Evolution by Natural Selection

Evolution What is it? A change in heritable (able to be passed on from generation to generation) traits of biological populations over many generations.

Charles Darwin One of many scientists that thought evolution occurred, first to publish the evidence to support it. Wrote ‘On the Origin of Species: By means of Natural Selection’ in 1859 Alfred Russell Wallace, research in Australia, published paper with Darwin in 1858, doesn’t receive the same recognition. Traveled around the world on the HMS Beagle and saw many different plant and animal species

Darwin Hypothesized that present-day species are the descendants of ancient ancestors that they still resemble in some ways Over millions and millions of years, present day species accumulated diverse adaptations that helped them to survive in their environment. Finches, tortoises

Evidence Fossils are the imprints or remains of organisms that lived in the past document differences between past and present organisms reveal that many species have become extinct

Fossilization Process Death decay burial/mineralization uplift/erosion discovery

Evidence The fossil record is incomplete because many of Earth’s organisms did not live in areas that favor fossilization fossils that did form were in rocks later distorted or destroyed by geologic processes not all fossils that have been preserved are accessible to paleontologists

Evidence Dating – Relative – no exact year but deeper fossils = older, higher = younger Absolute – can get close to the exact year, the older it is the less exact it becomes Radioactive dating compares radioactive isotopes in a specimen A few years – billions of years old depending on the element/isotope Carbon 14, Uranium 238

Evidence What does the fossil record show? Variety of life has constantly been changing Organisms have become more complex over time Very gradual changes over time Extinctions are common – at least 5 mass extinctions

Evidence Comparative Anatomy – homologous structures Similarities in anatomy between different organisms, similar structure but different function

Evidence Embryology Relationships between animals seen only before birth

Evidence Molecular biology Sequencing genomes of different organisms The more similar the genomes are, the more likely they are to be related

Evidence Vestigial organs An organ that is present but no longer serves a purpose Tailbone and appendix in humans Leg bones in whales Parts of eyes in cave fish