Voyage of the Beagle (Non-fiction fan fiction)

11/11/15

It’s #NaNoWriMo – National Novel Writing Month. In honor, and because I had the day off work and am procrastinating from other tasks, I spent the morning artistically imagining The Voyage of the Beagle by Charles Darwin* for a young audience.

Voyage of the Beagle

Preface

     Have you ever dreamed of having a truly grand adventure? Then this story is for you. But you must be prepared. You will sail across oceans, climb to the tops of mountains, come face to face with wild creatures, and have only the stars to guide you on the darkest of dark nights. Each day will have challenges and rewards. You will conquer your fears. You will make discoveries. This is the life of an explorer. Are you ready?

Chapter 1

     It was the wish of Captain Fitz-Roy to have a dog on board Her Majesty’s ship, a ten-gun brig, scheduled to sail from Devonport on the 27th of December, 1831, on a journey around the world. You see, dogs, especially hounds, were quite useful on expeditions such as this. Hounds are known for their friendship and steady assistance, as well as their keen sense of smell. The Captain did not himself own a dog, so it was through the kindness of the hydrographer, Captain Beaufort, who had recently acquired a young beagle that a dog was gotten for the voyage. Captain Beaufort had purchased the hound for his niece whose mother had died and who was under the care of her father. An offer was made by Beaufort of giving up part of his own accommodations so that the dog could accompany the Captains on their expedition, and this was sanctioned by the Lords of the Admirality. It was not, however, sanctioned by Henrietta, Captain Beaufort’s niece.

You see, though it had been but 10 days since the dog was gifted to Etty, the two had formed a substantial bond. The girl’s uncle did not doubt the strength of this connection, due to the aforementioned friendship so characteristic of such hounds and the child’s recent loss. The death of Etty’s mother one month prior certainly dictated that another loss in the child’s life would be a misfortune and could do harm. For this reason, Captain Beaufort requested that the child be granted permission to join him and the dog on the upcoming voyage.

You will not be surprised to learn that Etty’s father did not approve of this request. He included in a letter to Captain Beaufort the following list of concerns:

September XX, 1831

  1. It will be disreputable to my character as a father hereafter to allow a young girl to take part in such a wild scheme.
  2. To allow a young child on such a journey it must be a useless undertaking.
  3. The accommodations would be most uncomfortable for a child.
  4. I would consider it a distraction from Henrietta’s studies.
  5. Furthermore, a ten-gun brig is no place for a dog.

The same day, the Captain replied to the letter with what occurred to him upon reading each of the objections.

September XX, 1831

  1. I should not think it will be in any way disreputable to your character as a father, as I, the child’s uncle shall be responsible for her care and well-being on this expedition.
  2. Looking upon the child as a girl of enlarged curiosity, it affords her the opportunity of seeing people and things as happens to few.
  3. If sanctioned by the Admirality, we have a claim to be as well accommodated as the vessel will allow.
  4. The child would have definite objects on which to engage herself, and might acquire and strengthen habits of thought, and I should think would be as likely to do so as in any way in which she is likely to learn in the next two years at home. I can assure you her pursuit of knowledge in the expedition would be in the same track as she would have to follow otherwise.
  5. It is at the request of Captain Fitz-Roy that a young hound of the finest quality and character accompany the expedition and lend assistance, by its loyal tendencies and advanced nature of olfaction, to the Naturalist, one Mr. Charles Darwin.

*Note – Much of this text is taken directly from The Voyage and from The Autobiography of Charles Darwin (Barlow, 1958). I did not seek, nor have I received, reproduction permission for the adopted text, so I do not claim this as original writing, though the creative imagining is an original idea (including the characters of Henrietta, her father, and the hound). Since I do not claim that all of these words are my own, you should not attribute all of them to me. Any original text is copyrighted to the owner of this blog (C.M.S.) and may not be reproduced without permission.


Lucy in the sky…and on Nature Knowledge Project

I am pleased to share that a peer-reviewed article I wrote for the Nature Education Knowledge Project about the fossil human ancestor, Lucy, has been published online.

This article is tailored for high school classes and introductory-level undergraduate courses.

I am grateful to a number of people at Nature and to Dr. Holly Dunsworth for their determination to get this article and others in the Human Fossil Record room published; the Scitable resources are an excellent way for educators to incorporate into their curricula high quality, peer reviewed written materials.

You may reproduce the Lucy article, without modifications, in print or electronic form for your personal, non-commercial purposes or for non-commercial use in an educational environment.

Citation: Schrein, C. M. (2015) Lucy: A marvelous specimen. Nature Education Knowledge 6(7):2

Full URL: http://www.nature.com/scitable/knowledge/library/lucy-a-marvelous-specimen-135716086


Evolutionary Genomic Medicine: New approaches and challenges to understanding human health

The December, 2014, issue of Current Opinion in Genetics and Development (Vol 29) comprises a collection of review articles dedicated to the theme of “genetics of human origin.” The article by Rodríguez, Marigorta and Navarro[1] discusses the integration of genomic data and evolutionary medicine, a relatively new approach to the study of human health.

What is evolutionary medicine?

