Mechanisms of Evolution Ms. Klinkhachorn May 17, 2011 Biology

Evolution Evolution = descent with modification Evolution = changes in the genetic composition of a population from generation to generation

Historical Background The Old Testament says that species were individually designed by God and therefore perfect. – Scientists believed that the match of organisms to their environment was evidence that God had created them for a particular purpose

Lyell – Uniformitarianism says that mechanisms of change are constant over time Geologic processes that occurred in the past occur at the same rate in the future – Important because it indicates that Earth is old

Lamarck’s Hypothesis of Evolution Lamarck – the one other person besides Darwin to propose a mechanism for HOW organisms actually changed – Believed in evolution, but didn’t get the process – Two guiding principles: Use and disuse – parts of the body that are used a lot get stronger, while those that aren’t used get weaker Inheritance of acquired characteristics – acquired characteristics can be passed on to the next generation

Charles Darwin Father of Evolution Did most of his observational studies on the Galapagos Islands off the coast of South America Focused on ideas of adaptation and natural selection

Adaptations Adaptations are characteristics of organisms that enhance their survival and reproduction in specific environments – Improve function – Examples: Beak shape Behavior that allows prey to better avoid predators Produces protein that works more efficiently

Fig (a) Cactus-eater(c) Seed-eater (b) Insect-eater

Fig a (a) A flower mantid in Malaysia

Fig b (b) A stick mantid in Africa

Natural Selection Survival of the fittest Natural selection is the mechanism behind evolution – Individuals that have characteristics better-suited to the environment (adaptations) are able to survive and thus, have more offspring than others – Over time, NS increases the match between organisms and their environment – If an environment changes, NS will result in adaptations or new species

Misconceptions Evolution takes time. Populations evolve, NOT individuals. Natural selection only works for heritable traits – Acquired characteristics cannot be inherited Your work ethic is not encoded into your genes so you cannot pass it on genetically Favorable traits depend on the environment – Polar bears wouldn’t be happy at the equator

Evidence for Evolution Direct Observation Fossil Record Homology Biogeography

Direct Observation - Guppies Adult male guppies are brightly colored – Females are more attracted – Predators are more attracted Observation: The more predators there are, the less colorful the males are – Hypothesis: intense predation caused natural selection in male guppies, favoring drab colors

Fig a Predator: Killifish; preys mainly on juvenile guppies (which do not express the color genes) Guppies: Adult males have brighter colors than those in “pike-cichlid pools” Experimental transplant of guppies Pools with killifish, but no guppies prior to transplant Predator: Pike-cichlid; preys mainly on adult guppies Guppies: Adult males are more drab in color than those in “killifish pools” EXPERIMENT

Fossil Record By examining fossils, scientists can figure out similarities between organisms – Figure out ancestry Do radioactive testing to figure out the age of certain fossils – Can infer the age of other fossils

Fig b Bristolia harringtoni Bristolia mohavensis Latham Shale dig site, San Bernardino County, California Depth (meters) 1 1 2

Fig ab (a) Pakicetus (terrestrial) (b) Rhodocetus (predominantly aquatic)

Fig cd (c) Dorudon (fully aquatic) Pelvis and hind limb Pelvis and hind limb (d) Balaena (recent whale ancestor)

Homology Homology = similarity resulting from common ancestry – Species that are in some way related have characteristics that are similar, though the function might be very different Example: Humans and chimpanzees share 99% of their DNA (and about 60% with a banana)

Homologous Structures Anatomical structures that are similar within organisms but may have different functions Example: arm of humans, cats, whale and bats

Embryonic Homology Studying the embryos of organisms can reveal anatomical homologies that aren’t visible in adults Example: All vertebrate embryos have a tail

Fig Human embryoChick embryo (LM) Pharyngeal pouches Post-anal tail

Vestigial Structures “Leftovers” of features that used to serve an important function in a different time period Example: – Some whales have a pelvis and leg bones in their skeleton What does this indicate?

Evolutionary Tree Hawks and other birds Ostriches Crocodiles Lizards and snakes Amphibians Mammals Lungfishes Tetrapod limbs Amnion Feathers Homologous characteristic Branch point (common ancestor) Tetrapods Amniotes Birds

Convergent Evolution Organisms can be distantly related but still share similar traits – Faced similar environmental challenges that favored specific traits These are called analogous structures Example: – Penguins, dolphins, and sharks have torpedo- shaped bodies

Fig Sugar glider Flying squirrel AUSTRALIA NORTH AMERICA

Biogeography Biogeography = geographic distribution of species – Species are more closely related to species within their geographic area than species in distant areas Example: An animal found in the South American desert is more closely related to another SA desert animal than an African desert animal

Continental Drift Drift = slow movement of continents over time 250 million years ago, all of the Earth’s continents were one giant piece of land called Pangea

Application of Information 1.Graph the data found in the table 2.Examine the graph and hypothesize why the percentage of mosquitoes resistant to DDT rose rapidly 3.Suggest an explanation for the global spread of DDT resistance