Dissecting Behavior

Dogs, Science, and the Biology of Behavior

Month: February, 2014

What is behavior?

The Question of Behavior

What exactly is behavior?  What is it that we are examining when we inquire about the behavior of animals?  This question is not as straightforward as one might think.  There is a significant amount of disagreement on the subject that benefits from consideration.  In a paper by Levitis et al. (2009), the question of ‘what is behavior?’ was asked of professors and professionals from three different scientific societies.  Of the eight operational definitions the authors proposed from various texts, the highest agreement on any single definition only included 44% of the respondents.  Even more problematic is that 52% of the respondents showed contradictory answers—implying that the respondents’ conceptions of behavior was not guided by an operational definition of behavior but of their personal biases (most likely due to their individual areas of interest).  For instance, even though 99.1% of the respondents agreed that “geese flying in a V formation” constitutes behavior, 31% of the respondents answered that only individuals, not groups, are capable of behavior.  In argument form, this line of deduction would look like this:

Premise 1:       Only individuals, not groups, are capable of behaving
Premise 2:       Geese flying in a V formation constitute a group
———————————————————————————-
Therefore:       The group of geese is behaving

This is a flawed argument to say the least. The benefit of operational definitions is that they allow us to organize our observations through logical lines of reasoning, thus contradictions in logic are a significant red flag that bias has taken place of a scientific definition.  One potential explanation for this is that in Levitis et al.’s (2009) background research to gather published definitions for the term “behavior,” over one hundred publications that they felt should have had a definition for behavior had completely avoided defining the term, either by choice or due to the assumption that people intrinsically know what behavior is.  I hope it has been successfully illustrated that the latter conclusion is clearly not the case.

The Definition of Behavior

A quick thumb in the dictionary informs us about a common preconception: “behavior is the way in which an animal or person acts in response to a particular situation or stimulus.”  In fair agreement with this definition, Tinbergen defined behavior as “the total movements made by the intact animal” (Tinbergen, 1955).  However, what if we were to talk about the behavior of a plant?  Some species of orchids (e.g. Ophrys speculum) use chemical signals to mimic virgin females of their insect pollinators to deceive male insects into attempting reproduction with their flowers: thus causing the male insect to pollinate the orchid (Ayasse et al., 2003). Deception (the action of altering the perception of another to believe something that is not true in order to gain some personal advantage) is most certainly a phenomenon most anyone would associate with behavior.  However a plant is not an animal, so evidently the concept of behavior has to expand beyond just animals if it is going to include deception.

Looking-glass-orchid-flowers

Ophrys speculum evolved features which mimic female reproductive organs in order to deceive male insects, thus increasing their ability to be pollinated.

Conceivably then we could expand the parameter of the definition to multi-cellular organisms.  Having said that, such a classification would then exclude bacteria.  Bacteria are single-cell organisms that meet all eight of the requirements that define life: (1) they have an internal organization; (2) they store and retrieve information through the organization of nucleotides; (3) they have a metabolism that converts energy from an unusable to a usable form; (4) they respond to the environment; (5) they grow and develop; (6) they regulate and maintain homeostasis; (7) they reproduce; and finally, (8) they evolve.  One could argue that if you momentarily exclude reproduction and evolution, all of the requirements of life facilitate just one organismic phenomenon: homeostasis.  So the first argument from the skeptic must be to show that a living entity that is responding to its environment is not capable of behavior.

It might seem unorthodox for many readers to discuss the behavior of bacteria, however even Skinner was not without his philosophical views of the behavior of single-cell organisms and discussed the stretching of an amoeba’s limbs as a an example of early behavioral evolution (Skinner, 1984).  In fact, amoebas are part of the group Protozoa which comes from the Greek for “first animal.”  Protozoa were named this because of their animal-like behavior, from their movement to their reliance on consuming other organisms for survival.  While I share no disagreement with Skinner regarding the behavior of single cell organisms, where I do disagree is in the view that the work of Jacques Loeb (1915) is sufficient in providing a sound argument that the behavior of “lower” organisms only needs explication in what the organism does as a whole—a recurrent theme which Skinner also applied to the behavior of larger organisms as well (Skinner, 1987).

