I'm sorry but.......

DINOSAURS AND HUMANS NEVER COEXISTED TOGETHER.  THERE IS ZERO, I REPEAT, ZERO EVIDENCE FOR SUCH A CLAIM.  ANYONE WHO CLAIMS OTHERWISE IS EITHER IGNORANT OF THE FACTS, WHICH CAN BE FIXED, OR IS JUST A KOOK!    

However it is possible that other such factors exist in one's decision to deny history.  Usually, one's acceptance of the truth is often clouded by their professions of faith.  This is unfortunate considering that the truth is the truth, and the truth of evolution is NOT incapatable with belief in God.  Unfortunately there are people like Ken Ham, Kent Hovind, and others, who would have you believe such plain and utter nonsense.  Please excuse me for the bold caps at the begining of this post, I was having a Lewis Black moment.
 D 

Creationism and Public Schools

Below is an essay I wrote for my English class. It is an argument essay about whether we should allow the teaching of creationism in public schools. The only problem is that it is short, only five pages. Sorry, but that is all I was allowed to write; though I could've gone on for much longer. Anyway, I thought I would share it with you. Let me know what you think!

D

Creationism In Public Schools

Ever since the dawn of man, human beings have tried to make sense of their existence. “What is the purpose of life,” and “How did life come to be,” are just a couple of questions concerning human existence. These questions have been debated by scholars, the clergy, and general laypeople for centuries. But it wasn’t until 1859 when Charles Darwin published his seminal work, On the Origin of Species, which posited that all life shares a common ancestor. Thanks to Darwin, humans had finally started to grasp how life came to be and how it flourished, namely, though the Theory of Evolution. Before Darwin, the only answer to how life came to be was creationism. But even now, after One-Hundred and Fifty-Years after Darwin’s radical new idea, there are still some today who oppose evolution and want an alternative, creationism, taught in public science classes.

Creationism is the idea that all living things, plants, animals, and bacteria, were created, by God just as they are now. Creationists got this idea by taking a literal interpretation of the book of Genesis in the Bible, which says that God created the world in six days and rested on the seventh. Also, creationists typically have a young earth view concerning the age of the earth. They usually believe the earth to be somewhere between fourteen-thousand and six-thousand years-old (however, these numbers for the age of the earth are nowhere to be found in the Bible). Creationists vehemently deny that all life shares a common ancestor; however they generally accept that micro-evolution happens (i.e. adaptations occur). Ken Ham, the founder of the young earth creationist organization Answers In Genesis (AIG) and the Creation Museum, claims that “Evolutionists” and Creationists have the same evidence, but they have different interpretations of that evidence. It is this claim of difference of interpretations that is giving the creationist movement credibility. But does this sound like science or is creationism merely religion and should it be taught in public school science classes?

“Nothing makes sense in biology except in the light of evolution,” was penned by the evolutionary biologist and Russian Orthodox Christian Theodosius Dobzhansky, who criticized anti-evolution groups like Answers In Genesis (AIG) and the Institute for Creation Research (ICR); all of who want creationism taught in science classes. Dobzhansky was making the point that evolution occurs, and all of the evidence from all of the different scientific disciplines (e.g. geology, bio-chemistry, physics) adds to the theory of evolution. In other words, Evolution explains so much of what happens in nature that no other theory makes sense. The theory of evolution has multiple lines of evidence for it. It is time tested and makes positive predictions. Evolution is a working and verifiable science.

Even though evolution has more evidence for it than any other theory, besides Quantum Mechanics, there is still doubt from the general American public. AIG even states that according to surveys, most Americans are creationists; therefore, creationism should be taught in science classes along with the theory of evolution. This however, is a logic fallacy called the argument of popular sentiment (Argumentum ad populum). For instance, if ninety percent of the population believed UFOs exist it does make the preposition, UFOs exist, true. Popular opinion is not evidence. At one point, many people thought that the earth was the center of the universe (which it’s not even the center of the Milky Way) and it was flat. But both of those popular notions were shown to be false.

