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Biotechnology and Society---Part IX

The term Lamarckian genetics is named for French biologist Jean-Baptiste Lamarck (1744-1829) who proposed a theory of evolution which stated that evolutionary changes in organisms can be produced by naturally occurring environmental influences upon the germ-plasm of individual beings which then get passed on to the offspring.

The organism in question underwent physiological changes in its own lifetime which came about by responding to its survival needs. This hypothesis was in sharp contrast to Darwinian hypothesis which stresses selection of the fittest as the mechanism for the evolution of species and that evolution is not a need-based phenomenon, ie., evolution is random, not directed. Accordingly, the latter-day geneticists rejected the Lamarckian hypothesis as being incompatible with cellular mechanisms.

Lamarck proposed his theory based on use and disuse of body parts of animals. He observed that long legs and webbed feet of wading birds like the pelican arose when those birds ancestors responded to a need to feed on Fish. Stretching of legs was required to avoid getting wet. This trait got passed along over many generations. Likewise, stretching of toes caused the webbed feet.

Another example is the long neck of the giraffe. The stretching of the neck to reach leaves of a tree at higher levels not only increased the length of their necks but also got transmitted to their offspring.

Conversely, disuse of certain body parts would cause them to wither and disappear which explained how the snakes lost their legs in comparison to other reptiles. Now one can reconcile with the saying in Tamil, ‘pambariyum pambin kaal’ (only a snake is aware of another snake’s legs). Basically, Lamarck argued that function preceded form.

Darwin (1809-1882) accepted the idea of use and disuse. Darwin observed that the wing bones of domestic duck weighed less and the leg bones more than do the same bones of the wild duck because the former flew much less but walked more than its wild parents.

Similarly the development and inheritance of big udders in goats and cows in countries where they are habitually milked in comparison with these organs in other countries, is probably another instance of the effects of use. However, it was not Darwin who killed the Lamarckian theory of evolution. It is the neo-Darwinists, armed with Mendelian genetic mechanisms, who rejected Lamarck’s ideas for lack of supportive evidence.

In 1883, German biologist August Weismann developed the germ-plasm theory of heredity, according to which the body’s material (soma) was entirely separate from the hereditary material (germ-plasm). By insisting on the existence of a barrier between soma and germ-plasm, Weismann eliminated the idea of inheritance of acquired characteristics from being accepted.

Darwin

To prove his point, Weismann cut the tails of mice and bred them over several generations, but not one was born without a tail. He also argued that circumcision of young boys among Jewish and Islamic faiths did not result in that characteristic being inherited, i.e., the offspring were always born with the foreskin in tact.

However, the neo-Lamarckians countered that these two cases were injuries or mutilations not initiated by the organism and hence do not qualify for Lamarckian inheritance. Despite the continuing controversy, the neo-Darwinists carried the day. The current consensus is that the environment cannot cause hereditary changes.

So, shall we write the obituary of Lamarckian genetics? Let us not pull the trigger yet. Today’s heresy may be tomorrow’s accepted truth. Science, just like other disciplines, has its dogmas. Dogma, it is said, “is a fickle mistress in science”. The demolition of the central dogma of molecular biology (DNA--->RNA--> Protein) to account for the RNA initiated function of viruses is one example of the need for revision of dogmas. Lamarckian genetics may yet be revived if biological facts argue for it.

Antibody genes (the body’s protective immune system DNA) have a special characteristics. Their DNA sequence rearranges from the original reproductive “germline configuration” to an everyday “somatic configuration” in lymphocytes (a type of white blood cell) for the production of antibodies by B cells. When B cells respond to infection, the rearranged antibody genes undergo rapid mutation to target the attacking species.

Those mutant cells, which produce the most effective antibody, are then selected by a Darwinian process. Such a process is incompatible with neo-Darwinism which maintains that evolution occurs only via random mutation in germ cells followed by natural selection acting on the living organism that carries the mutation. It is, however, compatible with a neo-Lamarckian process of feedback to germ cells from somatic cells.

Epigenetics: This new discipline of genetics refers to the study of changes in genetic expression that are not linked to changes in DNA sequences but related to the influence of the environment on the genes being expressed or not – basically, whether a gene is silenced or activated. There are certain genes in the egg or the sperm which carry a placard, ‘Don’t pay attention to me’ - in effect, these genes are silenced. So, without a true genetic change (DNA mutation) one could experience physiological changes or diseases.

Epigenetic changes are involved in processes such as gene regulation, development or even cancer. While such changes can be transmitted to the “daughter cells” thereby enabling the spreading of cancer, it is generally recognised that such changes are normally “erased” when the germ cells, which give rise to the next generation, are formed. In rare instances such erasures do not happen.

Scientists in Australia and Scotland found a few years ago in an inbred strain of mice (which are all genetically identical and so should look exactly the same) the coat colours varied wildly, ranging from yellow to mottled (spots or blotches of different colors) with every combination in-between.

The coat colours were pretty much dependent upon the mother’s coat color very much in violation of the Mendelian principle (which states that traits are randomly distributed during reproduction). It is likely that the epigenetic gene regulation of the coat colour gets transferred from the mother through the germ line to the offspring.

While Darwin agreed with Lamarck that the inheritance of acquired characteristics played a role in evolution, Darwin stressed that natural selection of genetic alterations, rather than some “inner striving”, drives adaptive changes. Lamarck proposed that evolution was driven by an organism’s inner need to adapt to its environment. While the issue is not completely decided, research developments in the field of epigenetics are bound to keep the discussion alive for years to come.

National poet Mahakavi Subramanya Bharathi, while arguing for an egalitarian society, wrote:

vellai niraththoru punai -- engal vittil valaruthu kandir
pillaigal perrathap punai -- avai perukkoru niramagum

sambal niramoru kutti -- karun santhu niramoru kutti
pambu niramoru kutti -- vellaip paalin niramoru kutti

entha niramirunthalum -- avai yavum oretharamanro
intha niram cirithenrum -- ihdha erramenrum sollalamo?

(Meaning: A white cat can bring forth pups of various colours from white to gray to black and brown but whatever be the colour, the pups are all equal and one cannot say one is superior to the other.)

Bharathi was pretty much unwittingly echoing the principle of epigenetics here, viz., there is no real genetic difference between the pups although they were of different colours.

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To answer the question can acquired characteristics be inherited, even the avowed epigeneticists cannot answer this question in the affirmative although there are indications that certain traits acquired by the organism due to environmental influence get transferred across the germ line and manifest in the offspring.

Let us revisit our “sin gene” hypothesis mentioned in the previous article. Is there a possibility that the psycho-somatic effect of committing a sin or crime can cause an epigenetic change in a person and whatever the consequence of that change will get transmitted to his or her offspring? So far no scientific evidence can be provided for that possibility. Perhaps karma will prevail over dogma!