This view is incredibly limiting.  In the hundreds years following Loeb, we have discovered more about the behavior of all organisms (prokaryotes [archaea & bacteria] and eukaryotes) by investigating internal cellular functions.  Indeed, researchers recently discovered that bacteria are able to activate a host body’s immune response to attack an invading virus that threatens the survival of their host they are living symbiotically with (Ichinohe et al., 2011).  Researchers discovered this behavioral response by analyzing signals that lead to the synthesis of mRNA essential to the immune response—a discovery that has launched an entirely new field of inquiry to other ways medicine might fight deadly diseases.  However, this extraordinary level of symbiotic behavior is still poorly understood, so for our purposes let us take a look at a simple environmental response in a single cell of Escherichia coli as an example of adaptive behavior in bacteria.

When E. coli are in a high solute, hypertonic environment, their life is instantly endangered by diffusion’s closest relative: osmosis.  Osmosis is the movement of water from an area of higher free energy to an area of lower free energy (Saupe, 2013).  Solutes (dissolved molecules) affect this process by affecting the free energy of the water the same way that rush hour traffic decreases the kinetic energy of a freeway—the more traffic in the solution (presence of solutes), the less available free energy.  If the solutes from the E. coli’s environment diffuse across its membrane through its pores, osmosis might destroy and kill the cell because freely permeable water will pass across the membrane until the free energy inside the cell is equal to that outside.  If the presence of solutes is dense enough, the E. coli will explode and die.

E. coli would not have survived for the eons they have been around for if a handful of solutes made them explode, thus their behavioral response is an extremely effective defensive mechanism rooted in their DNA.  When E. coli senses the presence of solutes, they transmit a signal to begin transcribing and translating sections of DNA into proteins that will block the pores and prevent solutes from diffusing across the membrane—thus maintaining homeostasis.  There is no question that these actions of E. coli are essential for their survival and fit perfectly well along side the adaptive behaviors of plants and animals.

Permitting then that we include single-cell organisms in our definition of behavior, what then do we do about viruses?  Viruses have no cells.  They are purely microscopic packets of genetic code wrapped in a protein shell.  Consequently, viruses lack the essential organelles required for replication, thus in order for a virus to reproduce it literally breaks open the membrane of a host cell by using spikes on its protein shell that act like a medieval battering ram to break down the gates and invade.  This allows the virus to use the mechanisms within the fully functioning host cell to replicate its viral genetic code like nefarious molecular zombies (see Grove & Marsh, 2011).  Interestingly, scientists analyze viruses in terms of their (1) physical structure, (2) proximate causation, (3) temporal effect on the fitness of a host which impacts the virus’s capacity for survival, and (4) evolutionary development—Tinbergen’s four questions of behavior (Erkoreka, 2010; also see Tinbergen, 1963).  If viruses are incapable of behavior, are Tinbergen’s four questions irrelevant?  Such a claim would create an upheaval in the behavioral literature.

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Here is another way we might ask ourselves about the behavior of viruses.  Let us for the sake of argument claim that viruses are not capable of behavior.  If this is true and we are to exclude these molecular zombies from the definition of behavior, why then do we commonly say that viruses attack cells?  Are we just attributing the behavioral characteristics of animals to non-animal entities or is it really valid to say that these molecular zombies are truly attacking and threatening the homeostasis of an organism?  Even the dictionary cites a definition for “attack” as the aggressive action of a disease.  Viruses obviously meet this criterion so then are we to exclude the behavior of attacking from the definition of behavior just so we can deprive these mysterious molecules of behavior?  While colloquialisms are generally poor grounds for scientific exploration, in this case I would argue that they bear important consideration to the question at hand.  After all, it would be ignorant to deny that common expressions reflect our experiential perceptions of the world (known in science as empirical observation).

The fact that these molecules are nothing but packets of genetic material and literally straddle the definitional requirements of life yet have actions attributable to behavior quickly leads us into questions about non-living entities—for example, do rocks behave?  If an individual was to pick up a rock and throw it, is the rock behaving?  A definition that relied purely on the reactions of matter to its environment would require us to include every rock on Earth as a behaving entity since rocks are quite literally orbiting the Sun as the Earth moves through our solar system.  Using Newtonian physics, we would stipulate that the rock is exerting a force on the Earth equal to that of the force of the Earth on the rock.  Instead of thinking about a small rock, what if we were to look at hydrogen dioxide (water).  The behavior of water makes it one of the most unique molecules in existence.  Three of waters most important behavioral characteristics (i.e. properties) are that it is a powerful solvent, it sticks to itself because it is polar and thus can generate incredible surface tensions, and it is denser as a liquid than as a solid.  If any one of these three properties were different, life would not exist as we know it today.  Molecules have observable, quantifiable properties which respond to other molecules in the environment, therefore why can’t molecules behave?

