Tuesday, March 30, 2010


When a population's traits gradually revert to a past form, some consider it to be Devolution. An example of this is mammals going back to water (47). Coyne also notes that some populations experience little/no change over long periods of time. Horseshoe crabs and gingko trees have barely changed at all (4). As we trace the fossil record, we see the appearance of increasingly complex organisms. However, we often still see the simplest organisms thriving.

What are some living organisms that have simple anatomy. Why would there be a selective advantage for simplicity? How does the organisms rudimentary make-up affect structure and function of its biological mechanisms? How does the simplicity affect the evolution of its population (past, present, future)?


  1. In terms of having a simple anatomy, it seems to be a bit of a subjective question. Nevertheless, examples of the simplest living organisms range from bacteria to algae, while a simple anatomy may revolve around an organism that has less evolved body parts, such as a the Tiktaalik rosease who has a less developed neck and legs than the Acanthostega gunnari (Coyne). Once again, however, a simple anatomy is simply too subjective to describe an organism because that depends on the expertise of the person describing the organism.
    A selective advantage for simplicity would mainly lie in the fact that the organism is usually more out of reach because a simple anatomy usually implies a smaller body. As a result, when competition for food is evident between a predator and its prey, the organism with a simple anatomy, being smaller, is usually out of the way, and more likely to survive and reproduce. Inside an organism with a simple anatomy, there are less parts subject to clogging, damage, and overall tidying up to do. For instance, humans have a lot of organs, making them subject to more damage than organisms with a more simple anatomy. For instance, after a comprehensive study was done on the first generation GMOs used, 3 caused adverse affects—and on more than one organ. “The data ‘clearly underlines adverse impacts on kidneys and liver, the dietary detoxifying organs, as well as different levels of damages to heart, adrenal glands, spleen and haematopoietic system,’ reported Gilles-Eric Séralini, a molecular biologist at the University of Caen” (Ananda). Hypothetically speaking, giving GMOs to simple organisms would yield damage, but less damage because of the fewer amounts of organs, providing a selective advantage in surviving, while in humans it was detrimental.
    In regards to structure and function, I’d like to shift to an even simpler anatomy and that would be of bacteria. Unlike organisms with a complicated anatomy, bacteria have a very “economic” genome (Field, Wills), meaning that it isn’t long and more regions are used for regulations at a time. Interestingly enough, these genomes include “microsatellites” that “provide a general source of molecular markers to track disease outbreaks and the evolution of microorganisms.” Essentially, a more simple anatomy requires an organisms to use its genome in a way similar to that of more complex anatomical organism do, but in a different way, using less organs or organelles to make changes, and instead using its DNA directly to make changes. In order to tie this in with evolution, there is evidence that shows that the development of organs has been the medium for which more complicated functions could be completed instead of having the genome do all of the work, partly representing the difference between simple and complex anatomies.
    The problem with the last question is similar to that of the first because it all depends on how simple the anatomy of the organism is. For instance, bacteria can much more easily adapt to its environment and evolve rapidly (Campbell). One problem that lies with the evolution of simple anatomical organisms is the lack of vestigial organs. For example, animals with more complex anatomies that include vestigial organs have the opportunity to devolve and use them like they have in the past; unfortunately, the lack of vestigial organs in simple organisms takes away opportunities from evolution by taking away potential selective advantages. But once again, the evolution of simplicity is much more subjective so there are endless options to how this question could exactly be interpreted and answered.