In the burgeoning field of evolutionary medicine[2] the principles and habits of mind of evolutionary biology are considered foundations for and are integrated with traditional research, education, training, and practices of medical and health professionals. One goal of evolutionary medicine is to use the concepts of evolutionary biology (i.e., adaptation, maladaptation, population genetics) to explore the etiology and presentation of human disease, vulnerability to disease, and anatomical and physiological correlates of genetic and environmental influences on human health.

What is medical genomics?

Rodríguez, et al. (2014:97) explain that “the field of medical genomics focuses on immediate questions about how diseases appear and how they advance within an organism.” To understand medical genomics, it is helpful to review what is meant by “the human genome.” Nearly all of your cells contain DNA[3]. DNA has a “double helix” structure – think of a ladder that has been twisted around its long-axis. The “rungs” of the DNA ladder are molecules called bases. There are four bases—A, T, C and G—and they pair up in a specific way: A pairs with T and C pairs with G. A typical human’s DNA is composed of approximately 3,000,000,000 base pairs packaged in 23 pairs of chromosomes (in each cell!). Among those 3 billion base pairs are very specific sequences of bases that are functional, meaning they play a role in the body’s physiological processes.

DNA double helix

DNA double helix structure

Most functional sequences within the DNA are referred to as genes. Many genes contain the instructions (via the order of the As, Ts, Cs and Gs) that tell the body what proteins to manufacture[4]. Human nuclear DNA[5] contains tens of thousands of functional DNA sequences, and the sum total of all the genes in human DNA is considered the human genome. The study of the human genome is called human genomics.

There are some clear associations between disease and mutated genes; the most familiar may be that of breast and ovarian cancer and the genes called BRCA1 and BRCA2. Mutations in the BRCA genes can prevent the body from producing proteins that suppress tumor growth. Rodríguez, et al. (2014:97) point out that in the 1960s and 1970s, “prior to the genomics era,” certain human leukocyte antigen (HLA) genes were associated with specific autoimmune conditions. Over the last decade, genome-wide association studies (GWAS) have sought to explore the complete human genome to identify the genetic loci[6] most frequently associated with a particular phenotype[7]. For example, GWAS have identified correlations between celiac disease, an autoimmune disorder, and mutations in genes called HLA-DQ2 and HLA-DQ8.  But how can genotype-phenotype associations such as these be evaluated or conducted in an evolutionary context to better understand and predict not only who is susceptible, but why certain people are susceptible to particular diseases? And what is the role of evolutionary genomic medicine (EGM) in improving diagnosis and treatment?

Integrating medical genomics and evolutionary medicine

In an age of companies like 23andMe[8], more people are aware of connections between genotype[9] and phenotype; however, the general public may not realize just how much is yet to be understood by researchers about the full extent of genotype-phenotype relationships, particularly with regard to disease susceptibility and/or adaptation. In their review article, Rodríguez, et al. explain why EGM is still a nascent discipline and requires novel approaches to more fully develop as a field of research.

As Rodríguez, et al. discuss, there have been successful cases in evolutionary genomic medicine – for example, the research and discoveries regarding sickle-cell anemia and lactose tolerance. So, why is it not common sense and commonplace strategy to interface genomics, evolution and medicine to study and better understand human diseases? Rodríguez, et al. (2014:98) discuss two “glaring gaps in our knowledge: the twin dissociations between health and fitness and between genotypes and phenotypes.” Fitness refers to reproductive fitness—the primary measure of success in the world of living organisms. An individual is “fit” if he or she has offspring and those offspring can also have offspring (more healthy, viable offspring equates to greater fitness). Hence, “survival of the fittest” refers to survival of those members of a population who successfully reproduce, thereby passing on their genes to future generations. The authors point out that fitness may or may not be affected by health and disease in some circumstances; so, adaptive (or maladaptive) explanations for diseased states can be difficult to identify or test. Additionally, what we now consider diseased states—those that are detrimental to health and/or fitness in some or all modern human populations—may have been adaptive phenotypes or evolutionary trade-offs in the past (i.e., the Pleistocene).

A deeper awareness of the relationships between genotype and phenotype and between health and fitness are needed to further advances in EGM, but there are steps that can be taken today to elucidate the etiology, estimated occurrence, diagnosis, and treatment of human disease in light of evolutionary biology.

Part II* of this posting will consider the application of medical genomics and evolutionary medicine to the study of celiac disease, an autoimmune disorder estimated to affect approximately 1 in 133 people[10].*

*Addendum: Instead of writing a follow-up blog post, I am preparing a clinical brief to be submitted to a journal. I’ll let you know if it gets published!

[1] DOI: 10.1016/j.gde.2014.08.009

[2] See Nesse, R. http://www.randolphnesse.com/articles/darwinian-medicine for a list of useful articles and books about evolutionary medicine.

[3] Some cells, in particular red blood cells, which lack a nucleus, do not contain chromosomal DNA.

[4] Genes can also turn on and off, or regulate, other genes.

[5] Organelles called mitochondria also contain DNA, referred to as mtDNA.

[6] A genetic locus is a specific location in the DNA; loci are typically distinguished by letters and numbers that identify their position on a chromosome.

[7] Phenotype refers to the form or function of an organism’s body systems (e.g., eye color or whether or not a person exhibits the symptoms of a disease).

