Question

A common misconception about evolution is that it always leads to organisms getting "better" in some way.

a) What is one kind of evolutionary process that consistently causes individual fitness to increase?

b) Discuss three evolutionary processes that can lead to individual fitness going down.

essay style answer 300-500 words max

Answer 1

(a).Ans. Natural selection is the evolutionary force which consistently cause individual fitness to increase.

Genetic drift, migration and mutation are among the evolutionary forces which can lead to individual fitness going down.

Fitness is the survival of individuals to reproductive age and produce viable offsprings. The individuals that can leave maximum viable offsprings in the next generation are said to have higher fitness. More the fitness, more the number of viable offsprings in the next generation and the chance of survival increases. Genetic drift is random change in allele frequency in a population. Two aspects can be considered in genetic drift- bottleneck and founder effect. In bottleneck, there is sharp change in the allele frequencies in a population. The causes of this sudden change in genetic bottle neck include natural calamities such as flood, eathquake, fire etc. When there is flood, many individuals in a population can be killed due to high water level submerging the habitat. If many individuals are dead in the population due to the flood, it will lead to loss of alleles from the population and the allele frequencies will be altered. When such allele frequency change occurs, there is chance that majority of the favorable alleles are removed from the population and hence it leads to reduction in fitness. Likewise in case of unfavorable events such as earthquake, there can be sudden change in the allele and genotype frequencies due to the loss of life of individuals in the event.On the other hand, in case of founder effect the population arises from a small number of individuals. In this case, there might be less frequency of favourable alleles. If such favourable allele frequency is less,then the fitness would be less and the survival rate of individuals would be less. Hence, genetic drift can cause the fitness lo lower down. Migration is an important evolutionary force. In migration there is movement of individuals from one population to other. In such movement of individuals from one population to the other, the migrating individuals will carry alleles to the new population where they are entering into. This will cause change in allele frequencies in the original population.It leads to change in gene pool of the original population. If the migrating individuals carry harmful alleles, these harmful alleles will get into the offsprings to the next generation since the migrating individuals take part in reproduction by mating with the individuals in the original population. In such case, the fitness will be lowered down. The original allele and genotype frequencies are altered by the migrating individuals. When such event of migration is associated with small population, the change is more prominent and hence the effect of harmful or non-favourable allele will be observed in a shorter period of time. Mutation is an important evolutionary process which occurs spontaneously in a population. Mutation is the ultimate cause of change in a trait. Mutation Mutation can cause acquisition of new character or loss of a character.It is alteration in the genotype of an individual due to change in nucleotides itself or change in nucleotide sequence. In non-sense mutation, change in coden takes place leading to formation of a new codon which do not code for any amino acid. If such nonsense codon is produced at the initial nucleotide sequence in a coding sequence as a result of mutation, then the protein will not be produced since the codon is not coding any amino acid. Hence, the role of this protein will no longer be there in the individual. If this is a protein which perform important function, then it can lead to lowering of fitness in the individual. Once a protein performing vital metabolic activities is not synthesized, it will for sure be harmful for the individual and hence will lead to lowering of fitness. On the other hand, even though the mutation is not nonsense it may code a new amino acid due to change in nucleotide within the codon. In such condition it may cause production of protein of lower activity and hence it can also lower down the fitness. Hence, mutation can lower down the fitness.