The Theory of Evolution

What is Evolution? Change over time Fossil evidence shows that living things have not always been the same as today

History of the theory… James Hutton (1785) –Earth formed very slowly, earth is old –Forces beneath the earth’s surface act to form mountains, rocks, and valleys

History of the theory… Thomas Malthus (1798) –Predicted that the human population would grow faster and larger than the space and food supplies will allow –Predicted there would be a great struggle for survival, leading to wars and famine

History of the theory… Jean-Baptiste de Lamarck (1809) –Was the first to propose a mechanism for evolution –Hypothesized that the environment influenced the development of traits –Inheritance of acquired traits

Lamarck’s Theory Acquired traits are developed as needed –Example: long neck of giraffe Fins and tail of a dolphin

Lamarck’s Theory-problems… Acquired traits are passed on to offspring –We know that only traits that are controlled by genes can be passed down to future generations A trait that is not needed will be lost –We know that an organism cannot “lose” a trait it had at the start of its life, because traits are controlled by its genes

History of the theory… Charles Lyell –His book, Principles of Geology, explained that earth continues to change just as it has for millions of years –And processes that have shaped (and continue to shape) the earth are very slow

History of the theory… Charles Darwin (1832) –Set sail as ship’s naturalist on the HMS Beagle –Read the works of Malthus, Hutton, and Lyell while sailing around the world –Collected evidence that would be used to support his developing theory

History of the theory… Alfred Wallace (1858) –Wrote to Darwin speculating on evolution by natural selection

Darwin’s Theory On the Origin of Species (1859) Individuals differ and some of the variation is inheritable Many more offspring are born than can survive There is competition for resources Each individual has advantages and disadvantages in the struggle to survive Those most adapted to the environment will survive and pass their traits on

Evidence to support Darwin’s Theory Fossil record

Evidence to support Darwin’s Theory Fossil record Geographic distribution of living species

Evidence to support Darwin’s Theory Fossil record Geographic distribution of living species Homologous body structures

Evidence to support Darwin’s Theory Fossil record Geographic distribution of living species Homologous body structures Embryological similarities

Weaknesses of the theory… Cannot explain how the first life began –First single cell –First multi-cellular organism

Weaknesses of the theory… Relies on random mutation as the explanation for change –Most mutations are harmful

Weaknesses of the theory… A “missing link” is not known for any two species –All species seem to have come into being independently of any other

More like a lizard or a bird? Theory changes as more evidence is found –Dinosaur theory