Early Ideas About Evolution

1. Early Ideas About Evolution http://video.google.com/videoplay?docid=1735124145579653656&q=evolution+guinness+commercial&ei=V4gnSNbZC4T8-wGE-YnlCQ&hl=en

2. Evolutionary Theory: Early Ideas About the Earth • The generally accepted solution to the puzzle of the origin of life on Earth is the theory of evolution • Before this theory, scientists had different ideas about the origins of life Archbishop James Ussher (1650)calculated the age of the Earth based on history, astronomy, & biblical sourcesEarth came into being Sunday, October 23, 4004 B.C.

3. Archbishop Ussher, along with many others at the time, thought the Earth, things living on it were immutable (unchanging) • Before technologies like radiometric dating were developed, people generally thought the Earth was quite young (only about 6000 years old), as surmised by Archbishop Ussher

4. Evidence from the Past: The Fossil Record • Strong evidence to support the theory of Earth’s surface changing over time was provided by the study of fossils. • most easily recognized fossils  hard body parts such as shells, bones, and teeth • impressions of burrows, footprints, and even chemical remains are also fossils

5. Fossil formationorganisms become trapped in sedimentsimpressed into strataeventually harden into sedimentary rock

6. An organism may simply leave an impression in hardened material, or, if the decomposition rate is extremely slow, the organism’s cells may be slowly replaced by minerals, called a permineralized fossil. • Rarely, organisms may be preserved nearly intactlow oxygen levels prevent most decomposition • Occurs in tar pits, volcanic ash, peat bogs, permanently frozen ground, and amber (hardened tree sap).

8. Ideal conditions for fossilization are rare: - Dead organism usually eaten by other organisms - Soft parts decompose quickly as they are exposed to oxygen • Because of this, fossilized organisms usually had hard shells/bones & live in/near aquatic environments (as opposed to land-dwelling, soft-bodied species) • Smaller animalsmore likely to be fossilized (although the big animal fossils get all the attention because they’re rare) • Microfossil – microscopic fossilspollen and foraminifera most abundant

9. Palaeontology – The Study of Fossils • began in 18th century, most famously by Baron Georges Cuvier, an anatomist. Cuvier observed: - Many fossils were of extinct species - Different strata contained specific fossilized species - Fossils of simple organisms all depths, but more complex forms shallower depths - Fossils in shallower depths were more likely to resemble living species - Each layer contained many species not found in layers above or below it

10. These findings were puzzling to scientists of the time • Catastrophism – local catastrophes (i.e.: floods) cause widespread extinctionsnew species created to replace them • This was Cuvier’s way of explaining the patterns he saw • Explains different fossils in different rock layers BUT not the increasing complexity

11. Relative age – estimate of age of a rock or fossil in relation to another (i.e.: fossil A is older than fossil B) • Absolute age - estimate actual age of a fossil or rock, usually measured through radiometric dating (i.e.: 5000 years old) • Radioactive decay – the release of neutrons from the nucleus of an atom; results in changes over time from a parent isotope to a daughter isotope • Discovered by Pierre Curie in 1903; radioactive decay has been used in radiometric dating to determine the absolute age of the Earth4.6 billion years

12. Radiometric Dating • Radiometric dating – calculation of the age of rocks and fossils through measuring the decay of radioisotopes • Radioisotopes – atoms that undergo radioactive decay (decay rates can be measured very accurately) • Radioactive decay changes a parent isotope into a daughter isotope of the same element or a different element (i.e.radioactive potassium 40 [40K] can decay into argon 40 [40Ar] or calcium 40 [40Ca])

13. Half-life – time required for half of a sample of parent isotopes to turn into daughter isotopes • for any isotope the half-life is constant • each isotope has its own half-life

14. The half-life of an isotope isn’t affected by temperature, pressure, moisture, etc.; this makes it a perfect clock • Carbon-14 dating – used to determine the age of organic materials • short half-life (5730 years) only allows carbon-14 dating to be used on objects less than 100 000 years old • often used to date archaeological finds such as human remains

15. Early Ideas about Evolution • Sir Charles Lyell (1830) changed the way people looked at geological processes with his principles of uniformitarianism • Uniformitarianism – Earth’s surface has always changed and still changes today through similar, uniform, and very gradual processes • Georges Buffon (late 18th century) – suggested similar organisms may have a common ancestor

16. Jean Baptiste Lamarck (19th century) – first scientist to recognize the environment plays a key role in the evolution of species • for species to survive over long periods of time, they must be able to adapt to changing environments • did not believe a single species could give rise to several species • each species gradually became more complex, new species were continually created by spontaneous generation (living organisms arise from nonliving matter)

17. believed in the inheritance of acquired traits (i.e.: one generation of giraffes had to stretch their necks to get leaves at the top of trees, making their necks longer over their lifetime; their offspring would then also have longer necks) • such acquired traits cannot be inherited, but Lamarck’s ideas were an important step in the development of the idea of evolution

19. What Darwin Observed • 25 of the 26 bird species Darwin brought back from the Galapagos Islands were different species, mostly finches • Many of the finches were quite similar, but had beaks with different shapes depending on the finches’ diets • Darwin thought perhaps a single ancestral species transported from a nearby land could gave rise to several similar but distinct new species, especially when they were isolated on islands

21. Homologous and Analogous Features • Homologous features – structures that share a common origin but may serve different functions in modern species (i.e.: dolphin flippers and human hands)

22. Analogous features – structures similar in function but not in origin or anatomical structure (i.e.: bird’s wings and bee’s wings) • Organisms with homologous features share a more recent common ancestor than those with analogous features • Homologous features also appear during embryonic development; for example, human embryos possess a tail similar to those of chicken and fish embryos in the early weeks of development

24. Vestigial features – nonfunctioning structures that are homologous to fully functioning structures in closely related species • For example: • some beetles have fully developed wings underneath fused covers that make it impossible for them to use these wings • humans have muscles for moving their ears, but we can’t move them enough to improve our hearing (i.e.: swivel them in the direction of sound, as cats do)

25. some snakes and whales have vestigial hips that are homologous to functioning hips in animals with hind limbs • dogs have a vestigial toe • There are also vestigial genes in the DNA of living organisms; these genes don’t function, but they closely resemble functioning genes

26. Artificial Selection • Darwin became convinced that some mechanism of inheritance must be the key to evolutionary processes • As a result, Darwin became very interested in artificial selection (the intentional breeding of certain traits into animals over others) and started breeding his own pigeons • Humans have been using artificial selection for thousands of years • Most dog breeds we have today, from the Chihuahua to the Great Dane, came from a single species, the grey wolf, domesticated by humans only 10,000 years ago

27. In 1896 (40 years after Darwin presented his theory), researchers began artificial selection experiments that increased the oil content of corn kernels from a range of 4-6% to more than 14% in only 60 generations • The researchers selected seeds for each new generation from plants estimated to have the highest oil content per seed • This process of artificial selection led to corn kernels with oil contents far above the normal range in earlier generations

28. In both these examples, later generations came to be different from their ancestors • Darwin reasoned that if people could alter the appearance and behaviour of species through artificial selection, then the environment could have a similar effect on wild species

29. The Theory of Evolution by Natural Selection • Darwin’s theory was based on these observations: • Observation 1 – Individuals within a species vary in many ways • Observation 2 – Some of this variability can be inherited • Observation 3 – Every generation produces far more offspring than can survive and pass on their variations • Observation 4 – Populations of species tend to remain stable in size

30. These observations led Darwin to his theory of natural selectionorganisms with more favorable traits are more likely to survive and pass on these traits to the next generation than organisms with less favorable traits.