Evolution (liwat)

• The Earth is about 4.5 billion years old and contains Zircon crystals as the oldest materials found in the crust.
• Formation of the Earth

  1. Collisions of many meteorites

  2. Cooling and solidification of the surface into crust

  3. Erosion, sedimentation and volcanic activity led to the formation of small protocontinents that grew and reached the current size and shape we see today about 2.5 billion years ago
• Life on Earth began with single celled organisms such as cyanobacteria and stromatolites


  3.8 billion years ago
• Evolution of life forms

  1. Multicellular life forms evolved much later, starting with arthropods that made its appearance more than 500 million years ago (Ma), followed by land plants, 475 Ma and forest plants, 385 Ma

  2. Mammals started evolving into existence 180 Ma and Homo sapiens only 200,000 years ago
• Geologic Time Scale (GTS)


  A system of chronological dating that relates geological strata (stratigraphy) to time, used by geologists, paleontologists, and other Earth scientists to describe the timing and relationships of events that have occurred during Earth's history
• Divisions of the Geologic Time Scale

  • Eon (largest division spanning one billion years)
  • Era (division spanning tens to hundreds of millions of years, distinguished by extinction events and appearance of new life forms)
  • Period (division spanning no more than one hundred million years, characterized by a single type of rock system)
  • Epoch (smallest division characterized by distinctive organisms)
• Important Events in the Geologic Time Scale (in million years ago)

  • 4600 - Origin of Earth
  • 3800 - Earliest life forms
  • 3500 - First bacteria and archaea
  • 2400 - 'Great oxidation event' – oxygen started to build up in the atmosphere
  • 2300 - Ice age – Earth freezes over
  • 2000 - First eukaryotes (cells with nucleus)
  • 900 - First multicellular organisms
  • 770 - Ice age – Earth freezes over
  • 540 - First chordates (with backbone), including the primitive ones
  • 510 - First fish
  • 450 - Major extinction
  • 420 - First plants and animals on land
  • 370 - First amphibians
  • 365 - Major extinction
  • 315 - First reptiles
  • 250 - Major extinction, including most marine animals
  • 225 - First dinosaurs
  • 200 - Major extinction
  • 180 - First mammals
  • 150 - First birds
  • 130 - First flowering plants
  • 65 - Major extinction, including dinosaurs
  • 5 - Extreme global warming
  • 2 - First humans (genus Homo)
• Paleozoic Era


  Era of "old life" lasting from about 542 million to 251 million years ago, with many species of organisms living in the Earth's oceans and some amphibians and reptiles living on land by the end of the era
• Mesozoic Era


  Era of "middle life" beginning about 251 million years ago and ending about 65 million years ago, with reptiles as the dominant organisms including dinosaurs, and small mammals and birds also evolving
• Cenozoic Era


  Era of "recent life" beginning about 65 million years ago and continuing to the present, with mammals becoming more dominant after the extinction of dinosaurs
• Holocene Epoch


  The current period of geologic time, also called the Anthropocene Epoch, characterized by global changes caused by human activity, beginning 12,000 to 11,500 years ago at the close of the Paleolithic Ice Age
• The Holocene extinction, otherwise referred to as the sixth mass extinction or Anthropocene extinction, is an ongoing extinction event of species during the present Holocene epoch (with the more recent time sometimes called Anthropocene) as a result of human activity.
• The Geologic Time Scale provides data with regards to evolutionary successions, thanks to discovered fossils that date back to a specific time in the geological time scale.
• Through the Geologic Time Scale, we have discovered animals that have existed billions or millions of years ago, most of which are already extinct.
• Evolution is the unifying principle for all the biological sciences, providing an explanation for the differences in structure, function, and behavior among life forms, including the change in characteristics of populations through generations.
• Evolution


  The gradual process that occurs when the genetic composition of a population changes over successive generations, with changes that are inheritable, resulting in the diversity of organisms on Earth that are able to adapt to new environments
• Scientists and thinkers who contributed to the development of evolutionary thought

  • James Hutton
  • Thomas Malthus
  • Charles Lyell
  • Jean-Baptiste Lamarck
  • Charles Darwin and Alfred Russel Wallace
• Lamarckian Evolution


  Lamarck's theory of evolution based on the inheritance of acquired characteristics, where the use or disuse of body parts leads to their modification which is then passed on to offspring, later displaced by Darwinism
• Darwin-Wallace Evolution

  The mechanism of evolution accepted by many, based on the ideas of Charles Darwin and Alfred Russel Wallace
• Lamarck's Theory/ Lamarckian Evolution