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One might argue for a definition that stipulated some kind of internal propulsion or energy source which might allow us to exclude a rock.  But would this criterion be valid?  Even though the energy used by animals is converted from an unusable to a useable form through internal metabolic processes, we have already established that the source of all energy for every organism comes from the Sun.  The survival of any animal would be immediately threatened without the energy mitochondria (prokaryotic organisms) produce or the symbiotic benefits offered by gut flora (prokaryotic organisms like E. coli), thus the behavior of animals cannot be observed without the impact of the organisms acting on them.  In a similar fashion, no organism lives in a void.  We shouldn’t forget, as silly as the concept of a rock behaving may seem, all animal behavior is subject to the physical laws of nature.  A bird cannot fly without overcoming the necessity to generate lift, neither could energy be converted to facilitate homeostasis or motion without adhering to the intrinsic properties of atomic theory.  If an owl is diving on a field mouse, prey capture could not occur without the effects of gravity—thus the very action pattern depends on the same phenomenon that determines the travel path of a rock that is thrown.  It should be mentioned that the skill of a bird negotiating with the physical properties of lift is equal to any human pilot, even though the mechanisms are obviously different, and while the Border Collie is unlikely to recite Newton’s laws of motion, they have a skill in predicting the motion of a Frisbee equal to any Ultimate Frisbee competitor.

Any general definition of behavior must allow for all of the nuances mentioned so far if it is to permit our inferences to take into account the immense diversity of behavior in the world.  Thus, returning to Tinbergen, I will modify and broaden his insight and offer that behavior is the total measurement of movements (both internal and external—regardless of physical or biological limitations) of an entity through its environment.  More simply: behavior is the response of a system to a stimulus.  Therefore, since every particle in the universe is in motion and endlessly responding to stimuli, by this definition we can conclude that everything—even a subatomic particle—is in a constant state of behavior.

Such an incredibly broad definition may at first seem either ridiculous or of little value, yet I would contend that there is nothing more valuable than to question our preconceptions with a logical and unbiased deductive thought process.  There is no reason to exclude rocks as behaving entities in the world, and a rejection of this has more to do with the novelty of it (“well I just don’t like it..”-type of response) than of the reasoning to the question.  Furthermore, I would argue that the benefit of such a definition provides a common concept to be discussed whether the system involves entire populations or just a single atom.

Previously I cited the opinion from Levitis et al’s (2009) study that 31% of participants believed that only individuals, not groups, are capable of behavior.  Problematically, the behavior of the human body is the result of the sum of movement of molecules from within—therefore how can we say that the movement of trillions of molecules inside a single organism is “behavior” yet preclude the sum of a group of geese performing an action (such as flying in a V formation) as a behaving entity?  I have no doubt that a five-minute discussion with a police officer that has had to respond to a riot can attest to the behavioral differences of an angry mob versus that of an angry individual.  The tendency for human nature to warp their perceptions to fit their preconceptions makes the ability to integrate new information very difficult; especially if that information negates beliefs we have held for a long time.  As Tinbergen states:

“… if we overdo this in itself justifiable tendency of making description subject to our analytical aims, we may fall into the trap some branches of Psychology have fallen into, and fail to describe any behaviour that seems ‘trivial’ to us; we might forget that naïve, unsophisticated, or intuitively guided observation may open our eyes to new problems.  Contempt for simple observation is a lethal trait in any science, and certainly in a science as young as ours.”  (Tinbergen, 1963)

A definition for behavior that includes all matter in the universe, while useful for expanding our perceptive lens, may not initially seem to provide a productive answer for our question of what is animal behavior.  If narrow perspectives risk losing the forest through the tree, this might be like losing the forest in the galaxy.  What should be emphasized is that the question of what is behavior is only productive if the nature of the entity exhibiting the behavior is definitively described.  The behavior of organisms is thus our aim, and this behavior is intrinsically tied to the fact that organisms—regardless of their complexity—are bound to their biological nature.

