Wednesday, April 7, 2010

Lamarckian (Vestigial) Evolutionary Theory

At the very beginning of the book, Coyne establishes the basis of modern evolutionary theory (Coyne 1-19). On the other hand, Jean-Baptiste Lamarck, one of the “evolutionist biologists” prior to Darwin, proposed his own theory of evolution that has been overwritten with Darwin’s theory. First, describe the two key parts that make up Lamarckian evolution. Then, compare and contrast how these two parts relate to the six parts that compose the modern theory of evolution as described by Coyne. Predict why these two parts could have been more acceptable in a historical context over Darwin’s theory of evolution immediately after the publication of The Origin of Species.Finally, using examples from Why Evolution is True and outside research, briefly describe how either part or both parts of Lamarckian evolution can be disproven using this information.


  1. Larmarckian Evolution is described as gradual work of individuals in a species often using either an organ or muscle, and as it becomes stronger, offspring will benefit from its parents advantages by also developing the same muscles or organs, and eventually "evolving" into a species that would be drastically more complex and different. Also, organs or muscles that are used less will become smaller and weaker until they eventually disappear. Examples of Larmackian evolution is said to be explain the long necks of giraffes (them stretching their necks higher and higher each generation to reach the leaves of very tall trees). Looking into this, it would make sense in the context that as giraffes constantly stretched, their muscles would develop, and as their necks grew longer, they would also develop stronger heart muscles to go against the pressure gradient. This example would be categorized as "use and disuse" in which individuals will develop stronger muscles or organs in which they use or disuse. Lamarck's second point was that offspring will have their parents traits. Looking at just humans, a tall father and a tall mother will usually result in a tall son/daughter, or hair color, eye color, etc. Seeing that all these traits are similar to their parents. It wouldn't be wrong to assume that offspring would inherit other traits such as muscular development or the use of an organ.
    Coyne's six parts of evolution consists of: evolution (genetic change), gradualism (slowly changes), speciation (the division of species), common ancestry (LUCA), natural selection (individuals who aren't adaptable die), and processes other than natural selection can cause evolution (mutation).
    Comparing only observable facts such as physical traits, Lamarckian evolution seems to be much simpler, as well as having evidence in which offspring do look similar to their parents. However, examples such as the vast number of total species that ever existed, the fossil record, and genetic research shows that if Lamarck's theory had been true, then there would be no simple organisms such as bacteria. Even so, Lamarck's studies were created from observation of the current tools and world that they could observe, and at the time, it was quite revolutionary despite its flaws. However, new studies in epigenetics could prove that Lamarck's theory could still be half right.

    Biology book
    Why Evolution is True

  2. History of Lamarckian evolution: (source:

    During his lifetime, Lamarck’s scientific theories were refuted, ignored, or attacked. Today, his name is associated with the idea of “the inheritance of acquired traits” which is partially correct; Charles Darwin later on asserted that Lamarck was a forerunner of evolution.
    During his time, Lamarck did not receive accredited attention because he focused on invertebrates (coining the term). Naturalists of his time did not consider invertebrates “worthy of studying” and therefore, did not understand Lamarck’s interest in the greater diversity of invertebrates. Furthermore, Lamarck also commented on the “cellular tissue” component of invertebrates and also dealt with classifications, removing the tunicates and barnacles from Mollusca.
    Lamarck’s evolutionary theories took shape at around 1801; he considered time and favorable conditions to be the two “principle means” by which nature acts to produce existence. His assertions are similar to Darwinian Theory in the idea of evolution and natural selection. The fifth part of natural selection, as Coyne states, is the idea of natural selection: the notion that “good genes” will be ahead of the ‘not so good” genes because the good genes lead to a higher chance of survival and therefore chance of reproduction to pass along genes will increase (like Tianyu's examples of the giraffe, etc). Similarly, Lamarck claimed that organisms are not passively altered by their environment but that a change in the environment causes a change in the needs of the organism and therefore resulting in a change in the organism’s behavior to adjust. But this First Law of Lamarck’s was seen as ludicrous because scientists did not believe his assertion that altered behavior leads to greater/lesser use of a structure and therefore causing that structure to expand/shrink (maybe disappear) over generations. While Darwin states that mutations may alter gene expression, to go as far as claiming that organs may change in size is stretching the idea of evolution.
    Lamarck’s Second Law states that such changes expressed in the First Law were heritable.
    Therefore, the overarching idea of evolution is, in a sense, similar when comparing Lamarckian Evolution to Darwinism (the idea that adaptive changes, driven by environmental factors, may result in evolutionary changes), but the mechanism is different.
    While Lamarck should be given credit because he used evidence such as the presence of vestigial structures in animals and the presence of embryonic structures in embryos that later disappear in the adult, other specific parts of his theory are at fault – Lamarck viewed evolution as increasingly “complex” and that eventually a state of perfection is reached; he also thought that species did not become extinct but evolved, which is proven incorrect.
    Because in the beginning of the 20th century, Mendelian inheritance refutes Lamarck’s ideas on genetics, it can be seen that Lamarckian inheritance is in conflict with the current studies on genetics. But during Lamarck’s time, such mechanisms of heredity were not understood as well.

