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Theory of Evolution. must try to explain 1) the origin of life on Earth 2) diversity of life on Earth. Why? bc wide variety of ADAPTATIONS found among both living & extinct species. .
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Theory of Evolution must try to explain 1) the origin of life on Earth 2) diversity of life on Earth Why? bc wide variety of ADAPTATIONS found among both living & extinct species. 1. How did life on Earth come to be ? 2. how has it progressed from the relatively simple & few to the complex & diverse.
Evolution genetic change in a species over time
The theory of Evolution suggests • that “existing” forms of life on Earth have evolved from earlier forms of life over long periods of time. • Evolution accounts for differences in structure, function and behavior among all life forms.
Jean Baptiste de Lamarck • French biologist • Lamarck’s advice: “Use it or lose it” • Theory = use and disuse of body parts. • Suggested that traits acquired by parents during their lifetime were passed onto offspring.
Lamarck reasoned • eg. Giraffes have long necks - • bc- parent giraffes stretched their necks to reach lower branches; then with competition, to reach higher branches… That neck reach - is then passed on to offspring? Hence, acquired traits - passed on to offspring ? OK, so …what if…we….
Lamarck cont. • If we cut tails off of a group of mice, and their offspring, and their offspring, and their offspring. • What will we see in future mice? • will this acquired trait be passed on to their offspring?
Or crabs Who exercise their left claw, And over generations ? Not!!
Charles Darwin- Theory of “Natural Selection” Born: Feb 12, 1809 Same day as Abraham Lincoln
Charles DarwinTheory of “Natural Selection” • Right out of college, 1831 • signed on as “naturalist” on HMS Beagle - • 5 year - around the world cruise.
Darwin • Collected plants & animals at every port; • Was surprised? • saw - even in members of the exact same species, had slight variations = differences. • saw - different adaptations of organisms in diverse places like: • Brazil jungles, • Argentina grasslands • Way up…in Andes mts.
eg: iguanas Most of Galapagos Island animals live no where else in world. but resemble species on So. American mainland.
Darwin • Never used word “evolution” • Speculated • that descendants of earliest organisms spread into various habitats over millions of years. • accumulated different adaptations to all the diverseways of life. • saw history of life like a “tree” - branching and re-branching from common trunk (first organism) • Tips of Millions of twigs = species living today.
Evolution leaves evidence • Fossil records = preserve history • “Biogeography” = Geographical distribution of species. • why do animals of So. American tropics seem more related to animals of So. Amer desert, than species of African tropics? • Why is Austrailia home to marsupials ? • Could it be…that marsupials evolved from ancesters in that region?
Comparative Anatomy is • the comparison of body structures between different species. • here, functions of forelimbs are different; • Yet, notice - same skeletal elements…
continued • functions of - forelimbs differ; • whale flipper (water) vs bat’s wing (flying) • if limbs had separate origins, we’d expect this basic design = different. • However: similar limb structure means = descended from a common ancestor. • arms, forelegs, flippers & wings of different mammals = variations on a common anatomical theme, adapted to different functions. Similarity due to common ancestry = Homology
Comparitive Embryology = • the comparison of structures that appear during development of different organisms. • Closely related organisms - often have similar stages in embryonic development. • eg: gill pouches on sides of throat: fish, frogs, snakes, birds, apes…
Molecular Biology • Similarity of DNA and proteins (genes) • shows the “relatedness” of all forms of life.
O Darwin formulated an explanation of what he observed 1st: Overpopulation: within a population, there are more offspring produced in each generation than can possibly survive. = excessive #’s of offspring. Female frog lays approx: 10,000 eggs - Female cod produces 40 million eggs; how many live to reproduce? = two cod
C Darwin’s theory - • 2) Competition = Struggle for Existence. • The “natural resources,” such as food, water, & space, available to a population are limited, so… • bc there are more organisms produced than environment can support, there must be competition among them for the resources needed for survival = • Only a small% of offspring will survive from each generation. (the rest are starved, eaten, frozen, diseased, unmated, or unable to reproduce).
V Darwin’s theory includes 3rd: Variations among members of a population make some of them betteradapted to the environment than others. Such variability within populations means that, due to competition, the best-adapted individuals are most likely to survive + reproduce. (Survival of the fittest).
Darwin’s Conclusion • Natural selection = definition. • Individuals whose traits are best suited to the environment, are more likely to survive and reproduce. • ie: The environment is the agent of natural selection, determining which adaptations or variations are helpful and which are harmful.
continued • Reproduction. • Individuals with helpfulvariations tend to survive & reproduce at a higher rate than other members of their population…… …thus transmitting these variations to their offspring. Organisms do not consciously change/adapt!
Summary O C V • Overpopulation… • leads to Competition (struggle for existence) • Individual Variations = some carry better adaptations. • Favored traits - mean survival = are passed on. • Natural Selection = Survival of fittest (means those w/ best adaptations = will survive and reproduce (pass beneficial genes on to offspring!)
continued • Speciation: The development of new species, a process called speciation, occurs as certain variations or adaptations accumulate in a population over many generations. • Speciation occurs when a group within a species becomes reproductively isolated; • it’s members no longer inter-breed freely with all the other members of the species.
Today’s Evidence • Fossil record - is incomplete; • conditions have to be perfect to have specimen’s last this long. • Mutation = change in an organism’s DNA. • Genetic Variation • If this mutation is carried by a gamete, the mutation enters the gene pool (all the genes for all of the individuals that make up a population.
Evidence? Vestigial Structures seemingly lost all or most of their original function in a species through evolution.
Microevolution • Evolution on the smallest scale = generation to generation changes in the frequencies of genes within a population.
eg. Bacterial resistance to antibiotics. • Overuse of antibiotics! • Overprescribed by Doctors; • Commercial feed for chickens and farm animals. Mycobacterium tuberculosis
Easy to spot? Yet, they thrive ?
Convergent evolution • Organisms with separate ancestry, are adapted in similar ways to similar environments
Convergent • This is a favorite of most Australians. The Thylacine was a marsupial the same shape and size as the placental dingo. The Thylacine evolved in Australia from the same stock as quolls and native mice. It lived on the mainland as well as the island of Tasmania until the arrival of people. People brought with them dingoes, which are wild dogs. • The dingoes had the same lifestyle and diet as the Thylacines, but they had stronger jaws. Over a long time the dingoes out competed the Thylacines which wiped them out on the mainland. • Have a look at these two animals: Sadly the Thylacine is now extinct. European settlers in the island of Tasmania exterminated them because they thought they would kill the sheep, even though no incidences of this were ever recorded. http://www.all-about-reptiles.com/convergent-evolution.html
Convergent • Octopus vs Human eyes
Convergent • Shark, • Reptile • dolphin
