Notes

• The Engine of Evolution


  Natural selection is the driving force behind evolution, the gradual change in the heritable characteristics of biological populations over successive generations. Think of it like this: imagine a population of beetles, some green, some brown. If birds preferentially eat the green beetles because they are easier to spot against a brown background, more brown beetles will survive and reproduce. Over time, the brown beetle trait will become more common in the population. This is natural selection in action.
• Continuous Process: 


  Natural selection is not a one-time event; it's a continuous process operating over vast timescales – billions of years – shaping life on Earth. The environment is constantly changing, and the selective pressures (like bird predation in our beetle example) also change. This constant pressure leads to ongoing adaptation and diversification.
• Biodiversity: 


  The incredible biodiversity we see on Earth – the vast array of different species – is a direct result of billions of years of natural selection acting on populations. Each species has adapted to its specific niche (its role and place in the ecosystem) through this process.
• Genetic Variation: 


  Natural selection can only act on existing variation within a population. Where does this variation come from? Two primary sources are
• Mutations: 


  These are changes in the DNA sequence. Mutations can be beneficial, harmful, or neutral. Beneficial mutations provide an advantage, increasing the organism's chances of survival and reproduction. Harmful mutations decrease survival and reproduction chances. Neutral mutations have no significant effect. Mutations are the ultimate source of new alleles (different versions of a gene).
• Sexual Reproduction: 


  Sexual reproduction shuffles existing alleles into new combinations. This process, through meiosis (the cell division that produces gametes) and fertilization, creates genetic diversity within a population. It doesn't create new alleles, but it creates new combinations of alleles, leading to variation in traits. Think of it like shuffling a deck of cards – you still have the same cards, but they are arranged differently.
• The Struggle for Existence


  Organisms tend to produce more offspring than can possibly survive. This overproduction leads to competition for limited resources like food, water, shelter, and mates. This competition is a key driver of natural selection.
• Limited Resources: 


  Resources are finite. There's only so much food, water, and suitable habitat available. This creates a "struggle for existence," where individuals compete for these resources.
• Survival of the Fittest: 


  Individuals with traits that give them an advantage in this competition are more likely to survive and reproduce. For example, a plant with drought-resistant traits will be more likely to survive in a dry environment than one without those traits. This differential survival and reproduction is the essence of natural selection.