|
home | what's new | other sites | contact | about |
|||
|
Word Gems exploring self-realization, sacred personhood, and full humanity
Lamarckianism Heredity depends both on
return to "Evolution " main-page
Editor's note: The following is from Dr. Sheldrake's book, "The Presence of the Past."
GENES AND FIELDS Living organisms inherit genes from their ancestors. According to the hypothesis of formative causation, they also inherit morphic fields. Heredity depends both on genes and morphic resonance. The conventional theory attempts to squeeze all of the hereditary characteristics of organisms into their genes. Development is then understood as the expression of these genes through the synthesis of proteins and other molecules. The words hereditary and genetic are usually treated as synonyms, and inherited characteristics, such as the ability of an acorn to grow into an oak tree or of a wren to build a nest, are usually referred to as genetic or as genetically programmed. Certainly DNA is inherited genetically. Some DNA codes for the sequence of amino acids in proteins, some DNA codes for RNA such as that found in ribosomes, and some DNA is involved in the control of gene expression. However, in higher organisms only a small percentage of the DNA (in humans, only 1%) seems to be involved in such coding and control. The function, if any, of the vast majority [of DNA] is unknown although some probably plays an important structural role in the chromosomes. Moreover, the total genetic inheritance seems to bear very little relationship to the complexity of the organism. One of the big surprises of the Human Genome Project is that we have only about 20,000 – 25,000 genes, far fewer than the 100,000 expected. Sea urchins have more genes than we do, about 26,000, and many species of plants have more still – rice has about 38,000, and the cells of lilies contain about thirty times more DNA than human cells. Among amphibians, some species have one hundred times more DNA than others. There is also a poor correlation between the genetic differences between species and the form and behavior of these species. Thus, for example, human beings and chimpanzees have genes that code for almost identical proteins: “The average human polypeptide is more than 99% identical to its chimpanzee counterpart.” Direct comparisons of the DNA sequences believed to be of genetic significance show that the overall difference between the two species is only 1.1%. Just before the entire chimpanzee genome was published in 2005, Svante Paabo, the director of the Chimpanzee Genome Project, commented that “we cannot see in this why we are so different from chimpanzees.” By contrast, comparisons of species that are very similar to each other, such as different kinds of fruit flies in the genus Drosophilia, often reveal considerably greater genetic differences than those between humans and chimpanzees. From the point of view of the hypothesis of formative causation, DNA, or rather a small part of it, is responsible for the coding of RNA and the sequence of amino acids in proteins, and these have an essential role in the functioning and development of the organism. But the forms of the cells, tissues, organs, and the organisms as a whole are shaped not by DNA but by morphic fields. The inherited behavior of animals is likewise organized by morphic fields. Genetic changes can affect both form and behavior, but these patterns of activity are inherited by morphic resonance. Consider the analogy of a television set tuned to a particular channel. The pictures on the screen arise in the TV studio and are transmitted through the electromagnetic field as vibrations of a particular frequency. To produce the pictures on the screen, the set must contain the right components wired the right way and also requires a supply of electrical energy. Changes in the components, such as a fault in a transistor, can alter or even abolish the pictures on the screen. But this does not prove that the pictures arise from the components or the interactions between them, nor that they are programmed within the set. Likewise, the fact that genetic mutations can affect the form and behavior of organisms does not prove that form and behavior are coded in genes or programmed genetically. The form and behavior of organisms do not arise simply from mechanistic interactions within the organism or even between the organism and its immediate environment; they depend on the fields to which the organism is tuned. To pursue this analogy, developing organisms are tuned to similar past organisms, which [like the TV studio] act as morphic “transmitters.” Their tuning depends on appropriate genes and proteins, and genetic inheritance helps to explain why they are tuned in to morphic fields of their own species: a frog’s egg tunes into frog fields rather than newt or goldfish fields because it is already a frog cell containing frog genes and proteins. Genetic mutations affect morphogenesis in two main ways. First, they can lead to distortions or alterations in a normal morphogenetic process, just as “mutant” components in a TV set can lead to distortions or alterations in the form or color of the pictures. Second, they can result in the suppression of entire morphogenetic processes or in their replacement by different ones. These are analogous to the “mutations” in the tuning circuit in the television: the original transmission is no longer picked up; either the screen goes blank or the set picks up a different channel… [Dr. Sheldrake speaks of the DNA of fruit flies.] Because the genes are so similar in fruit flies and in us, they cannot explain the differences between flies and humans. It was shocking to find that the diversity of body plans across many different animal groups was not reflected in diversity at the level of the genes. As two leading developmental molecular biologists, J.C. Gerhardt and M. Kirschner, commented, “Where we most expect to find variation, we find conservation, a lack of change.” … THE LAMARCKIAN INHERITANCE OF ACQUIRED CHARACTERISTICS If plants of a particular species are grown under unusual conditions, for example, at a high altitude, they generally develop unusually. The modified form they take up is an “acquired characteristic,” which has come