Evolution

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A

Ginkgo biloba is a living fossil because its ancestors are unchanged for the last many hundred years while its relative disappeared.

Mimicry is the resemblance of one organism to another or to any natural object for the purpose of concealment, protection or for some other advantages. It is found in Iguana, Chameleon (girgit), leaf butterfly and stick insect.

The Darwin Wallace theory of Natural Selection can be generalised as the change in species by the survival of an organismal type exhibiting a natural variation that gives it an adaptive advantage in an environment. Thus leading to a new environmental equilibrium. The idea of the survival of the fittest explain the above evolution by natural selection. According to survival of fittest, some of the variations exhibited by living things make it easier for them to survive and reproduce thus more adaptive forms increase. Those which are not fit (or less adaptive) become eliminated.

Homologous organs are those which have the same essential structure, which they inherit from common ancestors though they may be very differently modified in adaptation to different functions.
Analogous organs are structurally different organs which get modified to perform similar functions.

All primates have a common ancestry (monophytic origin). Primate evolution began 80-100 million years ago. The evolutionary history of eutherian mammals dates back to early cretaceous period. The earliest eutherians were shrew-like terrestrial insectivores. They were small, ground dwelling mammals.

Cro-Magnon man emerged about 34000 years ago. Thus it is regarded as most recent ancestor of today's man. It has, therefore, been called as Homo sapiens fossilis. The Cro-Magnon man was like us, about 1.8 meters tall, well-built body. Its face was perfectly orthognathous with a narrow elevated nose, broad and arched forehead, moderate brow-ridges, strong jaws with man-like dentition and a well developed chin. Its cranial capacity was, however somewhat more than ours, being about 1650 cc(ours is 1400 cc). The Cro-Magnon man was the direct ancestor of the living man.

The phenomenon of development of a new species from pre-existing one is called speciation. A species is a collection of demes. The deme is a groups of populations with a common gene pool.

Homo habilis was the first tool maker and used tools of chipped stones extensively. It is also called handy man because heaps of tools found with these fossils included sharpened stones which indicates that Homo habilis was capable of "making tools". He also led community life in caves and greatly cared for the young ones.