Evidence for Evolution Section 10.2

Introduction In Darwin’s book On the Origin of Species, he listed evidence of evolution. He also discussed natural selection. More evidence has surfaced since then. Science has reveled more detailed knowledge right down to DNA.

Evidence Fossil Record Geographic Distribution of Living Species Homologous Structures of Living Organisms Vestigial Structures Similarities in Embryology Molecular Biology

Fossil Evidence Fossils are a window into the past. Paleontologists – scientists who find and study fossils. Fossils are used to understand the past. Example: the horse

Evolution of the Horse

Fossil Record By comparing fossils from older rock layers with fossils from younger rock layers, scientists can see how life on Earth has changed over time. Hundreds of transitional fossils have been found which show intermediate stages of evolution of modern species from species now extinct This is an “incomplete record” with many gaps

Geographic Distribution of Living Species Species living in different places with similar environments have similar anatomies and behaviors, even though they are unrelated They are exposed to similar pressures of natural selection so they evolve similar characteristics Example: Biogeography

Evidence from Biogeography Biogeography – the study of how and why plants and animals live where they do. Example: Camels

Camel Biogeography

Island Biogeography Islands are some of the best evidence of biogeography. The finches of the Galapagos islands are a good example. All descended from one bird that came from South America. The first bird was a seed eater. Each species adapted for a different food type.

Eyewitness to Evolution In the 1970s, biologists Peter and Rosemary Grant went to the Galapagos Islands to re-study the finches. While there a drought occurred. Fewer seeds became available for the finches. Birds with smaller beaks could only eat smaller seeds. The bigger beak birds were able to eat various sized seeds. The smaller beak birds died. In 2 years the average beak size increased.

Finches Again

Comparative Anatomy Comparative anatomy – the study of the similarities and differences in the structures of different species. Similar body parts may be: Homologous Analogous

Comparative Body Structures Homologous: develops from the same part of the embryo but have a different forms and functions; same basic patterns of bones, but have different functions (modified between groups) Analogous: parts with similar functions which develop from different parts of the embryo; different organisms with similar parts (similar function, different structure) (embryo is the early stage of development)

Comparative Body Structures http://evolution.berkeley.edu/evolibrary/home.php

Vestigial Structures Vestigial Structures - Organs so reduced in size that they no longer serve a function of homologous organs in related species. The presence of the organ does not affect its ability to survive and reproduce, so natural selection does not eliminate it. Examples: human tail bone, human appendix

Vestigial Structures Examples: wings on flightless birds, human coccyx and appendix The appendix, for instance, is believed to be a remnant of a larger, plant-digesting structure found in our ancestors.

Comparative Embryology Comparative embryology – the study of the similarities and differences in the embryos of different species. All embryos develop similarly Similarities in embryos are evidence of common ancestry. Vertebrate embryos have gill slits and tails.

Comparing DNA Darwin could only compare anatomy and embryos. Today we can compare DNA. DNA sequences are the strongest evidence for evolution. Cladogram – a diagram that shows the evolutionary relationships among a group or organisms. Cladograms and phylogenic trees are ways to see this clearly.

Phylogenetic Tree / Cladogram

Molecular Biology All organisms use DNA and RNA to transmit genetic information You can compare the similar amino acid sequences (i.e. proteins) Remember there are only 20 different amino acids.

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