The Inheritance of Acquired Characteristics Gains Prominence
Until the 21st century, the scientific community firmly rejected the Theory of Inheritance of Acquired Characteristics, a theory mostly associated with the name of Jean-Baptiste Lamarck (1774-1829). Disapproval of the hypothesis, in which certain acquired characteristics may be heritable, did not dissuade investigators from attempting to prove that the grand old man of evolution may have been right after all.
This has been done. Researchers have launched investigations of environmental effects on DNA and its genes, and shown in a multitude of verified experiments that "offspring can inherit traits their parents acquired." George Bernard Shaw's declaration in the preface of his 1921 book of five plays, Back to Methuselah, that if someone tells you that you are a product of Circumstantial Selection solely, you may offer the counter-assurance that you are the product of Lamarckian evolution," has been cautiously vindicated. Almost one century after Shaw's controversial statement, a July 2010 study, one of many, Epigenetic inheritance in mammals: Evidence for the impact of adverse environmental effects, Tamara B. Franklin, Isabelle M. Mansuy, Swiss Federal Institute of Technology, states "adverse environmental factors can affect not only the individuals directly exposed to these factors but also their offspring. Because the epigenome is sensitive to environmental influence and, in some cases, can, in part, be transmitted across generations, it provides a potential mechanism for the transgenerational transmission of the impact of environmental factors."
This new/old revelation of another mode of heredity has far reaching benefits. The Theory of Inheritance of Acquired Characteristics can eclipse a Darwinian theory of Natural Selection - a principle by which each slight mutation in a species, if useful, is preserved - that lacks total proof and has gathered detractors. The concept of survival of the fittest will be reconsidered. Evolution will graduate from a theoretical study to a practical philosophy that guides our lives.
After presenting the background that generated the vituperative attacks on Lamarck's theory, the results of laboratory investigations that support the Lamarck argument will be described.
Note: The words directed evolution, Inheritance of Acquired Characteristics, Lamarckian evolution, and adaptive mutations are expressions that have slightly different meanings to different persons. For this article the words will be used interchangeably and will have the same context.
The Losing Battle of Lamarck's Supporters
Darwin's Theory of Natural Selection obtained greater scientific recognition, but Lamarck's concepts had support. German Zoologist August Weismann, while performing experiments in the late1880's to prove Lamarck right, convinced himself that Lamarck had been wrong.
Weismann concluded that the cells in mammals that determine heredity (germline) became isolated before birth from the cells (soma) that determine the growth of the mammal. No mechanism had been determined by which changes in the soma could affect the germline, or by which soma changes could be inherited. This discovery, still known as Weismann's barrier, should have ended the discussion. However,in some animals and plants, the separation between germline and soma occur after birth. Those cases contained a possibility of inheritance of acquired characteristics. Weismann's conclusions only made Lamarck's supporters more eager to prove Lamarck's theories by experimentation. It took more than a century to find an alternate path by which the soma can determine inheritance, but not before one of the attempts had tragic consequences.
Austrian biologist Paul Kammer claimed to have living proof that toads (Alytes), which normally mate on land, developed calloused pads in order to hold slippery mates when they became seduced to mate in water.The land toads developed pads after only a few generations. Charges of investigative fraud countered Kammer's claims. He committed suicide six months after the charges appeared and his suicide seemed to confirm the charges. The hostility of the scientific community to Lamarck's supporters, and Kammer's suicide that resulted from this hostility, diminished the ardor of Lamarck's adherents, but not in the Soviet Union.
Russian plant breeder T.D. Lysenko attempted to improve plant yields by inducing "environmental" changes during plant germination with use of a process known as vernalization. Lysenko's work is still controversial. If he had some success, it became buried in the Cold War rhetoric. Having his theories championed by a leading scientist of the Soviet Union further deteriorated Lamarck's image in the West. Lamarckians graduated to Neo-Lamarckians.
The Neo-Lamarckian challenge to Darwin's Theory of Natural Selection hinged on whether mutations were directed or random. Without complete knowledge of the origin of mutations, neither evolutionary theory could claim complete legitimacy. In 1943, Salvador Luria and Max Delbruk showed that cultures of bacteria grown in laboratory dishes, and which survived lethal doses by a selective agent, obeyed the theory of random mutation --t he distribution of the surviving microbes could only have occurred if the bacteria had mutated before presentation of the lethal agent. The statistical distribution of survival indicated that post lethal dose mutations had not occurred. This final blow to Lamarck's concepts still did not permanently deter Lamarck's followers. It encouraged them to examine Luria's tests and devise new ones -- and for good reasons -- Natural Selection had not answered all the problems of its theory and Lamarck's theory had positive social implications that contrasted with the negative impact of Darwin's theory.
