EVOLUTION

EVIDENCES FOR EVOLUTION

Paleontological Evidence: Remains of hard parts of life forms; found in rocks; are called fossils. A study of fossils in different sedimentary layers indicates the geological period in which they existed. This shows the period in which a particular organism existed on the earth.

Homologous Organs: Organs which are similar in structure but serve different purposes in different organisms are called homologous organs. For example; forelimbs of humans and dogs have similar structure; in terms of constituent bones. But forelimbs of humans serve different functions than those of dogs. This indicates that humans and dogs have evolved from a common ancestor. Homology is based on divergent evolution.


Analogous Organs: Organs which are different in structure but serve similar function are called analogous organs. For example; wings of bats and wings of butterfly are different in structure but they are meant for flight in both organisms. Analogy is based on convergent evolution.

Artificial Breeding: Many plants and animals have been artificially bred by man since ages. The intensive breeding program has created numerous breeds in a single species, e.g. various breeds of dogs. If man could create new breeds within hundreds of years then nature could create new species over millions of years.

Dark Winged Moths: A collection of moths made before industrialization in England showed that there were more white-winged moths than dark-winged moths. The collection after industrialization showed that there were more dark-winged moths than white-winged moths. The tree trunks became dark due to pollution. So, white-winged moths could be easily spotted by predators. Dark wings gave survival advantage. Hence, number of dark-winged moths increased rapidly. This gives another proof that evolution can happen and has happened.


Development of Resistance: Doctors use various antibiotics to control infections. Over a period of time, bacteria develop resistance against an antibiotic. This also shows that evolution can happen. This also shows that evolution is not a direct process; in the sense of determinism.


ADAPTIVE RADIATION

The process of evolution of many varieties from a single variety of organism in a given geographical area is called adaptive radiation. It happens within a short span of time.

Darwin’s observation on finches of the Galapagos Islands showed interesting insights. Finches of that island show a wide variety; in terms of types of beaks; suited to different eating habits. Darwin proposed that all the varieties evolved on the island itself. From the original see-eating features, many other forms (with altered beaks) arose. This shows adaptive radiation.

Another example of adaptive radiation is seen in Australian marsupials. Different types of marsupials evolved from one ancestral stock; within the Australian island continent. Placental mammals in Australia also exhibit adaptive radiation.

Examples of marsupial mammals: Marsupial mole, numbat, marsupial mouse, spotted cuscus, flying phalanger, Tasmanian tiger cat, Tasmanian wolf.

Examples of placental mammals of Australia: Mole, anteater, mouse, lemur, flying squirrel, bobcat, wolf.

The rate of appearance of new forms is linked to the life cycle or lifespan. Microbes can multiply rapidly to become millions of individuals within hours. So, a new species can emerge in a microbe within a short time. But life cycle of a complex animal can be from a couple of months to many years. Origin of a new species in such animals would take millions of years.


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