A HISTORICAL PERSPECTIVE of change theories & evaluation

PRE DARWINIAN THEORIES OF CHANGE

The idea of evolution did not originate with ‘Charles Darwin. The ancient Greeks gave some ideas about the evolutionary changes.

  1. Empedocles (495-435 B.C.) and Aristotle (384-3228.c): They described concepts of change in living organisms over time.
  2. Georges-Louis Buffon (1707-1788): He spent many years studying comparative anatomy. He observed structural variations in particular organs of related animals. He especially observed vestigial structures. These observations convinced him that change has occurred during the history of life on earth.
  3. Erasmus Darwin (1731-1802): He was a physician and grandfather of Charles Darwin. He was also interested in questions of origin and change. He believed in the common ancestry of all organisms.AMARCK: AN EARLY PROPONENT OF EVOLUTION ean Baptiste Lamarck (1744-1829) was a French zoologist. He studied animal assification. He gave a theory how change occurs. He believed that species are ot constant. Therefore, the existing species were derived from preexistings ecies.Theory of inheritance of acquired characteristics

    L marck explained the mechanism of evolutionary changes. He proposed the

    t ory of inheritance of acquired characteristics. Lamarck believed that

    o     3anisms develop new organs or modify existing organs due to environmental

    • Problems. Thus the organs changes according to need. Lamarck used the

    example of the giraffe. He described that the ancestral giraffes had short necks Ilk- other mammals. It strains his neck to reach higher branches during browsing. T s it acquired higher shoulder and longer necks. These modifications were passed on to the next generation. The use of any organ make it highly de eloped. The disuse of an organ causes degeneration. Therefore, it can describe the evolution of highly specialized structures like vertebrate eyes.

    Criticism and objections on the theory of Lamarck

    Lamarck published his theory in 1802. He had to face the social and scientific cut sm. Society was not accepting his ideas of evolutionary changes. He did not have much evidence to support it. So this theory could not convince most scientists. Thus, Lamarck was much criticized for ideas of evolutionary change at that time. Today, he is criticized for his mechanism of inheritance and evolutionary change. This mechanism lack reasonable evidences. The changes are passed to the next generation by gametes. For example, change in neck of giraffe does not occur in genetic material. So it cannot be transferred to the next generation.

DARWIN’S EARLY YEARS AND HIS JOURNEY


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Charles Robert Darwin (1809-1882) was born on February 12, 1809. His father was a physician. Darwin collected dogs and hunting birds during ‘his youth. These activities reduced his interest in school education. He entered medical school in Edinburgh. Scotland in 1825. There, he enjoyed the company of the Scientists for two years. However Darwin could not see pain. Therefore, he was not i terested in career in medicine So his father sent him to the Church of England for the training of clergy. Charles was enrolled at Christ’s College in Cam ridge and graduated with honors in 1831 This training was also disappointing for Darwin’. But he enjoyed the company of Cambridge scientists. Darwin developed a keen interest in collecting beetles during his stay at Cambridge. Thus he made valuable contributions in beetle taxonomy.

VOYAGE OF THE HMS BEAGLE

John Henslow was botanist at Cambridge. He nominated Darwin to serve as a naturalist on a mapping expedition. This expedition was to travel around the world. Darwin was commissioned as a naturalist on the HMS Beagle. It set sail on December 27 1834 on a 5-year voyage. Darwin made numerous collections. He sent this collection to Cambridge. He explored tropical rain forests, fossil beds, volcanic peaks of South America and the coral atolls of the South Pacific during this voyage. Darwin spent 5 weeks on the Galapagos Islands. Galapagos is a group of volcanic islands. They are present 900 km away from the coast of Ecuador. He observed plant and animal life on these islands. These observations give him most of the revolutionary ideas. Darwin was just 27 years old at the end of the voyage. He spent the rest of his life examininc specimens and rereading notes. He made new observations. He prepared numerous publications. His most important publication is, On the Origin Species by Means of Natural Selection”. It was published in 1859. It revolutionized biology.

Voyage of Darwin

Fig: Voyage of Darwin

 

 

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