References:

Ayasse, M., Schiestl, F. P., Paulus, H. F., Ibarra, F., & Francke, W. (2003). Pollinator attraction in a sexually deceptive orchid by means of unconventional chemicals. Proceedings of the Royal Society B: Biological Sciences, 270(1514), 517–522. doi:10.1098/rspb.2002.2271

Erkoreka, A. (2010). The Spanish influenza pandemic in occidental Europe (1918-1920) and victim age. Influenza and Other Respiratory Viruses, 4(2), 81–89. doi:10.1111/j.1750-2659.2009.00125.x

Freeman, S., Quiliin, K., & Allison, L. (2013). Pearson – Biological Science (5th edition.). San Fransisco, CA: Benjamin Cummings.

Grove, J., & Marsh, M. (2011). Host-pathogen interactions: The cell biology of receptor-mediated virus entry. The Journal of Cell Biology, 195(7), 1071–1082. doi:10.1083/jcb.201108131

Ichinohe, T., Pang, I. K., Kumamoto, Y., Peaper, D. R., Ho, J. H., Murray, T. S., & Iwasaki, A. (2011). Microbiota regulates immune defense against respiratory tract influenza A virus infection. Proceedings of the National Academy of Sciences, 108(13), 5354–5359.

Levitis, D. A., Lidicker, W. Z., & Freund, G. (2009). Behavioural biologists do not agree on what constitutes behaviour. Animal Behaviour, 78(1), 103–110. doi:10.1016/j.anbehav.2009.03.018

Loeb, J. (1915). On the role of electrolytes in the diffusion of acid into the egg of Fundulus. Journal of Biological Chemistry, 23(1), 139–144.

Saupe, Stephen G. (2013). Letter to the Editor. American Biology Teacher, 75(1), 4-5.  DOI: 10.1525/abt.2013.75.1.2

Skinner, B. F. (1984). The evolution of behavior. Journal of the Experimental Analysis of Behavior, 41(2), 217–221.

Skinner, B. F. (1987). Whatever happened to psychology as the science of behavior? American Psychologist, 42(8), 780–786. doi:10.1037/0003-066X.42.8.780

Tinbergen, N. (1955). The Study of Instinct. Oxford: Clarendon.

Tinbergen, N. (1963). On aims and methods of Ethology. Zeitschrift für Tierpsychologie, 20(4), 410–433. doi:10.1111/j.1439-0310.1963.tb01161.x

Are dogs and wolves the same species?

The question of whether dogs and wolves are members of the same or different species is a controversial one.  To begin with, species classification is a convention used to help aid in our ability to organize nature and it is anything but definitively objective.  This should not decrease the importance of classifying species, but before we begin to try and understand the question, we will benefit from understanding that the nature of the question is very philosophical.  Always keep in the back of your mind that the personal preference of an individual will always be influential in subjective conclusions.  Therefore, to try and be objective about the conversation I would like to discuss the big picture, and in biology, the big picture is always evolution.

Evolution is often described as cumulative processes so slow that they take between thousands and millions of decades to complete (e.g. Dawkins, 1986).  This is only part of the picture.  We certainly have an in-depth archeological fossil record that shows gradual changes in species over millennia (such as the development of feathers in dinosaurs or the eye-migration of flatfish), however biological changes can also happen in the wink of an eye—at least compared to traditionally conceptualized evolutionary timescales.  Most simply, evolution can be defined as change over time.  But what kind of change?  Does any change constitute evolution? Does any duration sufficiently qualify for “time?”  These are important considerations because whatever definition is chosen will create a first premise assumption from which any arguments will flow from—like the way the lens of a camera manipulates light before entering the camera body and forming an image, so too can a first premise assumption influence our perceptions so that our observations fit a desirable theory instead of the natural phenomenon.

Some evolution happens very slowly (such as the previously mentioned examples of feathers in dinosaurs and the eye-migration of flatfish); however, these changes arose most probably due to mutation and sexual selection, not because these changes condoned a functional advantage in evading hazards or finding food.  Most examples of evolution are due to a change in the characteristics of a group that enable it to survive, thus evolution can be viewed in this light as a response to changes in the environment.  Typically, environments change very slowly and significant changes often ride on the back of natural disasters.  The evolution of dinosaurs into birds was due to a two-fold catastrophe.   Approximately 200 million years ago, atmospheric oxygen declined nearly 20% causing one of the largest extinction periods in Earth’s history (Berner et al., 2006).  This killed off an unprecedented amount of land dwelling animals and threatened aquatic living organisms as well.  For example, some species of fish such as tuna evolved ram-air induction (whereby swimming at high velocity forced water across the gills at a higher speed to ensure maximum oxygen diffusion from water).  As if global suffocation wasn’t bad enough, to add insult to injury, an asteroid the size of Manhattan slammed into Mexico just a few millennia later.  These two factors meant that the only dinosaurs which survived were small and could fly—what we call birds.  Predominantly, it is important to remember that changes to the environment are what drive these kinds of selection processes, especially when these changes create significant mortality rates—a concept I will return to later.

