Evolution Presenter notes: Evolution is one of the most important concepts in the Science of Biology. In fact Biology simply does not make sense without Evolution. Evolution is the idea that all living things arose from a single common ancestor in the distant past and that life continues to diversify today as new species appear. Evolution explains why we can classify organisms into different groups (because some organisms are more closely related than others). Evolution explains why the cells of all organisms use the same kind of biochemical machinery (because all life shares a common ancestor). This talk deals with the discovery of evolution, how evolution works, and the evidence for evolution.   Background note: A companion talk dealing with the History of Life from its earliest origins to the present day can be downloaded from the Your Planet Earth website: http://www.earth4567.com/talks/life.html. Although these two modules on Evolution and the History of Life can be delivered as stand-alone resources, they are best studied together. 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 Presenter notes: All living things share a single common ancestor in the distant past and all living things are related to one another. In much the same way that we might draw a family tree of our own ancestors, scientists can draw a Tree of Life to show how all living things are 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

…so no… humans were never monkeys

The central idea of evolution is that life has a history 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. Presenter notes: There is often considerable confusion as to whether the concept of evolution is a theory or a fact. Actually it is both! Evolutionary theory deals with how evolution happens. This is an area of active research and new insights are constantly emerging to explain how one species gives rise to another. However, Evolution is also a fact because there is a great deal of indisputable evidence, as we will see in this talk, in support of its occurrence. What is uncertain is exactly HOW it happens, NOT whether it has happened at all.   Further background reading: Stephen Jay Gould, "Evolution as Fact and Theory," Discover 2 (May 1981): 34-37; available here: http://www.stephenjaygould.org/library/gould_fact-and-theory.html Rodin’s “The Thinker”

Darwin’s Voyage From 1831-1836, a young naturalist called Charles Darwin toured the world in HMS Beagle. He was dazzled by the amazing diversity of life and started to wonder how it might have originated Presenter notes: In the early nineteenth century, Charles Darwin (1809-1882) rekindled ideas about evolution. In a sense, Evolution was in Darwin’s blood because, as we’ve already noted, his grandfather was an early supporter of the concept. From 1831-1836, Darwin toured the world on HMS Beagle as a young naturalist. He was dazzled by the amazing diversity of life, including some amazing fossils such as rodents the size of hippopotamuses and started to wonder how it might have originated. 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

Survival of the Fittest In his Origin of Species, published in 1859, Darwin proposed how one species might give rise to another. 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. Natural Selection explains adaption Presenter notes: On his return from the Beagle the jigsaw pieces started to fit together in his mind. Around 1842 Darwin read an essay about human population growth by Malthus. Malthus had argued that human population would grow more quickly than food supply. Consequently competition for food would become intense and only the fittest and most able would survive. Darwin applied these ideas to all of life and came up with his now famous concept of Natural Selection. Darwin reasoned that if an organism possessed a character that improved its chances of survival, then it would be more likely to pass on that character to the next generation. Therefore organisms would become progressively adapted to their environment, leading to the evolution of new species. Darwin published this idea in his “Origin of Species by means of Natural Selection” in 1859. Darwin in 1860 en.wikipedia.org/wiki/Image:Darwin%27s_finches.jpeg

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 or Migration Non-random mating Genetic Drift 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 However, occasional Types of mutation mutations or copying errors can and do occur when DNA is replicated. Mutations may be caused by radiation, viruses, or carcinogens. Mutations are rare and often have damaging effects. Consequently organisms have special enzymes whose job it is to repair faulty DNA. Types of mutation Mutant fruitfly Presenter notes: However, very occasionally, tiny copying errors can and do occur when DNA is replicated. These copying errors are called mutations. Mutations may be caused by a number of factors including radiation, viruses, or carcinogens (cancer-causing materials). As the genotype provides the blueprint for how each cell should grow and function, even a tiny mutation might mean that the cells fail to work properly. Take for example the common fruitfly: a single mutation in the fruitfly can change the colour of the eye from red (its normal colour) to white. White-eyed fruitfly are less successful at mating. Because of the potential for mutation, most organisms have a group of special enzymes whose job it is to go round and repair any 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 or Migration 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

Genetic Drift 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

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 Reproduction- brings 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."