological factor for adaptive responses. Predation risk also drives the evolution of social complexity. Groups become more cohesive under the threat of becoming dietary casualties. Organisms stay together to maximize their statistical chances of staying alive.
Sociality is not without costs, but these are far outweighed by the benefits. Hence, sociability is the norm for organisms throughout the tree of life.
Worldwide, coral reefs are presently under severe stress from ocean warming and acidification. Only to a limited degree can coral quickly adapt on their own. To better acclimatize, coral hire algal symbionts that can stand the heat. The coral gets improved temperature tolerance, and the algae find themselves safely harbored in a well-furnished home.
Evolutionary fitness is strengthened by cooperation. Life is not a hierarchy. It is an entangled web.
Adaptation
“The world doesn’t change in front of your eyes, it changes behind your back.” ~ English author Terry Hayes
Evolutionary biologists aim to answer a single question: how has the great diversity of life been productively generated?
“The apparent increase in adaptive complexity of organisms over the history of life is one of the great mysteries of biology.” ~ American evolutionary biologist Daniel McShea
While there are many common fallacies, there is no mystery. One common fiction is that randomness plays a part in evolution. Another is that evolution proceeds without objective.
Nothing in Nature is random. A provocation may be obscure, but it is there. Saltation and adaptation dispel the prospect that randomness is involved in evolution.
Many evolutionary biologists favor the idea of randomness because the implications of the alternative frighten them into befuddlement. Acts of Nature as intentional is termed teleology. Evolutionary biologists cringe from this concept because it puts natural causes outside the observable realm, and thereby makes the beating heart of Nature unscientific in their empirically minded minds.
Biological evolution obviously exhibits intent: survival and reproducibility. The entire history of life is a dramatic presentation of organisms’ will to survive and propagate. That calamities may render adaptation awry only makes the show a spectacular melodrama.
No sane evolutionary biologist denies survival and perpetuation as driving forces. The objection is only the obvious ramification, thereby creating a silly paradox of denial in refusing to ascribe any impetus behind evolution.
Pointy Eggs
Murres are sociable seabirds that live off northern coasts. They nest in tightly packed colonies on craggy seaside cliffs. The ledges on which murres lay their eggs can be quite narrow: sometimes as shallow as an egg is long.
Eggs are normally round and prone to roll if given the opportunity. Conicality is critical to an egg’s tendency to wander off under the influence of gravity when sitting on an uneven surface, such as a cliff ledge.
Unsurprisingly, the coherent force behind Nature saw fit to make murre eggs uniquely pointy. Otherwise, lacking eggs from which to hatch, murres would naturally be in short supply.
Lizard Tails
Lizard tails are variously colored to confuse or evade predators, depending on who the lizard killers are.
To have a predator think that its tail is its head, and so facilitate evasion, lizards with weasels or snakes as nemeses have vivid blue in their tails – a color which both snakes and weasels can see. In lizard populations where snakes are the main enemy, lizard tails reflect ultraviolet, which snakes can detect but weasels cannot.
Where birds are a threat, lizard tails are a cryptic brown. As birds have keen sight, the best a lizard can do is have a camouflaged tail.
“Nano-particle pigments in skin produce anti-predator tail coloration.” ~ Japanese zoologist Takeo Kuriyama
The precise arrangement of microscopic light-reflecting platelets creates the requisite visual effects which appear in lizard tails. Creative pigmentation techniques are employed by many animals and plants to create specific looks, some of which are quite dazzling, or rather drab, depending upon what works best for an intended purpose.
Such specific adaptations illustrate how localized coherence attunes the traits of organisms to provide at least fighting odds of survival.
Anglerfish
Anglerfish are a bony fish that arose 130 million years ago; long enough to have adapted to a wide variety of habitats, and so have a worldwide oceanic presence.
Different anglerfish do their angling at different depths. Some live on continental shelves. Most are deep-sea denizens. What unifies anglerfish is a fleshy growth (illicium) from the head that acts as a lure (esca).