  2. Sorry for the second post, but here are my sources for the post above:

    Jerry Coyne: Why Evolution is True

    Niel Campbell and Jane Reece: Biology: AP Edition 8e



  3. Simplicity in an organism can be found in many organisms. The reason is because natural selection does not occur where the environment or any other forces doesn't propose a force for the course of evolution. For example, compared to 1940s, most of the bacteria species do not get killed by the penicillin (Coyne 140-142). However, the 5% of the bacteria that was not killed proposes that some bacteria does not evolve, or go through natural selection. The reason is because there is no force, nor there is a drive or an ambition, for an organism to evolve in a specific way. In the early ancestral protists, the evolution initially branched off cnidarians and Calcareans. This branching off showed that there were differences in between these two species. For example, there is a gastrovascular cavity in the cnidarians. However, the Calcareans and Siliceans are described as a suspension feeders. Such differences show that an organ that is not developed in the calcarean is not required for that specie to survive. Another example of the simplicity of the organism is that many early branched species do not contain closed circulatory system. One major reason for the circulatory development is because closed circulatory provides a specialized pathway for gas exchanged. Because the diffusion of gas is slow, open circulatory system requires longer time to exchange the gas between the body cells and the outside. However, with the closed circulatory system, the gas exchange can occur much more efficiently. Although the open circulatory system seems to be 'simple,' in a specie that has not a big body size, such as some arthropods, do not require the closed circulatory system. Although, like Presman said, the simplicity is a subjective thought of a human mind, there are many systems that work for these species. That is why these species do not have to adapt and survive with new genetic mutations.


    Jerry Coyne: Why Evolution is True

    Niel Campbell and Jane Reece: Biology: AP Edition 8e

  4. Some organisms with relatively simple anatomy would include unicellular eukaryotes. Compared to more advanced organisms like humans, other animals with simple anatomy may be molluscs and arthropods as they have open circulatory systems. One selective advantage for simplicity is that the organism expends less energy than if it had several organs to regulate. In terms of structure and function, organisms with open circulatory systems have a central cavity with fluid lacking transport vessels. This fluid is pumped by a heart(s)into the general area of organs. An organism with a closed circulatory system has vessels to transport that vistitial fluid allowing the fluid to get closer to the intended organ. However, this requires greater energy and blood pressure. Simplicity affects evolution in different ways. We have seen simple organisms with mutations develop new traits or genes allowing for a selective advantage (much of popular evolution ie. ancestors of apes to humans)or even with bacteria overcoming antibiotics. We have also seen Devolution. Simple organisms have less of a chance for devolution because they lack the numerous/more complicated organs to simplify.

    Why Evolution is True, Coyne

  5. One example of a kingdom that houses organisms with simple anatomy is the Kingdom Archaea. These organisms can be considered simple because they have no nucleus or other organelles within their cells. One selective advantage that archaea have due to their simplicity is the prevention of DNA damage. The genome of the archaea is mostly held in a single circular DNA molecule. Because of the small size of the genome compared to those of more complex prokaryotic and eukaryotic organisms, there is a smaller probability that the DNA of an archaean cell be damaged extensively. Less DNA damage would lead to less chaos overall inside the cell, since the DNA codes for specific proteins that the cell needs to survive. Had the DNA inside an archaean cell been damaged, transcription and translation would result in the wrong mRNA and proteins being made, respectively. Archaean cells have a phospholipid bilayer cell membrane that is unique - the type of bond that joins the lipids to the glycerol group in the membrane is an ether bond, whereas in prokaryotic and eukaryotic cells, this bond is an ester bond. Ether bonds are chemically more resistant, which might contribute to the ability of some archaea to survive at extreme temperatures and in very acidic or alkaline environments, according to an article in "The Microbial World." A study conducted by Simonetta Gribaldo and Celine Brochier-Armanet in 2006 found that Bacteria derived directly from the last universal common ancestor (LUCA), whereas Archaea and Eukarya share a last common ancestor more recent than LUCA, and are thus sister lineages. This widespread vision of relationships among domains is the reason why the similarities between the informational mechanisms of Archaea and Eukarya are commonly perceived as derived features that appeared in the lineage leading to their common ancestor, while bacterial counterparts represent ancestral traits.However, it is also legitimate to postulate that Archaea and Eukarya have retained ancestral traits, while Bacteria are very derived. Eventually, all three domains may harbour derived traits, and none of them can be traced back to the LUCA.