NOTES – Evidence of Evolution

How is the theory of evolution supported? The theory of evolution is supported by two types of evidence: Evidence that shows species have changed over time Proves that species have not always existed in their current forms Evidence that shows different species come from common ancestors Proves that one species can split into two different species over time

Fossils

Dimetrodon

What types of evidence show that species have changed over time? Fossils – fossils are the remains of ancient organisms (bones, etc.) Fossils have been found that are not like any species alive today Fossils have been found that are similar to species alive today Fossils show that other kinds of life have existed and that species have changed over time

Fossils & Ancient Life Water carries small rock particles to lakes and seas Dead organisms are buried by layers of sediment which eventually forms new layers of rock The preserved remains may later be discovered and studied

Fossils & Ancient Life From fossils, scientists can infer what past life forms were like: their structure, what they ate, what ate them, & the environment where they lived They group similar organisms together & arrange them in the order that they lived, from oldest to most recent Together, all this information about past life is called the fossil record

Fossils & Ancient Life Relative dating - determining the age of a fossil by comparing its placement with that of fossils in other layers

Horse Fossil Record

Horse Fossil Record

Fossils & Ancient Life The fossil record shows that more than 99% of all species that have ever lived on Earth have become extinct The dodo has been extinct since the mid-to-late 17th century It is commonly used as the archetype of an extinct species because its extinction occurred during recorded human history, and was directly attributable to human activity

What types of evidence show that species have changed over time? Vestigial Organs – body parts found in species that have little or no use These organs are parts that had uses in the ancestors of the species but as new species evolved they were no longer necessary for survival EX. The coccyx, or tailbone, is the remnant of a lost tail. All mammals have a tail at one point in their development; in humans, it is present for a period of 4 weeks, during stages 14 to 22 of human embryogenesis. The tailbone, located at the end of the spine, has lost its original function in assisting balance and mobility, though it still serves some secondary functions, such as being an attachment point for muscles, which explains why it has not degraded further. Vestigial organs show that species have changed over time

Vestigial Organs Some snakes and whales show the remains of pelvis and leg bones from walking ancestors Non-functioning eyes on blind cave fish Human tail bone

Why would whales have pelvis and leg bones if they were always sea creatures?

Homologous Structures

What types of evidence show that species come from common ancestors? Homologous Structures – body parts in different species that are built in a similar way even though they may have different functions EX. the bones in the arm of a human are similar to the bones in the front leg of a cat and in the front fin of a whale Homologous structures are similar because the two species shared a common ancestor with a similar body part that evolved as the species changed over time

Homologous structures Forelimbs of human, cats, whales, & bats share same skeletal structures similar structure similar embryological development different functions evidence of common ancestor (branched off from common 4-limbed ancestor)

Homologous Structures

Comparative Anatomy Looking at structures in different organisms in order to determine relationships between them, how they are alike, and how they are different

Comparative Anatomy Looking at structures in different organisms in order to determine relationships between them, how they are alike, and how they are different

Embryology

What types of evidence show that species come from common ancestors? Embryology – the study of animal embryos (the early stages of development before birth) Different species go through similar stages in early development Closely related species have very similar embryos (EX. human and pig) If species are not closely related, the embryos begin to look different earlier (EX. human and fish)

Comparing Embryos

What types of evidence show that species come from common ancestors? Molecular Biology – studying the molecules that make up living things Closely related organisms have common DNA All living things have DNA which is built of the same ingredients All living things have some DNA in common The more closely related 2 different species are, the more DNA they have in common (EX. humans and chimps share about 99% of their DNA) Closely related organisms have common proteins

What does all the evidence mean? Species alive today are NOT the same species that have always been on the Earth Species have changed over time as the process of natural selection acted on natural variations in species characteristics Many species that have existed in the past are now extinct It appears that different species share common ancestors and that all life can be traced back to the appearance of the first living things – this explains why different species alive today share so many characteristics (cells, DNA, etc.)

Evolution explains both the unity and diversity of life