about in response to environment. Likewise, if rats learn a new trick, this is an acquired behavioral characteristic as opposed to an inherited instinct. Until the late nineteenth century, it was almost universally believed that acquired characteristics could be inherited. The zoologist Jean-Baptiste Lamarck (1744 – 1829) took this for granted, as did Charles Darwin. In this respect, Charles Darwin was a convinced Lamarckian. He believed that habits acquired by individual animals could be inherited and that they played an important part in evolution: “We need not … doubt that under nature new races and new species would become adapted to widely different climates, by variation, aided by habit, and regulated by natural selection.” Darwin provided many examples of the inheritance of acquired characters in his book The Variation of Animals and Plants under Domestication, and he also proposed a theory to explain it, the theory of pangenesis. The idea of Lamarckian inheritance has the great advantage of making sense of many of evolutionary adaptations of organisms. For example, camels, like many other animals, develop thick calluses on their skin as a result of abrasion. They possess such calluses on their knees just where the skin is subject to abrasion as they kneel down. Baby camels are born with thick pads on their knees at exactly the right places. From a Lamarckian point of view, such calluses were acquired by ancestral camels as a result of kneeling, and then over many generations this acquired characteristic became increasingly hereditary, developing even in embryos before they have ever had a chance to kneel. This idea is straightforward enough and has a strong “commonsense” appeal. However, it was denied dogmatically by neo-Darwinians, who, unlike Darwin, reject the possibility of such inheritance. From a neo-Darwinian point of view, camels are born with pads on their knees not because their ancestors acquired them as a result of their habits but because they arose as a result of chance genetic mutations that just happened to produce pads in the right places. The mutant genes “for” knee pads were favored by natural selection because they gave an advantage to camels born with pads on their knees… Editor’s note: I suspect that this could not have happened by mutation and natural selection, that is, by chance. As we learned concerning proteins which fold themselves in just the right way, a length of time equal to a duration of trillions of universes would be required to bring this about; even one would be one too many. So, too, baby camels born with perfectly constructed knee-pads, in just the right places, could not have happened via randomness. However, the math-challenged materialist will not be slowed down though one of his “religious doctrines” needs some buttressing; so much buttressing needed for this house-of-cards. [T]here is now good evidence that an inheritance of acquired characteristics does in fact take place.
EPIGENETIC INHERITANCE Around the turn of the millennium, the taboo against the inheritance of acquired characteristics began to lose its power with a growing recognition of a new form of inheritance called epigenetic inheritance.
The prefix “epi” means “over and above.” Epigenetic inheritance does not involve changes in the genes themselves but rather changes in gene expression. Characteristics acquired by parents can indeed be passed on to their offspring. For example, water fleas of the genus Daphnia develop large protective spines when predators are around; their offspring also have these spines even when not exposed to predators. Several molecular mechanisms of epigenetic inheritance have been identified. Changes in the configuration of the chromatin – the DNA protein complex that makes up the structure of chromosomes – can be passed on from cell to daughter cell. Some such changes can also be passed on through eggs and sperm and thus become hereditary. Another kind of epigenetic change, sometimes called genomic imprinting, involves the methylation of DNA molecules. There is a heritable chemical change in the DNA itself, but the underlying genes remain the same. Epigenetic inheritance also occurs in humans. Even the effects of famines and diseases can echo down the generations. The Human Epigenome Project was launched in 2003 and is helping to coordinate research in this rapidly growing field of inquiry. Morphic resonance provides another means by which the inheritance of acquired characteristics can occur. Its effects can be distinguished experimentally from other forms of epigenetic inheritance discussed below… [Dr. Sheldrake provides examples, the Waddington and Ho fruit-fly experiments, presented on this page.] For decades, the debate about Lamarckian inheritance has centered not so much on empirical evidence for or against such inheritance as on the question of whether such inheritance is theoretically possible. Editor’s note: Why wasn’t the evidence looked at? Because they considered it to be “taboo.” Consider the circular reasoning. Materialists for decades insisted that non-genetic transmission of characteristics was not possible, and therefore “we don’t need to look at the evidence, we already know we're right.” We discussed this faulty reasoning, how the ramshackle philosophical House of Darwin is constructed, on this page. According to the genetic theory of inheritance it is impossible because the genes cannot be specifically modified as a result of characteristics that organisms acquire in response to their environment or through the development of new habits of behavior. Lamarckians assumed that genetic modifications must take place but were unable to suggest how. Epigenetic inheritance through the modification of the DNA or the chromatin provides a new way in which the inheritance of acquired characteristics can happen. The hypothesis of formative causation provides another: acquired characteristics can be inherited by morphic resonance. This inheritance can take place without any transfer of genes at all. For example, as we have just seen, fruit flies may inherit a tendency to develop abnormally in response to ether from fruit flies of the same strain without inheriting any modified genes from them and, indeed, without any physical contact.
|
|||
|
|
