Evidence for evolution. In the early 1800’s prevailing belief was that: organisms were specially created and unchanged since their creation Species created independently of each other Earth not old. Ussher’s estimate: for Earth’s creation 4004 BC. Lamarck.
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Evidence for evolution • In the early 1800’s prevailing belief was that: • organisms were specially created and unchanged since their creation • Species created independently of each other • Earth not old. Ussher’s estimate: for Earth’s creation 4004 BC
Lamarck • Fact of evolution proposed in late 1700’s early 1800’s. • Jean Baptiste Lamarck 1809, 1815 proposed that all species were derived by gradual evolution from other species. • Lamarck’s idea was that evolution was driven by an innate tendency of organisms to become more complex over time.
Inheritance of Acquired Characteristics • Lamarck’s proposed mechanism of evolution was called the Inheritance of Acquired Characteristics (IAC) • IAC suggested that modifications to organisms during their life could be passed on to their offspring (e.g., a giraffe stretching its neck during its life passes slightly longer neck to offspring).
Inheritance of Acquired Characteristics • Obviously, Lamarck’s ideas about the mechanism of evolution largely contradict current biological knowledge. • The information required to build a body is stored in DNA and that information (influenced by the environment) determines the phenotype. Changes to the phenotype during life however do not affect the DNA sequence. Information flow is thus only in one direction from DNA phenotype, not in the reverse direction.
Epigenetics • However, recent research in the emerging field of epigenetics shows that Lamarckian effects may occur through changes in the control of gene expression caused by environmental effects e.g. food shortage during development.
Epigenetics • Epigenetics is the study of heritable changes in gene expression caused by mechanisms other than changes in the DNA sequence. • The DNA nucleotide sequence is not changed but whether and how much genes are expressed can be altered and some of these changes may be passed from one generation to another.
Epigenetics • One way in which epigenetic effects have been shown to occur is through environmentally induced methylation in which a methyl group (CH3) is added to cytosine nucleotides converting them to 5-methyl-cytosine. • More heavily methylated regions are translated and transcribed less frequently than non-methylated regions.
Epigenetics • One well documented example of epigenetic effects resulted from the Dutch winter famine of 1944/45 at the end of WWII. • The children of women pregnant during the famine were born smaller than normal (which was to be expected). • However, the children of those children were also born smaller than average. This suggests the famine induced epigenetic changes in mothers pregnant during the famine that were passed to their offspring.
Charles Darwin published “On the origin of species” in 1859.
Charles Darwin (1809-1882) • Son of a wealthy doctor. • Dropped out of medical school. • Studied theology, but was much more interested in natural history (e.g. he had a large insect collection). • After college signed on as captain’s companion on TheBeagle.
Voyage of the Beagle • Darwin companion for Captain Fitzroy on Voyage of The Beagle (1831-1836). • The Beagle’s mission was to map the coast of South America, but the ship traveled around the World. • Sites visited included Galapagos Islands a group of volcanic islands (hence of recent origin) off the coast of Ecuador.
Unique animals on Galapagos include giant tortoises, marine iguanas, and Darwin’s finches. Galapagos Giant Tortoise
Sharp- beaked Ground Finch
Influence of geological thinking on Darwin • By the time of “The Beagle” voyage the idea that Earth was young was being challenged. • Opposition based on principle of Uniformitarianism. • This is the idea that geological processes happening today are the same as have operated in the past.
Influence of geological thinking on Darwin • Uniformitarianism contrasted with Catastrophism which proposed that current geological formations had resulted from catastrophic events (such as the biblical flood) which occurred on scale unknown today. • Uniformitarianism first proposed by James Hutton and championed by Charles Lyell.
Influence of geological thinking on Darwin • During the voyage Darwin read Lyell’s new book “Principles of Geology.” • Lyell emphasized two points: • 1. Gradualism: Geological features can be explained by the slow gradual action of processes we observe every day e.g. erosion by wind and water, deposition of sediments in rivers. • 2. The Earth is very old: there has been lots of time for change to occur.
Influence of geological thinking on Darwin • Hutton and Lyell inferred Earth must be very old based on measurements of rate of ongoing rock forming processes (e.g. deposition of mud and sand). • These developments in geology focused Darwin on the potential importance of gradual change in shaping structures.
What Darwin observed • On the voyage Darwin noted many things that were puzzling from the point of view of a creationist explanation for the diversity of life.
What Darwin observed • 1. South American fossils resembled living South American animals. • 2. Parts of the world with similar habitats and climates (e.g. Australia and South America) are populated by very different animals. • 3. Plants and animals on each continent are different from those on other continents. • 4. Many species on remote oceanic islands are found only there (endemic). • 5. Endemic species on islands closely resemble species found on adjacent mainland.
