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We can see changes around us, sometimes good and sometimes bad, sometimes beneficial some time deleterious, but these changes have become part of our life. In books, magazines, assignment and many more of educational stuff we can learn about times when there were dinosaurs and large other mammals. In fact we have also read or heard somewhere that human has descended from monkeys. But do we know exact meaning of term evolution in biology?

A perfect definition for evolution can rarely be figured out because evolution is defined in several ways by different biologist. Still in simple words or biological language we can term evolution as changes that can take place in micro or macro level. In fact here evolution is defined in deeper sense. It looks upon ancestor of all living beings present on the earth today. Yes, here this term actually emphasizes on the overall idea that the reason for not just humans or animals are on the earth or about their ancestors but the common ancestor of all the living beings whether its micro organism or macro. Thus the main idea of evolution is the tree of life, the place or point where different species share common ancestor.

Hundreds of years ago, Charles Darwin was the first person to put forward idea of evolution and made everyone aware about the existence of living beings on the earth. But his evolutionary theories were raised not easily accepted and many questions were raised against his ideas. But with every passing generation several researches were done and hence, the theories that were put up by Darwin was dissected and hence reasons for different changes have now been accepted due to several evidences and facts. Evolution has several sides, and understanding evolution requires idea on various theories and experiments.

Today we can call evolution as the unifying force that connects different streams of biology such as microbiology, evolutionary biology, genetics, Paleontology etc. According to one of the Darwin theory, evolution means the descendent from past, but still to discover the reason behind this we need to see on depth of the subject.

Genetic variation has been proved as the main reason for evolution where selective forces acts, thus the mechanism of evolution are:

  • Descent with modification
  • Mutation
  • Genetic drift
  • Natural selection
  • Migration
  • Genetic variation

Descent with modification: in this case, evolution occurs when there is change in gene frequency in a population that lead to genetic variation, thus this leads to the transfer of difference from one generation to the other. Example: if we see an insect say butterfly whose maximum population is green in color but very less individual are brown whereas after some generation the population of brown butterfly extends and green gets almost diminished. This can be the best example for evolution and there are reasons behind this:

Mutation: mutation means the changes in gene that can be advantages or deleterious. Likewise, the green butterfly when undergo mutation can have brown offspring thus increasing the brown coloration in the population.

Migration: migration means the movement of people from one place to another. Hence, when any brown butterfly migrates to the population of green butterfly, the number of brown butterfly increases.

Genetic drift: it is the random change in population due to chance deviation resulting in change in allelic frequency. In case if some of the green butterflies dies due to any reason and but the more number of brown survives in comparison to the green, then in the next generation the number of brown butterflies will undoubtedly increase, thus describing genetic drift.

Natural selection: in natural selection, only those individual that has advantage for survival are selected by nature and others are slowly eliminated. If we continue with the example of butterflies, if green butterflies are easily spotted by birds and hence becomes their prey; then the chances for brown butterflies to survive increases in every upcoming generations. Selection is a special case of natural selection where individual with a particular genotype enjoy the advantage of survival and hence are preferred by the nature. All these above mentioned factors are important mechanism of evolution but they purely work only if there is some genetic variation in the population, most importantly genetic drift and natural selection. Therefore, to know the reasons or sources of genetic variation we must have a depth study on different factors such as:

  1. Mutation: mutation, as described earlier is the changes in gene or DNA, but we must be well aware that small mutations rarely bring differences but when these small mutations accumulate, it can bring changes in large scale thus leading to genetic variation and hence evolution. Since, mutation can be advantageous, harmful or neutral hence we can come to the conclusion that it is a random event. Mutation can be broadly classified into two types: somatic mutation and reproductive or germ line mutation. Somatic mutation at one hand is changes that occurs in somatic cells i.e. non- reproductive cells and hence is not passed from one generation to the other; therefore it does not matter in evolution. On the other hand genetic variation so caused due to germ- line mutation that occurs in reproductive cells and hence is passed from one generation to the other. Here, reproductive cells refer to egg cell or sperm cell. There are different reasons for mutation to occurs, it can be due to change in chromosome number or the change in chromosome structure; such as: deletion, duplication, inversion, translocation, and mutation due to chemicals, radiation, and many more. Therefore, this factor can result in mutation and hence cause genetic variation and when there is genetic variation in a population it leads to evolution.

  2. Gene flow: it is the other source for genetic variation, can also be termed as migration. When any genes that are carried to new place, where they didn’t exist, thus results in genetic variation and leads to evolution.

  3. Sex and gene shuffling: this is an important source of genetic variation. No two individual are identical, it is because the genes from parents are transferred to the offspring results in gene shuffling during the process and thus when there is shuffling of gene, new combinations are produced leading to evolution.

These are sources of genetic variation. Some of the other important concepts in evolution that brings change in allelic frequency or are responsible for genetic variation in a population are:

Sexual selections In case of sexual selection, those individual who are able to copulate successfully are selected in comparison to the other that fails to copulate. But sexual selection can sometime be harmful for an individual because the special character that attract the other partner, especially in animals can end up with harm by the predator. But in the cases where mating takes place successfully, they are selected by the nature.

In case of artificial selection, desirable traits in two species are its in two species are chosen and they are crossed, in order to produce an offspring that is better suited and advantageous. Mostly vegetables and fruits are artificial selected by the farmers and even animals are done artificial selection to increase their yield.

Fitness on the other hand, is individual’s genetic contribution to future generation. Genotype associated with high rate of reproductive success are said to have higher fitness thus, this is directly linked to sexual selection. Hence, natural selection along with its special types helps in process of evolution.

Adaptation: it is the process by which an individual adapt themselves in the environment they live, thus this provides some improved functions leading to evolution of that species and all the improved character will be inherited by the offspring of next generation. Like the mimicry of leaves by some insects to stay safe from the predators.

As said earlier, evolution can work on small scale changes and also on large scale, hence two terms micro evolution and macro evolution very well describes this fact.

Microevolution: it is evolution on small scale. Therefore, this can be defined as change in gene frequency within a population, thus defines evolution.

Macroevolution: it refers to evolution of species above the species level.

Some of the terms that also define evolution are species and speciation. Species are the individual that can actually or potentially interbreed and speciation is the event that divides a gene pool into two or separate gene pool. Therefore, it can take place slowly or in a few generation type and in this case geographic isolation, reductions of gene flow, reproductive isolation play an important role.

Therefore, evolution is a broad concept that has been made clear with evidences and proofs from fossil record and many more of recent technologies. In fact human evolution itself is a broader concept leading to several changes in form, structure and habitat thus resulting in what we are today.