[8] 23andMe.com is a DNA analysis service now required by the U.S. Food and Drug Administration to report only on ancestry; prior to this regulation, the company also provided genetic information related health and disease susceptibility.

[9] A person’s genotype is determined by which versions, or alleles, of genes the person possesses.

[10] This occurrence rate may vary for different countries.


Why Dwarfism? Celebrating #Hobbit10

For an updated version of this bit of writing, please see my 2016 blog post at SAPIENS.org: http://www.sapiens.org/blog/animalia/island-dwarfism

October, 2014

On Homo floresiensis and island dwarfism:

In honor of the 10 year anniversary of the publication of a description of what came to be known as the “hobbit” of Flores, I am sharing this paper, written in the fall of 2004.

Why Dwarfism?

Background

Specimens of a small bodied hominin species resembling Homo erectus were recently discovered in later Pleistocene cave deposits on the island of Flores in Indonesia.  This hominin species is unique because its stature and brain size are comparable to those of Pliocene Australopithecus, yet its skeletal morphology is primarily Homo erectus-like.  The species has been depicted as a dwarfed[1] descendent of Homo erectus that evolved in an insular island environment and is classified as a new species, Homo floresiensis, due to its unique combination of primitive and derived features (Brown et al., 2004).

A full grown adult female of the new species was described in October of 2004 (Brown et al., 2004).  The bones attributed to this specimen comprise the skull, thigh, leg and patella, a partial pelvis, manual and pedal bones, and vertebral, sacral, scapular, clavicle and rib fragments.  The specimen, Liang Bua 1 (LB1), is similar to members of Homo erectus in having small postcanine teeth, reduced facial height and prognathism, relatively thick cranial vault bones, similar cranial shape indices, an occipital torus, similar petrous morphology, a posteriorly oriented infraorbital region, (slight) frontal sagittal keeling, lack of a chin, and double mental foramina.  The stature of this individual, however, is estimated to be approximately 106 cm and its endocranial volume is estimated at 380 cc, both well below the accepted ranges for Homo erectus.  In addition to its short stature and small cranial capacity, this species differs from Javan Homo erectus by the greater cranial base flexion, arching browridges, a less prominent occipital protuberance, more anterior incisive canal, location of zygomatic over the first molar, overall morphology of the mandibular symphysis, relatively larger femoral medullary canals, more prominent intertrochanteric crests, and the tibial size and shape indices.

Bones from this individual were discovered in deposits that date to approximately 18 kyr (Morwood et al., 2004).  Other specimens from different sectors at the Liang Bua cave site, a mandibular left premolar and a partial radius, are thought to be representative of Homo floresiensis and have been dated to 37.7 +/- 0.2 kyr and 74-95 kyr respectively.  This implies that H. floresiensis may have inhabited the island of Flores for more than 75,000 years.  The earliest evidence of hominin occupation on the island, in the form of stone tools, dates to approximately 880 +/- 70 kyr at the site of Mata Menge (Morwood et al., 1998).  There is no hominin skeletal evidence to confirm what species made these stone tools, but it has been suggested that Homo erectus used watercraft to initially reach the island, maybe around this time (Morwood et al., 1998).  Due to the lack of evidence we do not know whether this early population arrived on the island “full-size” or in a dwarfed state.

Among the other animals found at Liang Bua is a dwarfed species of Stegodon thought to have survived on the island until approximately 12 kyr when it was forced to extinction by a volcanic eruption (Morwood et al., 2004).   Interestingly, the 880 ky old Manta Menge deposits contain fossils of a large Stegodon species. Morwood et al. (1998) and Sondaar (1987) both support the extinction of an earlier pygmy Stegodon species around 900 kyr, possibly as a result of predation by hominins (although the giant tortoises and giant Komodo dragons went extinct as well), and a secondary recolonization of Flores by the large species.  They do not indicate, however, whether this large species could have evolved into the later dwarfed species of Stegodon that is found at Liang Bua.

The presence of dwarfed mammals on the island of Flores lends support to the argument that Flores was an insular environment that drove the evolution of a change in body size of mammal species.  This follows Foster’s (1964) “island rule.”[2]  Foster examined 116 North American and European island taxa and showed that in an insular environment, smaller species (such as rodents) tend to get larger and larger species (such as carnivores and artiodactyls) tend to get smaller.  There are exceptions to this rule, however, as pointed out in Case (1978); species that are found on more than one island do not always do the same thing on those islands.  Changes in body-size that occur in island populations seem to be dependent on a number of basic factors, essentially tied to the island resources, competition and predation pressures, and energetics.

For a small mammal, an increase in body-size can result from an ability to exploit a larger body-size niche because of reduced competition or predation pressures and an availability of a wide range of resources.  This can occur in small-bodied dietary generalists (Lawlor, 1982).  A larger body size confers all the benefits of being bigger – dominance over competitors, the ability to eat big and small items, and the ability to have larger offspring that may be better equipped for survival.

In the case of body-size reduction, one may infer a reduction in predation pressures.  If an animal does not need to be large for fleeing or defense from predators, this particular selective pressure is relaxed and body size can decrease to reduce per capita energetic requirements.  A smaller body-size confers the benefits of reducing the amount of energy needed per capita in an environment where overpopulation and exhaustion of resources is a threat, particularly for dietary specialists.  This would allow individuals to allocate more energy to reproductive efforts (Raia et al., 2003).

