ZOOHCC - 602: Evolutionary Biology (Theory) Unit:1

    Historical review of evolutionary concept :- Lamarckism

    Lamarckism, also known as Lamarckian evolution or Lamarckian inheritance, is a theory of evolution named after the French biologist Jean-Baptiste Lamarck. Lamarckism was one of the earliest theories of evolution proposed in the late 18th century and early 19th century, before the publication of Charles Darwin's "On the Origin of Species" in 1859.

    According to Lamarck's theory, organisms could pass on acquired characteristics to their offspring. For example, if a giraffe stretched its neck to reach higher leaves on a tree, it would develop a longer neck. Lamarck believed that this longer neck would be passed on to its offspring, eventually leading to the evolution of longer-necked giraffes.

    Lamarckism also proposed that the environment played a role in the evolution of organisms. Lamarck believed that if an organism needed a certain trait to survive in its environment, it would develop that trait over time. For example, if a species of bird needed to develop longer wings to fly longer distances, it would do so over generations.

    While Lamarckism was popular in its time, it was eventually superseded by the theory of natural selection proposed by Charles Darwin. Darwin's theory emphasized the role of random genetic mutations and differential reproduction in the evolution of species, rather than the inheritance of acquired characteristics. Lamarckism is now considered outdated and has been largely discredited by modern biology.

    Key points of Lamarckism:-

    Lamarckism is a theory of evolution that was proposed by Jean-Baptiste Lamarck in the early 19th century. Some of the key points of Lamarckism include:

    Inheritance of acquired characteristics: Lamarck believed that organisms could pass on traits that they acquired during their lifetime to their offspring. For example, he proposed that a giraffe could stretch its neck to reach higher leaves, and over time, this stretching would cause the giraffe's neck to lengthen. The giraffe would then pass on this longer neck to its offspring.

    Use and disuse: Lamarck also believed that traits could be gained or lost based on an organism's use or disuse of them. For example, if a person lifted weights regularly, their muscles would grow stronger and this trait would be passed on to their offspring.

    Progression towards greater complexity: Lamarck believed that evolution was a progression towards greater complexity, with organisms becoming more advanced over time.

    Rejection of extinction: Lamarck rejected the idea of extinction, believing that every species had the potential to evolve into a more complex form.

    Examples:-

    Inheritance of acquired characteristics: Lamarck's example of the giraffe stretching its neck is a classic example of this concept. According to Lamarck, as giraffes continued to stretch their necks to reach higher leaves, their necks would gradually become longer over time. Another example could be the development of calluses on a laborer's hands. Lamarck believed that if someone performed manual labor for many years, their hands would develop calluses, and this trait would be passed on to their children.

    Use and disuse: An example of use and disuse could be the muscles of a bodybuilder. Lamarck believed that if someone lifted weights and developed large muscles, their offspring would inherit this trait. Similarly, he believed that if someone stopped using a certain body part, such as an arm, that arm would gradually become weaker over time and this trait would be passed on to their offspring.

    Progression towards greater complexity: Lamarck believed that evolution was a progression towards greater complexity. He thought that simpler organisms would gradually evolve into more complex ones over time. For example, he believed that worms would eventually evolve into insects, and then into birds and mammals.

    Rejection of extinction: Lamarck did not believe in extinction, instead proposing that every species had the potential to evolve into a more complex form. He believed that if a species did go extinct, it was because it had failed to evolve quickly enough to adapt to its environment.

    Historical review of evolutionary concept :-  Darwinism

    Darwinism is a scientific theory that proposes that all species of living organisms have evolved over time from a common ancestor through the process of natural selection. This theory was developed by Charles Darwin and Alfred Russel Wallace in the mid-19th century, and it is now widely accepted as the foundation of modern evolutionary biology.

    The key components of Darwinism include:

    Variation: Darwin proposed that within any population of organisms, there is a range of variation in physical and behavioral traits. This variation arises from genetic differences and environmental factors.

    Inheritance: Darwin recognized that some traits are heritable, meaning they are passed down from parent to offspring.

    Overproduction: Darwin noted that in every generation, more offspring are produced than can survive to adulthood. This leads to a competition for resources, and only the individuals with the most advantageous traits will survive and reproduce.

    Differential Survival and Reproduction: Darwin proposed that those individuals with traits that are best suited to their environment are more likely to survive and reproduce, passing their advantageous traits on to their offspring. This is known as natural selection.

    Adaptation: Over time, natural selection can lead to significant changes in a population as advantageous traits become more common. This process of adaptation can eventually result in the emergence of new species.

    Darwinism has been supported by a vast body of scientific evidence and has been used to explain a wide range of phenomena, from the development of antibiotic resistance in bacteria to the diversity of life on Earth. It remains one of the most important and influential scientific theories in history.

