Download NEO-LAMARCKISM AND NEO

 Title:
ANTHROPOLOGY
Paper:
PAPER No. 2
Course name: PHYSICAL ANTHROPOLOGY
Module:
NEO-LAMARCKISM AND NEO-DARWINISM (12/15)
The concepts and theories regarding the origin and evolution of organisms so far
discussed are not totally satisfied. Perhaps, Albert Einstein’s view that there is no absolute reality
but only relative truth is true. Theories which are accepted today may be wrong tomorrow. And,
many of the concepts and theories are modified and changed after deeper researches have been
carried out in course of time. Similarly, the theories of Lamarckism and Darwinism have been
discussed by many scientists and the shortcomings are shown and improved. We shall now
discuss the new developed theories of Lamarckism and Darwinism.
Neo-Lamarckism
Lamarckism also known as the theory of inheritance of acquired characters can be
defined as the changes in structure or function of any organ acquired during the life-time of an
individual in response to changes in the surrounding environment which is inherited by its
offspring and keep on adding up over a period of time. The changes are because of use and
disuse as demanded by the environmental pressure.
L
Lamarckism
has many drawbacks
d
a this is evident
and
from thhe experimeents carriedd out by various scientists.
Experimeents such as the one carrried out by Weismann
W
inn which
he mutilaated the tailss of white ratts and matedd them but foound no
loss of tail
t
in succeeeding geneerations, MccDougall’s
(1938)
experimeent on rats to
t observe that
t
acquiredd behavioural traits
are inherrited or not etc. Limitaations of Laamarckism as
a were
shown by
b many ressearchers led to the foormation of a new schoool of thouught that suupport
evidencees in support of Lamarckkism.
H
Harrison’s
ex
xperiment onn a pale varriety of motth, Selonia bilunaria
b
shhowed intereesting
findings. By feeding
g manganesse coated foood, these moths
m
in areeas where food
f
plants were
infected with
w mangan
nese salts froom industriaal smoke prooduce a diffeerent, a melaanic variety breed
b
moth shoowing that th
he influencee of mangannese can influuence on the germ cellss and acquirred to
the offspring.
T
Tower
exposed young onnes of potatto beetle to abnormal coonditions off temperaturee and
humidityy. The strong
g heat did not
n produce any somaticc changes inn the beetless themselvess, but
their offfspring show
wed markedd colour chhanges in thhe next genneration. Intterestingly, these
changes were
w found to
t pass on too the succeedding generattions.
M
Muller
also experimentted the rolee of X-rayss in produccing heritabble variationns in
Droshophhilia that rev
vealed the change
c
in thhe chromosoome structure. Likewise,, C. Auerbaack in
collaboraation with Robinson
R
annd Carr prodduced heritaable changess in Drosopphilia by usiing a
chemicall mutagen, mustard
m
gas.
Thus, Neeo-Lamarckiians proved that:
t
1. Germ cells are infl
fluenced by the
t environm
mental changges.
2. Germ cells may carry acquired or somaticc variations to
t the offspring (Harrisoon’s expt.)
3. Germ cells may bee affected dirrectly by thee environmenntal factors (Tower’s
(
exxperiment)
4. Somatic traits are the product of nature and nurture i.e. genes and environment interaction.
This infers that environment affect the gene expression of organisms.
Thus, we have seen that the difference in view point of Lamarckism and Neo-Lamarckism was
that Lamarck believed in the direct action of environment, which he thought was responsible for
achieving final perfection of the individual. Neo-Lamarckians modified the concept. They are of
the view that a considerable time period is required to act up to the level of germ cells that
produce visible and invisible traits.
Neo-Darwinism
The theory of natural selection or Darwinism is a
breakthrough in the history of evolution. It is a simple concept
easy to grasp. In a species, there are individuals that differ
genetically from one another as a result of which their ability to
adapt and survive to different environment differs. Nature is the
causative force that sorts out bad adapted ones replaced by best
and the their progeny is spread. In this course of nature’s scrutiny, the trait that changed and
adapted is selected by nature and the bad ones screened out.
