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WEEK 4 MECHANISMS AND DEFINITIONS COURSE REVISION Due to the extensive amount of material within evolution I will be splitting the last lecture into two separate classes this week and next week (the 16 th ) This week we’ll look at what evolution is and the mechanisms behind it. Next week we’ll deal with the evidence for evolution and (if there’s enough time) the story of Charles Darwin and evolution I feel this will be easier for me to successfully converse the idea of evolution in the short time we have. University courses take dozens of hours and they still only scratch the surface of the vast field of evolutionary biology so I feel another class will be crucial in communicating this fascinating field of study COURSERA Lots of free university courses without any tests or exams (though they are available for students wishing to earn a certificate of accomplishment) Video lectures provide instruction on learning almost anything you want https://www.coursera.org / STAR TALK RADIO Hosted by Neil Degrasse Tyson (an astrophysicist), this radio podcast explores questions regarding the universe and astronomy Many shows collect fan questions about certain topics (Venus, black holes, new discoveries ect) while others interview celebrities and people in science Great for learning about physics and astronomy http://www.startalkradio.net / A BRIEF RECAP Class 1: Evolution and Religion Worldwide most Christians are evolutionists In the American scientific academy, roughly 95% believe in evolution and roughly 40% believe in both a personal God as well This controversy is so profound in America (and nowhere near as much of an issue in the rest of the scientifically advanced nations) because it has its roots in American Christian Fundamentalism Class 2: Creationism and the Teach the Controversy Campaign “Creationism” covers a wide range of beliefs with varying acceptances of modern science but all hold an anti-evolution stance There have been several famous hoaxes in evolutionary science but all have been uncovered by scientists and not a single one by creationists “Teach The Controversy” was an Intelligent Design campaign designed to avoid scientific scrutiny by advocating that the controversy be taught. This controversy does not exist in the scientific community and public controversy are not grounds for requiring it be taght (eg Holocaust Denial) Creationist organizations continue to target primarily the public in relaying their ideas, rather than convincing the scientific community first as any other scientific idea would do. Class 3: Science and Creation Science Science uses evidence to construct testable explanations and predictions of natural phenomena Theories are the highest form of understanding, they help us explain and understand facts. They are constantly tested and are rigorously examined to ensure accuracy These ideas in science remain tentative, since there could always be information that we haven’t observed yet but which would disprove the theory Creation science is completely dogmatic in their methods: absolutely no evidence at all will prove them wrong Creation science is not concerned with what the evidence shows, all they care about is supporting their pre-conceived beliefs Creation science is the antithesis of science in that it opposes and rejects the principles that make science accurate, self -correcting, objective, explanatory and useful. SCIENTISTS MUST ADMIT WHEN THEY’RE WRONG In 1981 , Stephen Hawking proposed that black holes violated the Conservation of Information (a fundamental law of physics) Conservation of Information: information cannot be lost eg: A nuclear bomb will blow up everything, but down at the core of physical principles, the information (atoms ect) has not left the universe, it’s still there no matter how scrambled Black holes (according to Hawkings) however, would devour matter and leave no record. Rather than scramble information, they would obliterate it. If he was right, than most of modern physics would be seriously flawed Leonard Susskind, was skeptical and in 2009 he was able to complete his idea to explain information conservation in black holes. Stephen Hawking conceded that Susskind was right and black holes do not violate the conservation of information EXTRAORDINARY CLAIMS REQUIRE EXTRAORDINARY EVIDENCE GFAJ-1: a strain of bacteria found in Mono Lake California that can tolerate deadly levels of arsenic The authors of a 2010 paper published in Science, claimed it could thrive in a high arsenic environment without metabolizing phosphorus (an element essential to ALL forms of life) by incorporating arsenic into DNA instead If true, it would mean that this organism is unlike anything else on this planet, possibly so different as to be considered “alien” To encourage thorough investigation, the authors made the strain available upon request and Science made the paper freely available Subsequent studies and experiments showed that this strain does require phosphorus and goes to extraordinar y lengths to obtain it SCIENTISTS DON’T GET TO BELIEVE IN THEORIES Scientists don’t get a choice in “believing” in theories, they’re an evident conclusion and even when we don’t like that conclusion we can’t avoid its truth Eg. Birds (and penguins especially) have been the hallmark of monogamy in the animal kingdom as many