Presentation on theme: "Scientific Evidence for Evolution"— Presentation transcript:
1Scientific Evidence for Evolution It is tempting to see evolution as a grand progressive ladder with Homo sapiens emerging at the top. But evolution produces a tree, not a ladder—and we are just one of many leaves on the tree.
2FossilsFossils are a strong piece of evidence to support the theory of evolution.Fossil = preserved remains or marking left by organisms that lived in the past. (Latin fossilis means “dug up”)
3Types of FossilsSometimes full organisms can be preserved in sticky amber that hardens. Amber is a resin that is produced by trees – you should be familiar with this from Jurassic Park!
4Types of FossilsOrganisms can be preserved for millions of years in very cold environments. An example of this is the woolly mammoth found recently in Russia.
5Types of FossilsIn addition, animals can be trapped in tar and preserved like in the La Brea tar pits in LA.Located in the heart of Los Angeles, the La Brea Tar Pits is home to over three million fossils from the last Ice Age. It was here that huge mammoths, fierce sabertoothed cats, and giant ground sloths became trapped and entombed in the asphalt that has been seeping out of the ground for the past 40,000 years. Commonly called the "tar pits," the liquids that seep out of the ground at Rancho La Brea are actually comprised of asphalt, not tar.
6Types of FossilsBy far the greatest numbers of fossils form on the bottoms of lakes and seas. Sometimes the shape of an organism is preserved in rock as a mold. Sometimes a mold fills with minerals and forms a cast which is a copy of the original organism.When impressions are made in mud, such as animal footprints, they are called imprints.
7Age of FossilsMost fossils are found in sedimentary rock… so called because sediments from eroded rock on land collect in rivers, seas and oceans and harden.
8Age of FossilsOver millions of years, the shifting of the earth’s crust has raised some regions that one were under the seas and the layers are visible. The Grand Canyon is an example.
9Age of FossilsWhat can you conclude about the age of these organisms in the layers of sedimentary rock?
10Why Fossils are Strong Evidence The sequence of fossils is consistent all over the Earth = consistent evidence of change through timeMany transitional forms of fossils have been found (fish to amphibian, amphibian to reptile)
13Vestigial StructuresScientists hypothesize that at one point, our ancestors needed these extra teeth! They are an example of a vestigial structure. Vestigial is a scientific word for “left-over.” These structures are usually reduced in size and serve little or no function. Scientists use the presence of vestigial structures as evidence that evolution has occurred.Other examples…
14Vestigial StructuresIn the human body there are more than 100 vestigial structures!Take the tailbone, for instance. It is the evolutionary remnant of a ancestral, reptilian tail! No muscles attach to it, it has nothing to do with balance or anything else. So then why do we have it?
15Vestigial StructuresThis is a picture of an appendix that is being removed because it is infected.
16Vestigial StructuresHorses use their appendix to break down cellulose plant cell walls. Ours has no function! Does that mean ours lost its function as we evolved?
17Vestigial StructuresAnd why do we have muscles to move our ears when they don’t work?(Except for that friend of yours that can wiggle their ears when they concentrate )
18Vestigial StructuresWhat do you notice about this whale skeleton?
19Vestigial Structures It has “left-over” hind leg bones!!! The tail side of the snake below also has remnants of a pelvis….What could this mean??Scientists conclude that both whales and snakes evolved from four-legged ancestors…Why else would they have these structures?
20Vestigial StructuresFingernails on manatee fins which evolved from legsCave-dwelling organisms such as crayfish that have eyestalks but no eyesSpecies of flightless beetles and birds that have wings.
21Okay, now that I have your attention… Do you remember what the study of structure is called?
22Anatomical Similarities If you said ANATOMY, you are right!There are certain structural similarities among living things that scientists point to as more evidence for evolution.Let’s take a look…
23Anatomical Similarities The structure of the arm and hand of a human, the flipper of a whale, the limb of a cat, the wing of a bat and the wing of a bird are quite different in appearance because they are adapted to perform different functions.Even with these different functions though, inside the structures are surprisingly similar…
24Anatomical Similarities Parts of different organisms that have similar internal structures, but different forms and functions are called HOMOLOGOUS STRUCTURES.Homologous structures are regarded as evidence that some species evolved from a common ancestor.
25All are homologous structures All are homologous structures! Parts of different organisms that have similar internal structures, but different forms and functions
26Anatomical Similarities Be careful though! Sometimes animals have similar parts that are different in structure and development. Look below…
27Anatomical Similarities Although insects and birds both have wings, they are different in structure. An insect wing does not have bones at all – it is made of a tough substance called chitin.Structures that have similar external forms and functions but different internal structures are called ANALOGOUS STRUCTURES. These structures are NOT used as evidence for evolution.
28Two of these embryos are human, one is the embryo of a pig Two of these embryos are human, one is the embryo of a pig. Can you pick out the pig embryo?Embryo on right is the pig (says this on the next slide)
29Comparing EmbryosIt’s weird that you can’t really tell! But the one on the right is the pig embryoComparing the embryo development of different species can provide additional evidence of evolutionary relationships because embryos of closely related species show similar patterns of development.For example…
30Comparing EmbryosAll vertebrate embryos have gill slits, two-chambered hearts and tails at some point in their development.These similarities support the idea that they have a common origin.
31And now on to the last piece of major evidence for evolution….
32Biochemical Comparisons All forms of life have DNA. There are leftover sections of DNA that are called junk DNA because they don’t have a purpose. Maybe they did at one time?
33Biochemical Comparisons A wide range of organisms from fruit flies to worms to mice to humans have very similar sequences of genes that are active early in development.Remember from the movie scientists put mouse eye genes in an eyeless fruit fly & eyes developed!What can this mean?These genes were present in a very early common ancestor of all these groups.
34Biochemical Comparisons On top of that…Proteins in all organisms are composed of the same set of 20 amino acids.And hemoglobin is found in almost every multicellular animal.The more closely related two organisms are, the more similar their DNA code is.
35Biochemical Comparisons For example, chimp DNA and human DNA are 98.2% similar!
36Well, what do you think? You must agree that the observations themselves cannot be refuted. However, do you agree with the interpretation of these observations and their use to support evolution?
37The particulars of the jump from nonliving to living that occurred sometime in our planet's early history is a profound enigma and will likely remain that way for some time to come, says Harvard's Andy Knoll. The hard part, and the part that I think nobody has quite figured out yet, is how you get them working together. How do you go from some warm, little pond on a primordial Earth that has amino acids, sugars, fatty acids just sort of floating around in the environment to something in which nucleic acids are actually directing proteins to make the membranes of the cell?
38In the early 1950s, Stanley Miller essentially put methane (natural gas), ammonia, hydrogen gas, and water vapor into a beaker. This was a view of what the primordial atmosphere would have looked like. He put an electric charge through that mixture to simulate lightning going through an early atmosphere.Miller’s experiment lent support to the idea that conditions in Earth's early atmosphere could readily have given rise to organic molecules.
39After sitting around for a couple of days, all of a sudden there was this brown goo all over the reaction vessel. When he analyzed what was in the vessel, rather than only having methane and ammonia, he actually had amino acids, which are the building blocks of proteins. In fact, he had them in just about the same proportions you would find if you looked at organic matter in a meteorite. So the chemistry that Miller was discovering in this wonderful experiment was not some improbable chemistry, but a chemistry that is widely distributed throughout our solar system.