The Theory of Evolution What is Evolution Change

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

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

Weaknesses of 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