Although all this seems relatively straightforward, the relationships between all of the factors that may be directly or indirectly related to changes in body-size on islands are quite complex.  A desire to better understand these relationships has led to two primary models, which are not necessarily mutually exclusive, for explaining how larger-bodied species may dwarf in an insular environment.  Each involves a relaxation of predation and competition pressures, but emphasizes a different driving force behind the reduction in body-size.  I will examine each model and then discuss how I would go about testing which model best explains dwarfism on the island of Flores.

Models to explain dwarfism

The first model basically follows the idea that because island environments are structured differently than mainland environments, the ability for island species to exploit resources as effectively as they did on the mainland is diminished. This may be due to a lack of variety or absence of high quality resources on the island, or simply that there is a limited amount of resources to be exploited on an island, particularly for a population of large-bodied animals that exceeds a particular size with limited ability to migrate (due to island geography; Raia et al., 2003).  Essentially, this argument says that islands just don’t have “enough good stuff” to support larger body sizes for some mammals.  As a result, there are high levels of competition for resources and large animals might experience stunting of growth and lower reproductive rates.  If those species begin to produce smaller individuals that require less or lower quality resources, competition decreases and the smaller individuals may be relatively more reproductively successful and pass on their genes more frequently; hence, a reduction in species body-size occurs for the population.

This idea is illustrated in Lawlor’s (1982) study of insular animal populations in Mexico.  According to Lawlor (1982:64) “for animals specializing on particulate resources[3] and facing resource deprivation on islands, there may be a selective premium placed on additional measures to conserve energy. Because the metabolic demands for a small mammal are less than those for a large one, small body size should evolve.”  Lawlor (1982) makes a point of differentiating between specialist and generalist species by emphasizing that specialists will be most affected by depressed resource levels.  Sondaar (1977) also makes the point that when predation pressures are relaxed, and thus the need for large body-size for defense mechanisms is lost, smaller size would be selected for to increase survival in an environment with depleted resources.

Lamolino (1985) assessed degrees of dwarfism or gigantism in numerous island species as an expansion on Foster’s (1964) study.  Lamolino (1985:312) supported the idea that there is a “graded trend from gigantism in…smaller species of insular mammals to dwarfism in…larger species” and presented a model for how this occurs that coincides with Lawlor’s (1982) views that resource limitation, and thus the factors promoting dwarfism, become more important with increasing mammal size.  It can be noted, though, that other authors have documented some exceptions to this rule, though the use of this model as a possible explanation for body-size changes is still supported (Angerbjorn, 1985).

The other, more recently developed, model attempts to explain island-dwarfism by going beyond the resource based explanation of the first model, citing selection for an optimal body size for energy acquisition and use as the driving force behind dwarfism (Damuth, 1993).  According to Damuth (1993:748), “If on an island a species’ usual competitors and predators are absent, it should tend to evolve toward the optimum body size, and the adaptive advantages of doing so would be greatest for populations starting at body-size extremes.”  This optimum body size (100 g according to Symonds, 1999 or 1 kg according to Damuth, 1993) is described as the point at which “mammals attain an optimal energetic tradeoff between resource provisioning and offspring production abilities” (Raia et al., 2003: 294).  Some authors have argued against this model (Symonds, 1999; Roy et al., 2000) based on observed exceptions to this “rule.”

Raia et al. (2003) conducted a study of the dwarf elephant Elephas falconeri from the island of Sicily to assess the likelihood that this species was dwarfed as a result of selection for a more optimal, smaller body size or due to overcrowding and an ecologically restricted environment (the first model).  These small elephants were nearly 150 times smaller than large Elephas species, reached sexual maturity earlier than larger elephants, and had relatively high calf mortality rates.  Promislow and Harvey (1990) suggested that such high juvenile mortality rates would lead to selection for production of smaller offspring in higher numbers.  If the Elephas species dwarfed rapidly (dwarfing has been estimated to occur as quickly as 3000 years), then the small elephants minimized their individual energetic needs, and could prevent resources on the island from being depleted (note that limited resources is not driving dwarfism in this case, as in the first model).  The authors’ primary evidence that resource deprivation was not driving dwarfism is that an earlier species of elephant that dwarfed on the island, but to a lesser degree, was subject to even more constraints than E. falconeri.  Thus, Raia et al. (2003) supported the optimal body-size hypothesis.

Raia et al. (2003) thought that by aiming for an optimum body size (100 kg in this case) the energy the elephants were saving in growth could be put toward reproduction, specifically reproducing earlier and at faster rates, increasing intraspecific competitive success and reproductive fitness as a result.  Since the authors (Raia et al., 2003) documented a large percentage of juveniles in the assemblage, they assumed that reproductive output was high for the population.  Other evidence that they provided to support increased allocation of energy to reproduction includes a lack of tusks in females and paedomorphosis of the adults.  They note that organisms with fast growth rates tend toward high juvenile mortality rates, which would explain the estimated mortality rates for juveniles of this species (leading us back to selection for larger numbers of smaller offspring).

