Change in Populations over time Evolution Change in Populations over time

History- Ideas that Shaped our Understanding James Hutton (1785)- proposes that Earth is shaped by geological forces that took place over extremely long periods of time Scientists now believe Earth is 4.5 BILLION years old Thomas Malthus (1798)- predicts that human populations outgrow food supply and that Death and famine are inevitable Organisms must COMPETE to live History- Ideas that Shaped our Understanding

History- Ideas that Shaped our Understanding Jean-Baptiste Lamarck (1809)- Theory of the Inheritance of Acquired (developed) traits Organisms changed due to the demands of their environments Use or Disuse Principal- Organisms can gain or lose features if they were overused or not used at all, and that these traits could be passed on to offspring (this theory was Wrong) Proposed that organisms change over time (the only accurate part of his theory) History- Ideas that Shaped our Understanding

Use or Disuse Principal

History- Ideas that Shaped the Current Theory Charles Lyell (1833)- geological processes occurring now (weathering, erosion, volcanic activity) shaped Earth over millions of years Charles Darwin (1859)- After years of traveling around the world, he published “On the Origin of Species” explaining his theory of evolution by Natural Selection From 1831 to 1836 , Darwin served as naturalist aboard the H.M.S Beagle on a British science expedition Observed that fossils of extinct species were similar to modern species Noticed variations of similar plants and animals around the world History- Ideas that Shaped the Current Theory

Natural Variations (differences among individuals) exist in all organisms. These differences are called adaptations. An adaptation is a trait that helps an organism be more suited to its environment. Many more individuals are produced in each generation than will survive Natural Selection

Some individuals are better adapted to their environment so they survive and reproduce. Their traits are passed on to the next generation so that the gene pool of a population changes in favor of the “best” or “fittest” phenotype and genotype Organisms with traits that don’t help them survive will die and will NOT be able to pass these traits on. Over time, the frequency of the “bad” traits will decrease Natural Selection

Members of a population compete for resources (food, territory, mates) Only the organisms best suited to their environment (or “fittest”) will survive and reproduce. This is called “Survival of the Fittest” Natural Selection

Descent with Modification Another term for Evolution is “Descent with Modification” ALL organisms are related through a common ancestor Ancestors accumulate diverse (varying) modifications or adaptations that make them “Fit” for specific ways of life To explain Natural Selection, Darwin compared it to Selective breeding, or Artificial Selection Descent with Modification

Results of Natural Selection Directional Selection Environmental changes occur, causing one phenotype to replace another. As a result, there can be a rapid shift in allele frequencies Examples: peppered moth, antibiotic resistance Peppered Moth Video Results of Natural Selection

Results of Natural Selection Diversifying (Disruptive) Selection When individuals at the extremes have a higher fitness than the most common individuals in the population If the selection is strong and lasts long enough, the population can split into 2 different populations Results of Natural Selection

Results of Natural Selection Stabilizing Selection When the most common individuals in a population have a higher fitness than individuals in the extreme Intermediate forms increase and extreme forms decrease in the population Results of Natural Selection

Evidence for Evolution Fossil Record Darwin saw fossils as a record of the evolution of life on Earth By comparing fossils from younger layers with fossils from older rock layers, scientists can document that life on Earth has changed over time. Fossils can be used to trace the history of modern life http://www.pbs.org/wgbh/evolution/library/11/2/quicktime/e_s_3.html Evidence for Evolution

Evidence for Evolution- Geographic Distribution Darwin’s theory was that current living species descended from a common ancestor Over time, these species shared similarities, but each had adapted to their environments Adaptive Radiation- the evolution of many different species from a common ancestor Occurs when a population moves into an area with diverse conditions Many species become so different they can no longer breed with each other Evidence for Evolution- Geographic Distribution

Similarities in Early Development The same groups of embryonic cells develop in all vertebrates to produce the tissues and organs Similarities in Early Development

Evidence for Evolution- Genetics All species of life have the same basic genetic machinery of RNA and DNA and the genetic code is essentially universal Sources of genetic variation in species: Mutations Gene Flow- movement of genes between populations Sexual Reproduction- introduces new gene combinations Evidence for Evolution- Genetics

Evidence for Evolution- Comparative Morphology Study of body forms and structures in an organism Homologous Structures- structures have different forms, but come from same tissue Evidence that organisms descended from a Common Ancestor Evidence for Evolution- Comparative Morphology

Evidence for Evolution- Comparative Morphology Analogous Structures- structures that have similar function but different anatomy Similarities are due to similar function, but do not necessarily show common ancestry Evidence for Evolution- Comparative Morphology

Evidence for Evolution- Comparative Morphology Vestigial Organs- organs that are reduced in size, but are traces of homologous structures Structures have no current function, but can provide evidence for common ancestry Evidence for Evolution- Comparative Morphology

The process of two or more species becoming more and more different Organisms who share a common ancestor evolved into different species through divergent evolution Over millions of years, similar species become dissimilar as they adjust to their environment Divergent Evolution

The emergence of biological structures or species that have similar functions or appearance Organisms with analogous structures evolved independently of each other Convergent Evolution

The joint evolution of two or more species that closely interacted Example: Bumblebees and the flowers they pollinate have coevolved so they depend on each other for survival Coevolution

Microevolution Refers to evolution that occurs within a population Example: peppered moths (black or white) experience directional selection Causes Lead to changes in allele frequencies Asks WHY some characteristics are more common in specific populations Microevolution

Causes of Microevolution Genetic Mutations- some white moth genes mutate into black moth genes Very rare Gene Flow: some moths with black genes migrate from another population, some white moths leave the population Genetic Drift: When the moths reproduced, just by chance, more black moth genes ended up in the offspring Natural Selection- moths with black genes escaped predation and reproduced more frequently than moths with white genes, so that more black genes were passed on Causes of Microevolution

Macroevolution Refers to evolution that occurs on a large scale Speciation- produces a unique population of organisms Gene flow between the two populations is minimal Genetic differences gradually accumulate between populations Reproductive isolation develops as a consequence Macroevolution

Causes of Speciation Geographic Isolation Separation by geographic differences Temporal Isolation Reproduction takes place at different times of the year Behavioral Isolation Populations are capable of interbreeding, but have different courtship rituals Causes of Speciation

Gradualism- organisms descend from a common ancestor and evolve slowly over a long period of time Punctuated Equilibrium-new species appear suddenly after long periods of little change Rates of Evolution