BSC2010-evolution-11a-2024

Outline of Key Topics

• What is life? What does life require? How did life begin?

• Transition from protobionts to single-celled eukaryotes

• The evolution of multicellularity

• Diversification of multicellular eukaryotes

What is Life?

• Life is a dynamic system that:

  • Composed of elements that self-organize

  • Responds to the environment

  • Capable of replication

Requirements for Life

• Energy: Fuels metabolism for survival, growth, and reproduction

• Materials (Elements): Used for constructing biomass

• Information: Facilitates organization, response to stimuli, and replication

General Features of Life

• Homeostasis: Maintenance of a stable internal environment

• Organization: Structured arrangement of components

• Metabolism: Chemical processes to maintain life

• Adaptation: Evolutionary adjustments to environment

• Response to stimuli: Reacting to external changes

• Reproduction: Ability to produce offspring

• Energy, materials, and information are essential for each feature

Timeline of Life's Origins

• Formation of Earth: About 4.5 billion years ago

  • Created from a cloud of matter following the formation of the sun

• First life: Approximately 3.5 billion years ago

Historical View of Life's Origin

• Spontaneous Generation (Abiogenesis): Idea that life arises from inanimate matter

  • Aristotle: Observations, e.g., mice from hay

  • Francesco Redi (1668): Experiment disproving spontaneous generation with meat and flies

Biogenesis Theories

• Primordial Soup Theory:

  • Mid-19th Century: Darwin suggested a "warm little pond" with essential chemicals fostering life

  • Mid-20th Century: J.B.S Haldane proposed oceans as a "hot dilute soup"

Four Step Hypothesis for Life's Formation

1. Abiotic synthesis of small organic molecules (amino acids, nucleotides)

2. Joining small molecules into macromolecules (proteins, nucleic acids)

3. Packaging of molecules within membranes (protobionts)

4. Self-replication (origin of RNA)

Miller-Urey Experiment (1953)

• Simulated early Earth atmosphere to create organic compounds

• Materials used: Water (H2O), methane (CH4), ammonia (NH3), hydrogen (H2)

• Exposed to sparks to replicate lightning

• Found 22 amino acids

Packaging and Development of Protobionts

• Protobionts: clusters of molecules, precursors to prokaryotes

  • Form spontaneously; resemble phospholipid bilayers

  • Maintain different internal and external environments

  • Capable of simple replication and metabolism

Prokaryotes vs. Protobionts

• Protobiont: not a true cell

• Prokaryote: Fully functional cellular structure without a nucleus

Early Prokaryotes

• Lived in an oxygen-poor environment (3.5 billion years ago)

• Relied on photosynthesis for energy

The Oxygen Revolution

• Major oxygen (O2) production from photosynthetic bacteria

• O2 accumulation began around 2.7 billion years ago

• Oxygen-rich atmosphere led to both challenges and opportunities for life

Emergence of Eukaryotes

• Eukaryote fossils date back 2.2 billion years

• Characterized by membrane-bound organelles and a nucleus

Formation of Eukaryotes

• Arise from infolding of cellular membranes

• Endosymbiosis Theory (1967): Chloroplasts and mitochondria evolved from small prokaryotes living inside larger host cells

Supporting Evidence for Endosymbiotic Hypothesis

1. Similar inner membrane structure/function between organelles and prokaryotes

2. Organelles' cell division resembles prokaryotic fission

3. Chloroplasts and mitochondria can transcribe and translate their own DNA

4. Ribosomes of organelles resemble prokaryotic ribosomes

Evolution of Multicellularity

• Eukaryotic cell evolution led to a greater diversity of unicellular forms

• Multicellularity evolved to produce algae, plants, fungi, and animals

• Multicellular eukaryotes emerged around 1.2 billion years ago; early forms were colonial

Colonization of Land

• Fungi, plants, and animals started land colonization around 500 million years ago

• Arthropods and tetrapods became widespread land animals

• Tetrapods evolved from lobe-finned fishes approximately 365 million years ago

Important Dates to Remember

• 1.2 billion years ago: First multicellular eukaryotes

• 2.1 billion years ago: First eukaryotes (single-celled)

• 3.5 billion years ago: First prokaryotes (single-celled)

• 535–525 million years ago: Cambrian explosion (diversification of animal forms)

• 500 million years ago: Land colonization by fungi, plants, and animals