form life -long par tnerships However, countless studies are showing that extrapair paternity is a widespread phenomenon and the frequency varies greatly Roughly 20% of Black-headed gull chicks, 35% of eastern blue bird chicks and as much as 50% of tree swallow chicks are due to these parental affairs Of interesting note is that these extramarital af fairs are sometimes not for producing chicks. Female Adelie penguins may use copulation to bar ter for stones for nest materials, indicating a type of animal prostitution. We may wish to think of birds as symbols of faithful chastity, but we cannot given the evidence EVOLUTION: WARNING Biology is messy; it’s a complicated field of study with numerous simultaneously interacting mechanisms and processes In order to really understand evolution, you need a some understanding of paleontology, geology, genetics, morphology, biochemistry, developmental biology , ecology and many more These two classes will be the most technical of this course so please don’t be discourage if it’s hard to understand ALWAYS ASK QUESTIONS if you don’t understand something or if you want to know more. Please don’t be shy in asking, I want this course to be as clear and helpful as possible and it’s likely that if you have a question, someone else is thinking the same thing too. INTRO TO GENETICS DNA: the molecule which encodes the genetic instructions used in the development and function of ALL life DNA’s ladder structure: the “rungs” of the ladders are bases and there are four different bases in DNA, represented by the letters A, G, C and T DNA is the material we inherit from our parents and that is why we share similarities with them GENES Gene: a stretch of DNA that codes for a protein Proteins perform various functions in the body including but not limited to determining physical traits (such as hair color, number of limbs/digits), directing development (from a single cell to a full organism) and producing all the needed elements for the thousands of the biochemical processes that comprise life Genes are composed of certain sequences of the 4 DNA bases (G,C,T,A) Variations of genes(base sequence) (eg red hair, blonde hair ect) are called alleles Although they are important, genes can comprise a very small portion of the genome (roughly 2% in humans) as well as a very large portion (98% in bacteria) Non-coding DNA can have important functions too such as regulatory sites but some do not such as pseudogenes WHAT IS EVOLUTION? Very generally, evolution means change through time Biological evolution (specifically) means the change in genetic frequency within a population of organisms (i.e. it is when a gene/allele/trait becomes more/less common in a population). Natural selection is the main (but not the only) mechanism by which this genetic frequency change occurs. Darwin composed it of four facts Organisms show variation in traits (inheritable characteristics) More organisms are born than can possibly survive Some traits offer advantages in the resulting struggle to survive Individuals with those traits are more likely to reproduce and pass on those traits Successful variations accumulate over generations which are beneficial under the conditions to which the creature is exposed Individuals do not evolve (since it’s the change in genetic frequency of a population) but natural selection does act on individuals to produce this change CHANGE IN GENE FREQUENCY Here we have a population of beetles in which most of them carry the allele for green coloration. Some number of generations later, things have changed: Brown beetles are more common than they used to be in the population Thus evolution has occurred, since the brown gene is now more common (its frequency has increased) while the green gene is less common (it’s frequency has decreased NATURAL SELECTION This change could be due to natural selection (there are other mechanisms): Due to perhaps camouflage, the green beetles are preyed upon more than the brown beetles. Thus the brown beetles survive and reproduce more. Thus natural selection favors the individual brown beetles and this leads to an overall population change EXAMPLES RIGHT NOW In elephants, tusks provide major advantages (can be used to dig for food, dig up trees, self defense and sexual display) However, large tusks also make the individual more likely to succumb to poaching. In 1930, only about 1% of the elephants (male and female) were born without tusks (due to genetic mutation) in Queen Elizabeth National Park, Uganda. 1998 research has shown that now 15% of females and 9% of males in the park are being born without tusks Similar reports are found elsewhere 1997 found that more than 38% of Zambian elephants were being born without tusks. Natural unstressed populations show roughly 2% The advantages of tusks are not outweighing their risk and so natural selection is selecting against them EVOLUTION IN ACTION: CANE TOADS Introduced into Australia to deal with cane beetles but instead ate the local insects. They are also highly toxic. Many Australian snakes are susceptible to poisoning from these when they attack them as food The ability to eat a toad large enough for the snake to kill itself depends on the ratio of the head size to body size Since smaller heads restrict the size of prey that can be eaten and a larger body requires more toxin to kill it, snakes that