However, Darwinism also has certain drawbacks. He did not know the mechanism of
inheritance. He laid emphasis on individual variation and lack clarity in accounting the sources
of variation and ignored the role of recombination. This leads to the formation of a new school of
thought in the middle of the 20th century by combining all sources of knowledge from genetics,
palaeontology, ecology and others. Edward O Dodson and David J. Merrill called this new
theory of evolution as Neo-Darwinism. George Gaylord Simpson and his followers, however,
strongly refuted the labelling of Neo-Darwinism as synthetic theory of evolution. Simpson
argued that the synthetic theory had no Darwin. However, we shall consider the two labels as
synonymous.
The new concept of evolution is the product of two rival camps of thought. One
supporting the traditional Darwinian view centering around natural selection as the key role
player of evolution and the camp centering around the
central role of mutation and a whole new branches of
science, undreamt of by Darwin such as molecular
biology. The synthesis of these two camps leads to the
formation of Modern Synthetic Theory of Evolution.
Therefore, the theory has two stages of process: Natural
Selection whereby genetic differences in some individuals
lead to their higher reproductive success, and production
and redistribution of variation which are genetically influenced differences between individuals
which are inherited.
In order to understand the modern concept of evolution, one has to study and understand
the short term events of evolution called microevolution, the slow accumulations of changes seen
and unfold in every generation. Using such a modern population genetics perspective, we define
evolution as a change in allele frequency from one generation to the next. Alleles are the
alternative forms of genes that occur at the same locus. The synthetic theory considers evolution
to be the result of changes in the gene frequencies of populations that produces variations.
Following are the important factors of modern synthetic theory of evolution:
1. Natural Selection. This is a process of nature in which
continuation of one line of organisms which are selected
and the elimination of another from the evolutionary record
thereby making changes in the gene frequency of the
population. Through this process of natural selection, some
genotypes in a population develop advantage over others in
fertility and viability that leads to change in gene frequency
of the population. The proportion of an offspring genotype
contributes to the next generation is the Darwinian Fitness measured by reproductive capacity.
2. Mutation. The change in the genetic material of an organism result to the formation of new
traits thereby producing variation in the population of the organism. Such a change in the DNA
sequence is called mutation. The majority of mutations are thought to occur because of
occasional mismatching of the sequences of the chemical bases that make the DNA. This is just
like a typist making error in copying manuscript, so will DNA in duplicating itself. Though most
of changes through mutation are harmful, some of the changes are selected by nature, some are
eliminated and yet some are neutral in selection. The degree of severity of the effect of mutation
is based on place where the DNA regulates the production of proteins. All these lead to change
in the gene frequency of a population. One interesting case is of industrial melanism in which
grey moths which were adapted more than the black moths before pre-industrialization, become
adaptive after industrialization after which the tree trunks become darker and the black moth are
less seen to their predators from attack.
3. Genetic Drift. It refers to various random processes that affect gene frequencies in small,
relatively isolated populations. The isolation may be
because of social factors as in the case of a religious sect
of Dunkers who emigrated from Germany to the USA in
the early 1700s. As a result, blood group and other genetic
traits of the Dunkers are genetically drifted away from the
parental population Dunkers in Germany. According to
Hardy-Weinberg Law, in large populations (assuming
evolutionary forces are not operated), the gene frequency
of a population tends to remain in balance. But in smaller populations the probability and chance
play a great role in increasing or decreasing of alleles.
4. Gene Flow. Gene flow is a process by which genes from one gene pool or populations of a
species may be brought into another population. Since these flowed genes differ from their initial
frequency, they produce change in the gene pool which receives them. Such changes occur
through migration and hybridization.
Difference between Darwinism and Neo-Darwinism
After knowing the above discussed important factors
of Neo-Darwinism, lastly, let us try to see few important
differences between Darwinism and Neo-Darwinism. Neo-Darwinism is the advance and
updated theory of evolution.
1. Unit of evolution is a population not species as is mentioned in Darwinism, because
species are subdivided into local populations.
2. It is the gene pool of the population that evolves and not the individual level.
3. Differences among individuals in a population are the consequence from
accumulation of mutations and recombination of genes due to independent
assortment, crossing over and fertilization. These reasons of variations are not known
to Darwin.
Conclusion:
Lastly, understanding of modern theory of evolution needs knowledge of molecular genetics.
Students shall attempt to know the basic knowledge of it, without which they will face
handicapped in understanding the theory.