Problems with Natural Selection
(1) Why haven't the fossil remains displayed intermediary stages of growth expected from the gradual changes of Natural Selection?
(2) How can the unpredictable nature of random mutations provide a suitable mechanism for the development of complex systems such as the nervous system, eye and armed weapons in animals, such as sprays?
(3) Do a sufficient number of generations exist to adapt to the slow changes predicted by random mutations and evolve to the human species as it exists today?
(4) Does a slight superiority of a positive, but still not obvious benefit of a particular mutation, mean that mating will proceed quickly enough to capture the benefits of the mutation? Can't it more easily lag into obscurity?
Evolutionists have shown that nervous system and eye developments have a variety of intermediate patterns in the animal world and a gradual evolution of these systems is entirely possible. Neo-Darwinist Stephan Jay Gould, who did not have total acceptance from other neo-Darwinists, proposed a Theory of Punctured Equilibrium -- evolutionary changes occur in short and quick bursts. By using this theory, the lack of fossil records and incomplete number of generations become lesser limitations to Darwin's theory. Nevertheless, the perception that limitations remained in the Theory of Natural Selection prompted evolutionists to find a more complete scientific theory of evolution. Their more complete theory did not attempt to contradict Natural Selection; it attempted to complement and strengthen its acceptance.
The Social Elegance of Lamarckian Evolution
Scientific fulfillment was not the only reason driving the Neo-Lamarckians. Lamarckian evolution pleases social reformers. Natural Selection angers them.
- Darwin speaks of competition. Lamarck speaks of cooperation.
- Darwin represents survival of the fittest. Lamarck speaks of the species making itself fit.
- Natural selection makes humankind a pawn of random mutations that indirectly determine its fate. Inheritance of acquired characteristics has humankind more directly involved in its fate.
- Natural Selection is harsh, cruel and insensitive. Inheritance of acquired characteristics is optimistic, soothing and sensitive.
- Natural Selection has not shown practical applications. Inheritance of acquired characteristics promises practical applications that can benefit humankind.
- Random mutations can be lethal. Adaptive mutations are not lethal.The Direction of Proof that Favors Lamarck Efforts to qualify Lamarck's contributions to theories of evolution can be categorized: (1) Subjective reasoning indicated value to Lamarck's ideas. (2) Means for evolution to bypass the Weismann Barrier have been presented. (3) Earlier investigations before knowledge of the genome stimulated additional investigations. (4) Observation of unusually rapid genetic changes contradict Natural Selection. (5) Advanced DNA knowledge and testing methods enabled more conclusive proof of adaptive mutations.
A variety of observations sufficiently satisfied Darwin's followers for them to proclaim the theory of Natural Selection as inviolate -- finches in separated Galapagos Islands evolved to have different beak sizes in order to survive on variable diets; and the speckled peppered moth evolved to blacker varieties, which enabled it to avoid predatory birds by camouflaging itself against soot-covered trees in Britain, darkened by the grime of the Industrial Revolution.
Two problems -- these observations did not have theoretical support or laboratory evidence and did not qualify how the gene changes occurred. Justifications for natural selection as a driving force for specie changes were not more substantial than that for adaptive mutations. The latter more easily explained each one of the phenomenon -- environment determined the required changes in the genes. And these changes were not simply of one or two characteristics -- each one involved many changes in the functions and appearances of the species, something not easily accomplished by random mutations.
As one example, Clifford Tabin and colleagues at Harvard Medical School in Boston have shown that a protein (Bmp) determines beak size and shape in Darwin's finches. As the switch that can turn on genes involved in increasing beak length, the investigation focused on calmodulin, a messenger protein that transduces calcium signals by binding calcium ions and then modifying their interactions with various target proteins,
As for the camouflage process of the peppered moth, Michael Nachman and colleagues at the University of Arizona have pinpointed camouflage mutations of rock pocket mice to a gene MC1R, which acts as a control for how dark and light pigments are produced.
The mechanisms for reacting to the environment have been shown, but what stimulates the genes to remap themselves and how are the effects carried to future generations? The Darwin supporters claim random mutations with differences acted upon by natural selection, which results in the evolution of the species. Refusal to accept Lamarck's adaptive mutations as an explanation were based on the proposition that no means for inheriting gene modification seemed possible. This was true until transgenerational epigenetic inheritance was shown as a mechanism to bypass the Weismann barrier and by which changes in the soma can affect the germline.
