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2: Life’s Diversity and Origins

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    Biology is the science of organisms, how organisms function, behave, interact, adapt, and, as populations, have and can evolve. As we will see, organisms are discrete, highly organized, bounded but open, non-equilibrium, physicochemical systems. Now that is a lot of words, so the question is what do they mean? How is a rock different from a mushroom that looks like a rock? What exactly, for example, is a bounded, non-equilibrium system? The answers are not simple; they assume a working knowledge of thermodynamics, a complex topic that we address in Chapter 5. For the moment, when we talk about a non-equilibrium system, we mean a system that can do various forms of work. Of course that means we have to define what we mean by work. For simplicity, we will start by defining work as some outcome that takes the input of energy to achieve. In the context of biological systems, work ranges from generating and maintaining molecular gradients and driving other unfavorable, that is energy-requiring reactions, such as the synthesis of a wide range of biomolecules, including nucleic acids, proteins, lipids, and carbohydrates, required for growth, reproduction, the generation of movement, and so on.

    • 2.0: Introduction
      This page explores the essence of biology, emphasizing the diversity and characteristics of organisms as cellular systems that maintain non-equilibrium to enable energy use for growth and reproduction.
    • 2.1: What is life, exactly?
      This page explores the complexities of defining life in biology, highlighting the shared ancestry and DNA basis of all known life forms on Earth. It notes the uncertainty surrounding the origin of life and the implications for potential extraterrestrial life. Researchers recognize that while many life forms exist, they are fundamentally variations of a single type.
    • 2.2: The cell theory and the continuity of life
      This page covers the Cell Theory, stating that all organisms consist of cells that arise from pre-existing cells, underscoring the importance of cells in life. It notes a common ancestor for all organisms dating back 3.5 to 3.8 billion years, emphasizing ongoing cell division. The role of DNA in inheritance is highlighted, alongside the speculative origins of the first cells. Additionally, horizontal gene transfer is introduced as a significant process.
    • 2.3: The organization of organisms
      This page explores the differences between cells and organisms as fundamental life units, highlighting how multicellular organisms function as cooperative systems of specialized cells. It distinguishes germ cells, which create new organisms, from somatic cells, which rely on the organism's well-being.
    • 2.4: Spontaneous generation and the origin of life
      This page explores the origins of life and the evolution of organisms, contrasting spontaneous generation with natural processes. It outlines the historical shift from supernatural beliefs to scientific explanations, underscoring experiments by Redi, Spallanzani, and Pasteur, which confirmed that life originates from existing organisms.
    • 2.5: The Death of Vitalism
      This page discusses the shift from vitalism to a scientific understanding of organic chemistry, initiated by Friedrich Wöhler's synthesis of urea in 1828 from inorganic materials. It highlights the transition in perception regarding organic molecules as products of chemical reactions, rather than supernatural forces. This evolution prompts readers to explore significant scientific questions about life, cellular continuity, and the origins of organic compounds.
    • 2.6: Thinking about life’s origins
      This page explores three approaches to the origins of life: religious explanations lacking scientific testability, intelligence design claims that challenge evolution but lack validity, and panspermia, which suggests extraterrestrial origins but does not clarify ultimate origins. It underscores the importance of interconnected scientific disciplines and addresses historical misconceptions about science's role in explaining life’s beginnings.
    • 2.7: Experimental studies on the origins of life
      This page explores experiments by Miller and Urey that simulated early Earth conditions to produce organic molecules, such as amino acids, thought to be life’s precursors. It introduces "protocells," which are early molecular communities that facilitated evolutionary changes. Additionally, it raises philosophical inquiries about spontaneous generation and presents the Drake equation, a tool for estimating the existence of extraterrestrial civilizations.
    • 2.8: Mapping the history of life on earth
      This page explores the origins of the universe and Earth's history concerning life's emergence. It highlights the Big Bang theory, backed by Edwin Hubble's discoveries, and estimates the universe's age at 13.8 billion years and Earth’s at 4.5 billion years. Early Earth faced heavy bombardment, diminishing around 3.5 billion years ago. The text questions whether life originated multiple times or as a singular event approximately 3.8 to 3.5 billion years ago.
    • 2.9: Fossil evidence for the history of life on earth
      This page covers the Hadean period, detailing Earth's early history and the emergence of life. It emphasizes the significance of fossils in dating and understanding ancient life, highlighting methods used by paleontologists and geologists, such as isotope dating with uranium and lead. Various types of fossils offer insights into past organisms, despite many lacking records due to specific environmental conditions.
    • 2.10: Life's impact on earth
      This page covers the evolution of life on Earth, beginning with 2 billion years of only microscopic prokaryotic organisms. It details the onset of oxygenic photosynthesis, which transformed the atmosphere by introducing molecular oxygen, enabling the rise of complex life forms like metazoans and Ediacaran organisms. By the Cambrian period, diverse armored species appeared, indicating predator-prey interactions.

    Contributors and Attributions

    • Michael W. Klymkowsky (University of Colorado Boulder) and Melanie M. Cooper (Michigan State University) with significant contributions by Emina Begovic & some editorial assistance of Rebecca Klymkowsky.

    This page titled 2: Life’s Diversity and Origins is shared under a not declared license and was authored, remixed, and/or curated by Michael W. Klymkowsky and Melanie M. Cooper.