Chapter 7: Evolution

Ans: Hardy Weinberg Principle, also known as Hardy Weinberg Law.

The law states that the sum of allelic frequencies in a population remains constant from generation to generation in the absence of disturbing factors. 

Hardy Weinberg Equation: (p+q)2 = p2+2pq+q2=1

Where p is the frequency of dominant allele

q is the frequency of recessive allele

p2 is the frequency of  homozygous dominant allele

2pq is the frequency of individuals with heterozygous genotype

q2 is the frequency of individuals with the homozygous recessive allele

The extent of evolutionary change can be evaluated by measuring the difference between the values.

The factors that influence these values are as follows : 

(a) Gene migration or gene flow 

(b) Genetic drift 

(c) Genetic recombination 

(d) Mutation 

(e) Natural selection 

Ans: Divergent evolution is when there are two organisms or species having common ancestors but different characteristics due to adaptation. These organisms are in different habitats and share similar anatomical structures but perform different functions. This is known as Divergent evolution. For example, the forelimbs of Whales, bats, Human and Cheetah are similar in structure but they perform different functions. 

Divergent evolution occurs due to the changed environmental conditions. The driving force behind this evolution is an adaptation to a new habitat and altering environmental conditions.

Ans:  In England, Two varieties of Pepper moths were present in the population. But before industrialization, the number of White-winged Pepper moths was much higher than the black-winged moths. Colored wings help in camouflage. Therefore they were not spotted by the predators due to their camouflage they blended very well in the moss and lichens-covered tress. 

After the industrial revolution, tree trunks became dark, lichens did not survive. As a result, the black-winged moth population started increasing because the dark tree trunk helped them to camouflage. And the now the white ones were easily spotted and killed by the predators. Again if the industries are removed the population of Black-winged moths will decrease and the population of white-winged moths will increase.

Ans: Darwin’s theory of evolution was based on two key concepts:

Branching descent and natural selection.

• Branching descent: This is usually referred to as the “Tree of life”. Every organism originated from a single common ancestor. Every new species is developed by adaptation to new environmental conditions. Ex. Darwin’s finches arose from grain eaters, Australian marsupials evolved from common marsupials.

• As the following diagram shows that the various life forms we see today have evolved from one common ancestor. One branch evolved into fishes, another one evolved into amphibians. The third branch has given rise to various terrestrial animals: reptiles, aves, and mammals. 

• Natural Selection: According to Darwin's theory, only the fittest organisms can survive the changing environmental conditions. Every living trying to cope with the changed environmental conditions by developing certain adaptations. Only those organisms with suitable adaptation are capable of surviving. Therefore, natural selection is an important phenomenon in evolution.

Ans: Two organisms occupying a particular geographical area may show similar adaptive strategies, this phenomenon is known as convergent evolution. This is because both organisms are reacting to the same environmental conditions. 

For Example, Cereus peruvianus and euphorbia virosa, are desert plants and not related to one another.  Both of the species show similar adaptations:

• Stem modification: Fleshy stem, green succulent parts store water and perform the function of photosynthesis.

• Leaf modification: Leaves are modified into spines to reduce water loss.

• Root modification: Roots penetrate deep into the ground to access groundwater.

Analogous organs that are indications of convergent evolution are depicted in these examples.

Ans:  Evolution is a continuous process. Microevolution goes on continuously and there are inheritable gradual changes in the organism and its population. 

The evolution process is continuous in human beings also as it takes place in all living beings. All the modern-day organisms are descended from their ancestors.  Modern man Homo sapiens arose from the ancestors that are Ramapithecus, Australopithecus, Homo habilis, Homo erectus, Neanderthal man, Cro-Magnon man, etc.  

• The average human life expectancy has increased, it is almost double the of primitive times. 

• All the other animals develop lactose intolerance in adulthood. Other mammals do not have the facility to consume other mammals’ milk. But human beings can consume milk throughout life and rarely develop lactose intolerance.

• Humans have developed resistance to many infectious diseases.

These are the signs of evolution.  Although evolution can take place through geographical isolation and genetic drift.

Ans: Gregor Mendel and Charles Darwin were born in the same era. Darwin was apparently aware of Mendel’s work but could not explain the origins of Variation. Mendel proposed his theories and principles of genetics.  His work was extensively limited to particular species and he put forward laws about the inheritance and variations among the organisms. The parent’s genotype is responsible for offspring’s character has been proved by Mendal through his Pigeon Pea plant experiments. And at the time Darwin seems to ignore the fact that the variation among the population of the organism is due to their genes or alleles. There are many other factors that may change the allele frequency, for example, Mutation, Genetic recombination, genetic drift, etc. So, after many generations, there would be a change in the gene pool, organism’s characteristics, and therefore new forms appear to arise in the population.