Solution-Class 10-Science & Technology-2-Chapter-1-Heredity and Evolution-Maharashtra Board

• Approximately around 7 crore years back the ice age began on the earth.
• The dinosaurs became extinct around 7 crore years ago and from that point human evolution began.
• The evolution and diversity of mammals started during this time. Due to change in climate the forest cover also declined rapidly.
• Ancestors of monkey-like animals were Lemur like animals which evolved during this time period.
• The tails of these monkey-like creatures started vanishing very gradually around 4 crore years ago.
• The body and brain both increased in volume forming first ape like animals. The monkey like ancestors gave rise to two evolutionary links to apes and human like animals.
• Later, the human evolution took place by changes in the brain volume, the ability to walk upright, excessive use of hand for manipulations.
• This journey of human evolution began 7 crore Years ago. But the true wise and intelligent man arose around 50,000 years ago.

Stages of Human Evolution :

• Ancient animals like lemurs - 7,00,00000Years ago
• Egyptopithecus -4,00,00000Years ago
• Dryopithecus -2,50,00000 Years ago
• Rama pithecus -1,00,00000Years ago
• Austrelopithecus -40,00000 Years ago
• Skilled Human -20,00,000 Years ago
• man with erect posture -15,00,000 Years ago
• Neanderthal -1,50,000 Years ago
• Cro-Magnon man -50,000 Years ago

• Every species survives in specific geographical conditions. The requirements of food and habitat is specific for each species. Their reproductive ability and period is also different.
• Therefore, the individuals from one species cannot reproduce with individuals from other species.
• When they are separated by a distance or geographical barriers they are said to be isolated geographically.
• When they cannot reproduce with each other, they are said to be isolated reproductively.
• The ancestor species of both these subspecies may be the same but due to isolation over a very long-time duration, there is genetic variation between the two. Therefore, the isolation leads to speciation.

• Due to some natural calamities the organisms get buried during ancient times.
• Fossils are the remains of organisms that once existed on Earth. The hot lava also traps some organisms or their impressions.
• They represent the ancestors of plants and animals, which are alive even today. 
• Fossils offer palaeontological evidence for the evolutionary process.
• Study of -fossils help the researcher to understand the characteristics of the organisms that existed in the past.
• Carbon dating method also helps in finding out exact age of the fossil. According to the structure of earth’s crust the fossils are obtained at specific depths.
• There is evidences of fetal science among chordates.
• The oldest ones are obtained at the depth while the relatively recent ones occupy the upper surface. Thus fossils of invertebrates were seen in very old Palaeozoic era. Later were seen fossils of Pisces, Amphlibia and Reptilia. The Mesozoic era was dominated by reptiles While Coenozoic era showed presence of mammals.
• In this way, study of fossils unfold the evolutionary secrets.

• Fetal science or embryology is used as an evidence of evolution.
• Comparative study of embryos in vertebrates/chordates shows that there is lot of similarity in them at the initial stages whereas this similarity decreases gradually.
• This similarity in the development of embryos represents common origin of organisms.

The causality behind the sudden changes was understood due to mutation principle of Hugo de Vries.

The proof for the fact that protein synthesis occurs through gene was given by George Beadle and Edward Tatum.

Transfer of information from molecule of DNA to mRNA is called as transcription process.

Evolution means gradual development.

Vestigial organ appendix present in human body is proof of evolution.

Lamarckism consists of two ‘theories which were proposed by Jean Baptiste Lamarck. These are as follows: (a) Use and disuse of the organs (b) Inheritance of acquired characters.

• In theory of use and disuse of organs, Lamarck says : The characters of organs develop because specific activities that the organisms perform. If such organ is not used it gets degenerated. Thus the morphological changes take place due to activities or laziness of a particular organism.
• To emphasise this theory, he quoted following examples. Due to constant extension of neck to eat foliage from the top of the trees, giraffe’s neck became long. Similarly blacksmith has strong arms due to constant work. He further adds that flightless ostrich and emu did not fly and hence their wings became useless. Aquatic birds like swan and duck made their feet suitable for swimming by living in water. Snake lost limbs as it tried burrowing mode.
• Such acquired characters are passed from one parental generation to the offspring. This is called inheritance of acquired characters.
• The theory of inheritance of acquired characters is not accepted as such transmission of acquired character does not take place. Only genetic characters are transmitted.