It’s clear to see how these two models are connected with one another. Both are dependent on a reduction in predation and competition pressures and both emphasize the importance of maximizing individual reproductive success. The difference is that one is driven by the fact of diminished resources and the other by the selective advantage of maximizing energy allocation for reproduction by balancing it with a reduction in energy utilized for growth.

Problem

Homo floresiensis is the first documented example of a hominin “following” the “island rule.”  The researchers who discovered the material believe that there is enough anatomical evidence to show that this species is most likely a dwarfed descendent of a physically larger population of Homo erectus that may have used watercraft to reach the island.  This could be the case if the dates at the Mata Menge site are accurate and Homo erectus did inhabit the island at approximately 900 kyr.  It is feasible that this population was the one that came to the island with stone tool technology, hunted already dwarfed Stegodon, became dwarfed themselves, potentially in as little time as 3000 years, and survived in a dwarfed state for nearly a million years.  It is also possible, of course, that it was not this Homo erectus population that evolved into Homo floresiensis, but a later population of Homo erectus (or another species) and that Homo floresiensis only inhabited the island for 75,000 years.  Regardless,  if one accepts that Homo floresiensis is the product of island dwarfism of a larger hominin species, then these tiny hominins beg one question in particular, among many: Why dwarfism?

Why did a large bodied hominin species become dwarfed?  In order to get at the marrow of this question, we can approach it in the context of the two models of dwarfism presented earlier.  Therefore I would ask: Did Homo floresiensis evolve because of diminished resources that affected the stature of a population trying to survive in such conditions or was dwarfism a more complex process related to a need to expend energy on reproduction in order to maintain fast growth rates, a young age for sexual maturity and high reproductive output?

In a brief discussion of this issue, Brown et al. (2004) proposed that Flores offered a limited supply of energetic resources for hominins.  They proposed that such a low caloric environment would favor individuals that were smaller and required less caloric intake.  Essentially, they support the first model presented earlier for why body-size reduction occurs in large mammals on islands.  Brown et al. (2004) do not investigate this issue any further, however, and do not supply strong evidence for this explanation, except for mentioning that other authors have shown that modern human foragers in tropical rainforests, in the absence of agriculture, do not have access to an abundant supply of calories.

Therefore, I feel that a more in-depth analysis of the question, “Why dwarfism?,” as it applies to the Flores hominins, is necessary.

Methods 

As a first step to this investigation, predation pressure would be assessed.  Predation affects both models, as they both call for reduced predation pressure as a precursor to dwarfism.  This is fairly simple to address.  The only potential hominin predators on the island are the Komodo dragon and another varanid (Brown et al., 2004).  Today, Komodo dragons on the island of Komodo near Flores eat “any and all of the other large animals on the island, including wild boar, deer, water buffalo, dogs and goats. If hungry, a Komodo will eat snakes, birds, and even smaller Komodos” (PBS Online, 2004).  The bite of a Komodo is extremely poisonous and deadly.  These large reptiles have been clocked at speeds up to 20 miles per hour.  Clearly, a small hominin would be susceptible to being attacked by a Komodo, but potentially the hominins were able to avoid these large predators somehow or were able to defend themselves with weapons.  Examining Komodo bones for evidence of cut marks would be worthwhile to determine whether the hominins defended themselves against, or even hunted, these animals.  If one could conclude that the hominins were able to defend themselves against these large predators easily, or that veranids seldom attacked hominins, one could assume that predation pressures were low on Flores.

The next step is to assess interspecific competition.  Brown et al. (2004) report that the fauna of Flores comprised monkeys, deer, and birds.  If the Flores hominins were greatly dependent on fruits, these species may have been competition for them.  One way to investigate this would be through dental morphological, microwear and isotope analyses.  Microwear and isotope analyses could be informative regarding the composition of the hominin diet. If the evidence did not suggest that hominins were incorporating significant amounts of tropical fruits into their diet, to the degree that they were the primary staple of their diet, then interspecific competition may have been low, as is required in both models.

Another way to assess interspecific competition would be to try and determine whether the hominins were in fact hunting with the stone tools found in the assemblage.  If evidence of hunting (cutmarks on mammal bones) were found, then this could also support reduced competition with primates, browsing artiodactyls and bird species.  The only interspecific competition then would be with the other predators on the island – the veranids.  If the relative population sizes of hominins and veranids could be estimated, this could possibly be used as an indicator of whether they were competing for resources.  An analysis of dwarfed Stegodon bones (the species most likely preyed upon by both) for hominin cut marks or reptile damage could be used to assess this, as well.

If established that predation pressures and competition levels were low for the Flores hominins, one could investigate which of the models of dwarfism is more applicable.  Brown et al. (2004) presented an argument that modern foragers in tropical forests face low caloric resource availability, but this research is not specific to island foragers.  A study of any non-agricultural island forest populations would be a more appropriate analog since it has been documented that island environments tend to differ dramatically from their mainland equivalents.  Also, an assessment of growth and development in island tropical forest forager populations would shed light on whether this purported reduction in caloric intake does affect their stature.  Such a study may be quite challenging, as any such population may not be accessible (geographically or culturally) to researchers.

