Extinction

The permanent disappearance of a species from the earth as a result of environmental events or human actions Mass extinctions have occurred twice – 435 and 370 million years ago 80% of species died

What killed the dinosaurs? 1.Change in climate 2.Change in vegetation  Rapid evolution of plants (developed poisons)  Dinosaurs weren't evolving fast enough 3.Competition  Small scavenging mammals and birds were faster, and ate their eggs

1. Crashing of an asteroid Yucatan peninsula of Mexico has a crater 9.6 km across and 300 m deep

Recent extinctions Passenger pigeon disappeared in 1914 Between 1600 and 1900 one species became extinct every four years It is estimated that species become extinct every year Tasmanian Tiger: extinct after 1936

Reasons for extinction Hunting (all animals get wiped out)  Ex: Dodo bird Loss of habitat  Resulting from lack of food  Nowhere to breed and nest Are we in danger of a mass extinction event?

Genetic causes of evolutionary change 1.Mutations: a)Chromosomes mutations: too many or too few chromosomes (this causes down's syndrome)

a)Genetic mutations: Change within a gene Much more common, good or bad Ex: Sickle cell anemia, cystic fibrosis, Tay-sachs Believed to be the original source of variations If a mutation is recessive it may be “masked” for a few generations and not affect the popuation even if harmful If the environment changes the harmful gene may provide an advantage

Sickle cell anemia

2. Genetic drift Random factors affect the frequency of a particular gene in a population Ex: if only one out of 10 guinea pigs is black and that guinea pig does not mate, then the allele will be lost

3. Migration Immigration: movement of organisms into a population Emigration: movement of organisms out of a population Both of these will change the gene pool, which is the total number of genes within a population