Means for evolution to bypass the Weismann Barrier have been presented - Transgenerational Epigenetic Inheritance.
Can epigenetic traits, specific molecular mechanisms that alter gene expression, similar to those shown in finches and peppered moths, bypass Weismann's barrier and be inherited? Recent investigations have solidified a positive response. Two of several studies, none of which are easily paraphrased for the lay reader, clarify the transgenerational epigenetic process.
Rocking the foundations of molecular genetics, John S. Mattick, Garvan Institute of Medical Research, Darlinghurst, Australia, PNAS, October 9, 2012
The available evidence not only suggests an intimate interplay between genetic and epigenetic inheritance, but also that this interplay may involve communication between the soma and the germline. This idea contravenes the so-called Weismann barrier, sometimes referred to as Biologys Second Law, which is based on flimsy evidence and a desire to distance Darwinian evolution from Lamarckian inheritance at the time of the Modern Evolutionary Synthesis. However, the belief that the soma and germline do not communicate is patently incorrectas demonstrated by the multigenerational inheritance of RNAi-mediated phenotypes delivered to somatic cells in Caenorhabditis elegans.
Epigenetic inheritance in mammals: evidence for the impact of adverse environmental effects, Tamara B Franklin, Isabelle M Mansuy, Brain Research Institute, Medical Faculty of the University of Zürich and Department of Biology, Swiss Federal Institute of Technology, Zürich, Switzerland. Neurobiology of Disease, Nov. 2009;
The epigenome is the overall epigenetic state of a cell and represents the ensemble of chromatin modifications. It is an essential mechanism for the regulation of the genome that depends on modifications of DNA and histones but does not involve any change of the DNA sequence. It was previously assumed that in order for appropriate cellular development and differentiation to occur in mammals, the epigenome was fully erased and reestablished between generations. However, several examples of incomplete erasure at specific genes have been reported, and this is suggested to be associated with the epigenetic inheritance of gene profiles. Although the existence of such a mode of inheritance has been controversial, there is increasing evidence that it does occur in rodents and humans. In this review, we discuss the evidence that adverse environmental factors can affect not only the individuals directly exposed to these factors but also their offspring. Because the epigenome is sensitive to environmental influence and, in some cases, can, in part, be transmitted across generations, it provides a potential mechanism for the transgenerational transmission of the impact of environmental factors.
Earlier Attempted Proofs of Lamarckian Evolution
Many experiments have been performed to prove Larmark's concepts. A few of the earlier tests will be briefly mentioned, most of which have their critics and alternative explanations. Recent investigations, which will be mentioned in a later paragraph, have proved more convincing and give Lamarck's theory more recognition.
In 1988, a team of Harvard biologists under the leadership of Joseph Cairns challenged the previous experiments performed by Luria and Delbruck in 1943, which seemed to prove that all mutations occurred randomly and none could be directed. Cairns group reasoned that in the earlier investigations the bacteria had been given too lethal a dose. They died before they could develop and propagate self-directed mutations.
The Harvard experimenters used bacteria that could not grow in a specific environment because they lacked a working gene for an enzyme needed to metabolize the only available food. By genetic engineering, the bacteria were given versions of the necessary gene in which the coded message was, in effect, scrambled and therefore useless. Most, if not all, the bacteria failed to grow. After a few days they began thriving, feeding and reproducing. The distribution of bacteria colonies that survived showed that many bacteria had unscrambled the code and performed self-directed mutations that corrected the deficiency.
Barry G. Hall, an evolutionary biologist at the University of Rochester, NY, damaged cell DNA by two different forms of genetic damage. Mutations that might occur to repair either of the damages were not sufficient to benefit the cell. Both damages required repair for any benefit. In one of two 1991 experiments, which are too complicated and lengthy to describe in this space, he showed that the cells repaired themselves by producing the correct mutations at a rate billions of time sooner than if chance alone had caused the changes. (Washington Post, April 20, 1992, p.A3)
Note: Both of these investigations were criticized as lacking effective controls, and ascribed to known physiological processes. Subsequent work by Hall with more controlled experiments eventually led to experimentally verified acceptance. (Johannes Wirz, Progress towards complementarity in genetics, Elemente der Naturwissenschaft, 64(1), 37-52 1996)
Mohan Raizada at the University of Florida in Gainesville, Florida and others inserted a therapeutic gene into a modified virus, and delivered the gene into the hearts of rats that are predisposed to high blood pressure. These rats and two subsequent generations were protected from hypertension.