  Environment requires greater use of that body part--> gets bigger as a result . Less use-/ not required-> deteriorated/ disappear
• There is however no evidence to support that acquired characteristics can be inherited and today, Lamarck's theory seems absurd
• Lamarckism was later displaced by Darwinism
• Lamarck's best known example - the giraffe

  • The giraffes stretched their necks to feed on leaves on treetops
  • As a result, their necks became slightly longer
  • Their offspring had longer necks and stretched even further to reach higher treetops
  • Eventually, the giraffes ended up with long necks
• Darwin-Wallace's Evolution

  The mechanism of evolution accepted by many biologists today
• Darwin was on board a research vessel called HMS Beagle

  Between 1831 and 1836
• After surveying South America for three years, the HMS beagle landed in the Pacific Ocean
• Darwin developed his theory of evolution after comparing the organisms found on the Galapagos Islands with those found on the South American mainland years
• Alfred Russel Wallace wrote to Darwin describing a theory of evolution identical to Darwin's own


  In 1858
• Darwin published his historical 'Origin of Species by means of Natural Selection'


  1859
• Observations and Conclusions on Darwin's Theory of Evolution

  • Observation 1: In a population, organisms are capable of producing far more offspring than is required to replace the parents
  • Observation 2: However, the number of individuals in the population remains the same over time except for seasonal fluctuations
  • Conclusion 1: There is competition between the individuals to survive and reproduce. Some individuals will die young, fail to reproduce or produce few/less fit offspring leaving only the fit to survive to the next generation
  • Observation 3: Members of a population differ from one another in their ability to obtain their needs, withstand extreme environments and to escape predators
  • Conclusion 2: These differences will determine which members will survive and reproduce successfully, leaving the most offspring. Individuals whose traits best adapt them to their environment will leave a larger number of offspring. This process is known as natural selection
  • Observation 4: Much of the variation among individuals is due to genetic differences and can be inherited
  • Conclusion 3: Better adapted individuals will leave more offspring. Hence their traits will be passed on to the subsequent populations. Over many generations, the genetic composition of the population will change. This process is called evolution by natural selection
• The classic example is the evolution of the giraffe

  • The ancestral giraffes had various neck lengths; long, average and short
  • Over many generations, longer-necked individuals were more successful probably because they were able to feed on taller trees and pass the long neck traits to their offspring
  • On the other hand, those with short or medium length necks could not reach leaves on taller trees and died of food shortage
  • As a result, the short neck trait was not passed on to the next selection concept as the cause of adaptive generation
  • In times of food shortages, giraffes with long necks were able to feed on tall trees. These survived and reproduced more offspring
  • Giraffes with shorter necks were not favoured by natural selection and died
  • The offspring inherited their long neck trait resulting in long-neck giraffes in subsequent generations
• Wolves

  • A swift and slim wolf will have a better chance of surviving from predators such as lions and to be favoured by natural selection
  • These wolves will have a better chance of surviving and leaving offspring compared to the slower and fatter ones
  • The offspring of these wolfs will inherit the beneficial structures or habits forming a new variety
  • The same can be applied to its prey. The ones which are fastest or more alert will be able to avoid the predator and therefore survive longer to reproduce offspring with similar traits
• Lamarckian vs Darwinian Evolution

  • Theory of Use and Disuse- environment dictates the need to use body parts to survive
  • Acquired transmission- the inheritance of acquired characteristics
  • Increasing complexity- organisms are driven to become more complex from simple to more complex forms, toward human "perfection"
  • No extinction- acquired/improved characteristics will just fade/shrink through time and from the population
  • Variation- Darwin acknowledged the existence of variants in a species
  • Extinction/speciation- species can either go extinct or turn into new species
  • Heritability- inheritance of characteristics that are favored by nature/environment
  • Selective pressures- nature selects individuals that are best suited to their environment. Drives organisms to adapt and evolve. (natural selection)
• Heritability (Lamarckian)


  Acquired characteristics can be passed down to the next generation and become more dominant in the population
• Selective pressures (Lamarckian)


  Drive organisms to constantly change or die (predation, change in environment)
• Descent with modification (Darwinian)


  Generations display subtle differences but remain in the same species
• Generations (Darwinian)


  Display advantageous traits/adaptations while those who don't become rarer in the ensuing generations
• Natural selection acts on individuals within a population
• Over time, a population will change as a larger percentage of its individuals acquire favorable traits
• A population can evolve, but not an individual