7B Natural Selection Subtitle

Everyone has heard of Darwin and natural selection, but what does it really mean?

Natural Selection: Must have FOUR factors 1. A species must be able to increase in number The organisms must be able to reproduce and pass their genetics on to the next generation *in nature organisms often produce more offspring than can survive

Natural Selection: Must have FOUR factors 2. The heritable genetic variation is due to mutations and sexual reproduction There must be variation in the traits. Can come from mutations or sexual reproduction. The offspring can be different from the parents

Natural Selection: Must have FOUR factors 3. Competition for limited resources If there is competition, then some traits will make organisms better suited to survive. Better able to feed. Better able to fight. Etc. “Survival of the Fittest” *fitness means ability to survive

Natural Selection: Must have FOUR factors 4. The offspring of those organisms that are the “fittest” will be better able to survive and reproduce The offspring of the fittest, will also be the fittest. They will survive better and pass on the traits generation after generation

Adaptations If there is one trait that helps an organism survive and it is passed down from generation to generation, what will happen to the population over time? More individuals will have that trait The resulting trait is called an adaptation

What are some things that could help natural selection occur? Biotic factors Introduction of a new species Abiotic factors Seasonal temperature ranges Long-term climate change Acidity Light Geographic barriers

Environmental Changes Deforestation Fishing Fertilizer application Drought Flood Rate of change of the environment can affect the distribution or disappearance of traits in species

Death of Your Lake Activity

Types of Natural Selection

Directional Selection

Directional Selection What could cause this type of selection?

Stabilizing Selection

Stabilizing Selection Why would this be better?

Disruptive Selection

Long Term Effects of Environmental Changes Some species may grow and flourish Emergence of a new species (speciation) Extinction of a species

Over many generations… With biotic and abiotic pressures, over time adaptations occur You can from your parents  grandparents  great grandparents  great great grandparents  etc, etc, etc We all come from descendants Darwin argued that we are all descendants with modification We all possess adaptations that have occurred over time