Natural Selection

Phylogeny The evolutionary history of a species. Based on developmental, structural and molecular traits. Creates a phylogenetic tree

Organisms likely share common ancestry if: They show similar stages of embryo development. Eg. All vertebrate embryos go through stage with gills-similar to fish Pg. 377

Organisms likely share common ancestry if: 2. They have similar anatomical structures, regardless of function. -These are known as homologous structures E.g. Bat wing and whale flipper (Pg. 377)

Organisms likely share common ancestry if: 3. They are genetically similar.

Natural Selection ~150 years ago Charles Darwin (who happened to look like Santa Claus!) proposed this theory. It went against the views of the church...he was seen as a heretic!

Artificial vs. Natural Selection In A.S., humans choose the strong animals and breed them. Eg. Over 14 000 years humans have ‘designed’ ~400 breeds of dogs from Canis lupis (the wolf)! In N.S., environmental factors determine which animals will mate.

Natural Selection Organisms with characteristics unsuited to the environment will either die off or be unsuccessful at finding a mate. Organisms that are suited to the environment have a better chance at surviving longer, mating and producing offspring. This has led to biodiversity!!

The 4 Assumptions of N.S. Variation -All members of a species display a variety of characteristics in their appearance and behavior. -Many are inherited.

The 4 Assumptions of N.S. 2. Competition The number of offspring produced by individuals in a species exceeds the number of offspring that will survive to adulthood

The 4 Assumptions of N.S. 3. Fitness Some offspring, because of their differences, are better able to adapt to the conditions of the environment than others.

The 4 Assumptions of N.S. 4. Adaptation The better-adapted organisms pass on their characteristics to their offspring and, as a result, the population changes.

Asexual Vs. Sexual Reproduction Asexual: One parent, identical offspring. Sexual: Two parents, variation in offspring. Meiosis causes the crossing over and random assortment of chromosomes. The odds of having 2 identical humans (excluding twins) is 1 in 14 trillion!

The Importance of Variation The greater amount of variation among individuals, the greater chance for the survival of the species if the environment changes. Changes include climate, toxins, food shortages, predator changes, new diseases etc. Eg. The peppered moth in England.

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