Our data support the notion that the AT1R-AS is integrated into the parental genome and is transmitted to the offspring. (Permanent Cardiovascular Protection From Hypertension by the AT1 Receptor Antisense Gene Therapy in Hypertensive Rat Offspring, Circulation Research. 1999;85:e44.)
Observation of unusually rapid genetic changes contradict Natural Selection.
The gradual changes that occur from random mutations in individuals of a species dictate that Natural Selection has abrupt but slow evolutionary changes. Lamarck's hypothesis predicts that characteristics change in large populations and can have a more rapid evolution. Recent studies have shown that evolutionary changes can be quick and therefore favor Lamarck's concept.
- Andrew P. Hendry and colleagues at the University of Massachusetts, learned that just after only 13 generations, sockeye salmon developed distinctly different sizes depending on whether they spawned in a river or lake.
- Ruth Shaw, University of Minnesota, and University of California researchers, David N. Reznick and F.H. Rodd captured guppies from two downstream pools and placed them in pools upstream of waterfalls. In the downstream pools the guppies had been plagued by large predators but in the upstream pools, only small predators were around. After four years, the latter guppies began reaching maturity. They quickly adapted to their new and less threatening surroundings by growing larger and by producing fewer offspring.
Advanced DNA knowledge and testing methods enabled more conclusive proof of adaptive mutations.
Parental olfactory experience influences behavior and neural structure in subsequent generations, Brian G Dias & Kerry J Ressler, Department of Psychiatry and Behavioral Sciences, Emory University School of Medicine, Atlanta, Nature Neuroscience,Dec. 01, 2013.
Using olfactory molecular specificity, we examined the inheritance of parental traumatic exposure, a phenomenon that has been frequently observed, but not understood. We subjected F0 mice to odor fear conditioning before conception and found that subsequently conceived F1 and F2 generations had an increased behavioral sensitivity to the F0-conditioned odor, but not to other odors....In addition, in vitro fertilization, F2 inheritance and cross-fostering revealed that these transgenerational effects are inherited via parental gametes. Our findings provide a framework for addressing how environmental information may be inherited transgenerationally at behavioral, neuroanatomical and epigenetic levels.
A Modest Comeback for Lamarck, and a Reminder of the Edge of Evolution, Evolution News & Views December 7, 2011.
In a modest comeback for long-discarded Lamarckian ideas of offspring inheriting traits their parents acquired, Columbia University Medical Center researchers have succeeded in showing how such a mechanism could actually work. Anyway, in roundworms. What's interesting is that the mechanism involves passing on an adaptive advantage by breaking or silencing gene functionality.
The forbearers picked up immunity to the Flock House virus, the only virus known to afflict this particular hearty species (C. elegans), and communicated the benefit to their descendants in a germ line extending up to 100 generations. That's about a year's worth of worms. Researchers conferred the initial immunity by inducing RNA interference (RNAi), an essentially destructive process that can happen in nature or in the lab. It involves introducing a double-stranded variety of RNA (dsRNA), which in turn wipes out messenger RNA (mRNA) associated with a gene. This renders the gene, bereft of its vital mRNA, inoperable.
It was the now inactive gene that accounted for the helpful resistance to the virus. Surprisingly, this gift got passed down in the somatic cells (as opposed to gametic ones) -- inheritance by a kind of chain of "memories," which actually work by the receipt of viral RNA molecules (viRNA) from parents to children.
A Comeback for Lamarckian Evolution? Two new studies show that the effects of a mother's early environment can be passed on to the next generation, Emily Singer, MIT Technology Review, February 4, 2009
... mice genetically engineered to have memory problems were raised in an enriched environment-given toys, exercise, and social interaction -- for two weeks during adolescence. The animals' memory improved -- an unsurprising finding, given that enrichment has been previously shown to boost brain function. The mice were then returned to normal conditions, where they grew up and had offspring. This next generation of mice also had better memory, despite having the genetic defect and never having been exposed to the enriched environment.
In a second study, researchers found that rats raised by stressed mothers that neglected and physically abused their offspring showed specific epigenetic modifications to their DNA. The abused mice grew up to be poor mothers, and appeared to pass down these changes to their offspring.
Previous research has shown that bad rat mothering can be passed down through this kind of DNA modification-but those changes are thought to be triggered specifically by maternal behavior. In the new study, researchers also had healthy mothers raise the offspring of stressed mothers, and found that the problems were only partially fixed. That suggests that the changes "were not due to their neonatal experience," says David Sweatt, a neuroscientist at the University of Alabama at Birmingham, who oversaw the study. "It was something that was already there when they were born."