Modern pygmy populations live in forests and have reduced stature, but this has been shown to be related to other factors besides diminished resources (Brown et al., 2004).  And although their stature is reduced, brain size and cranio-facial proportions in pygmies are not reduced in the way they are in the Flores specimen.  As a result, pygmies and other modern human forest foragers may not be an appropriate analog for the Flores hominins.

Therefore, it may be more useful to assess the other Flores island animal that dwarfed to determine if the cause for dwarfism in that species, Stegodon, may have been a result of stunting from resource deprivation.  An investigation into the dietary habits of the dwarfed Stegodon, based on dental morphology or isotope analysis, could be informative in this case, in particular determining whether Stegodon was a specialist, or like other elephants, an effective generalist, in which case resource deprivation would not likely have been the cause for reduction in body-size.  Notably, most of the Stegodon from Liang Bua are juveniles, a pattern seen in Raia et al.’s (2003) study of Elephas falconeri, possibly indicating a high reproductive output and fast growth rates associated with high juvenile mortality.

It must be addressed here that relatively fast growth rates and a relatively young age at sexual maturity are both characteristics that have been inferred for Homo erectus (Dean et al, 2001).   Analyses of growth and development of the Nariokotome skeleton of Homo erectus, from studies of the dentition, have concluded that Homo erectus had a more ape-like (vs. Homo sapiens-like) growth trajectory.  This means that Homo erectus grew faster and became sexually mature earlier when compared to modern humans.  The Nariokotome skeleton provides an estimated stature of at least six feet for that individual and an age estimate of only 8 years.  This is relevant here because if Homo floresiensis did evolve from a Homo erectus ancestor, it is possible that the first population to inhabit this island already had to maintain fast growth and development rates.  This is only possible when high quality resources are available, otherwise there will be a trend toward lower reproductive rates.  It doesn’t seem reasonable that a species with an already high demand for high quality resources could migrate to a low caloric environment, experience decreased reproductive rates and stunting of growth, and yet be so successful for so long, whether that was 75,000 years or a million years.

It order to determine whether growth and development of Homo floresiensis was similar to that documented for Homo erectus an analysis of dental growth and development similar to that of Schwartz and Godfrey (2003) or  the analysis of the Nariokotome skeleton (Dean et al., 2001) should be conducted.  This could be used as evidence that Homo floresiensis was phylogentically predisposed to having a fast growth rate and an early age for sexual maturity.

If the resources on Flores were so poor that the original hominin inhabitants were subject to resource deprivation, one could question (though probably not test) whether they would have survived long enough to become dwarfed (even though this is a relatively fast process). A species with such high energetic demands would probably suffer from low reproductive rates and a reduction in growth rates as a result.  If an analysis of the dentition showed that Homo floresiensis maintained a growth curve like that of Homo erectus, or even increased the rate an which they reached sexual maturity (as documented in dwarfed Elephas) one might conclude that the resources on Flores were of relatively high quality.  Evidence for successful hunting of Stegodon or veranids by the hominins could support this argument.

So if resources were adequate and caloric intake was reasonably high, then why was a reduction in body size selected for in these hominins?  We can revisit Raia et al.’s (2003) study of Elephas falconeri.  Elephants have a long pregnancy duration, precocial offspring, and only have one offspring at a time.  Raia et al. (2003) suggest that if Elephas evolved toward an optimum body size (100 kg in this case) the energy the elephants were saving in growth could be put toward reproduction, and even allow for earlier and faster reproduction, increasing intraspecific competitive success and reproductive fitness in an environment with finite resources (both energetic and reproductive).  But, if Homo erectus already had fast growth rates and were producing offspring at a maximally young age, this might imply that a reduction in body size was predominantly a result of reduced predation pressures and interspecific competition.  In an environment with adequately high quality resources and relaxed selection pressures such as these, Homo erectus may simply have had no reason to be big.  A trend toward a body size that was optimal for survival – one that balanced energy expenditure for resource acquisition and for reproduction may have been inevitable and unavoidable.  And once this was achieved, the species was able to thrive in that environment for tens of thousands of years.

In order to test the hypothesis that this Homo population got smaller mostly as a result of relaxed selection pressures – “just because it could” – the relationship between Homo erectus and Homo floresiensis body size needs to be clearly understood.  A thorough analysis of the material using allometric formulae needs to be performed.  If the size and shape of Homo floresiensis’ skeletal features do not correspond with it being a “scaled down” version of Homo erectus other avenues of explanation of how and from what taxon Homo floresiensis evolved would need to be explored.  In addition, as assessment of whether any of Homo floresiensis’ features can be considered paedomorphic is important.  The dwarf species of Elephas appears to exhibit paedomorphism, and this is evidence used to support the reallocation of energy away from growth and development and toward reproduction.  If Homo floresiensis is thought to be peadomorphic in any way, this could support the second model.

Summary

Homo floresiensis provides evidence for the first identified case of island dwarfism in a hominin population.  Some authors (Brown et al., 2004) have suggested that the dwarfism was a result of an initial population (on Flores or a nearby island) having to survive in a low caloric environment.  Calorie restriction, however, has been associated with delayed sexual maturity, decreased reproductive efforts, and a “shift toward a greater investment in somatic maintenance” (Raia et al., 2003:302).  This trend would not be consistent with the fact that this hominin population could have thrived on the island for anywhere between 75,000 and one million years.  A more likely explanation might be that, given a phylogenetic predisposition for fast growth and reproductive rates, respectable resources, and, most importantly, reduced pressure from predation and interspecific competition, this hominin species evolved toward an optimal body size “just because it could.”

