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Dollo’s Law

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Definition of Dollo’s Law

MVSAT 2024

Dollos law is also known as the dollos principle. This law was proposed in the year 1893. It is also known as Dollo’s law of irreversibility. This law states that an organism never gets back to its original state. Even if the conditions are favorable to its previous conditions, still it does not return back to its original state. There are some of the steps in between through which the organism has passed in its lifetime and thus is never able to return back to its original state. Dollos law was stated by Louis Dollo. He was a Belgian paleontologist. Thus, the organism goes through an irreversible type of evolution. It should not be interpreted that evolution is not reversible in nature. This Dollos law is applied to the field of morphology and especially for the study of fossils. This law can also be used to describe the molecular events that must have taken place during the course of the evolution of that organism. This can thus be used to study the individual mutations and also to understand gene losses. This is a definition of the Dollo’s law of irreversibility. Furthermore, we will understand the different fields in which this law finds its uses. 

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Devolution, as the name implies, means backward evolution. Dollo’s law of irreversibility states that the organism cannot come back to its original form because there are some irreversible changes or steps that have taken place in the course of evolution. Devolution states that the organisms can get back to their original forms over the course of time if it is necessary according to the needs of the organism. This type of evolution is known as devolution. Evolution is due to the fact that the organisms start adapting to their environment and then some changes are brought into their bodies that can be natural in nature or induced changes such as by the help of mutation. But in the field of evolutionary biology, no such types of changes are feasible. Dollo’s law denies the possibility of devolution. Orthogenesis is the basis on which the idea of devolution is based. When we get a closer look at the theories of evolution then we can see that evolution brings about changes that are complex in nature and they are to ease the adaptability of the organism towards the environment. 

Dollo's Law in Phylogenetics

In brief, we can say that according to Dollo’s law, the organism acquires certain characteristics during the course of evolution and these factors are irreversible in nature. So the characteristics that are lost during the course of evolution can be regained in the lifetime. For example, in vertebrates, the loss of teeth can be well modeled under this law. The teeth though evolved multiple times in the course of the evolution of animals and were also lost in some organisms like that in birds, turtles, and seahorses. So this Dollo’s law can also be applied to molecular genetics that the individual organism inactivates the genes by itself. This can be seen by the loss of gluconolactone oxidase. This enzyme is the final enzyme required in the final step of the synthesis of vitamin C. This enzyme got lost and thus cannot be traced back and so we need to take vitamin C in our dietary supplements. 

Molecular Example

There was a study proposed in 2009 for the evolution of protein structure and this proposed a new mechanism for Dollo’s law. There was a hormone receptor that was examined and it evolved from an ancestral protein. This protein had the ability to bind the two hormones to a new protein and this new protein was specific in nature. Amino acid substitutions helped in bringing out these changes. Also, these changes helped in preventing the binding of the second hormone. Also apart from these some changes also took place that was neutral in nature and did not affect the hormone binding. When artificially these changes were tried to bring back, they seemed to have destabilized the ancestral structure of the proteins. So, in the end, it was concluded that if these changes had to be brought back then the proteins need to evolve in the reverse direction and they must regain their ability to get bound to the two hormones and along with these several other neutral mutations need to take place. 

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FAQs on Dollo’s Law

1. What is the Difference Between Variations and Mutations?

Answer: By the process of speciation, new species arise in nature. It is an evolutionary process. Evolution is said to occur when new species arise from older species. Darwin said that there are inheritable variations that start accumulating in the organism and then they are responsible for evolution. Vries states that mutations are the cause of evolution. The nature of mutations is random and directionless. Both mutations and variations are the causes of evolution but still, there are some changes that are present in these both terms. They are:

  • Variations are very small in nature and because of this, they do not have the capacity to bring about sudden changes in the body of organisms. Variations are needed for the long run so as to bring about changes in the organism. On the other hand, mutations are very strong in nature and they are responsible to bring sudden changes in the body of the organism. 

  • The nature of mutations is directionless and random in nature. The variations are directional in nature. 

  • Variations bring about small changes in organisms so it was stated that evolution is a very slow and gradual process. On the other hand, mutations bring single changes that are very strong in nature and they easily bring about evolution. 

2. Archaeopteryx Was a Transitional Species. What Reptilian Characteristics Were Present in It?

Answer: The reptilian characteristics of archaeopteryx were:

  • Their body axis was more like that of a lizard.

  • They had the presence of a long tail.

  • Pneumatic bones were not present in them. 

  • Their sternum was weak in nature.

  • Teeth were present in their jaws.

  • Claw was present on their fingers. 

  • A free caudal vertebra was also present on their hand.

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