The controversy over the classification of dogs and wolves can be seen on numerous levels, but one that stands out for me is the way in which many wolf-dog hybrid enthusiasts are very passionate that the correct term is not “hybrid” but “wolf dog”—since both the dog (Canis lupus familiaris) and the wolf (Canis lupus lupus) are according to some scientists taxonomically sub-species of Canis lupus.  While this is a relatively recent distinction (originally, Carl von Line classified the dog as Canis familiaris, a different species than the wolf) the taxonomic nomenclature does not determine whether the mating of two animals qualifies as a hybrid.  Hybridization is the interbreeding of individuals from genetically distinct populations, regardless of their taxonomic status (Stronen & Paquet, 2013).  Wolves and dogs may be amazingly similar in their genetics, however they are clearly genetically distinct populations (e.g. vanHoldt et al., 2011).

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Principal component analysis of all wolf-like canids for the 48K SNP data set: PC1 represents a wild versus domestic canid axis, whereas PC2 separates wolves (n=198) and dogs (n=912) from coyotes (n=57) and red wolves (n=10). Result shows dogs and gray wolves are genetically distinct (Fst=0.165). PC2 in this analysis of the data demonstrate a geographically based population hierarchy within gray wolves and coyotes (vanHoldt et al., 2011)

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Plots show ancestry blocks and their assignments for representative individuals of canid populations with average size of blocks, percent ancestry, and number of generations since most recent admixture (t) indicated. Two-ancestor (coyote, A; gray wolf, B) analyses are presented for a Great Lakes wolf from Minnesota (C), a captive red wolf (D), and an Algonquin wolf (E). Three-ancestor analyses (coyote, A; gray wolf, B; dog, F) are presented for a Northeastern coyote from Vermont (G), a Southern coyote from Louisiana (H), and a Midwestern coyote from Ohio (I) – (vanHoldt et al., 2011)

The supposedly infallible “fact” that dogs are descended from wolves took the world by fire with research into mitochondrial DNA and a publication which appeared in Science titled “Multiple and Ancient Origins of the Domestic Dog” (Vila et al., 1997).  In this paper, the authors concluded that dogs were 135,000 years old—a conclusion which is sheer nonsense (Larson, 2011; Larson et al., 2012).  Over the last decade, geneticists have published paper after paper pointing at different dates and different locations for domestication with very little consensus but most supporting the conclusion that dogs are direct descendants of the wolf.  One important reason for this is because the methodology behind examining mitochondrial DNA (mtDNA) has a very debilitating first premise assumption: that the rate of mtDNA mutation is constant in dogs and wolves despite a massive wolf population bottleneck and an exploding dog population.  This is a problem because both of these population effects cause genetic drift.  Imagine if you take a population and reduce it to a mere handful.  How do you tell whether you are looking at the first members of a new species or the surviving members after a population endangerment?  Likewise, imagine taking two dogs and deciding you will start your own breed.  If your new breed goes through a population explosion, then their DNA will make up a unrepresentative sample of the historical population (this is called the “founder effect”).

Genetic research is awesome, don’t get me wrong, and it cannot be underappreciated that innovations in genetics have opened up wildly exciting new scientific avenues of investigation into organisms.  However, genetic analysis is relatively new to the question of speciation in the animal kingdom and some insight to the Canis lupus dilemma can be gained by looking at the overall ecology of dogs and wolves instead of just their sequence of nucleic acids.  Research that examines genotypes, high-density single nucleotide polymorphisms, epigenetic methylations, mitochondrial DNA, etc., is literally a whole new world, but it is not the whole picture.  The expression of a plant or animal’s DNA is what creates its phenotype (from morphology to behavior), and it is the phenotype that is thus selected for in the environment and we can learn lots by simply examining the phenotype in and of itself.