A detailed paleoecological analysis of the flora and fauna in deposits associated with Homo floresiensis skeletal remains will be very informative, particularly with regard to estimating predation and interspecific competition levels.  This information, combined with dental morphological, microwear and isotopic analyses of the Homo floresiensis specimens, as well as zooarchaeological analyses of the skeletal remains of the Stegodon and the veranid species, will shed light on the diet of these diminutive hominins.  The combination of dietary information with knowledge of the growth and development of this species, allometric relationships between Homo erectus and Homo floresiensis and any evidence of paedomorphism could elucidate the driving mechanisms for this incidence of island dwarfism.

References

Angerbjorn, A., 1985. The evolution of body size of mammals on islands: Some comments. American Naturalist 125, 304-309.

Brown, P., Sutikna, T., Morwood, M.J., Soejono, R.P., Jatmiko, E.W.S., Due, R.A., 2004. A new small-bodied hominin fossil from the Late Pleistocene of Flores, Indonesia. Nature 431, 1055-1061.

Case, T.J., 1978. A general explanation for insular body size trends in terrestrial vertebrates. Ecology 59, 1-18.

Damuth, J., 1993. Cope’s rule, the island rule and the scaling of mammalian population density. Nature 365, 748-750.

Dean MC, Leakey MG, Reid D, Schrenk F, Schwartz GT, Stringer C & Walker AC., 2001. Growth processes in teeth distinguish modern humans from Homo erectus and earlier hominins. Nature 414, 628-631.

Foster, J.B., 1964. The evolution of mammals on islands. Nature 202, 234-235.

Lawlor, T.E., 1982. The evolution of body size in mammals: evidence from insular population in Mexico. American Naturalist 119, 54-72.

Lomolino, M.V., 1985. Body size of mammals on islands: the island rule reexamined. American Naturalist 125, 310-316.

Morwood, M.J., O’Sullivan, P.B., Aziz, F., Raza, A., 1998. Fission-track ages of stone tools and fossils on the east Indonesian island of Flores. Nature 392, 173-176.

Morwood, M.J., Soejono, R.P., Roberts, R.G., Sutikna, T., Turney, C.S.M., Westaway, K.E., Rink, W.J., Zhao, J.-x., vandenBergh, G.D., Due, R.A., Hobbs, D.R., Moore, M.W., Bird, M.I., Fifield, L.K., 2004. Archaeology and age of a new hominin from Flores in eastern Indonesia. Nature 431, 1087-1091.

PBS Online, 2004.  Wild Indonesia.  http://www.pbs.org/wildindonesia/

Promislow, D.E.L., Harvey, P.H., 1990. Living fast and dying young: a comparative analysis of life history variation among mammals. Journal of Zoology London 220, 417-437.

Raia, P., Barbera, C., Conte, M., 2003. The fast life of a dwarfed giant. Evolutionary Ecology 17, 293-312.

Roy, K., Jablonski, D., Martien, K., 2000. Invarient size-frequency distribution along a latitudinal gradient in marine bivalves. Proceedings of the National Academy of Science 97, 13150-13155.

Schwartz, G.T., Godfrey, L.R., 2003. Box 3. Big bodies, fast teeth. Evolutionary Anthropology 12, 259.

Sondaar, P.Y., 1977. Insularity and its effects on mammalian evolution. In: Goody, P.C., Hecht, M.K., Hecht, B.M. (Eds.), Major Patterns in Vertebrate Evolution. Plenum Press, New York, pp. 671-707.

Sondaar, P.Y., 1987. Pleistocene man and extinction of island endemics. Mem Soc Geol Fr 150, 159-165.

Symonds, M.R.E., 1999. Insectivore life histories: further evidence against an optimum body size for mammals. Functional Ecology 13, 508-513.

VanValen, L., 1973. Pattern and balance of nature. Evolutionary Theory 1, 31-49.

[1] It has been suggested that the term “nanism” is more appropriate for describing evolution of reduced body-size than dwarfism (Gould and McFadden, 2004).  Despite this, I will use dwarf and dwarfism to reflect terminology used by the authors that published the description of the Flores material.

[2] This term was actually coined by Van Valen (1973; Lomolino, 1985).

[3] Lawlor (1982) is specifically referring to seed specialists here, but remarks, “food deprivation…must occur commonly in large mammals on islands [and]…selection should favor small body size as the metabolically most expeditious way to contend with prolonged food shortages” (67).

[A writing assignment submitted for credit at Arizona State University in December, 2004.]

Why Dwarfism? (.pdf download)


An Open Bar Graph to the Supreme Court

In May, 2009, a USA Today survey conducted by the Gallup Organization*asked 608 U.S. adults age 50 and over if marriages between same-sex couples should or should not be recognized by the law as valid, with the same rights as traditional marriages.

Of those 608 U.S. adults age 50 and over, 35% responded that same-sex marriage should be recognized by the law as valid.

62.7% of them responded that same-sex marriage should NOT be recognized by the law as valid.

