Darwin Day: Micro & Macroeconomics of “Endless Forms Most Wonderful” - Gary Greer
Presented by Gary Greer, PhD, Associate Professor, Biology, Grand Valley State University
About the Speaker
Gary Greer was born and raised in Greeley, CO. he received is Bachelor’s of Arts in Biology from the University of Northern Colorado (1987), he later received a Master’s of Science in Plant Biology at Humboldt State University in California (1993) and defended his Thesis on the “evolution of mating systems in a hybrid fern complex.” In 1997 Greer received his PhD in Environmental and Plant Biology from, Ohio University. His Doctoral Dissertation addressed “phenotypic plasticity as a determinate of ecological distribution in ferns.”
He is currently Associate professor of Biology at Grand Valley State University, before coming to GVSU Greer was Assistant professor at West Virginia State University from 1997-2003. Dr. Greer is the Associate Editor, American Fern Journal,s and a peer-reviewer for scientific journals regarding plant ecology. His research interests address “the evolution and ecological importance of adaptive phenotypic plasticity in ferns and invasive plants; i.e., the ability of a genotype to match its phenotype (anatomy, physiology and behavior) to its environment such that its fitness is maximized.”
About the Event
Summary with commentary for the CFI- MI meeting held on February 9, 2011.
Our presenter, Dr. Gary Greer, spoke on the micro- and macro- economics of Darwin’s poetic phrase: endless forms most beautiful. His specialty is in flora and so he opened with the concept that if humans developed as plants do, that the torso would remain the size that it was in infancy, while the fingers and toes of the developing being would extend on and on.
Evolution takes place in an economical system. It is no surprise that writers on economics were highly influential to early evolutionary thinkers. Both deal with competition for resources and the dynamics involved when more beings complete for those same diminishing resources. These insights do not only extend to the macro world plants and animals, but also down to the chemical action within those bodies, energy transfer and cellular function. These tend to move in a cyclic manner requiring input to be maintained for continued growth and development and act as an engine, just as with economies.
At the micro level, bodily components operate in a way that disallow elements from the environment that are detrimental or that do not aid in function to enter, while making use of what does allow the organism to function effectively. The chemical memory is established as DNA which creates forms that work within the local economy that they inhabit.
Most of the phenotypic variation in a population is heritable. Organisms exhibit differences within populations that include behavioral, anatomical, degree of robustness of physical characteristics, etc. Organisms in a population, therefore, have differing degrees of fitness to their environments and this is what evolution works with. Those organisms that exhibit superior fitness to their environment tend to produce more offspring which, over time, gets the genes that produced those heritable traits for environmental fitness represented more and more within the population. Those lacking that fitness produce fewer descendants and their genetic contribution diminishes in the gene pool.
Evolution is not about progress toward the future but about success in the current environment. Organisms adapt to changing environments that occur through the blind contingencies of nature. If plants require a longer beak to extract nutrition from them, then the bird that does the extracting acquires a longer and slimmer beak. If seeds that are the food source for another species of bird become tougher due to climatic conditions, beaks that are more vise-like and stronger and blunter will become more prevalent within this avian population.
Predators push their prey to make use of random variations (which are NON-randomly naturally selected) that permit it to elude capture more effectively. This becomes an arms race that we see played out everywhere: the predators that have the genetic potential to better capture their prey are more successful and produce more young that share those traits. Creatures co-evolve in this and other ways. Some that have a disparate genotype will develop a similar phenotype due to competing over the same resources that push the body plan in a shared direction. Conversely, when populations of a given species are split off from each other over a long enough time period, with different environmental factors in which to adapt, they will eventually diverge from each other in behavior and body type until they reach a point where, if they are reintroduced to each other, they will no longer be able to interbreed; they become a different species, in effect, since the ability to interbreed is a defining feature of what it means to be a member of the same species.Variation is both restricted and enhanced by the environment and the organism’s response to it via natural selection. The environment also includes breeding partners, which are selected via choice (typically made by the female in most creatures) as is seen in the mechanism of sexual selection.
After this introduction, GVSU Professor, Gary Greer, got into the specific focus of his lecture, which dealt with allometry or the relationship between size and shape in living forms as played out in growth and development. There are internal constraints within a given organism which produce different rates of growth in different parts of it, thus creating new forms or new functions for older, modified, forms.
A key concept in all of this is the relationship between surface area and volume in different beings and that surfaces supply volumes! Those of us who are not specialists, consider the entire root structure of a plant to be absorbing nutrients from the soil but it is actually the root tips alone that do this. These are what supply the volume of the plant itself.
As entities increase in size, the surface to volume ratio decreases. The metabolic rate of the organism is dictated by the surface to volume ratio, so organisms that get bigger have a metabolism that slows down as the surface, which remember supplies the volume, decreases relatively.
The prediction would be a 2/3 ratio but life evolved to do better than this and is actually at a ¾ rate. This mass to metabolic scaling holds true for all forms of life and we can give predictions about all the factors of this system if we know any one of them in a given organism. Ability to supply the cell from the environment goes down as mass goes up (surfaces feed volumes.)
This can even be witnessed within populations, where smaller and slighter individuals (exhibiting less volume) will tend to have a higher metabolic rate (the internal economy) than those individuals that are larger and therefore slower, with a more turgid (relatively) economy of metabolic rate.
This allometric scaling is seen not only between life forms and within populations but even at the level of constituent components of organisms, such as the rate of metabolic exchange between molecules and the mitochondria and cells.
