11.4

The Diversity of Species Result of the formation of different species How? A possible explanation: evolution through NATURAL SELECTION - Proposed by Charles Darwin in 1859 in his book “The Origin of Species by means of Natural Selection’

Genetic Variation The basis of natural selection Changes in the characteristics of a species are produced by a combination of Random genetic mutations Selection for a particular characteristic which increases survival and breeding success. Sexual Reproduction: provides genetic variation within a population  reassortment of genes Selection is then made amongst this variation.

Natural Selection Environment selects individuals with the characteristics that allow them to survive over other individuals with characteristics that are not suited for the environmental conditions.

Shell Activity Demonstration.

Selection occurs within the variation of the population Selected organisms produce more offspring More may survive to reproductive age May be more attractive to opposite sex

Determining Relatedness One goal of taxonomy: to determine the evolutionary history of groups of organisms. Use different types of evidence to study evolutionary relationships. Anatomy Development Biochemistry DNA Read pages on these topics. Briefly summarize how each type of evidence is used to study evolutionary relationships.

Phylogeny The evolutionary history of organisms. The ‘root’ represents the oldest ancestral species Forks represent points in past at which ancestral species split into two new species. Primitive characteristics: general characteristics that are shared by all species evolved from it Determine the Order Ex// Artiodactyla all have even number of hooved toes on each hindfoot and have specialized teeth and digestive systems adapted to eat plants. 150 members: goats, deer, cattle, camels, pigs, etc. Derived characteristics: new additional features giving rise to new species. With continuing evolution, further new derived characteristics are added.

Cladistics Classification scheme based on phylogeny. Each group of related species has one common ancestor, and organisms retain some ancestral characteristics and gain some unique derived characteristics as they evolve and diverge from the common ancestor. Cladogram Branching diagram that resembles a phylogenetic tree Can be used to test alternate hypotheses.

Example: Three species share a primitive characteristic from a common ancestor. Which species diverged first? Which are more closely related?

Seatwork/Homework Page 408, #1,2,3, 4, 5, 6, 7