In the Fall semester, 2010, and Spring semester, 2011, I obtained the following responses to an anonymous online survey of 468 U.S. adults age 18-22.

Same sex marriage

Survey results based on 486 anonymous online questionnaire responses. Sample: U.S. adults, ages 18-22 inclusive, enrolled in at least one course at a large state university, who graduated from a public high school in the U.S.

Bar Chart Citation: Schrein, C.M. (2013) Unpublished data. paleophile.wordpress.com (Access date).

*Acknowledgement: The survey results reported here were obtained from searches of the iPOLL Databank and other resources provided by the Roper Center for Public Opinion Research, University of Connecticut. Citation: Gallup/USA Today Poll, May, 2009. Retrieved Mar-27-2013 from the iPOLL Databank, The Roper Center for Public Opinion Research, University of Connecticut. http://www.ropercenter.uconn.edu.proxygw.wrlc.org/data_access/ipoll/ipoll.html


What is evolution?

Evolution is a phenomenon.

A phenomenon is an occurrence, a circumstance, or a fact that is perceptible by the senses (Source: http://dictionary.reference.com/browse/phenomenon, accessed Sept. 17, 2012).

What humans perceive is that populations of living organisms have changed and are changing over time.

“The theory of evolution” is shorthand for the set of explanations that seek to explain the phenomenon of evolution. Sometimes “the theory of evolution” is also called “evolution,” and this can be confusing.

Really, the theory is “the theory of evolution BY natural selection, genetic drift, gene flow and mutation.” In science, a theory is a set of well-tested hypotheses and repeatable experiments that together provide an explanation for a phenomenon.

Again, evolution is the phenomenon.

Scientists have demonstrated that the processes, or mechanisms, of natural selection, genetic drift, gene flow and mutation, together explain WHY and HOW the phenomenon of evolution occurs.

If you want to be clear, you should use “evolution” to refer to the perceivable fact and “the theory of evolution” to refer to the scientific explanation for why and how evolution occurs.

To be even clearer, you should say, “TTOEBNSGDGFAM” for “the theory of evolution by natural selection, genetic drift, gene flow and mutation.” Pronounce that any way you like, I suppose.

There are not currently any scientific alternatives to TTOEBNSGDGFAM.

So, any legislation that states that public school teachers should be able to teach alternatives to TTOEBNSGDGFAM in their science classrooms is bad legislation that is not based on valid science.

Public school science teachers who state in their classroom that evolution is not a real phenomenon and/or promote (or denigrate) non-scientific views regarding the origins and diversity of life on Earth are at risk of violating the Establishment Clause of the First Amendment of the Constitution (i.e., breaking the law).

p.s. The theory of gravity seeks to explain the phenomenon of gravitation.


Why Intro Bio Should Blow Your Mind…and Why It Probably Doesn’t.

Hey, Mom and Dad,

Classes are going ok, I guess. I dunno. I thought I liked biology, but I really don’t. Now I’m not sure what I’m going to major in. Sigh. It’s not that it’s hard, really, I just don’t get all these stupid experiments we’re doing because we go so fast and just follow all the stupid steps in the lab manual and I don’t even learn anything. And the professor goes so fast and the lectures and the labs don’t match up with each other. I feel like I’m in high school biology again, but there’s just 100x more stuff to know. Whatever. I like that art class I’m taking. Maybe I’ll major in that. Maybe if the other kids in my bio class actually cared about what we’re learning, it would help, but they don’t. And the teacher is always so grouchy. She’s a grad student or something (you went to grad school, right, Mom?) and always seems tired. I thought I wanted to do the cancer research thing, but it just seems so unrealistic now. Grr…can’t wait to come home for my birthday.

Love,

me

vs.

Hey, Mom and Dad,

Classes are going really well. I can’t believe I’m saying this, but I actually think biology is my favorite class. Who knows, maybe I can be a doctor or something one day! I have a pretty good teacher and the lab is really fun. You’re not gonna believe this. Last week we learned how to extract DNA from our own cheek cells!! It was awesome. My group made a few mistakes, but by the third try we got it and we were even able to compare our DNA on this thing called a gel that used electricity to move the DNA. It was really cool. This week we learned how to put DNA from one organism into the cells of another organism! It’s like I’m a bioengineer! Next week, we’re going to take the DNA from jellyfish that glow green under a black light and put their DNA into bacteria cells (the bacteria are E. coli, but don’t worry, I won’t get sick from it!) and then the bacteria will glow green, too, if we do it right! (Remember the green glowing bunny on that episode of Sherlock on PBS!? It’s just like that!) But first we have to figure out how to do it. That’s the best part — figuring it out. My group is pretty good and messes up a lot, but we usually get it right before the other kids in the class, which appeals to my competitive side! I can’t believe how much better this class is than I thought it would be. It helps that the lab instructor is really enthusiastic and takes her time to explain stuff to us. Some of my other teachers aren’t like that. And the best part is, she explains why this is important. We’re not just doing stuff for the sake of doing it. She’s a grad student and she actually uses this stuff in her Ph.D. research. I mean, she said one day I could probably work in a lab doing cancer research or something! Wouldn’t that be awesome? I could cure cancer! Woo! Gotta run. Lots of laundry to do.

Love ya!

me


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