Darwin’s theory of Evolution

Evolution is the change that takes place over a period of time.

About Charles Darwin Full name : Charles Robert Darwin

Birth place: England

Birth date: 12th February, 1809

He was the great English naturalist.

His work mainly focused in understanding the life on the Earth.

Darwin’s work

He wrote 20 books of different volumes on nature including Origin of species, Voyage of Beagle.

Thousands of letters.

More than 200 articles.

Manuscripts.

Trip to HMS Beagle Turning point in Darwin’s life.

Trip started on 27th December, 1831 and lasted for five years.

Trip conducted under the supervision of captain FitzROy.

Lots of observation made by Darwin during the trip.

Collected several evidences to support the observations.

Darwin’s observations during the trip

Adaptation of plants in the natural environment.

Birth and survival of different species.Fossils of different species that got extinct.Fossils of species that have similarity to

the existing species.

The Galapagos islands

Landed on Galapagos island on 15th September , 1835.Important fauna for Darwin’s study: iguanas, giant

tortoise and finches.Different islands of Galapagos with tortoise variable in

looks and weight.Iguanas on different island had variable appearance.The beak of finches and their feeding habit differ in

islands of Galapagos.

Finches with modified beak

Darwin’s studyAfter he returned from trip, he closely studied all the

specimens and evidences that he collected from different island. His study included deep research and findings on each species.

He was highly motivated by Hutton and Lyell theory on earth in geology.

Hence, he linked all his findings with past theories given by many other biologist and naturalist.

He got a letter from Alfred Russel Wallace on his findings.

Darwin’s result

Finally after lots of research and findings, Darwin came to the conclusion on origin and evolution of species.

Darwin’s theory

Common descent

Gradualism

Multiplication

Natural selection

Common descentAll the organism have one common ancestor in the past

and with the change in climate and habitat, they descended from that unknown ancestor.

Over a period of time, the changes within them got collected resulting in their survival for the changing environment also termed as adaptation.

GradualismOrigin and evolution of new species

depends on the accumulation of changes. After a period of time when different changes get piled up resulting in adaptation, then the species is said to evolve. Hence, evolution is a slow and gradual process.

Multiplication

Over a time period, changes takes place. These changes can result in the species with similar in appearance or completely different in appearance and behavior. Hence, species multiply either having similar characteristics to their ancestor or different characteristics than that of them.

Natural selection

Darwin termed natural selection as the major mechanism in origin and evolution of species.

Overproducti

on

Competition

Variation

Adaptation

Natural selection

Overproduction

Every species in this planet have potential to give birth to young ones and increase in its number. This is known as overproduction where there is no limit set for any species to give birth a particular number of offspring's.

Competition

More the number of species , higher will be the competition for their survival. It is because, our environment have finite resources that supports the survival of only some species. Hence, those offspring who meets the environmental criteria can survive. Thus even after overproduction the population of species generally remain constant with slight variation in the overall data.

Variation

Variation is the key ingredient for survival of the species. Those species who have suitable variation that benefits them have higher chances of survival than those species who have no variation or who lack beneficial variation. Hence, as a result of variation species possess morphological and character differences.

Survival of the fittest

Species that have variation and can tackle the environmental condition are fit for reproduction and survival. Hence, fitness depends upon the adaptation of species to the particular environment. Therefore, any species with low fitness die and that with higher fitness can survive.

Natural selection

After a particular time period, the changes or variation acquired by the species results in natural selection. This means that nature selects the beneficial variation and increase the survival rate of offspring having those characters.

Example of natural selection

Drug resistance in bacteria.

Shape of beak in finches.

The peppered mothDifferential color in beetles

Natural selection and artificial selection

Natural selection It operates in the natural method.

It is a slow process and takes time.

It does not require human interference.

Moth color, beak shape of finches.

Artificial selection It operates in the artificial or man

made method.

It is fast process.

It requires human ideas and effort.

Breeding, artificial insemination.

Outline of Evolution

Convergent evolution

Divergent evolution

Co-evolution

Convergent evolution

Convergent means to converge at a point. Hence, species that have no common origin but looks or behaves in similar way due to adaptation to same environmental condition comes under this group.

The best example for this is humming bird and sunbirds. Both these birds are from different family but their feeding habit is same. Other examples include silk spider and silk moth, bat and birds etc.

Divergent evolution

Divergent means landing at different points. Hence, species that have common origin but have difference in morphology or show difference in their behavior comes under this group. Example include limbs with five digit of bat and whale; that evolved from common ancestor but their use and function are different.

Co-evolution

Co-evolution refers to effect of two species on each other’s evolution. This can be seen in insects and plants where one act as predator and other as prey thus affecting the morphology of each other.

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