Charles Robert Darwin (1809— 1882) was born on February 11 1809. His lather as a physician. Dan’ in collected dogs and hunting birds during his youth. These activities reduced his interest in school education. lie entered medical school in Edinburgh. Scotland in 1825. There, he ell,loved the company of the scientists for two years. However Darwin could not see pain. therefore, he was not interested 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 Cambridge and graduated with honors in 1831. This training \A as also disappointing for Dank in. 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 S. henslow was botanist at Cambridge. He nominated Dar in to serve as a naturalist on a mapping expedition. this expedition was to travel around the \writ]. Darwin was commissioned as a naturalist on the II MS Beagle. It set sail on December 27 1834 on a 5.-year 0) age. Darwin made numerous collections. He sent this collection to Cambridge. he explored tropical rain forests, fossils 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. lie observed plant and animal life on these islands. These observations give him most of the revolutionary ideas. Darwin was just27 years old at the end of the voyage. He spent the rest of his life examining 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.
EARLY DEVELOPMENT OF DARWIN’S IDEAS OF EVOLUTION
Darwin started his work on his theory of natural selection. It was a long hardworking process. Darwin wanted to convince him that change occurs over time. Dam in accepted the opinion of most scientists before starting voyage. These opinions say that the earth and its inhabitants were created 6.000 years ego. They had not changed since then. Darwin made important observations during his voyage. These observations suggested that change does occur. he also realized that the organism arose through gradual changes. But the diversity of modern species could not form in 6,000 years. Thus Darwin developed the idea of change in his mind, lie studied this idea for 20 years. Then he gave the mechanism of this change. Darwin died without knowing the genetic principle. These principles supported his theory.
The study of the earth is called geology. Darwin read the book of Charles LyeII called Principles of Geology. LyeII developed the ideas of another geologist. James Hutton into the theory of uniformitarianism. According to this theory, forces of wind, rain, rivers, volcanoes, and geological uplift shape the earth of today. They have also changed the earth in the past. LyeII and Hutton believe that these forces shaped the face of the earth over hundreds of millions of years. Catastrophic events do not play any role. This book developed two important ideas in the mind of Darwin:
I. The earth was much older than 6,000 years
2. The face of the earth changed gradually over long periods. Therefore, living forms also changed gradually during this period.
The histological dead remains of the-organism or their imprints preserved in the rocks are called fossils. The HMS Beagle reached South America. Darwin dug the dry river beds of the pampas (grassy plains) of Argentina. Darwin found two types of fossils.
(a) Fossils different from other animals: He found the fossil of an extinct hippopotamus like animal. It is now called Toxodon. He also found fossils of horse like animal, Thoantherium. Both of these fossils were animals. They were clearly different from any other animal living in the region. Modern horses were present in South America. But Spanish explorers brought these horses to America in the I500s. The fossils suggested that horses were present and became extinct long before the I 500s.
(b) Fossil similar to other animals: Darwin also found fossils of giant armadillos and giant sloths. Darwin also found similar fossil in the region. They had different size. But they were very similar to each other.
Concept of fossil
Fossils were not new to Darwin. It was believed that the remains of animals were formed by catastrophic events. One of the catastrophic events was Noah’s flood. But Darwin believed that fossil were evidence of the change of species composition of the earth. Some species became extinct without leaving any descendants. Others became extinct. But they give rise to new species before their extinction.
- Giant tortoises of the Galapagos
the F1MS Beagle stopped at the Galapagos Islands. These islands are present in the western shore of South America. They are named after the large tortoises (Sp. galapago. tortoise) that inhabit there. The tortoises weigh up to 250 kg. They have shells up to 1.8 in in diameter. They live far 200 to 250 years. The governor of the islands told Darwin that the shapes of the tortoise shells were different in different parts of Albemarle islands. Darwin also noted some other differences. Tortoises from the drier regions had longer necks. But the tortoises from wetter habitats have smaller necks. But still the tortoises W. ere quite similar to each other. They were also similar to the tortoises on the mainland of South America.
Interpretation of Darwin
There should be some reasons or their similarities. Darwin explained that a few ancestral an triw el from the mainland. Thecred
about 900 km of ocean. the reached the Galapagos. ‘They gave rise to the fauna of island. But the Islands are volcanic. They arose out of the seabed. Therefore. no land connection with the mainland exists. There is one modern hypothesis. According to this hypothesis the tortoises floated from the mainland on mats of vegetation. Vegetation regularly break from coastal river banks during storms. [here were no predators on the islands. therefore. the tortoises gradually increased in number.
Darwin found two types of tortoises. They– were found in different regions. Dank in explained the differences in their distribution.
(a)Tortoises with longer necks: They were found in the dry regions. [here was little vegetation in the dryer regions. Therefore, the tortoises with longer necks have advantage in this region. ‘Hwy can reach higher to get food. Therefore. this region favors tortoise w ii h longer necks.
(b)Tortoises with shorter necks: They live in moister regions. ‘lids region does not favor tortoises with longer necks. Therefore, the shorter-necked tortoises survive in these regions.
- Galapagos finches
Galapagos finches were sparrow like birds. Darwin studied different types of finches. Dank in noticed that the Galapagos finches have common ancestry. Scientists now think that the ancestor of finches inhabited the mainland of South America. These ancestors gave rise
to Galapagos finches. Some finches arrived in Galapagos Island. They form single or multiple colonization. They set up the first bird populations on the islands. Early finches lived in many different habitats. These habitats were without other birds and predators. Ancestral finches were seed eaters. They multiplied rapidly and filled the seed-bearing habitats. Fourteen species of finches arose from this ancestral group. One of them was found on small Cocos Island. This island is present northeast of the Galapagos Islands. Each species is adapted to a specific habitat on the islands. These finches had difference in the size and shape of their bills. It relates to different dietary adaptations in these finches.. The finches of the Galapagos Islands provide an example of adaptive radiation.
The formation of new forms from an ancestral species in response to the opening of new habitats is called adaptive radiation.
THEORY OF EVOLUTION BY NATURAL SELECTION
Dar in formulated his ideas of natural selection by 1844. There are following points of his theory of natural selection:
- Overproduction of population
All organisms have great reproductive potential. For example:
- A female oyster releases about 100,000 eggs with each spawning.
- A female sea star releases about 1 million eggs each season. “‘Thus A half million female sea stars can produce another million eggs. If this repeated over just a few generations, it will soon fill up the oceans.
- A female robin (bird) lays four fertile eggs each season. If each produces four more robins. It will cause unimaginable resource problems in just a few years.
- Genetic variation
Inherited variations arise by random mutation. Two individuals are never exactly alike. Some of these genetic variations give advantage to the individuals. But some variations are harmful to an Individual. Some other variations are neither helpful nor harmful. These variations are called neutral. These variations can be passed on to offspring.
- Struggle for survival
The resources are limited. Therefore, a constant struggle started.Many more offspring are produced than resources can support. Therefore, many individuals die. Darwin reasoned that these individuals have less adaptive traits. Some individual remain alive. These individual have adaptive traits.
- Natural selection
Adaptive traits are transferred in subsequent generations. The organisms with maladaptive traits have less chance to reproduce. Thus the maladaptive traits become less frequent in a population. Finally they are eliminated.Darwin formulated a theory with these ideas. This theory explains following points:
- How the tortoises and finches of the Galapagos Islands changed over time.
- It also explains how some animals like ancient South American
horses can become extinct. Sometimes, a group of animals face a new environment. It can not adapt in the climatic changes, food shortages, and other environmental stressors. Therefore, they become extinct.