• Darwin’s theory of natural selection: Darwin is famous for the theory which he published in the book titled ‘Origin of Species’.
• In this book he explained the theory of natural selection which talks about the survival of the fittest.
• He stated that there is a continuous competition between organisms for survival and the strongest of all survives.
• The chances of survival are higher for organisms which show modifications which will help them to survive.
• He also said that, nature also plays an important role in the selection of the fittest. Nature selects only those organisms which are capable of adapting to the changing situations while the rest which are incapable to do so perish away.
• The organisms which are selected by the nature then reproduce and give rise to new species which have their own characteristics

• Embryology is the study of the formation and development of embryo and foetus.
• Embryology is used as one of the evidences of evolution.
• Comparative study of embryos in vertebrates shows that there is lot of similarity in them at the initial stages whereas this similarity decreases gradually.
• This similarity in the development of embryos represents common origin of organisms.

• Evolution refers to the slow sequential changes that occur in groupings of living creatures.
• The emergence of new species as a result of natural selection is sometimes referred to as evolution:
• The evolution process takes millions of years for various creatures to mature and speciate.
• Changes in stars and planets in space, as well as changes in the biosphere on Earth, are all included in the study of evolution.
• As a result of evolution, animals grow fitter, biodiversity increases, and new species are born.
• Various scientists have proposed hypotheses to explain the evolution process. Among these is Charles Darwin's theory of natural selection and speciation, which is widely recognised across the world.

Connecting link: Some living creatures have characteristics that distinguish them as belonging to various groupings or phyla. These individuals are regarded as connective links because they share the characteristics of both groups.

Examples: 

• (i) Peripatus is considered a connecting link between annelida and arthropoda. It has characteristics like segmented body, thin cuticle and parapodia-like organs which are similar to annelids. It also shows tracheal respiration and open circulatory system which is similar to arthropods.
• (ii) Duck billed platypus which is a connecting link between reptiles and mammals as it lays eggs like reptiles and has mammary glands like mammals.
• (iii) Lung fish : Lung fish is a connecting link between fishes and amphibians. Though a fish, it shows lungs for respiration as in amphibian animals.

Connecting links indicate the direction and hierarchy of evolution.

Heredity : Heredity is the process by which, the biological characters from parental generation are transmitted to the next generation through genes.

The mechanism of hereditary changes :

• Mutation : Sudden change in the parental DNA can cause mutations. This results into changes in the hereditary characters.
• At the time of meiosis, the crossing over takes place. This creates new recombination of the genetic information. Therefore, the haploid gametes produced carry changed hereditary characters. 

• Vestigial organs is a term used for organs which are degenerated, underdeveloped or useless for an organism.
• Presence of vestigial organs is an indication that they were useful for our ancestors but as we evolved with the changing surroundings, these structures lost their functionality but still found in our bodies.
• According to the principle of natural selection, such organs are on the verge of disappearance. But it takes many millions of years for its complete vanishing.
• The vestigial organs in one animal may be of use but to other kind of the animal they still perform regular functions. ’
• Appendix is vestigial for humans, it does not perform any function but in ruminant animals it is concerned with digestion.
• Ear muscles are vestigial for us but in monkeys and cattle they are functional.

• Heredity is the passing of traits from parents to off springs.
• These traits which are passed from one generation to another are called inherited traits as they are inherited from the previous generation.
• Evolution refers to the changes which occur in these inheritable traits over a long period of time.
• These changes allow organisms to survive with changing environment and provide an advantage over other species who cannot survive in that environment.
• Changes in these inheritable characters, provide better chances of survival and reproduction and thus result in the evolution of species.
• The fuel for evolution is thus truly supplied by the hereditary changes.

The synthesis of proteins occurs according to the central dogma. The central dogma explains how genetic information flows from DNA to RNA to make a functional protein.  
It suggests that DNA contains all the information required to synthesise a protein and the RNA acts as a messenger which carries this information to ribosomes (a type of cell organelle). The proteins are synthesised in following steps, viz. transcription, ‘translation and translocation

(i) Transcription : In the process of transcription, m-RNA is produced as per the nucleotide sequence on the DNA. For this the two strands DNA are separated. Only one strand participates in the formation of m-RNA. The sequence of nucleotides which is complementary to that of present on DNA is copied on m-RNA. Instead of thymine present in DNA, uracil is added on the m-RNA. Transcription takes place in nucleus but the m-RNA leaves nucleus, carries the genetic code and enters the cytoplasm.

