7A Evidence of Common Ancestry

Summary of Darwin’s Theory Individuals with the VARIATIONS/ ADAPTATION best-suited to their environment will survive and reproduce. Those not suited will be less likely to breed (Survival of the fittest!)

Summary of Darwin’s Theory Species change over time, by passing on their useful (and harmful?) traits to their offspring

Summary of Darwin’s Theory THEREFORE, All species alive today have therefore descended with modifications from ancient ancestors

Summary of Darwin’s Theory Ultimately, ALL organisms on Earth are united into a single tree of life… Darwin’s original sketchbook drawing

This is…. Common Ancestry – the concept that a group of closely related species are all descended with some modifications from the same ancestor Descent with modification –idea that living species have descended with changes due to adaptations and natural selection from species that lived before them

 Fossils – preserved remains or traces of ancient organisms  evidence that the world was much older than once thought  Fossils show how organisms have changed over time 99% of species that once lived are now extinct!!! Did you know???

The Geological Timescale Based on fossil evidence, it appears that the nature and diversity of life on our planet has changed dramatically throughout Earth’s history

Fossil Record When comparing fossils found in rock layers, the deeper the layer, the older the fossil.

Index Fossil – fossils of species that are easily recognizable, that lived during a specific geological time period, with a wide geographic range Are used to determine age of other fossils by comparing.

Evidence of Evolution #2: Biogeography Biogeography ►The study of where species live now and where species and their ancestors lived in the past. ►Shows common ancestry two ways: 1.Provide evidence as to how closely related species change in different environments/selection pressures 2.How distantly related groups have evolved similar traits under similar selection pressures Beaver Capybara Muskrat Coypu Beaver Muskrat Beaver and Muskrat Coypu Capybara Coypu and Capybara

Evidence of Common Ancestry #3: Homology Homology is the study of similar characteristics between organisms There are three major branches of homology: 1. Anatomical Homology 2. Embryological Homology 3. Molecular Homology

Anatomical Homology Homologous Structures Same structure, different function - Same structure, different function - Same ancestor, different function On first appearance, would you say that a human hand, a bat’s wing and a whale’s flipper were the same structure?

Beneath The Surface… Homologous Structures – Same structure different function

Evidence of Evolution Analogous Structures: structures similar in function, but not inherited from a common ancestor. Same function, different structure different ancestor Flight Protection

Analogous structures have the same function but evolved from different places. -Analogous structures are also evidence for evolution because they show that two organisms that came from different ancestors, when placed under the same environmental pressures can evolve the same adaptations.

Vestigial Structures Structures that are inherited, but reduced in size and not used anymore Human tailbone Whale pelvic bone Human appendix

Embryological Homology Embryology - the study of developing animals in its earliest stages Embryos give evidence for evolution because many different kinds of organisms have embryos that look alike, suggesting that they all evolved from a common ancestor. The diagram below shows embryos of five different species: pig, chicken, fish, turtle, and human. Can you tell which is which?

Figured it out yet?

How about now?

Did you guess correctly?

Human – 31 days Chicken – 2 ½ days Pig – 21 days

Pig – 30 days Human – 9 weeks Lemur – 3 ½ weeks

Human face – 5 weeks

Pig – 30 days Human – 6 weeks Macaque monkey – 4 weeks

Limb Buds Pig foot – 30 days Human hand – 6 weeks Chicken foot – 5 days

Chimpanzee – 18 weeks Human – 16 weeks

Macaque monkey – 10 weeks

4 weeks Human Embryo Development Time Lapse Animation: Click here for a time lapse animation.

Molecular Homology All living things contain DNA and RNA. Changes in Proteins, DNA and RNA can be traced from ancestors to their descendents. The fewer differences there are between these molecules in different organisms, the more closely related they are Apple Protein Celery Protein

DNA of Chimpanzee, Human, & Chicken Note – there are more differences between the human and chicken than the human and chimp With which organism do we share a more recent common ancestor?

Chromosome 1 of different species

Chromosome comparison of human, chimpanzee, gorilla, and orangutan ChromosomeHomology

Human & Chimpanzee Chromosomes Human on the left Chimp on the right Notice that Human Chromosome #2 appears to be a combination of Chimp Chromosomes #2 & 3

Checkpoint AnimalDNA % Overlap with Chimpanzee Dog54% Cat47% Gorilla87% Human97% Giraffe68% The table below demonstrates the amount of DNA overlap that five animals have with the DNA of a chimpanzee. Order the Animals From More Closely Related to Least Closely Related in their ancestral relationship with chimpanzees.