The General Sherman Giant Redwood tree has a mass of 6,000 metric tons, which is equivalent to 30 Blue Whales. Life could not achieve this on the 2/3 level. Taking the fictional character, Godzilla, as an example, Dr. Greer spoke of how this monster could not actually exist at the proportions that it is rendered at. It simply would not have the necessary surface to feed that much volume and supply the muscle mass in a sufficiently adequate manner to move this gargantuan creature. The volume’s demand would far exceed the surface area’s ability to supply it.
Even correcting for all sorts of variables and factors, such as temperature differences, the differences between immobile plants and mobile animals, and so on, we find the ¾ ratio to remain as a constant. This is due to, Professor Greer explained, the fact that metabolism relies on hierarchal, fractal-like internal distribution networks. Again, we see the language of economic concepts applied. All throughout his talk, Dr. Greer referred to the restrictions of supply upon the demands of a growing organism, setting limitations; about networks of distribution and about how breakdowns within the systems create stasis. With regard to organisms, this means death.
The vascular network inside an organism is organized in a fractal-like way—with a central, thick trunk that splits off into proportionately decreasing branches and further into twig-like parts—dividing and decreasing in size with each division—each iteration—as it goes further from the core. When we think of our own condition we note that we cannot consume food products from our grasping hand itself but must ingest it. Internally, we see the different organs operating on this fractal-like system as well— the lungs and heart and system of arteries, veins and capillaries.
The efficient layout of the vascular system in larger creatures creates less internal turbulence and a better matching between the push and pause pulse rate from the heart; resistance is decreased and more cells are supplied due to shorter distribution distances in this fractal layout.
Our speaker next talked about the vascular system of plants which have no pumping heart but contain a system that mirrors an animals, in that they have thicker transport systems that narrow down as they move away from the source of necessary sustaining fluid. The vascular system of a plant is like straws and these straws are created when cells die. The nutrient- laden moisture is drawn from the root tips through the straw-like complex by the sucking action of the atmosphere upon the plant’s surface. This becomes a passive pumping mechanism; no heart or muscular action is involved.
Dr. Greer displayed images to us of xylem, which are plant tissues that conduct water and appear as clusters of tiny straws. This is a single tissue type that has two jobs, he explained: it serves as a transport system and adds rigidity and support to the plant. Vertebrate animals have their vascular and support systems (in the form of skeletons) existing separately. The xylem taper as they extend up into the higher portions of the plant, but become larger and more conductive as they go down to the base, which is analogous to our system of arteries, veins and capillaries.
The xylem used to have only the single task of transport in the deep past when plant life was closer to the ground. Ferns, which are an ancient plant, still exist in their ancestral form. As plant life began to extend higher and higher, the xylem was pressed into the service of being a support system too. This is classic evolution. Evolutionary changes operate on what is there to begin with. There is no divine creator seen at work that can whip up a perfectly engineered body part or entity in an optimal way, so different components are exapted, modified, and made to do different tasks, as environmental conditions dictate, for survival and increased reproductive success.
As the xylem took on more structural duties, it pushed out further toward the edges, which provided it with a wider stance, so to say, and which, therefore, increased stability. The xylem quantity increased as well, as plants extended further upwards. What we see from the fossil record and all the way to the present is that the amount of xylem and the degree of branching and tapering; the fractal organization, is exactly consistent with what is required to maintain that ¾ ratio that had been addressed throughout Professor Greer’s presentation.
The predictions that can be made extend not only to size, metabolic rate and structure, but also to the lifespan and rates of development of different living beings. Those beings that reproduce fast and explosively also develop faster, live faster and die sooner than organisms which breed less dynamically, with fewer progeny that develop slower and live longer. Very small creatures actually experience life perceptually in a sped- up manner. It is believed that insects see a strobe effect in florescent lights; they exist in a different sense of time than larger organisms. The beings that have extreme rates of reproduction—a veritable Big Bang, as Greer expressed it, can also e expected to experience a more massive die off of their progeny. The larger beings produce slower- developing offspring, which are far less numerous, are nurtured and protected better and longer until they attain the stage of development where they can become reproductive agents themselves.
Evolution is solely concerned with passing genes into the next generation. There is no deeper mystery or meaning or purpose to life than this. This is why we see some insects that experience their entire lifespan in one day—long enough for their hyper-accelerated rate of development to get them to a point, during that day, where they can replicate themselves.
The ubiquitous ¾ ratio even extends into what we see with natural forest thinning! Large trees fall and small thin ones come up, as more light is, then, available to them. As they grow larger they create a canopy that harvests sunlight. The individual trees complete for the light and those that lose out contribute toward the thinning. This is part of why we see what appears to be a carpet of treetops in aerial views of forests, as there is only so large that trees can become to outcompete with their neighbors while not overextending their surface to volume ratio. The thinning process removes the outliers in developmental rates.
Even if one has grasped this concept earlier on, it is still rather exciting to ponder upon the fact that the Blue Whale has the same NUMBER of heartbeats over its lifespan as a much, much smaller organism! It is just that the great cetacean’s heart beats so much more slowly while the wee being has a very quick heartbeat. They live in different streams of time. And, to reinforce what has already been stated, this size and the rate of existence for all life are at a consistent ratio throughout all levels of scaling. The smaller the animal, the more internal turbulence that occurs in its system due to shorter distances between branching off points, which creates a less efficient creature, as the heart actually works against itself more.
Professor Greer pursued this surface supplying volume ratio with us further and further out and always we saw that the ratio held true, whether we were examining energy in the form of watts used for different operating scales, population densities and energy use, environmental niches that are created and removed with a consistent filling in and dying off of those that occupy them, or even highway systems with greater or poorer fractal-like branching that are, therefore, more or less efficient. More energy is squandered in less efficient systems—human made or naturally occurring— but with humankind, we can artificially maintain inefficiency to a far greater extent than nature allows for the rest of its products.
Summarized by Charles LaRue
