Lecture #3 Evidence of Evolution Unit 6: Evolution

Evidence of Evolution Based on a large amount of evidence, most scientists agree on the following three major points Earth is about 4.5 billion years old. Organisms have inhabited the Earth for most of its history All organisms living today evolved from earlier, simpler life forms.

There are 4 major areas of evidence that exist for evolution 1. Fossil Evidence Fossils provide an actual record of Earth’s past life forms. Change over time (evolution) can be seen in the fossil record. Fossils - Remains or traces of a once-living organism   Fossil specimens found in older rocks are different from those found in newer rocks.

Evidence for Evolution – The Fossil Record Darwin and His Theory Evidence for Evolution – The Fossil Record 4/22/2017 G. Podgorski, Biol. 1010

Darwin predicted that intermediate forms between the great groups of organisms would eventually be found. Since Darwin’s time, many of these links have been found. Ex: Archaeopteryx links birds and reptiles

The fossil record is far from complete. Finding fossils is no easy task. Not all organisms lived in areas where fossils form. Paleontologists - scientists who study fossils. They can determine the age of fossils using different techniques.

Radiometic dating is used to get an actual age (absolute age) You can also compare a fossils position in the rock strata to the position of another fossil (relative age).

How does this help us? When fossils are organized from oldest to youngest, orderly patterns of evolution can be seen. Example Evolution of the horse

Evolution of the Whale

2. Molecular Evidence (Comparative biochemistry) Darwin could only study traits that could be seen but molecular genetics supports his theory All living organisms have the same molecular code Many organisms have homologous genes Example: Hox gene directs growth of limbs; the protein hemoglobin carries oxygen

Prediction: A species that descended from a common ancestor in the distant past should have more differences in the amino acid sequences of the same protein than do species that shared a common ancestor more recently. Common ancestor - species from which two or more species have diverged.

Comparing Proteins This predication was tested by analyzing the amino acid sequences of hemoglobin in humans and several other species. The data supported the prediction. Humans and gorillas have fewer differences than do humans and chickens.

Comparing DNA Scientists can compare the # of nucleotide changes in a given gene as well. Closely related organisms = fewer base differences in the same gene Phylogenetic tree

Phylogenetic trees branching diagram which shows how organisms are related through evolution. These provide strong evidence supporting evolution because they show the same relationships indicated by the fossil record.

Cladogram- a diagram used in which shows ancestral relations among organisms. It is based on shared characteristics.

Humans and Chimpanzees are 97% genetically identical. This supports the claim that chimpanzees and humans have a common ancestor

3. Homology ‘Same structure, different function’ Homologous Structures Structures found in organisms that share a common ancestry but have since evolved for different functions. Example The forelimbs of ALL vertebrates are made from the same basic groups of bones, hooked up in the same way.

‘Same function, different structure’ Analogous structures – Similar features of organisms that evolve independently. Example - Wings of a fly and the wing of a bird ‘Same function, different structure’

Vestigial Structures – Structures that are reduced in size and function. They are considered to be evidence or an organism’s evolutionary past. These structures have no apparent function. (evolutionary leftovers)   Examples- human appendix, wisdom teeth, tailbone

Example- internal hind-leg bones in whales

4. Early Embryological Evidence Early on in development, vertebrate embryos are strikingly similar. Each has A tail Pharyngeal pouches (develop into gills in amphibians and fish) Buds that become limbs

Structures develop at different rates in different groups of vertebrates, and are called homologous structures when its all said and done.

Take 2 minutes to summarize what you have learned regarding the different sources of evidence of evolution that exist.