Natural Selection Chapter 17

Evolution Change over time in the genetic composition of a population –Individuals do not evolve Natural Selection – the mechanism by which evolution occurs Evolutionary adaptation – result of natural selection – increase in frequency of traits in a population

Darwin Published Origin of the Species in 1859 Common ancestor –All modern species descend from ancestral species that were different Natural selection –Population will change from generation to generation, those who are best fit for their environment will go on to live and reproduce

Precursors to Darwin Aristotle – species were fixed and unchanging Linnaeus – classified diversity – taxonomy –Binomial nomenclature – genus and species Hutton – gradualism – slow and continuous change Cuvier – catastrophism – each boundary in layer represents change –Opposed gradualism Lyell – uniformatarianism – changes in the present occur at the same rate as the past –Modern geology 22_03GrandCanyon_SV.mpg22_03GrandCanyon_SV.mpg Lamarck – Acquired characteristics –Characteristics gained during an organisms lifetime are passed to offspring: Incorrect, your scars don’t show up in your children –Ex: giraffe Wallace – developed a similar theory of natural selection as Darwin

Darwin’s Studies HMS Beagle South American coastline –Noticed organisms resembled European species in similar climates Galapagos Islands –Studied finches and noticed many similarities with key differences in many species of animals –Common ancestor

Origin of the species 1. Descent with modification –All organisms are related from an ancestor in the remote past –Similar to a tree – more similar species have a common ancestor in the nearer past. –99% of species that have ever lived are now extinct  not all common ancestors are still alive. Protists: –Our knowledge of the Eukarya domain is changing rapidly. –Protists are mostly unicellular prokaryotes Grouped into 5 supergroups w/ tremendous variation Trypanosoma: Protist that causes sleeping sickness (fatal w/out treatment)

Fig a Green algae Amoebozoans Opisthokonts Alveolate s Stramenopiles Diplomonads Parabasalids Euglenozoans Dinoflagellates Apicomplexan s Ciliates Diatoms Golden algae Brown algae Oomycetes Excavata Chromalveolata Rhizaria Chlorarachniophytes Forams Radiolarians Archaeplastida Red algae Chlorophytes Charophyceans Land plants Unikonta Slime molds Gymnamoebas Entamoebas Nucleariids Fungi Choanoflagellates Animals

Origin of the Species 2. Natural Selection –All species would increase exponentially in size if all organisms that were born reproduced and all offspring survived to reproduce. –Populations tend to remain stable in size. –Resources are limited. Competition for resources occurs –Organisms within a population demonstrate variation. –Most variation is heritable. Individuals who inherit favorable traits for their environment are more likely to survive and reproduce. Unequal reproduction leads to a gradual change in a population toward favorable traits.

Natural Selection Differential success and reproduction among individuals that vary in their heritable traits based on environment Creates adaptations of organisms to their environment If the environment changes new adaptations may arise through mutations or previous characteristics become advantageous in the new enironment: possibility of speciation Acts on populations NOT individuals Only affects heritable traits Environmental factors vary from place to place  not all adaptations are favorable in all environments.

Figure (a)A flower mantid in Malaysia (b)A stick mantid in Africa

Fig l 100 µm Endocytosis Ameoba: single celled protist

Types of Selection 1. Disruptive – extreme phenotypes are favored and the average is selected against 2. Directional – One extreme phenotype only is favored 3. Stabilizing – Average individuals are selected for and extremes are selected against.

Types of Selection 4. Sexual Selection – mating selection –Intrasexual – within the same sex Ex: males competing –Intersexual – between the sexes Ex: Females choosing the males 5. Artificial Selection - Modification of species due to selective breeding to produce organisms with desired traits –Ex: pets

Evidences for Evolution 1. Paleontology Fossils – remains or traces of organisms from the past. –Found in sedimentary rock Igneous and metamorphic involve heat so living organisms don’t remain long enough to preserve –Older fossils found in lower layers (strata) –Biogeography – geographic distribution of species Closely related organism are found in the same geographic regions

Figure HumanCat Whale Bat Evidences for Evolution 2. Homologous Structures – comparison of similar structures that have different functions between species. –Ex: human arm and bat wing Same bone structure with different functions

Evidences for Evolution 3. Embryology – comparison of the early stages of development –Ex: all vertebrate embryos have a tail and pharyngeal pouches during embryonic development Figure Pharyngeal pouches Post-anal tail Chick embryo Human embryo

Evidences for Evolution 4. Vestigial Organs - structures with little significance in a modern species, yet present and functional in ancestors. –Ex: snakes have small leg bones –Ex: humans have an appendix

Species Human Rhesus monkey Mouse Chicken Frog Lamprey 14% 54% 69% 87% 95% 100% Percent of Amino Acids That Are Identical to the Amino Acids in a Human Hemoglobin Polypeptide Evidences for Evolution 5. Molecular – comparison of organisms at the molecular level –Ex: DNA, RNA or protein sequences –The more similar the molecular sequences the more similar the organisms –The closer the common ancestor