Homework Directed Reading Chapter 5 Section 1 #1-17
Create a Species Project
Learning Targets I can explain how comparing organisms can provide evidence that they have common ancestors.
What is the evidence for evolution? 1. Fossil Evidence 2. Homologous Structures 3. Vestigial Structures 4. Comparative Embryology 5. Genetic (DNA) Comparisons Which piece of evidence do you think is the most important for evolution?
I. THE FOSSIL RECORD
I. THE FOSSIL RECORD Importance Provides the best proof of the history of life showing how extinct species have led to today s species Lucy, 3.2 MY Archaeopteryx, 150 MY
Becoming a Fossil (Part 1) (excerpts from Bill Bryson s book) In order to become a fossil, several things must happen. First, you must die in the right place. Only about 15% of rocks can preserve fossils, most being sedimentary rocks. So the deceased usually needs to become buried in sediment, the best chance is being buried underwater and decomposing without exposure to oxygen, allowing the bones and hard parts, and sometimes soft tissue, to be replaced by dissolved minerals, creating a petrified stone version of itself. Then as the sediments in which the fossil lies are pressed, folded and pushed about by Earth s processes, the fossil must somehow maintain an identifiable shape. Finally, after tens of millions to hundreds of millions of years of being hidden away, it must be found and recognized as something worth keeping. Why do you think the fossil record (almost 95% of it) is mostly marine life? Formation of Fossils (Summary) Organism is buried in sediment under water (sometimes: ice, amber or tar) Hard parts (bone& shell) are slowly replaced by minerals dissolved in water
Transitional Species (Common Ancestors) Location where two species evolutionary path connect on the tree of life Scientists search for common ancestors in the fossil record to show the evolutionary connection between species & how they change over time.
The Mammalian Family Tree A dead end branch represents an extinction. Where is the most recent common ancestor between squirrels and whales? All these species can trace their lineage back to this common ancestor, essentially the first mammal.
Cladogram
Transitional Species Example Whale Evolution * Read more on Whale Evolution in the textbook (pgs 112-113) * Whale Evolution video clips
Becoming a Fossil (Part 2) (excerpt from Bill Bryson s book) It isn t easy to become part of the fossil record. The fate of nearly all living things (over 99.9% of them) is to decompose to nothing. Even if you make it into the small pool of organisms, that don t breakdown to nothing, the chances of being fossilized are very small. Only about one bone in a billion, it is thought, ever becomes fossilized. If that is so, it means that the complete fossil legacy of all the Americans alive today (that s about 300 million people with 206 bones each) will only be about 50 bones, one quarter of a complete skeleton. That s not to say that any of these bones will actually be found. Fossils are in every sense extremely rare. Most of what has lived on Earth has left behind no record at all. It has been estimated that less than 1 species in 10,000 has made it into the fossil record. What we have in the fossil record is the smallest of samplings of all the life that has existed on Earth.
Completeness of the Fossil Record?
How do we know how old a fossil is? TWO Ways to Date Fossils Relative Age Dating Approximation of dating by comparing rock layers Absolute Age Dating Precision of dating by measuring radioactive decay of elements in rock
Relative Age Dating Relative age dating follows the Law of Superposition (older rocks are found under younger rocks) Exception to the rule unconformities (break in the rock record) Index Fossil an organism that lived during a specific period of time and is abundant.
Absolute Age Dating Radioactive Elements: unstable atoms give off radiation (protons & neutrons) to become stable. Ex: Uranium-238 & Carbon-14 Radioactive dating: Radioactive decay (going from unstable to stable) occurs at a constant rate called a half life. Each radioactive element has its own half life. Half life: the amount of time it takes for half the radioactive atoms in a substance to become stable. Examples: Uranium-238 has a half-life of 4.5 billion yrs (becomes Lead) Carbon-14 has a half-life of 5730 yrs (becomes Nitrogen) Example of Absolute Age Dating Red Dots are radioactive elements Green Dots are stable elements
Uranium-235 has a half-life of 700 million years. How much of the 12 g sample of Uranium-235 will be left after : a. 700 million years b. 1400 million years
II. Comparative Anatomy Homologous Structures Vestigial Structures
Homologous Structures Body parts from different organisms that have the same structures, but different functions, supporting the idea of a shared common ancestor EX: vertebrate forelimb bones
Homologous OR Not? Cephlopod Cnidarian Arthopod Mammals
Homologous OR Not Homologous Structures between species provide evidence that the species shared a common ancestor, as shown in the mammal forelimb examples All display the same structure but adapting different functions for their forelimbs. Some times in nature, unrelated species will evolve similar functions through different evolutionary paths using unrelated structures. These types of structures are called Analogous Structures and they do not show evidence of evolution from a common ancestor.
Bird wings
Bird wing Bat wing ***Bird and bat wings have separate evolutionary origins BUT are superficially similar because they evolved to serve the same function!!!
Common Ancestors Homologous structures are inherited from common ancestors. The octopus limb could only be homologous to the lizard limb if they both inherited the limb from a common ancestor. This family tree shows how the octopus is related to vertebrate limbs. Vertebrate limbs and octopus limbs evolved independently after their point of common ancestry Not inherited from a common ancestor Not homologous, they are considered analogous. The same is true of the grasshopper leg.
Vestigial Structures Structures that are found in an organism but appear to serve no function (reduced in size) they are remnants or left overs of an organism s evolutionary past Ex: Whales and snakes have pelvic bones; manatees sea cows have finger nails on their fins Humans? ear muscles canine teeth Goose bumps appendix Tail bone Wisdom teeth
Tailbone Wisdom teeth. Remnant of earlier primate ancestors with tails Leftover from our ancestors with larger jaws This is why wisdom teeth are so commonly removed. Modern humans jaws tend to be too small, so the teeth get impacted. Some people never even develop wisdom teeth.
The same muscles (arectores pilorum) that enable a cat to do this: also enable us to do this:
Hiccups, which occur in many other animals, are a result of a nerve misfiring and telling your epiglottis to close off your trachea. Its purpose can be traced back to the first organisms with lungs (which incidentally still had functioning gills as well). This function can still be seen in modern tadpoles. It s what keeps their lungs from filling up with water while they re still using their gills.
III. Comparative Embryology Similarities in the developmental pattern of organisms exist because of a common ancestor vestigial gill slits/pouches bony tail covered in a fine hair Two chambered hearts Human embryo Pig embryo Chicken embryo
Can you guess what type of animal this is?
Can you guess what type of animal this is? Turtle embryo See the developing shell?
Comparative Embryology in Vertebrates All vertebrates (related species) are similar in early stages of development. Differences accumulate as development continues. New development instructions are added to old instructions inherited from common ancestors.
Comparative Embryology in Vertebrates
Human embryo 5 weeks after conception 1 cm
What animal is this? Notice the leg buds Spotted dolphin
Both embryos at about 5 weeks gestation!
IV. Comparing Genetics An organism s evolutionary history is held in their DNA sequence (genetic code) If a species changes, their DNA changes Genetic testing compares the similarity of DNA between organisms The more closely related the species are to each other the more similarities they share in their DNA
Tomorrow we will explore how well you understand the evidence for evolution EGG HUNT
What is the evidence for evolution? 1. Fossil Evidence 2. Homologous Structures 3. Vestigial Structures 4. Comparative Embryology 5. Genetic (DNA) Comparisons Exit Ticket - Which piece of evidence do you think is the most important for evolution? Why?