Evolution commons.wikimedia.org/wiki/Image:DNA_double_helix_vertikal.PNG commons.wikimedia.org/wiki/Image:Charles_Darwin_1881.jpg The Tree of Life • All living things share a common ancestor. • We can draw a Tree of Life to show how every species is related. • Evolution is the process by which one species gives rise to another and the Tree of Life grows en.wikipedia.org/wiki/Image:Phylogenetic_tree.svg The central idea of evolution is that life has a history. The living things on Earth have changed over time, and that the different species on Earth today share common ancestors. Over a great period of time evolution can result in SPECIATION Speciation - The formation of a new species How does speciation occur? Extinction • Millions of organisms that lived in the past have gone extinct. We know of their existence from fossils or rarely from frozen specimens. Related Species • There are many organisms that are different species, but are obviously very closely related. It is very apparent that the American cougar and the African lion are related. They both share a common ancestor from the past. Related Species • All of the many cat species are related. They have very similar anatomy and DNA. Cats share a common ancestor that lived in the past. Not all cat species that evolved are alive today. Related Species • The saber- toothed cat became extinct about 10,000 years ago It has the same basic skeleton as other cats. The most distinguishing feature of this cat is its long canine teeth. Evolution as Theory and Fact • Confusion sometimes arises as to whether Evolution is a theory or a fact. Actually it is both! • The theory of Evolution deals with how Evolution happens. Our understanding of this process is always changing. • Evolution is also a fact as there is a huge amount of indisputable evidence for its occurrence. Rodin’s “The Thinker” Darwin’s Voyage • From 1831-1836, a young naturalist called Charles Darwin toured the world in HMS Beagle. Voyage of the Beagle en.wikipedia.org/wiki/Image:Charles_Darwin_by_G._Richmond.jpg en.wikipedia.org/wiki/Image:HMS_Beagle_by_Conrad_Martens.jpg • He was dazzled by the amazing diversity of life and started to wonder how it might have originated Survival of the Fittest • In his Origin of Species, published in 1859, Darwin proposed how one species might give rise to another. Natural Selection explains adaption • Where food was limited, competition meant that only the fittest would survive. • This would lead to the natural selection of the best adapted individuals and eventually the evolution of a new species. en.wikipedia.org/wiki/Image:Darwin%27s_finches.jpeg Darwin in 1860 Evolution is possible because of…. • Genetic Variation Why Genetic Variation? If a population was 100% the same… the processes that cause evolution would have NO effect because the genetic make-up would never change. Evolution only occurs when there is a change in gene frequency within a population over time. 1st generation of Beetle population Many generations later of the same population What causes these changes? There are 5 main mechanisms for evolutionary changes: 5 Agents of evolutionary change Mutation Gene Flow Genetic Drift Non-random mating Natural Selection Mutation •A change in a DNA sequence, usually occurring because of errors in replication or repair. Mutation is the ultimate source of genetic variation. Fruit Fly Example Mutation Types of mutation • However, occasional mutations or copying errors can and do occur when DNA is replicated. • Mutations may be caused by radiation, viruses, or carcinogens. Mutant fruitfly • Mutations are rare and often have damaging effects. Consequently organisms have special enzymes whose job it is to repair faulty DNA. upload.wikimedia.org/wikipedia/commons/7/79/Types-of-mutation.png humansystemstherapeutics.com/bb.htm Sometimes mutations are beneficial Only if they help the organism survive… • Mutations produce the genetic variation needed for evolution. Gene Flow Either by immigration or emigration (individuals move to another population and shares their genes there). • Gene flow moves alleles from one population to another. Genetic Drift The change of allele frequencies in a population over time due to random events forming successive generations. Genetic Drift • A random change in allele frequency • These individuals may carry alleles in different relative frequencies than did the larger population from which they came • If so, the population that they found will be genetically different from the parent population • This cause is not natural selection, but chance Genetic Drift For example: Green beetles reduce in numbers because an external factor has caused them to produce less offspring causing a more dominant brown population. • Genetic drift changes allele frequencies due to chance alone. Natural Selection A process of evolution in which traits that result in better fitness of an individual survives to the next generation. • Natural selection selects for traits advantageous for survival. Non-Random Mating (Sexual Selection) Peahens choose their mates by the size and shape of his tail. This makes sense in evolutionary terms -the largest tail would indicate a healthy bird and a better chance for healthy offspring. The process by which organisms choose their mates based on advantageous traits that will be carried to the next generation. Sexual Reproductionbrings together a new combination of genes. • Introduces new combinations of genes every generation. Sexual reproduction = Genetic Variation • In nature, populations are expected to evolve because a population can’t maintain equilibrium forever. – Population numbers will always be threatened by different factors – Individual organisms will continue to migrate – New genetic mutations occur frequently – Species select mates; random mating rarely occurs – The environment has changed on Earth and continues to change Evolution at work Although evolution cannot be seen on the small scale of time, the works of evolution are occurring all the time in populations. These processes are what contribute to the evolutionary changes between all species. "One obstacle to understanding evolution is the common misconception that individual organisms evolve. It is the population, not its individuals, that evolves, as some heritable variation becomes more common at the expense of others."