A group of pregnant women living in the Netherlands, labouring under starvation conditions imposed by a harsh winter and food embargo, gave birth to relatively small babies. When their children grew up, in relative prosperity, to have children of their own their babies were unexpectedly small. So the effects of poor nutrition on Dutch mothers carried through to their grandchildren. The study seemed to support the scientific heresy of Lamarckism the idea that physical changes acquired during an individuals lifetime could be passed on to their offspring. But how can diet affect inheritance, given that it cant change the DNA sequence in eggs or sperm?
We now know that the effect seen in the Dutch families arose from changes to epigenetic markers on their DNA, caused by the deficiency of crucial molecules in the diets of the grandmothers. One of the most important epigenetic changes is methylation. Some methylation modifications that regulate gene expression are heritable and cause genomic imprinting.which usually labels genes that are switched off. In order to faithfully maintain the correct patterns of methylation through cell division, new methyl groups are stuck onto freshly-copied DNA. This requires a constant supply of new methyl groups, which can be provided directly from our food, including the trio of molecules methionine, betaine and choline.
In the case of the Dutch mothers, its likely that their meagre rations deprived them of the nutrients they needed to set up the correct patterns of methylation in their offspring, and that these epigenetic quirks were also passed on to the next generation.
Transgenerational epigenetic imprints on mate preference, David Crews, Andrea C. Gore, Timothy S. Hsu, Nygerma L. Dangleben, Michael Spinetta, Timothy Schallert, Matthew D. Anway, and Michael K. Skinner, Proc Natl Acad Sci U S A. 2007 April 3.
Environmental contamination by endocrine-disrupting chemicals (EDC) can have epigenetic effects (by DNA methylation) on the germ line and promote disease across subsequent generations. In natural populations, both sexes may encounter affected as well as unaffected individuals during the breeding season, and any diminution in attractiveness could compromise reproductive success. Here we examine mate preference in male and female rats whose progenitors had been treated with the antiandrogenic fungicide vinclozolin. This effect is sex-specific, and we demonstrate that females three generations removed from the exposure discriminate and prefer males who do not have a history of exposure, whereas similarly epigenetically imprinted males do not exhibit such a preference. The observations suggest that the consequences of EDCs are not just transgenerational but can be transpopulational, because in many mammalian species, males are the dispersing sex. This result indicates that epigenetic transgenerational inheritance of EDC action represents an unappreciated force in sexual selection. Our observations provide direct experimental evidence for a role of epigenetics as a determinant factor in evolution.
Where Lamarcks Adaptive Mutations are Today
Consider the possible advances that can occur from the discoveries that authenticate the Theory of Inheritance of Acquired Characteristics.
We may proceed from the origin of the species to understanding the development of the species. Did mankind, as it extended out from Africa, lighten its complexion due to a natural selection or due to an innate intelligence that told the species it would be more beneficial? Did the human eye actually develop from random mutations or from a self-directed process that constantly improved the organ?
Germs have understood the theory and have adapted to protect themselves against the antibiotics designed to silence them. Humans have resorted to drugs in order to conquer disease. Do these drugs prevent the proper response to the external harmful environment? Without the use of drugs, many will probably die but the species might be preserved. With excessive drug use, a few will survive but the species may perish.
The battle against the environment enters a new stage where mankind realizes the effects of pollutants, toxicants, inadequate diet, and stress on future generations. They may receive the epigenetic impact of fear, depression, traumatic events, famine and war. On the positive side, later generations might also inherit the abilities, optimism and smiles of their ancestors.
Despite the intensive investigations of Lamarck's theories and claims made from them, Lamarck's Inheritance of Acquired Characteristics has not sufficiently interested the scientific community. One reason is that Natural Selection has been widely accepted and its dogmas have become an integral part of academic life. The leaders of laboratories, institutions and universities have a clear interest in maintaining a status quo in evolutionary thinking. But that is not the major reason.
Science is again revolutionized with a challenge of immense proportions. A frightening and new perspective changes thought and outlook, and its acceptance has severe implications: If humankind is able to respond to the environment, then the intervention of a higher authority in the evolutionary process will become superfluous. The last nail in the coffin of creationism will be hammered.
Acceptance of the Theory of Inheritance of Acquired Characteristics leads to investigating the validity of directed evolution. If proven true, then mankind will learn to live with less fear and more cooperation. All are one against the environment and the individual is only an active participant in perfection of the species.
Totally revised December 2013
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