Survey
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Evolution part 2 Made just for You by: The Biology 1 Science Team International School Bangkok Evolution and Natural Selection • What do we mean when we say that life on Earth has evolved and is evolving? – Living things change over time, in shape, size, behavior, etc. and in their DNA code. – Evidence also suggests that one species can give rise to multiple new species, and that all living things today share a common ancestor • What is the alternative possibility? – Living things have not changed over time. Their shape, size, behavior etc. and DNA has always been the same. Species do not share ancestor species. Let’s look at the evidence! Evidence relating to Evolution by Natural Selection* • • • • • • • • Artificial Selection Fossils Biogeography Embryology Vestigial Features Homology and Analogy Biochemistry Observed examples *These represent just SOME of the lines of evidence that support evolution by natural selection and this course only addresses them at a basic level. Artificial Selection Instead of the natural environment leading to differences in survival and reproduction, humans can artificially select for different traits. Is there actually enough variation to make members of the same species look really different? What should we expect if life has evolved? If it has not evolved? Dogs diverged from wolf ancestors thousands of years ago but most modern dog breeds are only a few hundred years old. Size, color, loyalty, hunting behaviors, body shape, etc. have been selected for. Artificial selection in Brassicas Evidence For Evolution: FOSSILS • Traces of pre-historic living things. What should we expect if life has evolved? If it has not evolved? Fossil analysis Fossil record extends back billions of years 1. The fossil record (millions have been analyzed) is 100% consistent with ordered change over time; the oldest forms being most unlike more recent / modern forms. 2. Many fossils are transitional, with characteristics in between earlier and later group known groups. 3. Many fossils are unlike any existing organisms. 4. Zero authenticated fossils have been found outside the time range predicted by evolution. Is this what we would expect if life has evolved, or if it has not? Why? Orderly change: oldest fossils most unlike recent. • What trends (orderly changes) can you see in these hominid skulls? – Increasing brain size – Flattening of face – Drecreasing brow ridges Evidence For Evolution: Fossils! Transitions: How is Archaeopteryx like a reptile? How is it like a bird? Fossil Analysis Scientists have often predicted transitional forms, and later such forms have been discovered. Darwin hypothesized that mammals evolved on land, therefore water mammals like seals must have evolved from land animals. He predicted a fossil intermediate between land mammals and seals. Seal Puijila: a “walking seal”, fossil discovered 2007 Fossil analysis • We do not find fossils “out of order”. J.B.S. Haldane, when asked what hypothetical evidence could disprove evolution, replied "fossil rabbits in the Precambrian era" Biogeography What species live in different places around the world? Let’s suppose there are two ponds on different continents with the same climate and conditions. Will the species living there be the same? Or will the species be different, but related to nearby species? What should we expect if life has evolved? If it has not The Wallace Line – in native species, placental mammals dominate to west, marsupials to the east. An example of biogeographical variation. Mammals • Placentals and marsupials are fundamentally different in structure • However, in a large ecosystem with similar niches, similar traits are helpful • Similar features are seen in animals with similar niches • Ex. The placental wolf is more closely related to the placental mouse (or any placental) than to the Tansmanian Wolf (or any marsupial). Embryology All sexually reproduced animals begin as a single cell, and must begin developing from there. What should we expect if life has evolved? If it has not evolved? Not the similarities at early stages, with increasing differences. Note the early formation of GILL SLITS in vertebrate embryos. Note the post-anal TAIL in human embryos. The early embryonic stages of the (a) lemur, (b) pig, and (c) human. Vestigial Structures Left-over structures that were useful in ancestor species, but no longer serve any function in the modern organism What should we expect if life has evolved? If it has not evolved? The (a) salamander and (b) whale, inherited hind limb bones from a common ancestor; the bones remain functional in the salamander but are vestigial in the whale. Homology: A shared underlying structure modified to different purposes. What should we expect if life has evolved? If it has not evolved? ANALOGY Fundamentally different structures that look similar because they serve a similar function. What should we expect if life has evolved? If it has not evolved? Even true in flying (gliding) fish. The wings are modified gills! Let’s take the example of flight (or gliding). What features would be useful? • Large flat surface • Brace / support system Understanding check: What is ANALAGOUS in this picture? What is HOMOLOGOUS? Biochemical Evidence The chemistry of life is controlled by DNA. DNA codes for proteins, and protein perform most functions in the cells. What should we expect if life has evolved, especially from a common ancestor? If it has not evolved? • • • The code from DNA to protein is UNIVERSAL the same in every species (always triplets of bases, always the same 20 amino acids to build proteins) No matter what they look like, species that share a more recent ancestor will have more similar sequences of DNA The genes will be similar, with “gene families” showing various degrees of mutation, and inactivated genes DNA Code is Universal • The “code” for DNA to protein is universal – we can even make genes from one species work in another! Similar Sequences of DNA: How Closely Does Our DNA Compare to Another Human? All humans have the same genes, but some of these genes contain sequence differences that make each person unique. With these variations the DNA between 2 Humans is 99.9% similar. Similar Sequences of DNA A chimpanzee? 