are more susceptible to toad toxin have evolved smaller heads and larger bodies in response and these were more pronounced the longer the snakes had been in contact with the toads Snakes that are not vulnerable do not show this change OTHER MECHANISMS OF EVOLUTION Sexual Selection: a special case of natural selection in which one gender’s preferences (usually the female’s) for the other gender’s characteristics leads to an increase in frequency of these traits Eg. Peacock tails: females will mate only with males that have large and colorful tails (thus, the genes corresponding to these traits are continuously passed on). Over time, as females continue to choose the biggest and most colorful tails, the average tail size and brightness increases, leading to the current creature’s appearance OTHER MECHANISMS OF EVOLUTION Migration: When individuals from one population of a species moves to another population they often carry with them dif ferent traits. This changes the genetic frequency of the population Migration Genetic Drift Genetic Drif t: Random genetic fluctuation. By chance, individuals with a cer tain trait in a population may die before they reproduce. Thus the next generation will only have a fraction of the parent’s alleles. This is not due to any benefit. Mutation: can cause parents with one trait to give bir th to of fspring with a dif ferent trait, making the new trait more frequent than before (ver y slow process alone) SOURCES OF VARIATION In order for evolution to occur by any of these mechanisms, variation in traits must exist in the population. So where does this variation come from? 1 . Mutations: these change the sequence of the bases in DNA (G,C,T,A). These can occur during replication, by the movements of mobile genetic elements, by viruses or by damage to the DNA: Point mutation: a single base is changed ( eg C is swapped for a T). May or may not have an effect. Insertions: add one or more bases. Deletions: removes one or more bases, or whole regions Amplifications: duplicate entire areas such as genes Fusion: genes can be fused together, creating a hybrid which may have a unique protein product Mutations are only important to evolution if they occur in the reproductive cells (eggs or sperm) since these cells will pass on their DNA . Mutations in the rest of the body’s cells will not be inherited MUTATIONS AND NEW INFORMATION A more recent creationist claim is that mutations do not produce “information”. This term is vaguely defined if defined at all, but it increased information can be defined as: Increased genetic variety in a population Increased genetic material Novel genetic material Novel genetically-regulated abilities All of these have been observed wither in the lab or in the wild, any other definition of information is not relevant to evolution in the first place Creationists will argue that mutations can only lead to the loss of information; a counterintuitive claim, since anything mutations can do they can also undo, thus if they can cause the loss of information, they can also add it MUTATIONS, FITNESS AND NATURAL SELECTION Fitness: the ability to survive and reproduce Mutations which increase an animals fitness are beneficial while mutations which decrease it are harmful. Mutations which have no af fect on fitness are neutral Mutation rates themselves are quite low and thus do not change a population very quickly by themselves But with natural selection, the process happens a lot faster: any beneficial mutations are quickly amplified and any negative mutations are weeded out. This allows beneficial mutations to accumulate while deleterious mutations are kept low. The more beneficial/harmful a mutation is, the stronger natural selection acts to propagate/remove it. Neutral mutations will also accumulate over time due to no natural selection acting against it, but it will be at the rate of mutation itself since natural selection also isn’t favoring it. OTHER SOURCES OF VARIATION 2. Gene flow: movement of genes from one population to another adding variation to the recipient population 3. Sex: recombines genetic material from two dif ferent parents which can lead to new gene combinations, and thus new variety 4. Recombination: During meiosis (the process which replicates egg and sperm cells) the chromosomes (a structure of DNA , protein and RNA , used to package the DNA) may swap segments, which can lead to new alleles Horizontal gene transfer: single celled organisms and other organisms can acquire new genetic material by means other than traditional reproduction For example: taking up DNA found in the environment, viruses may inject new DNA , organisms may acquire new DNA from their food ELYSIA CHLOROCTICA (EASTERN EMERALD SEA SLUG) GLAUCUS ATLANTICUS (THE BLUE DRAGON SEA SLUG) DESCENT WITH MODIFICATION AND COMMON ANCESTRY Common ancestry: all life shares a common ancestor, one from which they are all descended. This also means that all organisms share a degree of relationship similarity to one another (each organism has a common ancestor with every other organism; those that are less similar will have a more distant common ancestor than those which are more similar) Descent with modification: Parent’s of fspring often look and behave slightly dif ferent from their parents and their siblings: They descend from their parents with modification This also means primarily “new” traits are the results of existing traits being modified from the parental condition It also means that a lot if not most of the biodiversity (the astounding number of dif ferent forms, shapes and traits) are due to redundancy (changing the same structure and using it in a novel way or changing its appearance) BIODIVERSIT Y AND REDUNDANCY: TEETH Elephant tusks are elongated incisor teeth, narwhals have an elongated canine tooth (the upper left one) while walruses have extended both BIODIVERSIT Y AND REDUNDANCY: RIBS The tor toise and tur tle shells are the results of the ver tebrae and ribs fusing together Cobras raise their hoods by expanding their ribs BIODIVERSIT Y AND REDUNDANCY In development, the zygote (the fusion of sperm and egg) develops neither as male nor as female. It is gender neutral, but produces structures that later sex hormones will change into the dif ferent reproductive systems (these hormones dif ferentiate the fetus in humans at about 6 weeks). This is why male mammals have nipples Penises and clitorises both develop from the same tissue and both show erectile function in response to stimulation by engorging with blood. The labia lips and the scrotum also both form from the same tissue, and fetal gonads will develop into testes or ovaries SPOTTED HYENA GENITALS Female spotted hyenas exploit these similarities by enlarging their clitoris 90% and developing more pronounced erectile function and the labia lips fuse to form a pseudo-scrotum (even with fat and tissue to resemble testicles). The female urinary tract also runs through the pseudopenis as does the vaginal opening The similarity between the two gender’s organs is so remarkable that early philosophers (like Aristotle) thought hyenas were hermaphrodites (creatures with both sex organs) and researchers today can’t distinguish the genders visually. BIODIVERSIT Y AND REDUNDANCY Despite its exceptionally long neck, giraffes still have the same number of neck vertebrae as other vertebrates do (including us) , they’ve just modified them to be longer HOW DO NEW SPECIES ARISE The process of how new species arise is called speciation. It has been observed so many times that we’ve had to distinguish between the number of different ways it can occur but in order to know how a new species arises, we must know what a species is This is not easy. Generally a species is defined as the largest group of organisms that can successfully breed and this works most of the time. However, some organisms which we would consider separate species can still reproduce (such as polar and grizzly bears), leading to a problem in biology called “The Species Problem” Creationists have pointed to this to demonstrate that since we cannot define species biologically, they should not be expected to define their “kinds” either. However, this kind of pattern is exactly what we should expect given that species are continually evolving (it would blur the distinction between them). Created kinds on the other hand, should be distinct and readily identifiable if they were created separately, but they aren’t T YPES OF SPECIATION 1.ALLOPATRIC SPECIATION The most common A population of individuals becomes isolated from the parental population and separated by a barrier, meaning that the two populations can no longer interbreed Since the two populations can’t interbreed, they can’t share genetic traits; therefore, a beneficial mutation in one population will not be able to travel to the other Over time, the two populations acquire more and more mutations and new traits that the other population does not. This successive accumulation of different traits over time, leads to the populations becoming fundamentally different from one another. If they diverge so much that they can no longer reproduce, the two populations can come into contact again but continue to diverge. But if the barrier is removed before reproductive isolation, the two populations can resume breeding; traits and mutations are shared once again and the two populations recombine into a single species ALLOPATRIC SPECIATION Here we have a population of beetles that have been separated, accumulate different mutations and traits, to the point that the two populations become sufficiently different to be considered separate species 2.RING SPECIES In species with huge geographical ranges (such as sea birds), a single population can extend to such great lengths, that the organisms at one end of the population don’t mate with the individuals at the other end Being dispersed over such a wide range can also mean that there are dif ferent environmental factors acting at each geographical area, leading to dif ferent pressures and dif ferent 3. PLOIDY AND 4.ASSORTATIVE MATING New species can also arise without geographic isolation, and this is one of the ways Very common in plants In normal gamete (sex cell) formation, half of the organism’s DNA is packages inside them. By mutation, a gamete cell may instead contain a full copy. If the plant self fertilizes, it will produce a plant with twice the normal genetic material and these of fspring will be unable to reproduce with the original population. Snails can also show this: if a mutation reverses the spiral form of the snail’s shell, they will be unable to mate Assortative Mating: if dif ferent females in a population begin to favor dif ferent male characteristics, the