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Evolution Notes :-

Introduction to Evolution

What’s Evolution?   Evolution is gradual change in species traits over time, usually in genes & we know that genes pass from one generation to the next.

• • What are the Factors Responsible for Evolution?
    • • There are Several Factors Responsible for Evolution. Evolution is gradual change studied in Population degree only, Not a Single Species degree Evolution may do due to Natural Selection, inheritable Variations, Genetic Drift, Mutations (Favorable Mutations Which are Heredity In Function).
    • • There are Several Theories of Evolution: –

• • Preformation Theory :
    • •  According to this thesis, all living organism were created at same time. Originally there were small creatures (small living organism like Homunculi (small mortal organism) Animalcule (small living animal)) from these creatures’ life is Evolved. All these Creatures were Present on Earth Since from Beginning.
    • • According to Aristotle, firstly there was no Egg or Chick it was Acquired Gradually, the enclosing material formed Heart that Started Beating & it acquired all other region like legs eyes etc. & Chick formed gradually over time.  An individual organic life requires a “soul” which must be there from the onset and that resides within the material body. The soul directs the step-by-step epigenetic growth, following Aristotelian beliefs rather than Christian ideology. The soul includes vegetative (all organisms), locomotor (moving organisms, like animals), and rational (thinking beings, like humans). This soul resides in the combination of manlike and womanish. The soul sets the living apart from the deceased, driving gradual development from potential to actual, as per Aristotle.
    • • Theories of evolution apply primarily to living organisms and their development over time.
    • • Inorganic evolution pertains to changes in non-living matter and physical processes in the universe.. Then is an explanation of both   Organic Evolution (Biological Evolution)
    • • Organic evolution, also called natural evolution, explains how living organisms change and diversify over time through descent with modification. It focuses on the processes that lead to the emergence of new species and the diversity of life on Earth. The crucial hypotheses of organic evolution are   Darwinian Evolution (Theory of Evolution by Natural Selection) As mentioned before, Charles Darwin’s thesis of elaboration by natural selection is a basic concept in organic evolution. It suggests that variations within populations, along with natural selection, drive the adaptation and evolution of organisms over generations.”

• • Neo-Darwinism : It blends genetics into the evolution theory, explaining how it shapes diversity and adaptations in living organisms.

• • Punctuated Equilibrium : 
    • • This theory, proposed by Niles Eldredge and Stephen Jay Gould in the 1970s, suggests that evolution occurs in  fairly short,  rapid-fire bursts of change( punctuation) followed by long periods of  counterpoise( equilibrium). It challenges the traditional view of gradualism in evolution.
    • • Inorganic evolution refers to the changes and developments that  do in non-living matter,  similar as elysian bodies and physical processes in the universe. While this conception isn’t directly related to the evolution of living organisms, it helps us understand the history and development of the universe and its  colorful  elements. crucial theories of inorganic evolution include   Cosmic Evolution This  proposition describes the development and evolution of the universe as a whole, from the Big Bang to the  configuration of  worlds, stars, and planets.

• • Astral Evolution :- Astral evolution focuses on the life cycles of stars, including their birth, main sequence phase, red giant phase, supernova explosions, and eventual fate( white dwarfs, neutron stars, or black holes).

• • Planetary Evolution:- Planetary evolution explains the  configuration and changes that  do on planets over geological time,  similar as the arrangement of atmospheres, the impact of asteroids and comets, and the shaping of planetary surfaces.

• • Chemical Evolution:- 
    • • This theory deals with the formation and evolution of chemical rudiments in the universe, including the processes by which  rudiments are synthesized in stars and distributed throughout space. Inorganic and organic evolution are separate fields, addressing distinct aspects of the universe and life. Organic evolution focuses on the diversity and changes in living organisms, while inorganic evolution deals with the physical and chemical processes that shape the non-living  factors of the universe.
    • • Darwinian Evolution, also known as the  theory of Evolution by Natural Selection, is a groundbreaking scientific thesis proposed by Charles Darwin and singly by Alfred Russel Wallace in the mid-19th century. It’s one of the most abecedarian and extensively accepted concepts in biology,  furnishing a comprehensive explanation for the diversity of life on Earth. Let’s claw into the  crucial  factors of Darwinian Evolution   Variation The first critical element of Darwinian Evolution is the presence of variation within populations of living organisms. Individuals within a species display differences in traits, similar as size, color, actions, or other characteristics. These variations are the result of  inheritable diversity, mutations, and other factors.