What Darwin observed • These observations taken together don’t make sense if organisms were specially created. • Why should similar habitats in different parts of the world have different faunas? • Why should remote islands have unique faunas that differ from but resemble those on adjacent land masses? • Together these observations suggested to Darwin that species change over time i.e., that evolution occurs.
Darwin and Wallace • After returning from the voyage Darwin spent more than 20 years developing his ideas and gathering the evidence to support them. • In 1858 Charles Darwin and Alfred Russel Wallace jointly proposed natural selection as the primarymechanism by which evolution takes place. • In 1859 Darwin published his book On the Origin of Species, which summarized his ideas about evolution and presented the evidence to support them.
The “modern synthesis” • Idea of evolution was accepted rapidly by scientists. • Lack of understanding of heredity and population genetics, however, prevented natural selection being accepted as the principal mechanism of evolution until 1930’s. • The “Modern Synthesis” in the 1930’s of combined the ideas of population genetics and natural selection to explain gradual evolution, speciation, and macroevolution.
Evidence for Evolution • Evidence of change in organisms over time • An example in a living species: • evolution of beak length in soapberry bugs. • Soapberry bugs use long beak to penetrate seeds in fruits and eat them. • Native host plant is balloon vine which has thick fruits.
Evolution of Soapberry Bugs • In 1926 flat-podded Golden rain tree introduced to Florida. Has thin fruits. • Today soapberry bugs feeding on Golden rain trees have much shorter beaks than those living on balloon vines.
Comparison of beak lengths in areas with and without golden rain trees
Data from museum specimens documents change in beak length over time.
Antibiotic resistance in bacteria • In 1947 only four years after the mass production of penicillin began resistant strains of Staphylococcusaureus began to be reported. • Antibiotic resistance is now widespread and in the US half of all S. aureus infections are resistant to multiple antibiotics including penicillin, tetracycline, erythromicin and methicillin.
Antibiotic resistance • Bacteria have evolved resistance quickly in part because of their rapid reproduction, but also because antibiotics were misused (e.g. by being overprescribed or prescribed for non-bacterial infections and by people not completing their course of antibiotics)
The evidence for evolution • Fossil evidence • Vestigial structures • Homologous structures • Atavistic structures • Other evidence • Jerry-rigged structures • Adaptive radiation • Artificial selection
Fossil evidence • Fossils are mineralized copies of the remains of organisms preserved in sedimentary rocks. • In the process of fossilization a dead organism is covered by sediment and the organic matter is replaced by minerals leaving behind an impression of the organism.
Fossil evidence of evolution • Millions of fossils have been collected and it is clear from fossil evidence that many species (in fact almost all that have ever existed) have become extinct. • Equally clearly the faunas of different geological eras are very different and have changed over time.
Fossil evidence of evolution • Law of Succession: Fossil and living organisms in same area are related to each other and differ from organisms in other areas. • South America contains both fossil and living armadillos
Extinct glyptodont (2,000 kg) resembles the modern-day South American armadillo (2 kg).
Fossil evidence of evolution • Similarly modern Australia is filled with marsupials and fossils in Australia are of similar marsupial forms. • Extinct short-faced kangaroo. http://msnbcmedia2.msn.com/j/msnbc/Components/Photos/061226/061226_kangaroo_vmed_1p.widec.jpg
Fossil evidence of evolution • Transitional forms • If fossil organisms are ancestral to modern organisms then there should be transitional fossils that show characteristics intermediate between the older and more recent groups.
Archaeopteryx • Archaeopteryx the oldest known fossil bird (name means “ancient wing) has mix of reptilian and avian features. • Reptilian: long tail, teeth, long clawed fingers • Avian: feathers, ribs with uncinate processes, avian shoulder girdle.
Archaeopteryx (oldest known fossil bird) Jurassic 150mya
Evolution of mammals • There are numerous excellent fossil series that document the transitions from ancestral species to later species. • For example: the evolution of mammals from synapsid reptiles. • An extensive series of fossils documents the changes in the synapsid lower jaw from a jaw made of multiple bones to the modern mammals single dentary and the incorporation of some synapsid jaw bones into the inner ear.
Tiktaalik roseae • Another example is the evolution of the first amphibians from lobe finned fishes. • The transitional fossil Tiktaalik roseae possesses an intermediate suites of characters. • It has fish-like scales, palate and jaws, but an amphibian-like mobile neck and head, an ear that could hear in air, and the bones in its fins are intermediate between those of fish such as Eusthenopteron and Panderichthys and early amphibians such as Acanthostega.
Vestigial structures • Many organisms possess rudimentary or functionless versions of body parts that function in close relatives/ancestors. • The fact that structures are rudimentary implies they had ancestors in which these structures were functional. This suggests an evolutionary history.
Examples of Vestigial structures • Cave populations of Mexican tetra fish have eye sockets, but no eyes. • Kiwis have tiny, stubby wings • Boas have tiny remnant hind limbs