Only female anglerfish have illicium. Much-smaller males live solely to find a mate, to which they attach and provide a continuing sperm supply, fed by their mate as compensation. Those males that fail in their life mission quickly die.
The illicium is a modified dorsal fin. Dorsal fins typically stabilize fish: preventing unintentional rolling and assisting in sudden turns. In anglerfish, the illicium acts as a fishing rod.
In deep-sea anglerfish, at depths where sunlight does not penetrate, an esca is bioluminescent. This little light lures small fish upon which the anglerfish preys, and as well advertises for mates.
The source of anglerfish luminescence comes from colonies of symbiotic bacteria that dwell in and around the esca. Some bacterial species only light up when fed by the fish, which provide the vital food ingredients for the bacteria to luminate.
Esca precisely strobe on and off based on anglerfish control. To accomplish this, an anglerfish communicates with its esca bacteria energetically, as chemical communication would be too slow to signal the millions of luminescent symbionts to act synchronously at sufficient speed.
The anglerfish is one of innumerable examples of intricate symbiotic adaptation that only be explained teleologically, and, in the instance of anglerfish, with interspecies communication links that are beyond purely physical means.
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The blueprints for manufacture of organisms are physically accomplished via genetics. From an evolutionary perspective, this field of study has been ripe with confusion between mechanics and process.
“Evolution is merely a reflection of changed sequences of bases in nucleic acid molecules.” ~ English evolutionary biologist John Maynard Smith
Smith’s laughable oversimplification is ridiculously wrong. Examining the microscopic mechanisms of DNA and its companions is nothing more than looking under the hood of Nature’s vehicle to inspect the pistons. It does not explain how the engine works, or how it came to be.
Functionally, genes are encoded molecules of designs for development. There simply cannot be a design without conceptual and compositional processes. This is the irrefutable teleology of Nature.
Convergent Evolution
Evolution is not mystical. Instead, its tendency toward certain traits makes its outcomes frequently foreseeable.
“Is evolution predictable? To a surprising extent the answer is yes.” ~ Canadian evolutionary biologist Peter Andolfatto
The predictability of evolution is amply illustrated by convergent evolution (aka parallel evolution), whereupon vastly different organisms come to the same solution. Flight, vision, singing, parasitism, toxins, and camouflage are but a few of countless examples of convergent evolution.
Plants present a litany of parallel evolution. To begin, there were at least 5 independent evolutions of single-celled photosynthetic organisms into multicellular plant forms by 600 million years ago (MYA). Green algae alone gave birth to the land-based life commonly called flora, which became a prodigious potpourri.
Plants independently developed precise nanostructures to harvest light and channel it to the molecules which perform photosynthesis. Engineering at the nanometer scale enabled plants to translate light energy into chemical energy with an incredible 90% efficiency.
Despite striking differences in climate, soils, and evolutionary lineages, plants share common needs and means of achieving them. If one were to design an organism to optimize light collection, a branched structure with flat-bladed leaves might seem obvious. Nature created a wild variety that all aim at the same end, constrained in assortment only by biomechanics. An astonishing diversity of appearance belies functional convergence.
Phloem is the conductive tissue in green land plants which transports sugars from sunlit tissue to those tissues that live in perpetual shade; an essential distribution of nutrients. Kelp is a large seaweed that forms marine forests. It has cells like phloem.
As all plants are photosynthesizers, they have the same need to capture light and internally exchange water and nutrients. Relationships in body-plan geometry are crucial, and thereby constrained in terms of practical possibilities.
Over 350 MYA, competition for access to sunlight drove plants in divergent families to reach for the sky. Vast forests of towering trees emerged during the Carboniferous period (359–299 MYA). Independent innovations for height continued since then. Many tall plants employ wood, but others, such as palms and bamboo (an ambitious grass), do not.
Acquiring carbon dioxide for photosynthesis through controllable pores (stomata) causes water loss by transpiration. Although plants evolved various mechanisms to alleviate this problem, one well-established solution is C4: a technique that independently evolved at least 45 times, starting 32 MYA, and most recently 4 MYA.