population can begin to diverge WHAT EVOLUTION IS NOT The controversy regarding creationism as well as a general lack of education on the subject has led to great confusion regarding evolution. It is important to know both what evolution is and what it isn’t and why 1.EVOLUTION IS NOT PROGRESS Evolution does not have a goal in mind; it is not a ladder system. Instead it is a continuously branching tree, with organisms changing all the time to suite whatever requirements natural selection puts on them. Sometimes that will be towards new forms, other times it will be a regression back. The organisms alive today are not “better” than those in the past, they are just different. Complexity has generally increased over time but it by no means needs to REGRESSION “BACKWARDS” On islands without predators (or in similar instances where flight is not required) birds have evolved the loss of flight and some have lost their wings entirely Flight is the most energetically expensive method of travel so if an animal can do without it they will REGRESSION “BACKWARDS” Parasites are an excellent example of evolution from complexity to simplicity They have lost much of what they would need in order in to live independently as result of their dependence on their host: if their host can supply the parasite with what they need, than there is no need to waste energy generating it for itself Some ant species (such as Polyergus rufescens) raid other ant specie’s nests and abduct their larvae. They then raise these larvae into worker which care for them. These species have become so dependent on their slaves that they have lost almost all ability to feed themselves and will die without them REMEMBER THAT BACTERIAL STRAIN IN MONO LAKE? It could live in a lake that has one of the highest arsenic concentrations in the world. No “complex” organisms can do that In fact, there are whole groups of microbes which stake out their lives in some of the most inhospitable locations on earth (they’re called extremophiles), including extremely acidic/basic conditions, conditions without oxygen, extremely salty conditions and at temperatures between 45 -122 degrees Celcius. If the earth were to drastically shift its environment to more extreme conditions, the “complex” organisms would not be the survivors. Being simple has its advantages Like any trait, the advantages of complexity is dependent on the environment; change the environmental conditions and you can change which traits are advantageous Stephen Jay Gould (evolutionary biologist): “Life is a copiously branching bush, continually pruned by the Grim Reaper of extinction, not a ladder of continual progress ” 2.INDIVIDUALS DON’T EVOLVE As said before, natural selection operates on individuals in that the environment exerts pressures, meaning some individuals reproduce more than others Since some individuals reproduce more than others in a given population, their genetic traits will become more common over time (over successive generations) This leads to change in the population which is what evolution is 3. NATURAL SELECTION DOESN’T PLAN FOR THE FUTURE Natural selection only acts in the present, as a result it has no way to plan for future changes. This is why more than 95% of all life that has ever existed is extinct; when drastic change or even mild change that lasts too long occurs not a lot of organisms are prepared for it and many go extinct as a result In this way, structures do not evolve with a future goal function in mind (eg feathers did not evolve for flight initially and gills didn’t evolve for breathing initially). Instead their structure is often modified to suit a new function, a process known as exadaptation Gills evolved from structures originally used for filter feeding which were then repurposed for respiration. This is reinforced by the fact that some organisms, such as oysters, still use their gills for both functions FEATHERS Many dinosaur species had feathers, as indicated by fossil impressions (some so well preserved that they have even preserved the cells responsible for color and have allowed scientists to reasonably estimate the coloration) However, not all were suited for flying and some species were too large to fly Sinosauropteryx (pictured bottom) was covered in primitive feathers but were likely used for insulation Ornithimimus adults had large feathers on their forearms, forming a sort of half wing, likely used for sexual display The fact that feathers are used for more than flight are seen in today’s flightless birds, such as ostriches (insulation and display) and penguins (insulation) WINGS AS BROOD PROTECTION Here, a Citipati uses its wings to shield its eggs from a sandstorm which ended up killing and fossilizing it 4. NATURAL SELECTION CANNOT PRODUCE PERFECTION This is because improving one trait may compromise another trait. These are known as trade -offs Natural selection also acts on existing variants which may already have problems Some forms of evolution may actually favor structures that are impractical or even detrimental Natural selection may be unable to select against certain degenerative traits IMMUNE SYSTEM TRADE-OFFS A healthy immune system is extraordinarily helpful in avoiding disease and dealing with infections It is based upon the destruction of material considered to be foreign. Unfortunately, this includes the developing