As previously mentioned, when two genetically distinct species reproduce the offspring is called a hybrid.  However in animals, hybridization is a pretty big deal.  When sperm meets egg, a zygote is formed, thus ecologists look at both prezygotic (before reproduction) and postzygotic (after reproduction) barriers that make hybridization difficult.  Examples of prezygotic barriers include: habitat isolation (where two species are geographically isolated, sometimes living in the same area but rarely meet), behavioral isolation (where two species do not recognize the signals/mating cues of each other or employ different foraging strategies), temporal isolation (where one species might breed in the spring while another breeds in the fall), mechanical isolation (where the “wedding tackle” of one species doesn’t fit in the “hoo-ha” of another species), and genetic isolation (where the sperm and egg of two species are unable to form a zygote).  Postzygotic barriers include reduced hybrid viability (where hybrids fail to develop or reach sexual maturity), reduced hybrid fertility (e.g. mules are hybrids of horses and donkeys and are all sterile), and hybrid breakdown (where the offspring of hybrids have further reduced viability and/or fertility).

The behavioral isolation of dogs and wolves is astronomical because behaviorally there are almost no commonalities between them.  In fact, leaving dogs aside for a moment, very important behavioral distinctions exist just between different groups of wolves that affect their offspring viability (postzygotic barriers).  For example, one of the most important criteria for mate preference in wolves comes down to hunting strategies: wolves with similar hunting and foraging strategies are more likely to mate and teach these strategies to their offspring.  Foraging behavior is a phenotypical characteristic that plays a major role in determining the ecological niche of a species—so much so that wolves who employ different foraging strategies also display different types of social relationships.

Very few dogs hunt for food.  Even in societies which still use dogs for hunting (such as the indigenous Mayagna people of Nicaragua), dogs rarely make the kill.  Their role in the hunt is to bring an animal to ground and make a loud ruckus until the humans can find it and make the killing blow with their machete.  In this capacity, dogs are pound for pound as efficient as a rifle in bringing in meat for the indigenous people of Nicaragua, and the dogs benefit by being given leftovers (Koster, 2008).  It is certainly true that some dogs (some) opportunistically take down and on occasion eat small animals such as rats, possums, cats, etc.  However, dogs like other scavengers fill an important role in the grand ecological picture regarding the flow of biomass (Wikenros et al., 2013).

Hunting in the wild is simply not an available strategy for dogs to survive.  One important reason for this is that the energy dogs would expend to take down and eat small prey animals would be much greater than the energy gained by hunting them.  This is illustrated with African wild dogs (Lycaon pictus), who pound for pound hunt, kill, and consume more meat than any other predator in Africa—this is not because they are greedy, this is because of their metabolic needs.  When you look at African wild dogs, small prey like African hares make up only an average profitability of 0.6kg per hunt (4.8kg per kilometer chased), whereas Wildebeest weighing approximately 100kg make a profitability of 35.2kg per hunt (51kg per kilometer chased).  African Wild dogs not only make significantly more meat off of larger prey animals, but they also have a higher success catching them than they do small animals like African hares (38% success versus 31%) (see Creel & Creel, 1995 for Lycaon pictus data).  If humans were to go extinct tomorrow, dogs could never fill the role of these kinds of predators.  Simply put, dogs are more likely to try and play with a deer than to try and kill it.

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Trophic diagram of organisms in relation to predators since reintroduction (Freeman et al., 2013)

As if there is very little difference, dogs are frequently labeled carnivores like their wolf cousins (implying a predatory nature); however ecological foraging models are much more nuanced than simply whether or not the food consumed is animal or plant-based.  Dogs are detritivores (i.e. scavengers—animals which live off of dead food sources).  Whether it is the kibble we drop in the bowl, the dump which feral dogs scavenge at, or even raw meat or table scraps being tossed from the table, dogs do not kill their food.  Whether feral or companion pet, the dog’s niche relies on their ability to live in close proximity to humans—a quality which is typically severely impacted by interbreeding with wolves.  Dogs utilize a very different and elongated socialization period that enables them to develop interspecies social bonds much easier (Lord, 2013), and thus the viability of hybrid offspring between dogs and wolves is severely impacted through both prezygotic and postzygotic barriers.  Quite simply, just because two animals are capable of interbreeding, claiming they are the same species does not make sense in light of almost all aspects of their phenotype outside of morphology (and even then, calling a Chihuahua a wolf is simply absurd).

