BIOLOGICAL EVOLUTION
Science
Biological evolution is the process through which the characteristics of organisms change over successive generations through genetic variation and natural selection. It explains the diversity of life forms on Earth and their adaptation to changing environments.
TYPES OF EVOLUTION
Microevolution:
• Refers to small-scale changes in gene frequency within a population from one generation to the next.
• A population is a group of organisms that interbreed with each other.
• Examples include antibiotic resistance in bacteria and changes in beak size of finches.
Macroevolution:
• Refers to large-scale evolutionary changes over long geological time periods.
• It involves the origin of new species and higher taxonomic groups from common ancestors.
• Explains the diversification of life over billions of years.
ORIGIN OF LIFE
• It is generally agreed that all life evolved by common descent from a single primitive life form.
• Early Earth atmosphere was reducing in nature and rich in hydrogen.
• Organic molecules formed under suitable conditions laid the foundation of life.
Oparin–Haldane Hypothesis:
• Proposed independently by Alexander Oparin (1924) and J.B.S. Haldane.
• Suggested that life originated in a “primordial soup” of organic molecules in early oceans.
• This process of chemical evolution is also called biopoiesis.
Miller–Urey Experiment:
• Demonstrated that organic molecules like amino acids could be synthesized under simulated early Earth conditions.
• Provided experimental support to chemical evolution theory.
Earliest Cells:
• First life forms were simple, unicellular organisms similar to bacteria.
• Fossil records show bacteria-like cells as the earliest known life forms.
FUNDAMENTAL PROPERTIES OF LIFE
Cellular Organization:
• All living organisms consist of one or more cells enclosed by membranes.
Sensitivity:
• Living organisms respond to stimuli from their environment.
Growth and Metabolism:
• All living organisms assimilate energy and use it for growth and maintenance.
• Photosynthesis and respiration are key metabolic processes.
Development:
• Multicellular organisms show gene-directed growth and differentiation.
Reproduction:
• Ability to produce offspring ensures continuity of life.
Regulation:
• Living organisms regulate internal processes through biological control mechanisms.
Homeostasis:
• Maintenance of stable internal conditions despite external changes.
Heredity:
• Genetic information is stored in DNA and passed from one generation to the next.
• Enables variation, adaptation, and evolution.
THEORIES OF EVOLUTION
Lamarckism:
• Proposed by Jean-Baptiste Lamarck.
• Based on inheritance of acquired characteristics.
• Use and disuse of organs lead to their development or degeneration.
• Largely rejected due to lack of genetic basis.
Darwinism:
• Proposed by Charles Darwin in “On the Origin of Species” (1859).
• Based on natural selection.
• Key principles: overproduction, struggle for existence, variation, survival of the fittest.
• Provided a scientific explanation for evolution.
Mendelian Inheritance:
• Proposed by Gregor Johann Mendel.
• Explained inheritance patterns through genes and alleles.
• Laid the foundation of genetics and modern evolutionary biology.
Genetic Drift:
• Random change in allele frequencies in a population.
• More significant in small populations.
• Can lead to loss of genetic diversity.
Modern Evolutionary Synthesis:
• Combines Darwinian natural selection with Mendelian genetics.
• Integrates concepts of mutation, recombination, genetic drift, and gene flow.
• Explains evolution as change in allele frequencies over time.
SIGNIFICANCE OF EVOLUTION
• Explains origin and diversity of life.
• Helps understand adaptation and survival.
• Provides basis for fields like genetics, medicine, agriculture, and conservation biology.
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Subject: Science
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