• • Heredity – The alternate important aspect is that some of the variations observed in  individualities can be inherited and passed down to their offspring. This heritable transmission occurs through the passing on of  inheritable information from one generation to the coming.

• • Overproduction: Organisms have the capacity to produce more offspring than the environment can support. This results in competition for limited resources, including food, water, and shelter. Only a fraction of offspring make it to adulthood; others may perish from predation, disease, or resource scarcity.

• • Differential Survival and Reproduction: In any given environment, individuals with certain variations or traits may have a better chance of surviving and reproducing than others. These advantageous traits increase an individual’s fitness—their ability to survive and reproduce successfully in a particular environment.

• • Natural Selection: The core mechanism of Darwinian Evolution is natural selection. Traits in a population change over time due to variations in survival and reproduction. Consequently, when advantageous traits help individuals survive and pass them on to their offspring, those traits become more common across generations.

• • Less advantageous traits lead to lower survival and reproduction, reducing their frequency. Natural selection shapes populations by favoring traits that enhance survival and reproduction in a given environment.

• • Adaptation – 
    • • Over many generations, natural selection can lead to the accumulation of beneficial traits that are well-suited to a particular environment. We call this process of accumulating advantageous traits adaptation. Adaptations enable organisms to better survive and thrive in their specific ecological niche.
    • • Organisms evolve and diversify over long periods, forming new species through natural selection and adaptation.
    • • Evidence from paleontology, anatomy, and genetics solidly backs Darwinian Evolution as a fundamental concept in biology.

What is REPRODUCTION?

The lifespan of an organism refers to the period of time from its birth to its natural death. An organism’s lifespan is not necessarily determined by its size. For example, crows and parrots are similar in size but have very different lifespans. Similarly, a mango tree has a much shorter lifespan compared to a peepal tree. Every individual organism is certain to die eventually, with the exception of single-celled organisms which can be considered immortal.

Definition of Reproduction: It is defined as the biological process by which an organism produces young(babies) that are similar to itself. The offspring (babies) grow and mature, then go on to reproduce themselves. This creates a cycle of birth, growth, and death. An organism’s habitat, internal physiology, and other factors collectively influence how it reproduces.

Asexual reproduction occurs with or without gamete formation involving a single parent, while Sexual reproduction involves the fusion of male and female gametes from two parents of opposite sex.

What is ASEXUAL REPRODUCTION?

When one parent makes babies all by itself, the babies will be exactly like the parent and each other. They will be genetically identical. We call genetically identical individuals clones. This means they look the same and have the same genes.

Many single-celled organisms like bacteria and protists make copies of themselves by splitting in half. This is called binary fission.

Fungi and algae make special spores, without needing males and females, to make more of themselves. These spores are called zoospores.

Conidia (Penicillum) buds (Hydra) and gemmules (sponge) are other common asexual reproduction structures the fleshy bud which produces new plants in hydrophytes is called Turion.

Asexual Reproduction in Plants/ Vegetative Reproduction

Is making new plants from plant parts called vegetative reproduction? Yes, it is also a type of asexual reproduction.

Are the new plants formed from vegetative reproduction called clones? Yes.

In animals we just say, “asexual reproduction” but for plants we often say, “vegetative reproduction”.

Plant parts like stems, roots, tubes, and bulbs can grow into new plants. These parts are called vegetative propagules.

Water hyacinth was brought to India but spreads very fast through its stems and leaves in water. It grows so much it takes up all the oxygen, killing fish. It’s hard to remove from lakes and rivers.

Why was Water hyacinth was brought to India?