Thinking about the foraging strategy of the dog as more closely related to fungi, archaea, worms, and dung beetles as opposed to the apex predator wolf might seem rather unglamorous, however in truth it highlights their ecological and evolutionary success.  All life is built on the need for energy and nutrients.  Energy needed for life comes from the sun, regardless of the species.  Plants use the energy from photons to produce sugar, which is natures way of storing energy from the sun.  For this reason, plants are termed “producers” because they create available energy and nutrients for other organisms (such as hydrogen, carbon, nitrogen, oxygen and phosphorus—among other nutrients).  Through nutrients, organisms manipulate the stored energy and use it to produce proteins that enable the organism to survive and reproduce.  The availability of these resources on a large scale is quantified in ecology as Net Primary Productivity (NPP).

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Data: NASA
Image: Freeman et al., 2013

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Image: Freeman et al., 2013

NPP is essentially a quantification of the available resources organisms need to survive.  If you look on the map above, you will see that NPP is highest in the tropics and lowest in the tundra.  The niche of the wolf, compared to the tropics, is in regions of the world where NPP is strikingly low—emphasizing their need to hunt and kill large prey.  Humans appropriate 24% of the NPP of the entire planet.  Think about that for a moment… nearly one-quarter of all available energy on the planet, yet we are just one of thousands if not millions of species cohabitating this blue ball in our corner of the solar system.  We can appreciate that with the laws of the conservation of energy, large consumption leads to large waste, waste that is still rich with hydrogen, carbon, nitrogen, sulfur and phosphorus.  While dogs most certainly share a common ancestor with the wolf, their emergence as a species is due to the tremendous advantage of having proximity to the largest appropriation of nutrients on the planet.  Coppinger has long emphasized the difference between “domestic” (living amongst humans) and “domesticated” (made to live amongst humans).  With no evidence that humans were ever sophisticated enough to establish breeding programs to artificially select for tame qualities like the silver fox experiment, it is not logical to believe that dogs could have emerged through careful pup selection.  Even today, it is extremely difficult to create human-socialized wolves (who still behave nothing like dogs) and inbreeding is an enormous issue within current populations—how would humans have overcome these issues when we still hadn’t become sophisticated enough to harness agriculture?

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Data: Vince, 2011
Image: Freeman et al., 2013

It is hard to imagine that sometimes we forget just how much we have changed this planet.  If the consumption of nearly 25% of the planet’s NPP doesn’t make you think for a moment, then consider that 90% of all mammalian biomass on the planet consists of humans and domesticated animals.  10,000 years ago, this number was approximately 0.1%.  While rambling around since approximately 200,000 years ago, human population did not reach one billion until 1804.  By 1927, human population reached two billion.  1960: three billion.  1974: four billion.  1987: five billion.  1999: six billion.  By the year 2011, human population reached seven billion (population data and biomass percentages taken from Vince, 2011).  In parallel with increasing human population, it is estimated that there are approximately one billion dogs around the world now, whereas wolves are on the brink of extinction.  At this rate, it is only a matter of time before human population will exceed the appropriable NPP of the planet and very few undomesticated species will exist outside of detritivores feeding on human waste as the human population crashes into unsustainability.

The story is very romantic: man and wolf, hunting and foraging together.  Unfortunately there is simply no evidence; and if I’m being charitable, the probability that dogs evolved directly from grey wolves is extremely unlikely.  While many similarities are perceived to exist between dog and wolf, upon closer examination, the similarities are almost impossible to find.

References:

Berner, R. A., VandenBrooks, J. M., & Ward, P. D. (2007). Oxygen and Evolution. Science, 316(5824), 557–558. doi:10.1126/science.1142654

Brucker, R. M., & Bordenstein, S. R. (2012). Speciation by symbiosis. Trends in Ecology & Evolution, 27(8), 443–451. doi:10.1016/j.tree.2012.03.011

Creel, S., & Creel, N. M. (1995). Communal hunting and pack size in African wild dogs, Lycaon pictus. Animal Behaviour, 50(5), 1325–1339.

Freeman, S., Quiliin, K., & Allison, L. (2013). Biological Science (5th edition.). Benjamin Cummings.

Koster, J. M. (2008). Hunting with Dogs in Nicaragua: An Optimal Foraging Approach. Current Anthropology, 49(5), 935–944. doi:10.1086/595655

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