98% - Chimpanzees are the closest living species to humans. Similar Sequences of DNA A mouse? 92% - All mammals are quite similar genetically. Fruit Fly? 44% - Studies of fruit flies have shown how shared genes govern the growth and structure of both insects and mammals. DNA and Evolution Yeast? 26% - Yeasts are single-celled organisms, but they have many housekeeping genes that are the same as the genes in humans, such as those that enable energy to be derived from the breakdown of sugars. DNA and Evolution A weed (thale cress) 18% - Plants have many metabolic differences from humans. For example, they use sunlight to convert carbon dioxide gas to sugars. But they also have similarities in their housekeeping genes. Biochemistry • Duplicated genes often have related functions but also evolve differences. Observed Evolution • Significant genetic change over time usually takes longer than a human lifetime to observe, however there are many exceptions. • Ex. Anolis lizards colonized 14 Caribbean islands which previously has no lizards. Over 20 years, marked diversification occurred in size, color, diet, and behavior. It appears than new species may even have developed. OBSERVED EVOLUTION and DOES IT MATTER IF PEOPLE UNDERSTAND EVOLUTION? What do you do if you get a bacterial infection, like an infected cut, or a cough that gets worse, or a UTI, or strep throat? Often you take ANTIBIOTICS, special drugs that cause death in bacterial cells. Antibiotics were first widely used in 1945 and more types have been developed. Antibiotics have saved many millions of lives. By the 1970s there were antibiotics effective against almost all types of diseasecausing bacteria! What next? When should we use antibiotics? Do we need more research, or should we focus on solving other problems? Is our “bacteria problem” solved? Discuss. I do NOT understand evolution / natural selection! I understand evolution and natural selection! We have figured out how to defeat bacteria. Game over, we win! We can use our antibiotics as much as we want, on animals and plants as well as humans. We don’t need to spend money researching new antibiotics since we already have all we need. Antibiotics are a change in the environment, and any mutation that helps bacteria survive antibiotics will increase through natural selection. Over time, resistance will evolve. We are ahead, but the war will never be over. We need to use antibiotics sparingly and carefully. We need to continue research into new drugs. MRSA: methicillin-resistant Staphylococcus aureus: A bacteria that causes life-threatening infections Resistance in Neisseria gonorrhoeae 10 8 % Resistant Strains E. Coli 6 4 2 0 1980 1982 1984 1986 1988 1990 • What could this mean? – People begin to die from infections that we could easily have cured a few years ago • What can we do? – Take antibiotics as directed – Limit antibiotic use for non—medical uses (in hand soap, livestock and crops) – Give antibiotics only when needed for bacterial infections Why would the directions above help limit evolution of antibiotic resistance? Other Vocabulary for EVOLUTION: • CONVERGENT evolution leads to Analogous Features • DIVERGENT evolution leads to Homologous Features • SPECIATION in the emergence of new species from an older species CONVERGENT EVOLUTION: Let’s take the example of predators in a watery environment. What traits would be successful? Lots of teeth! A big powerful tail! A streamlined shape – like a torpedo! Short, stubby fins for agile maneuvering but little drag! Darker color above than below to help approach prey! Sounds like a shark, doesn’t it! Or a dolphin. Or a Northern Pike. Or a Barracuda. Or even a Penguin! Same Problems, Similar Solutions, Different Origins! REMEMBER – this is called CONVERGENT EVOLUTION SPECIATION – AN EXAMPLE When there is GEOGRAPHIC ISOLATION between populations, they will evolve differently. They do NOT share the same gene pool! This cat-sized camel ancestor migrated throughout the world during the past ice age. Old World New World They crossed the Beringia land bridge! Their isolation has led to today’s relatives. An “Old” World Camel, the BACTRIAN CAMEL. The DROMEDARY CAMEL, another Old World example. The Llama: A “New” World Camel MORE NEW WORLD CAMELS Vicuna Alpaca . . . and another, the Guanaco Kaibab squirrel on The north rim. Abert’s lives on the south rim. Another speciation case – Abert’s squirrel and the Kaibab squirrel. Reproductive isolation caused by the Grand Canyon has formed these 2 species. DIVERGENT EVOLUTION: From the same starting point, features are modified to different ends. REMEMBER – this is called DIVERGENT EVOLUTION Look at the range of beak sizes and shapes evolved for different functions in the finches of the Galapagos Islands.