Water hyacinth was originally brought to India because its flowers and leaves are beautiful. However, it can produce new plants from its parts very quickly. It spreads all over lakes and rivers in a short time. Because there are so many new plants, it is very difficult to remove it from the water body.

 What is SEXUAL REPRODUCTION?

• Sexual reproduction involves the formation of male and female gametes, which can come from the same individual or different ones of opposite sex. This process results in the fusion of these gametes to create a zygote, which develops into a new organism. Compared to asexual reproduction, sexual reproduction is a complex and slow process.
• Because of the fusion of male and female gametes, sexual reproduction results in offspring that are not identical to the parents or amongst themselves.
• A study of diverse organisms, such as plants, animals, or fungi, reveals that despite significant differences in external morphology, internal structure, and physiology, they share a similar pattern in their sexual reproduction process. Let us first discuss what features are common to these diverse organisms.
• All organisms must reach a certain stage of growth and maturity before they can reproduce sexually. This phase is called the juvenile phase in plants and is also known as the vegetative phase. The duration of this phase varies among different species.
• In some plants that produce flowers more than once, the inter-flowering period is considered mature.

Plants, such as annual and biennial types, have distinct vegetative, reproductive, and senescent phases. However, it is difficult to clearly define these phases in perennial species. Some plants exhibit unusual flowering patterns, such as bamboo species, which flower only once in their lifetime and produce a large number of fruits before dying.

Another plant, Strobilanthus kunthiana, flowers once every 12 years. This plant flowered in September-October 2006 and transformed large areas into blue stretches, attracting a large number of tourists in Kerala, Karnataka, and Tamil Nadu.

The end of the reproductive phase can be seen as a parameter for senescence or old age, and it is accompanied by concomitant changes in the body, such as slowed metabolism, leading to eventual death.

What are the Advantages of Asexual Reproduction?

• Super efficient: Asexual reproduction lets organisms reproduce quickly and easily without needing to find a mate. This means their population can grow faster than those that rely on finding a partner.
• Genetic Twinsies: Asexual reproduction creates offspring that are just like their parents, genetically speaking. This is really handy in places where the parents’ traits are perfect for survival and making babies.
• Perfect for steady environments: Asexual reproduction is great when the environment doesn’t change much. The offspring inherit their parents’ traits, which already work well in that environment. So, they can thrive without needing to mix up their genes.
• Reproduction backup plan: Asexual reproduction ensures that an organism can keep making babies even when there aren’t many suitable mates around. This is especially helpful for organisms that are alone or not very good at moving around.
• Saving energy: Asexual reproduction is a real energy-saver. It doesn’t need all the fancy stuff like dating, fancy dances, and special reproductive cells that sexual reproduction does.

Remember, while asexual reproduction has its perks, sexual reproduction has its own advantages too, like having different genes that can help a species adapt and survive in changing environments. Different organisms have different ways of making babies based on where they live and what works best for them

What are the Disadvantages of Asexual Reproduction?

At the molecular level, asexual reproduction also has certain disadvantages. Here are a few

• Lack of genetic recombination: Asexual reproduction does not involve the exchange or recombination of genetic material between two individuals. This means that there is no opportunity for the mixing and shuffling of genes, which can limit the generation of new genetic combinations. Genetic recombination, as seen in sexual reproduction, allows for the creation of novel gene sequences that can contribute to the survival and adaptation of organisms.
• Accumulation of deleterious mutations: Asexual reproduction can lead to the accumulation of deleterious mutations within a population. Since there is no genetic recombination, any harmful mutations that arise in an individual will be passed on to its offspring without being diluted or eliminated. Over time, this can result in a higher frequency of detrimental genetic variations within the population.
• Reduced repair mechanisms: Asexual reproduction may result in reduced efficiency in DNA repair mechanisms. Sexual reproduction allows for the exchange of genetic material, which can help in repairing damaged DNA by using the undamaged copy as a template. In asexual reproduction, there is no such opportunity for DNA repair through recombination, potentially leading to a higher accumulation of DNA damage and mutations.
• Limited ability to adapt to changing environments: Asexual reproduction can limit the ability of organisms to adapt to changing environments at the molecular level. Without the introduction of new genetic variations, organisms may struggle to develop new traits or mechanisms to cope with environmental challenges. Sexual reproduction, with its genetic diversity, provides a broader range of genetic combinations that can enhance an organism’s ability to adapt and survive.
• Reduced immune system diversity: Asexual reproduction can result in reduced diversity in the immune system. The immune system relies on genetic diversity to recognize and combat a wide range of pathogens. In asexual reproduction, where offspring are genetically identical to the parent, the immune system may lack the necessary diversity to effectively respond to new or evolving pathogens.