  3. Like Tianyu said Lamarck evolution stated that traits are acquired in one lifetime by a parents and any traits common to both parents are passed down to the offspring. While at first this seems very dissimilar to Darwinian evolution there are many similarities, and even a possibility that both Darwin and Lamarck were correct to some extent. Firstly both Lamarck and Darwin agreed that traits are passed to the offspring from the parents due to an effort of the parents to survive. There are several differences here however. Firstly Lamarck lacks the gradualism aspect of Darwin's theory. Lamarck stated that evolutionary change happened within one generation and that traits common to both parents will be passed. Lamarck is saying that change can happen within one generation a main difference between his and Darwin's theory. Secondly he states that the traits must be common in both parents to be passed on. This is also untrue, as Tianyu already proved, its is not necessary that tall parents will have tall children. Another discrepancy is that Lamarck believed that believed that adaptations came through conscious use and effort from animals. While it is true that our muscles get stronger as we use them it is not a genetic alteration and offspring are not born with that same strength. It is stated by both Darwin and Lamarck that change occurs due to environmental stress, Lamarck, however, believed that adaptations came through increased use while Darwin simply believed that the fittest survived. Lamarck is lacking the process of natural selection.

    While Lamarck seems to be wrong at first, there is some credibility to his theory not initially thought of. For a long time it has been believed that change does not occur in one generation but recent research in the area of epigenetic suggests that change can and does occur in single generations. In this way both Lamarck and Darwin were both partial right. As research progresses in this area there may by a change in our view of evolution possibly a switch in the explanation of the whole theory. This new combined theory may account for some of the unexplained changes seen in todays evolutionary records.

  4. As Tianyu, Mehul, and Mary noted in their posts, a main factor of Lamarckian Theory is that evolutionary changes can be made in a single generation. In that sense, Lamarckian theory may be viewed as a sort of Darwinian Evolution on the micro scale; rather than a diverse range of individuals being naturally selected based on their ability to survive and contribute to the gene pool (Darwin's laws of diversification and selection), Lamarckian theory dictates that a range of organs is constantly being "selected" for continued existence based on their usage in an environment, the first portion of his theory. The second portion states that individuals acquire the traits of their ancestors; ie, a giraffe's neck will be taller if its ancestors' necks were taller.

    Taking into perspective the historical context of the time these theories developed, it is easy to see why Lamarckian theory may have been favored. As Mary noted, there was little to no knowledge of genetics during this time period. Thus, there would have been no knowledge of the permanence of an organism's genetic predisposition, or 'hard inheritance' from its ancestors. More generally, the simple fact that Lamarck's theory contained fewer principles that required proving may have also contributed to its popularity; for Darwin's theory to be proven true, there would need to be conclusive evidence backing each of his 5 principles of evolutionary theory.
    Another element that also may have contributed to this contrast in popularity may have been the fact that evolution spans such a long period of time. Speciation is not something that can simply happen in one lifetime; in happens over hundreds of generations in gradual amounts. Lamarckian theory, on the other hand, could have been backed up readily by examples that individuals of the mid 19th century could view with their own two eyes: the growing muscles of a blacksmith due to their use, on the other end of the spectrum muscular atrophy, the lengthening of giraffe's necks.
    Another key difference between the two theories is that in Darwin's evolutionary theory complexity is not a conscious goal that organisms continually move toward; new organisms are simply the result of gradual processes that may or may not exhibit complexity. Many organisms have remained 'frozen' in time, like the horseshoe crab mentioned by Coyne, not increasing in complexity unless evolutionary pressures dictate that it must to survive. In contrast, Lamarck believed that regardless of use of disuse, over time natural fluid movement would etch out organs from tissues, leading to complexity no matter the environmental pressures.
    Contrary to their respective historical popularities, with the arrival of new advances in genetics and the fossil record, it is evident that Lamarckian modes of thinking conflict with many aspects of our modern knowledge of biology.
    However, with new research into the field of epigenetics, as Mehul mentioned, Lamarck appears to be vindicated to a degree. Epigenetics is the study of factors that affect the methylation of genetic material, which causes it to bunch up and in turn inhibits transcription of the particular sequence it is bunched over. It has been discovered that this methylation can be altered in an individual's lifetime and can be passed on to one's children, in affect the 'soft inheritance' of Lamarck's theory.