B6

• Individuals with traits that are advantageous for their environment are more likely to survive and reproduce.
• Natural selection leads to changes in populations over generations as certain genetic variations become more common than others.
• Over time, these individuals pass on their favorable genes to the next generation through reproduction.
• The origin of the first single-celled life marked the emergence of cellular organization as a primitive form of complexity.
• Organisms with characteristics that give them an advantage in this competition have a higher chance of surviving and passing on those beneficial traits to future generations.
• The process of natural selection is driven by competition between organisms for limited resources such as food, water, shelter, and mates.
• Evidence supporting Darwin's theory includes fossil records showing gradual changes in organisms over millions of years, similarities between living and extinct species indicating shared ancestry, and biogeography revealing patterns of distribution consistent with evolutionary relationships.
• Darwin's theory of evolution through natural selection explains how species change over time due to the accumulation of small genetic differences.
• The process of natural selection is driven by the struggle for survival, where only those individuals best adapted to their environment can survive and pass on their genes.
• Fossil records show gradual changes in organisms over millions of years, providing evidence for evolution.
• Darwin's theory of natural selection explains how new species arise from existing ones over long periods of time.
• Evidence supporting evolution includes fossils showing gradual change over millions of years, similarities between species indicating shared ancestry, and DNA evidence revealing relatedness among organisms.
• Cells evolved into multicellular organisms, which allowed them to perform specialized functions and increase survival rates.
• Natural selection occurs when some members of a population have traits that make them better suited to their environment than others.
• Natural selection occurs when there is variation within a population, some members of which possess heritable traits that make them better suited to their environment than others.
• Advantageous traits may include physical characteristics such as camouflage or protective features, or behavioral adaptations like migration patterns.
• Over generations, populations evolve as advantageous traits become more common due to natural selection.
• Variation


  All the differences in the characteristics of individuals in a population
• Main causes of variation

  • Genetic causes (alleles inherited)
  • Environmental causes
  • Combination of genes and environment
• Genetic variation


  • Examples: hair color, eye color
• Environmental variation

  • Examples: flower color, language
• Variation from genes and environment


  • Example: height in humans
• Mutation


  Random changes to DNA that occur all the time
• Most mutations have no effect on the phenotype
• Some mutations can influence the phenotype
• Rarely, a mutation can lead to a new beneficial phenotype that can spread rapidly in a population
• An example is a mutation that made rabbits resistant to a virus in the UK in the 1950s
• The earth is teeming with living organisms, including large animals such as mammals and fish, smaller animals such as insects, and plants such as ferns and trees
• There are nearly 9 million different species of animals and plants on the earth, and that number does not include microbes such as bacteria
• It is thought that all these species have only 1% of the total that have ever lived on earth, and the rest are now extinct
• Life first developed on earth more than 3 billion years ago, and these first life-forms were very simple, such as single cells
• Evolution


  The process by which all species of life have evolved over time from common ancestors through the mechanism of natural selection
• Natural selection

  1. Genetic variation within a population

  2. Individuals with advantageous traits are more likely to survive and reproduce

  3. Beneficial traits are passed on to offspring

  4. Over many generations, the population evolves to have more of the advantageous traits
• Rabbits have genetic variation, with some having alleles for thicker fur, better eyesight, and better hearing
• Colder environment


  Rabbits with thicker fur are more likely to survive
• Predator (fox) moves in

  Rabbits with better eyesight or hearing are more likely to survive
• Speciation

  When two populations of the same species become so different in phenotype that they can no longer interbreed to produce fertile offspring, they have become two separate species
• Pygmy rabbits are a separate species from normal-sized rabbits because they cannot breed successfully with them
• This video is a continuation of the previous video on DNA
• Selective breeding

  Also called artificial selection