Evidence supporting evolution Fossil record –shows change over time Anatomical record –comparing body structures homology & vestigial structures embryology & development Molecular record –comparing protein & DNA sequences Artificial selection –human caused evolution
Why use fossils? Scientists have used the fossil record to construct a history of life on Earth. –Earths life forms appeared 3.5 billion years ago –Fossil record is not complete, but pretty good for general information
Fossil record Layers of rock contain fossils –new layers cover older ones creates a record over time –fossils show a series of organisms have lived on Earth over a long period of time
Fossils tell a story… the Earth is old Life is old Life on Earth has changed
Fossil of Archaeopteryx lived about 150 mya links reptiles & birds Todays organisms descended from ancestral species Evolution of birds
Land Mammal ? ? ? ? Where are the intermediate fossils? Ocean Mammal Someones idea of a joke! But the jokes on them!! Complete series of transitional fossils We found the fossil no joke!
Evolution from sea to land 2006 fossil discovery of early tetrapod –4 limbs Missing link from sea to land animals
Fossil Evidence Fossils are formed when organisms become buried in sediments, causing little decomposition of the organism. Over time the calcium in their bones and other hard tissues is replaced by minerals as the sediment itself is changed to rock. As time progresses various sedimentary layers get deposited, with the oldest on the bottom and the youngest on the top. By observing the appearance, abundance and types of fossils in each of these layers we can understand the progression of the species that lived in that location over time. Fossils are also formed through freezing, being embedded in amber, preserved in tar, or even footprints and imprints.
Scientists can tell how old a fossil is by carbon or radioactive dating them. Once the fossil has been dated it can be used as an index with other fossils from the same period of time. This allows for a comparison of evolutionary evens at different locations by comparing the fossils that are in the time periods before and after them. It has been found that fossils of similar organisms show large or small differences with the ones that are in other time periods. In some cases fossil evidence allows scientist to trace animals alive today to early ancestors that may now be extremely different in appearance.
This stratigraphic column shows the order in which organisms appeared. Each layer represents a particular time frame and shows an organism which was found during that time. The oldest fossils appear in lower layers, and the most recent fossils at the top. This allows for placement of fossils to be used as an aid in dating the organism found. Figure 2
Comparative Anatomy Comparative Anatomy includes Homologous and Analogous structures as well as vestigial features. Comparisons of anatomical features in different organisms often provides evidence to support the theory of evolution. As Organisms are often classed together according to similarities in their structures. It was through comparing the anatomy of organisms that scientist discovered phylogeny, meaning the evolutionary history of a group of organisms. What can be more curious than that the hand of a man, formed for grasping, that of a mole for digging, the leg of a horse, the paddle of the porpoise, and the wings of the bat, should all be constructed on the same pattern, and should include the same bones, in the same relative positions. -Darwin.
Homologous Structures Homologous structure are structures that share a common origin but may serve different functions in modern species. These structures are evidence that organisms with similar structure evolved from a common ancestor. Examples include the forelimbs of a variety of mammals. For example, human, cat, whale and bat. These species show the same skeletal elements. Is in the humerus, radius and ulna. However these skeletal elements have been modified over time to suit the different functions suitable for the type of mammal. Homologous structures result from divergent evolution meaning their ancestral lines started out fairly similar, but evolved along different paths, becoming more different over time.
Anatomical record Animals with different structures on the surface But when you look under the skin… It tells an evolutionary story of common ancestors
Compare the bones The same bones under the skin –limbs that perform different functions are built from the same bones
Homologous structures Structures that come from the same origin homo- = same -logous = information Forelimbs of human, cats, whales, & bats –same structure on the inside –same development in embryo –different functions on the outside –evidence of common ancestor
But dont be fooled by these… Analogous structures look similar on the outside same function different structure & development on the inside different origin no evolutionary relationship Solving a similar problem with a similar solution
Structures that are similar due to evolutionary origin, such as the forearm bones of humans, birds, porpoises, and elephants, are called homologous. However, structures that evolve separately to perform a similar function are called analogous. The wings of birds, bats, and insects, for example, have different embryological origins but are all designed for flight. Figure 3
Analogous Structures Analogous structures are a contrast to homologous structures. They serve the same function between organisms but are different in internal anatomy. Such as the wings of birds and butterflies or the eyes of lobsters and fish. These structures are of no use in classifying organisms or in working out their evolutionary relationships with each other. Figure 4
Analogous structures Dolphins: aquatic mammal Fish: aquatic vertebrate both adapted to life in the sea not closely related
Convergent evolution 3 groups with wings –Does this mean they have a recent common ancestor? Flight evolved 3 separate times evolving similar solutions to similar problems Flight evolved 3 separate times evolving similar solutions to similar problems NO! They just came up with the same answer!