These molecular-level disadvantages of asexual reproduction highlight some of the limitations it poses in terms of genetic variation, DNA repair, adaptation, and immune system diversity

What are the Advantages Sexual Reproduction?

Sexual reproduction has some awesome advantages

• Mix and match genes: Sexual reproduction involves combining genetic material from two parents, resulting in offspring with unique combinations of genes. This creates diversity and allows for the development of new traits that can help a species adapt to different environments.
• Evolutionary superpowers: Sexual reproduction helps drive evolution. It allows for the accumulation of beneficial genetic changes and the removal of harmful ones through natural selection. This means species can change and improve over time.
• DNA damage control: Sexual reproduction has a built-in DNA repair system. When reproductive cells are formed, errors in DNA replication can be fixed. This reduces the chances of passing on harmful mutations to the next generation.
• Super immune system: Sexual reproduction can boost disease resistance in offspring. By mixing genes from two parents, there’s a higher chance of inheriting traits that make them more resistant to diseases, parasites, and other harmful invaders.
• Bye-bye bad traits: Sexual reproduction helps get rid of harmful recessive traits. When two individuals with different recessive traits mate, the harmful traits are less likely to show up in their offspring. This means fewer harmful traits in the population overall.

Remember, sexual reproduction does require more time, energy, and resources compared to asexual reproduction. But it’s a powerful way for species to adapt, survive, and keep evolving in a changing world. Different organisms have different ways of making babies based on what works best for them and their environment.

What are Disadvantages of Sexual Reproduction?

• Need for a mate: Sexual reproduction requires finding a suitable mate, which can be challenging and time-consuming. Organisms need to invest energy and resources in finding, attracting, and competing for mates, which can divert resources from other important activities.
• Reduced population growth rate: Compared to asexual reproduction, sexual reproduction generally leads to a slower population growth rate. This is because only half of the offspring’s genetic material comes from each parent, resulting in fewer offspring produced per reproductive event.
• Risk of Sexually transmitted Disease: When organisms engage in sexual reproduction, there is a higher chance of transmitting sexually transmitted infections (STIs) due to direct physical contact between individuals. This can lead to negative health effects for individuals and potentially affect their ability to successfully reproduce.
• Cost of producing specialized reproductive cells: Sexual reproduction requires the production of specialized reproductive cells (sperm and eggs) that are energetically costly to produce. Meiosis, the process of cell division that produces reproductive cells, is more complex and energy-intensive compared to mitosis. This investment in producing and maintaining these cells can be a disadvantage compared to asexual reproduction, which does not require such specialized cells.

At the molecular level, Sexual Reproduction can have some disadvantages,

2. Genetic load: Sexual reproduction can lead to the accumulation of harmful genetic mutations in a population. As each parent contributes a set of genes, including potentially harmful ones, there is a chance that these harmful mutations can be passed on to offspring. Over time, this can increase the genetic load of a population.

3. Cost of meiosis: The additional steps and energy required for meiosis can be considered a molecular-level disadvantage of sexual reproduction.

4. Loss of advantageous alleles: Sexual reproduction can result in the loss of advantageous alleles from a population. When two individuals with different advantageous traits mate, their offspring may inherit a mix of genes that dilutes or eliminates those advantageous traits, reducing the overall fitness of the population.

It’s important to note that while sexual reproduction has these molecular-level disadvantages, it also provides benefits such as genetic diversity and the potential for adaptation to changing environments. The advantages and disadvantages of sexual reproduction are balanced in different ways across different species and depend on various ecological and evolutionary factors.