This genetic code is always in triplet form and hence is known as triplet codon. The code for each amino acid always consists of three nucleotides.

(ii) Translation : Each m-RNA may carry thousands of codons. But each codon is specific for only one amino acid. The t-RNA molecule brings the required amino acid as per the code present on m-RNA. There is anticodon on each t-RNA which is complementary to the codon on m-RN A. This process is known as translation.

(iii) Translocation : In translocation, the ribosome keeps on moving from one end of m-RNA molecule to other end by distance of one triplet codon. While this process is taking place, r-RNA, helps in joining the amino acids together by peptide bonds. The peptide chains later come together to form complex protein molecules.

• According to the theory of evolution, first living material was in the form of protoplasm which was formed in ocean.
• Gradually, it gave rise to unicellular organisms. Changes took place in these unicellular organisms which made them evolve into larger and more complex organisms.
• All evolutionary changes were very slow and gradual taking about 300 crore years to happen.
• Different types of organisms were developed as the changes and development that occurred in living organisms was all round and multi-dimensional.
• Hence, this overall process of evolution is called organizational and progressive.
• Variety of plants and animals developed from the ancestors having different structural and functional organization during the process of evolution.

There are various evidences which support evolution are follows :

• Morphological evidence
• Connecting links
• Embryological evidence
• Anatomical evidences.
• Palaentological evidences
• Vestigial organs

• Anatomical evidences help us to study how species have evolved over a period of time.
• There are similarities in the structure and anatomy of different animal groups. E.g. human hand, forelimb of cat, patagium of bat and flipper of whale are all similar in their internal anatomy. There is similariy in the bones and joints of all these specimens.
• External morphology does not show any similarity. Use of each of the organ is also different in different animals. Structurally, they may not he related.
• However, the similarities in the anatomy is an evidence that they may have a common ancestor.
• In this Way, the anatomical evidence throws light on the process of evolution.

• Fossils offer palaeontological evidence for the evolutionary process.
• Due to some natural calamities the organisms get buried during ancient times.
• The impressions and remnants of such organisms remain preserved underground. The hot lava also traps some organisms or their impressions. All such formations form fossils.
• Study of fossils help the researcher to understand the characteristics of the organisms that existed in the past.
• Carbon dating method also helps in finding out exact age of the fossile. According to structure of earth’s crust the fossils are obtained at specific depths.
• The oldest ones are obtained at the depth while the relatively recent ones occupy the upper surface. Thus fossils of invertebrates were seen in very old Palaeozoic era. Later were seen fossils of Pisces, Amphibia and Reptilia. The Mesozoic era was dominated by reptiles while Coenozoic era showed presence of mammals.
• In this way, study of fossils unfold the evolutionary secrets.

The evolutionary history of modern man is as follows:

• Around seven billion years ago, human ancestors evolved from animals that resembled lemur-like animals.
• Around four billion years ago, in Africa, the tails of these monkey-like creatures gradually disappeared, while their body and brain volume grew.
• Hands were also enhanced, and an opposable thumb was added. Ape-like creatures developed in this fashion.
• These ape-like animals independently gave rise to two lines of evolution, one giving rise to apes like gibbon and orangutan in the South and North-East Asia and gorilla and chimpanzee which stayed in Africa around 2.5 crores of years ago.
• The other line of evolution gave rise to human like animals around 2 crore years ago.
• The climate became dry and this resulted into reduction of forest cover. This made arboreal apes to descend on the land and start terrestrial mode.
• Due to this, there were changes in the lumbar bones and vertebral column. The hands were also freed from locomotion and thus they became more manipulative.
• Later, journey of hominoid species started from around 2 crores years ago. The first record of human-like animal is ‘Ramapithecus’ ape from East Africa.
• Ramapithecus from Africa -> Australopithecus —> Neanderthal man -> Cro-Magnon are the important steps in human evolution.
• Neanderthal man was said to be the first wise man. The increasing growth of brain made man more and more intelligent and thinking animal.
• Later, more than biological evolution, it was cultural evolution, when man started agriculture, animal - rearing. There was development of civilizations, arts and science etc. About 200 years ago there were industrial inventions and thus man now rules the earth.