EVOLUTION BY NATURAL SELECTION

• KEY POINT:

  • LIFE on EARTH- first DEVELOPED more than 3 BILLION years AGO
  • Life forms- SIMPLE
  • All SPECIES of living THINGS -> evolve from SIMPLE lifeforms
  • This called EVOLUTION by NATURAL SELECTION
• EVOLUTION EXAMPLE- THROUGH A RABBIT:

  • Each rabbit INHERITS different ALLELES from its parents e.g. better HEARING, eyesight
  • Some may receive ALLELES for thicker FUR
  • If the ENVIRONMENT changes e.g. it becomes colder, the rabbits with the THICKER fur are more likely to SURVIVE & REPRODUCE
  • Their OFFSPRING may then receive ALLELES for thicker fur so are more likely to SURVIVE in colder conditions and REPRODUCE
  • Over time, these ALLELES may become more COMMON in rabbits, and they may have THICKER fur than BEFORE
  • We say the species has EVOLVED
• EVOLUTION:

  • Change in INHERITED characteristics of a POPULATION over TIME
• KEY POINT:

  • If 2 POPULATIONS of 1 SPECIES become so DIFFERENT in PHENOTYPE, they can no longer INTERBREED and produce FERTILE offspring
  • They are now 2 different SPECIES