    Explanation:-

    The main points of Darwinism are

    Natural selection: It is the process through which populations of organisms with traits that make them better suited to their environment tend to survive and reproduce more successfully than those without such traits. Over time, this process results in the accumulation of advantageous traits in the population, which can lead to the evolution of new species.

    Competition: It refers to the struggle between individuals or populations for limited resources such as food, water, and shelter. Competition is an important driver of natural selection, as it creates a selective pressure that favors individuals with traits that give them an advantage in obtaining resources.

    Adaptation: It is the process by which organisms develop traits that help them survive and reproduce in their environment. Adaptation can be the result of natural selection acting on random mutations or genetic variation within a population.

    Overproduction: It occurs when a population produces more offspring than can possibly survive to maturity. This leads to competition for resources and a selective pressure for individuals with advantageous traits that increase their chances of survival.

    Speciation: It is the process by which new species evolve from existing ones. This can occur through various mechanisms, such as geographic isolation, genetic divergence, or changes in behavior or morphology. Speciation is an important outcome of natural selection and a key driver of biological diversity.

    Examples of each points

    Natural selection: One example of natural selection is the evolution of antibiotic resistance in bacteria. When antibiotics are used to treat bacterial infections, some bacteria may have a natural genetic variation that makes them resistant to the antibiotic. These bacteria will survive and reproduce, passing on the resistant trait to their offspring. Over time, the population of bacteria may become dominated by those with the resistant trait, making the antibiotic less effective.

    Competition: An example of competition is seen in the struggle between plants for access to sunlight. In a dense forest, taller trees may have an advantage over shorter ones in reaching sunlight, leading to competition for resources and the selection of individuals with traits that allow them to grow taller.

    Adaptation: An example of adaptation is the evolution of long necks in giraffes. Giraffes with longer necks are better able to reach the leaves on tall trees, giving them a greater chance of survival and reproduction. Over time, this advantage has led to the evolution of giraffes with longer necks.

    Overproduction: An example of overproduction is the large number of offspring produced by fish. Fish often lay hundreds or thousands of eggs at once, but only a few of these will survive to adulthood due to predation, competition, or other factors.

    Speciation: An example of speciation is the evolution of Darwin's finches in the Galapagos Islands. The finches on different islands evolved different beak shapes and sizes to adapt to different food sources. Over time, this divergence in traits led to the formation of new species with distinct beak morphologies.

    Neo-Darwinism

    Neo-Darwinism is a modern synthesis of Charles Darwin's theory of evolution by natural selection with the discoveries of genetics, molecular biology, and other fields of science. It was developed in the mid-20th century as a response to criticisms of traditional Darwinism and a growing body of knowledge about genetics and the mechanisms of inheritance.

    The central tenet of Neo-Darwinism is that evolution is driven by the interaction between genetic variation and natural selection. Genetic variation arises through random mutations in DNA, which can create new alleles or versions of genes. Natural selection acts on this variation, favoring those traits that increase an organism's chances of survival and reproduction in a given environment. Over time, these favorable traits become more common in a population, while less favorable traits are eliminated.

    Neo-Darwinism also emphasizes the importance of genetic drift, which refers to random fluctuations in the frequency of alleles due to chance events such as genetic bottlenecks, founder effects, or small population sizes. Genetic drift can lead to the fixation of certain alleles in a population, regardless of their fitness.

    Other mechanisms of evolution that are considered part of Neo-Darwinism include gene flow, which is the movement of genes between populations due to migration, and recombination, which is the shuffling of genetic material during sexual reproduction.

    INeo-Darwinism is a comprehensive theory of evolution that incorporates both Darwin's original ideas about natural selection and modern understandings of genetics and other mechanisms of inheritance. It is widely accepted as the current paradigm for understanding how species evolve over time. 

    The main key points of Neo-Darwinism are:

    Evolution is driven by the interaction between genetic variation and natural selection.

    Genetic variation arises through random mutations in DNA, which can create new alleles or versions of genes.

    Natural selection acts on this variation, favoring those traits that increase an organism's chances of survival and reproduction in a given environment.

    Genetic drift, which refers to random fluctuations in the frequency of alleles due to chance events, can also play a role in evolution.

    Other mechanisms of evolution that are considered part of Neo-Darwinism include gene flow and recombination.

    Evolution is a gradual and continuous process that occurs over long periods of time.

    The diversity of life on Earth can be explained by the process of descent with modification, where new species arise from existing ones through the accumulation of small genetic changes over time.

    Neo-Darwinism is supported by a wealth of empirical evidence from fields such as genetics, molecular biology, biogeography, and paleontology.