Class 10 SELINA Solutions Biology Chapter 14 - Human Evolution

(c) Lamarck

(d) Darwin

(b) Moth

(a) Ramapithecus

Neanderthal man and modern man exhibit different characteristics, and hence, they are considered two distinct species. Below are the characteristic differences between Neanderthal man and modern man:

(a) Use and disuse:

Parts of the body which are used extensively become larger and stronger, while those which are not used deteriorate.

(b) Inheritance of acquired characters:

An organism could pass its modifications to its offspring.

Three vestigial organs found in humans are wisdom teeth, vermiform appendix and pinna.

Biston betularia is a classical example of 'natural selection'.

(a)The fossil history of humans is fragmentary.

(b)The first remarkable human fossil was that of Homo habilis.

(c)Evolution is an ever continuing process. 

(a) Evolution: Evolution is a slow and continuous process whereby complex forms of life have emerged from simpler forms through millions of years.

(b) Vestigial organs: Vestigial organs are those organs that have ceased to be of any use to the possessor but still persist generation after generation in a reduced form.

(c) Speciation: Speciation is a process of origin of new species by gradual modification. 

(a) Differences between Australopithecus and Cro-magnon (Chin):

(b) Differences between Australopithecus and Modern man (Body hair):

(c) Differences between Homo habilis and Homo sapiens (Posture):

Differences between Lamarck's Theory and Darwin's Theory:

The Darwin's theory of Natural Selection is based on four observable facts which are as follows:

(i) Overproduction:

• All organisms have the capacity to reproduce at a very high rate.
• However, organisms cannot survive by reproduction alone.
• Due to lack of food and space, offspring soon begin to die.
• Some are eaten by predators, while some get destroyed due to adverse environmental conditions.

(ii) Struggle for existence:

• Overproduction of organisms results in a struggle for existence among organisms.
• The struggle is to obtain food, space and mate.

(iii) Variation:

• Progeny of the same parents are not exactly alike. Such differences are known as variations. The variations may be harmful or advantageous.

(iv) Survival of fittest:

• In the struggle for existence, organisms that develop new favourable characteristics will survive in the long run. This idea is called 'Survival of the fittest'.
• Organisms which survive will transmit favourable characters to their offspring.
• These characters get accumulated and give rise to new species.

• The best example is industrial melanism showing the effect of industrial pollution on the moth population on a nearby tree.
• Before industrialisation, light-coloured lichen used to grow on trees and moth predators could not spot white moths easily, while dark moths were lesser in the moth population. However, due to industrial pollution, lichens could not grow on trees and it became difficult for predators to spot dark moths on the dark background of the stem bark, and thus, the population of white moths became less than that of dark moths.
• This process is termed industrial melanism. Before industrialisation, white moths were better adapted towards nature, but after industrialisation, dark-coloured moths were more fit towards the changed environmental conditions.

Stage A: Australopithecus

Stage B: Homo sapiens sapiens

(a) Contrasting characters between Australopithecus and Homo sapiens sapiens:

(b) Stages of human evolution in their correct sequence:

Australopithecus → Homo habilis → Homo erectus → Neanderthal man → Cro-Magnon man → Homo sapiens sapiens

(c) Characteristic features of stage B (Homo sapiens sapiens):

• Bipedal locomotion with four reversed curves in the spine

• Forehead steep, reduced brow ridges

(a) Industrial melanism

(b) Common name: Peppered moth

Scientific name: Biston betularia

(c) Reasons for changes in the two figures:

• Before the Industrial Revolution, a thick growth of white-coloured lichen covered the trees. As a result, the light-coloured moths were camouflaged and survived under this cover, while the dark-coloured moths were easily spotted by predators.
• After the Industrial Revolution, pollution resulted in a decline in the growth of lichens. The tree bark got exposed due to the absence of lichens. As a result, dark-coloured moths now got an advantage of a dark background, were camouflaged and survived, while the light-coloured moths were easily picked by predators.
• This showed that in a mixed population, those moths which could adapt to the changing environment after the Industrial Revolution survived and increased in number, while the ones which could not adapt were slowly wiped out from the population.

(d)

(i) Natural selection. During the struggle for existence, only those individuals which have advantageous variations survive while the ones which lack these variations are wiped out. Nature selects only those variations which are suitable for existence. This process is called natural selection.

(ii) Charles Darwin