Zoology

Lamarck, Darwin and The modern synthetic theory of Evolution

Theories of Evolution

Theories of Evolution (Lamarck, Darwin and The modern synthetic theory of Evolution and human evolution)

Lamarck, Darwin and The modern Theories of Evolution

Lamarckism (Lamarck’s Theory of Evolution)

●Jean Baptiste de Lamarck was a French naturalist who born in 1744. He proposed Theory of Inheritance of Acquired Characters.

Lamarck’s theory regarding evolution was published in 1809 in ‘Philosophie Zoologique’. It has the following postulates known as Lamarckian doctrine.

(i) Living organisms and their components tend to increase in size as a result of internal forces of life.

(ii) Reproduction of a new organ results from a new need and from the new movement, which this need starts and maintains. .

(iii) The development and degeneration of organs will be based on use and disuse of organs respectively.

(iv) Inheritance of acquired characters All changes acquired by the organism during its life are transmitted to offsprings by the process of inheritance.

●Theory of Continuity of Germplasm was proposed by August Weismann in 1886. He criticised the theory of inheritance of acquired characters by removing the tail of mice continuously for 22 generations though, he was failed to obtained tailless mice till 22nd generation.

●August Weismann (1834-1914) suggested that the changes occurring in germplasm are inherited by offsprings Whereas in somatoplasm are not transmitted to next generations.

●A group of scientists has further studied Lamarck’s theory of evolution and some scientists like Spencer, Giard, Lawrence, Mc Dougall Cope, Rechard, Wells Giard, Dali, etc., supported the modified form of Lamarckism which is termed as ‘Neo-Lamarckism’.

●Neo-Lamarckism explains that only those acquired characters are inherited by offsprings which influence the germ plasm or germ cells.

Darwinism (Darwin’s Theory of Evolution)

theory of Evolution

● Darwin started a travel in 1831 by H M S Beagle for a voyage of world exploration planned by British Government With Dr Henslow.

●Darwin found a living laboratory of evolution in Galapagos Island during his journey and found closely related species of finches known as Darwin’s finches.

●In 1838 Darwin found an essay of T R Malthus on population entitled ‘The Principles of Populations’.

●Darwin and Wallace jointly propounded the ‘Theory of Natural Selection’ and published a joint paper titled ‘Origin of species’ in 1858.
Darwin’s theory of Evolution is based on the following five principles

(i) Overproduction
(ii) Struggle for existence
(iii) Variations and their inheritance
(iv) Survival of fittest
(v) Natural selection and species formation

●Continuity of existence of the fittest was called survival of the fittest by Herbert Spencer, While Darwin called it natural selection.

●Later in November 1859, Darwin published his observation and conclusion in a book On the Origin of Species by means of natural selection.

The theory proposed by Darwin and Wallace has been modified in the light of modern evidences from Genetics, Molecular Biology, Palaeontology, Ecology and Ethology, and known as Neo-Darwinism. Weismann, Mendel and de Vries were the supporters of Neo-Darwinism.

Synthetic Theory of evolution

●The modern synthetic theory of evolution was born in 1937 With publication of Dobzhansky’s Genetics and The Origin of Species Which was supported by Huxley (1942), Mayr (1942), Simpson (1944) and Stebbins (1950).

●According to synthetic theory of evolution there are five basic factors involved in the process of organic evolution. These are

(i) Gene mutations
(ii) Change in chromosome structure and number (iii) Genetic recombinations
(iv) Natural selection
(v) Reproductive isolation

●Stebbins (1950) provided an account of variations, heredity, isolation and natural selection.

Human Evolution

theory of Evolution

●Humans and human like ancestors are called homonins or hominid.

●The study of human evolution and culture is known as anthropology.

●Carolus Linnaeus (Father of Taxonomy) coined the scientific name (Homo sapiens) to human which stands for Man who is wise. He placed human along With monkeys and apes.

●T H Huxley (1863) explained origin of humans scientifically in his book ‘Man’s Place in Nature’.

Lamarck, Darwin and The modern synthetic Theories of Evolution

Important Hominids

Dryopithecus (Common ancestor of man and apes)

(i) Fossil of Dryopithecus africans was obtained from rocks of Africa and Europe.
(ii) Dryopithecus afn’cans shows close similarity to Chimpanzee.
(iii) It’s cranial capacity was 400 cc.

Ramapithecus (Earliest man like primate or oldest of man’s ancestor or forest hominid)
Edward Lewis (1932) obtained fossil of Ramapithecus from Pliocene rocks of Shivalik hills of India.

Australopithecus (First ape man)

(i) Prof. Raymand Dart (South African anthropologist) discovered the skull of 5-6 year old baby which appeared about 5 million years ago. This baby fossil was termed as Australopithecus africanus (African ape man or tuang baby).

(ii) It was the ancestor of man who first stood erect,i.e., fully bipedal hominid.

(iii) It’s cranial’capacity was 500-700 cc, i.e., equivalent , to modern gorilla.

Java man (Pithecanthropus erectus or Homo erectus erectus)

(i) In 1891 Eugene Dubois obtained fossils from Pleistocene deposits in central Java.
(ii) It was named Pithecanthropus erectus by Eugene Dubois and Homo erectus erectus by Mayer (1950).
(iii) Java man was the first pre-historic man who began the use of fire for cooking, defence and hunting.
(iv) It’s cranial cavity was 940 cc which is about intermediate between Australopithecus (600-700 cc) and modern man (1400-1600 cc).

Peking man (Homo erectus pekinensis or Pithecanthropus pekinensis or Sinanthropus pekinensis)

(i) The fossils of Peking man were discovered by WC Pai (1924) from the lime stone caves of Choukoutien near Beijing during middle Pleistocene period.

(ii) WC Pai named Java man Sinanthropus whereas Davison Black (1927) named it Sinanthropus pekinensis and Mayer (1950) called it Homo erectus pekinensis.

(iii) The cranial capacity of Peking man was 850-1200 cc that is more than Java man.

Neanderthal man (Homo sapiens neanderthalensis)

(i) Fossils of Neanderthal man was discovered by C Fuhlrott (1856) from Neander valley in Germany.

(ii) Neanderthal man arose about 1,50,000 years ago and flourished in Asia, Europe and North Africa.

(iii) Neanderthal man existed in the Late Pleistocene period.

(iv) The cranial capacity of Neanderthal man was about 1400 cc.

(v) It is also called ceremonial burial of the dead.

Cro-magnon man (Homo sapiens fossilis)

(i) Mac Gregor discovered the fossils of Cro-magnon man from Cro-magnon rocks of France in 1868.
(ii) Cro-magnon arose about 3,40,000 years ago and lived in Europe and other parts of world.

(iii) Cranial capacity was about 1650 cc i.e., much more than modern man (1450 cc).

(iv) They could run fast and lived in families and considered as the direct ancestor of living modern man.

Living Modern Man (Homo sapiens sapiens)

(i) It is believed that living modern man first appeared about 10,000 years ago in the regions of Caspean sea and Mediterranean sea.

(ii) Its cranial capacity is average 1450 cc which is lesser than Cro-magnon.

(iii) Human species (sapiens) have white or caucaroid, mongoloid and black or negroid races.

Future man (Homo futuris)

(i) It is believed that in future, human could be change as a result of gene mutation, gene recombination and natural selection.

(ii) According to H L Shapiro, an american anthropologist, the Future man will contain following characters.

(a) Height will be higher.

(b) Hair will be reduced and skull become dome shaped.

(c) Body and cranium will be more developed.

(d) The fifth finger probably will be reduced.

(e)The age will increase.

These are the theory of Evolution

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