Evolution, Biodiversity, and Ecology

• Total diversity of eukaryotic organisms on Earth is 8.7 million species.

  • 1.2 million species have been identified.
• Millions of species have overcome the various challenges to their survival through time by

  • evolving
  • establishing themselves in every kind of environment on Earth;
  • flourishing
• Anoxic - no oxygen
• RNA - first genetic material that existed
• In the early history of the Earth, life did not exist for the following reasons:

  • The condition of earth is not suitable to support life.
  • The atmosphere is toxic
  • Frequent volcanic eruptions
• Chemicals present and the atmosphere formed the first:

  1. Organic molecules,
  2. Amino acids
  3. Nucleotides, and 
  4. Fatty acids
• Catalytic RNA (ribozyme)

  • First genetic material that existed
  • Capable of catalyzing its self-replication and protein synthesis. 
  • Can synthesize DNA using the RNA template
  • Crucial for the transformation of RNA to DNA
• Organic substances present combined to form the first  cells, prokaryotic cells.
• Obtained their energy via fermentation.

  • Fermentation - convert carbohydrate into alcohol or acid and release energy.
• Some prokaryotes undergo genetic changes resulted to the appearance of photosynthetic bacteria called cyanobacteria.
• Lynn Margulis - the mitochondrion and chloroplast may have

  originated as an aerobic bacterium and a cyanobacterium, respectively, which were engulfed by a bigger prokaryote one and then the other.
• Endosymbiont theory - two bacteria established a symbiotic relationship with the host cell, forming a plant cell.
•  In endosymbiotic theory, consistent with general evolutionary theory, all organisms arose from a single common ancestor. This ancestor probably resembled a bacteria, or prokaryote with a single strand of DNA surrounded by a plasma membrane.
• After the formation of the eukaryotic cell, unicellular eukaryotes may have aggregated and formed colonies. This is called the colonial hypothesis of the origin of multicellularity.
• Living organisms were also able to move from the seas to the land when the high concentration of O2 in the atmosphere led to the formation of ozone that protected organisms from damage to their DNA due to high energy UV radiation.
• • Ancestral prokaryote formed organelles
  • When the mitochondria was engulfed, it formed a symbiotic relationship with the prokaryote.
  • Some prokaryotes that engulfed the mitochondria also engulfed cyanobacterium, which is photosynthetic, that is why we have photosynthetic eukaryotes.

  
• Chares Darwin - All organisms came from a common ancestor. The diverse organisms that existed before or exist at present came to be because of modification of earlier species.
• Charles Darwin referred to evolution as descent with modification. Organisms differ because they evolved in different environments.
• Several factors influenced Darwin to think otherwise and made him

  formulate his theory of natural selection as a mechanism of evolution such as:

  1. His five-year voyage in the HMS Beagle when he was 22;
  2. The book Principles of Geology by Charles Lyell;
  3. Fossil evidences;
  4. Essay on the Principle of Population by Thomas Malthus; and
  5. Artificial selection done by farmers.
• Principles of Geology by Charles Lyell - stated that changes in the appearance of the Earth's surface were result of forces like wind, rain, rivers, volcanic activity and geological uplift that occurred gradually in millions of years. The idea was supported when Darwin found seashells embedded in rocks and watched mountain torrents that eroded the Earth. He concluded that Earth was older than most people believed.
• While in South America, Darwin saw fossils of mammals similar to present-day sloths and armadillos. He saw the fossil of a giant sloth

  that stood on the ground and could reach up to get the leaves of trees, and a living sloth with a smaller body and climbed trees.
• In Galapagos Islands, Darwin stayed for 5 weeks. He observed giant tortoises that varied form island to island, but still resembled tortoises living along South America's Pacific coast.
• THE ENVIRONMENT PLAYED A ROLE IN EVOLUTION

  Darwin noticed that tortoises which lived in drier regions had long necks that helped them to reach for vegetation found on higher ground while tortoises that lived in places with more moisture had short necks.
• Darwin observed 14 species of finches in the different Galapagos Islands. All had similarities suggesting that they came from a common ancestor. However, they differed in the shape and size of their beaks, depending on the kind of food that was present in the islands.
• SURVIVAL OF THE FITTEST

  Fittest - refers to those individuals that survive and reproduce and contribute the most offspring to the next generation
• Main points of natural selection

  1. Variation exists
  2. Competition for resources
  3. Differential reproduction
• Variation exists

  • members of a population vary in traits, with certain individuals having traits that favor their survival in a particular environment over others. Variations are heritable
• Competition for resources

  • there is overproduction of offspring by many organisms, more than what the environment can support, resulting in competition for food and a struggle for existence.
• Differential reproduction

  • Because of variation in their traits, some individuals have greater chances of reproducing and passing the genes for the favorable traits to their offspring while those with unfavorable traits, die.
• Artificial selection

  • also influenced Darwin's formulation of his theory of natural selection since he saw around him farmers preferring certain kinds of cows, chickens or pigs and also cultivating particular plants for food.
• Since the change in the trait occurred only in a population and did not produce a new species, genus, etc., the kind of evolution is microevolution