Evolution and Natural Selection How species change over time

Evolution and Natural Selection Genetic variations are passed on through reproduction Evidence for evolution illustrates how organisms are related Natural selection leads to evolution Our understanding of evolution has changed over time

Evolution The theory that organisms today developed from more simple life forms and have changed (evolved) over time.

Natural Selection The theory that states that those organisms best adapted to their environment have a better chance of surviving and reproducing.

Evolution Pre-Darwin Beliefs Earth was only a few thousand years old. We now know it is billions of years old. Neither the planet nor the species that inhabited it had changed since the beginning of time. We now know the planet has changed and, through fossils, discovered organisms have changed, as well.

Evolution Pre-Darwin Beliefs Jean Pierre Lamark believed that organisms can change their traits during their lifetime by use or disuse. He thought that these traits are passed on to offspring. Over time this would cause change in a species. Lamark was wrong

Charles Darwin

Scientist credited with the Theory of Evolution & Natural Selection Voyage of the HMS Beagle – a 5 year voyage to South America and the South Pacific, collecting specimens, making observations and keeping a scientific journal of his findings.

Voyage of the Beagle What did Darwin find? The finches on each island in the Galapagos had different types of beaks.

Voyage of the Beagle What did Darwin find? The tortoises on each island in the Galapagos had different types of shells.

What was Darwin’s hypothesis? Darwin hypothesized that organisms had a common ancestor, but had adapted to their particular environments and changed over time. Darwin published his research in 1859

Natural Selection For natural selection to occur, there must be at least two varieties of a species. For example: the peppered moth

Peppered Moths At the beginning of the Industrial Revolution in England, coal burning produced soot that covered the countryside in many areas

What do you think happened?

Evolution/Natural Selection White moths became easier to see, while the black moths became harder to see. The black moths were more likely to survive and pass on the gene for dark color to their offspring. Over time, the black moths have become more common.

Evidence for Evolution: Common Ancestry Common Ancestry: If species evolved from a common ancestor, then they should share common anatomical traits Hawaiian Honeycreeper: family of birds in Hawaii that have similar skeletons and muscles, indicating they are closely related. Over time, their common ancestor evolved into several species, each with a specialized bill for eating certain foods. Just like Darwin’s finches on the Galapagos!

Evidence for Evolution: Homologous Structures If animals evolved from a common ancestor, then they should share common structures – and they do! These are called homologous structures

Evidence for Evolution Embryo Development What do you notice? List 2 observations

Evidence for Evolution: Vestigial Organs Some organisms have structures or organs that no longer have a useful function. These structures or organs may have been useful to the ancestors of a species, but over time have evolved into what we term vestigial organs.

Examples of Vestigial Organs Kiwi (flightless bird) Whales (hind leg bones) Humans (tailbone, appendix)

Evidence for Evolution Fossils Fossils provide a look into the past Scientists can trace how a species has evolved by studying fossils

Wrap Up the Evidence Common Ancestry Homologous Structures Vestigial Organs Embryonic Development Fossils