fetus if a woman is pregnant (since half of its DNA comes from its father, the mother’s immune system can see it as foreign) If the mother’s immune system can reach the developing fetus, it can attack it and cause a miscarriage In addition to the placenta acting as a immunological barrier, the mother’s immune system’s sensitivity is decreased to avoid this but this leaves the mother more vulnerable to infectious diseases THE SPANISH FLU (1918) SUBOPTIMAL DESIGN SUBOPTIMAL DESIGN The recurrent lar yngeal ner ve star ts at the brain and inner vates the lar ynx. In tetrapods it loops down around the ar teries coming of f from the hear t, making an unnecessar y detour. This ner ve originated in fish as a direct link from the brain to gills near the hear t (fish don’t have necks so the looping around the hear t provides a direct route) However, when tetrapods evolved from the lobe-fined fish and star ted developing necks, this looping became exaggerated since the hear t was pushed down into the chest and the brain and lar ynx were pushed up. This is a minor deviation in humans but in giraf fes the ner ve has to travel 2 meters down and 2 meters back up to reach a destination about two inches from its star ting point THE IRISH ELK (MEGALOCEROS) Sexual selection (female’s preference to mate with males with certain traits) led to the evolution of huge antlers One of the likely factors that drove it to extinction, was climate change which led to vegetation change Growing huge antlers requires LOTS of nutrients and with the loss of vegetation to provide those nutrients, they were unable to meet these demands ALZHEIMER’S AND HUNTINGTON’S DISEASE These genetic diseases are weakly selected against by natural selection despite their negative ef fects It is likely that natural selection would be unable to get rid of these and similar diseases from the population Why? 5. NATURAL SELECTION DOESN’T ACT FOR THE GOOD OF THE SPECIES Natural selection acts on individuals and can select for selfish behavior Eg. Lion infanticide When a new male lion takes over a pride of lions, one of the first things he does is to kill the cubs of the preceding leader. This not only brings the females back into heat but it also ensures that the only cubs he provides for are the ones carrying on his genetic legacy This is not good for the species as a whole, since they ef fectively make all the time and energy spent on raising those killed cubs useless but it does ensure that the individual’s genes are passed on and so natural selection favors it. However, natural selection can also select for altruism in social groups, as well as cooperation 6. EVOLUTION IS NOT RANDOM Though the mutations that produce the variation in populations arise by chance, evolution itself IS NOT RANDOM and absolutely NO evolutionist claims that the complex structures arose by chance Natural selection is what chooses from the random variation and leads to the formation of complex structures but selection is the very opposite of random Variation combined with selection in laboratory settings has produced complex formations including circuits and robots. It has also been useful in designing new drugs, designing better enzyme detergents and as genetic algorithms for many other applications 7. ANIMALS ARE NOT THE ONLY THINGS TO EVOLVE ALL life evolves, including animals, plants, fungi and single celled organisms Viruses (not technically life) can evolve as well In fact anything can evolve, so long as it reproduces, mutates and selection is applied FURTHER READINGS A complete introductory guide to evolution http://evolution.berkeley.edu/evolibrary/article/evo_01 How Stuff Works: How Natural Selection Works http://science.howstuf fworks.com/life/evolution/natural selection.htm Your Inner Fish: A PBS documentary based on the bestselling book by Neil Shubin Why Evolution Matters https://www.youtube.com/watch?v=V6zaRW5dL5w&feature=yout u.be How Evolution Works https://www.youtube.com/watch?v=hOfRN0KihOU What is Natural Selection https://www.youtube.com/watch?v=0SCjhI86grU How Does Evolution Work https://www.youtube.com/watch?v=hOfRN0KihOU What is Evolution https://www.youtube.com/watch?v=GhHOjC4oxh8 REFERENCES Arsenic-Tolerant Bacteria Need Phosphorus http://www.nature.com/news/arsenic -life-bacterium-prefersphosphorus-after-all-1.11520 Through the Wormhole (S01E02): The Riddle of the Black Hole Monogamy and Parental af fairs in birds http://beheco.oxfordjournals.org/content/2/4/339.abstract?i jkey=ccf6846ca4ad67deef5abcf31b28efdd94ede024&keytyp e2=tf_ipsecsha Adelie Penguins: Af fairs and prostitution https://www.google.ca/webhp?sourceid=chrome instant&rlz=1C1CHFX_enCA549CA549&ion=1&espv=2&ie=UT F-8#q=extrapair%20paternity%20in%20adelie%20penguins (click the researchgate.net one) Descent with Modification http://evolution.about.com/od/Evolution -Glossary/g/DescentWith-Modification.htm REFERENCES Elephants evolving their tusks away http://news.bbc.co.uk/2/hi/africa/180301.stm Descent with Modification http://animals.about.com/od/d/g/descentwithmodification.ht m Parasitism : Mother Nature is Trying To Kill You by Dan Riskin Mutations (Wikipedia Article): http://en.wikipedia.org/wiki/Mutation#By_effect_on_structur e Mutation FAQ http://www.talkorigins.org/faqs/mutations.html Hyena Genitals http://books.google.ca/books?id=dASsUFtN57sC&pg=PP1&re dir_esc=y#v=onepage&q=hyena&f=false