Convergent evolution led to mimicry Why do these pairs look so similar? Monarch male poisonous Viceroy male edible flybeemothbee Which is the fly vs. the bee? Which is the moth vs. the bee?
Vestigial organs Hind leg bones on whale fossils Why would whales have pelvis & leg bones if they were always sea creatures? Because they used to walk on land!
Comparative embryology Development of embryo tells an evolutionary story –similar structures during development all vertebrate embryos have a gill pouch at one stage of development
Evidence from genetics. All organisms share the same basic mechanism of heredity (DNA/RNA) –E.g.: mtDNA evidence for human evolution A branching tree radiating from a common ancestor – phylogenetic tree We can conduct research on other species to understand our own genes.
Molecular record LampreyFrogBird Dog MacaqueHuman Comparing DNA & protein structure –everyone uses the same genetic code! DNA compare common genes compare common proteins compare common genes compare common proteins number of amino acids different from human hemoglobin
How do we know natural selection can change a population? –we can recreate a similar process –evolution by human selection Artificial selection descendants of wild mustard
Selective Breeding Humans create the change over time descendants of the wolf
Artificial Selection …and the examples keep coming! I liked breeding pigeons!
Insecticide resistance Spray the field, but… –insecticide didnt kill all individuals variation –resistant survivors reproduce –resistance is inherited –insecticide becomes less & less effective
NichePlacental MammalsAustralian Marsupials Burrower Mole Anteater Mouse Lemur Flying squirrel Ocelot Wolf Tasmanian wolf Tasmanian cat Sugar glider Spotted cuscus Numbat Marsupial mole Marsupial mouse Anteater Nocturnal insectivore Climber Glider Stalking predator Chasing predator Parallel Evolution marsupial mammal placental mammal filling similar roles in nature, so have similar adaptations not closely related
Vestigial organs Structures on modern animals that have no function –remains of structures that were functional in ancestors –evidence of change over time some snakes & whales have pelvis bones & leg bones of walking ancestors eyes on blind cave fish human tail bone
Vestigial Organs Vestigial organs provide further evidence for evolutionary change. These organs are usually dwarfed and useless to the organism. Examples of these include: The human appendix which is useless in humans, but in other mammals it is necessary for digestion of high cellulose diet. The human external ear muscles. The tail bone. Wisdom teeth. Some snakes have skeletal limbs. Sometimes vestigial organs may be adapted for new uses e.g. penguin winds cant be used for flight, yet they are adapted for swimming. Even though organisms have these organs there is no significant disadvantage to the organism.
Examples of Vestigial Structures Vestigial organs associated with eye structures Vestigial remains of a pelvic girdle in a whale
Embryology Embryology of organisms can be used to demonstrate the existence and even degree of relatedness of organisms. In the early stages of development embryos of many organisms look extremely similar. Embryos in mammals, birds, reptiles and fish have many body similarities in common e.g. Gill slits, two chambered heart, and tail. As the embryos develop further, the similarities gradually disappear. This embryonic resemblances indicated that organisms are related by their common ancestors.
Homeobox (Hox) genes that regulate the expression of hundreds of other genes appear to determine the path that embryo development follows. Depending on the Hox genes control the expression of other genes, parts of organisms develop differently. Similarities in Hox genes give strong indications of the presence of a relatively recent common ancestor. Also, homologous features can appear during embryonic development. These features serve no function as the organism grows In the early weeks of development, human embryos posses a tail similar to that in chicken and fish embryos.
2. Geography The study of geography provides evidence of evolution. –island species most closely resemble nearest mainland species –populations can show variation from one island to another
Summary The layers of fossils in sedimentary rock shows the progression of organisms through time. Homologous structures are structures that are similar in appearance but not In function. Analogous structures are structures that are similar in function but not in appearance. Vestigial Features are organs and structures that still remain in animals, however they serve no function or purpose in the organism. Embryology shows the similarities that organisms have at a very early stage of development.