Shouldn’t the American educational system be teaching students all sides of the origins of life? Students have a right to know and decide for themselves. Knowledge should never be withheld from anyone. This is another argument espoused by AIG and ICR. At first the argument seems on the level and sincere. It appeals to Americans sense of fair play and self-determination. Knowledge should never be withheld from anyone, but sadly, the truth is not democratic. Parents could vote on the sex of their child, but it doesn’t change the child’s sex. But for the sake of argument imagine that creationism can be taught in public schools. Would this now mean that in order to be fair and not withhold knowledge from students, schools would have to teach alchemy in chemistry class? Would it mean that in history class, schools should teach Holocaust denialism? Both “theories” claim to have evidence for them.

To complicate the matter is the First Amendment, which states, “Congress shall make no law respecting an establishment of religion, or prohibiting the free exercise thereof; or abridging the freedom of speech, or of the press; or the right of the people peaceably to assemble, and to petition the Government for a redress of grievances.” Creationism is a violation of the Establishment Clause of the First Amendment. Creationism is expressly religious in its intent and therefore cannot be taught in science class. This opinion has been expressed in several court cases, one of the most famous being Edwards v. Aguillard (1987), which established that creationism absolutely could not be taught. Though the Edwards case didn’t stop the creationist movement. After the Edwards ruling, a new branch of creationism evolved known as Intelligent Design (ID). However, in the Kitzmiller v. Dover case (2005) it was determined that ID had no secular purpose and was expressly religious in its intent, thus violating the First Amendment.

Because of the religious intent behind groups like AIG and ICR, the real underlying problem seems to be where evolution puts man. Evolution makes man an animal, which ironically enough, the creationist Carl Linnaeus was the first to classify man as a member of the great apes. According to the Bible, which AIG and ICR adhere to, man is special; evolution threatens this idea. Science has seen such battles before in cases of Copernicus and Galileo. They took away mans special status of being the center of the universe. But does knowing such facts make humanity less special? The late Stephen Jay Gould Ph.D, Harvard Zoologist, and science popularizer argued in his essay, “Non-Overlapping Magisteria (NOMA)” that science and religion answers two separate questions. Religion answers questions of meaning while science answers questions dealing with the natural world. Science can inform religion, but it is not designed to answer the existential questions. Even Pope John Paul II wrote in his edict “Truth Cannot Contradict Truth” (1996) that evolution, in the neo-darwinian sense, is not just an hypothesis. Pope John Paul agreed with Gould’s NOMA. Creationism is more concerned with man’s place in the universe as opposed to how man came to be. There is no evidence for any of the tenets of creationism: a worldwide flood, a young earth, dinosaurs coexisting with humans, or a literal six day creation of the earth and cosmos. Therefore, creationism is solely a religious movement intended to spread religion and misinformed ideas about the origin of species, and thus doesn’t fit within a public school science class.

In a recent survey, half of all Americans responding when asked if the the earth orbits the sun or the sun the earth, got the question wrong. The fact that half of those respondents got that question wrong says a lot about the science education in the United States. This survey shows why it is important for the United States to take its science education seriously. Doing so requires that the most up-to-date factual content is taught to students. There is no time to be wasted with misinformation. There are no cures for HIV, cancer, and the hundreds of other diseases that kill men, women, and children each year. The theory of evolution is the cornerstone of modern biology and to dismiss it simply because it endangers one’s position on man’s purpose in the cosmos could be a grave mistake.

Evolution Lesson 2

More from the University of Berkeley on the evidences of evolution.

Re-posted from: http://evolution.berkeley.edu/evolibrary/home.php

Artificial selection

Artificial selection provides a model that helps us understand natural selection. People have been artificially selecting domesticated plants and animals for thousands of years. These activities have amounted to large, long-term, practical experiments that clearly demonstrate that species can change dramatically through selective breeding. Broccoli and brussels sprouts bear little superficial resemblance to their wild mustard relatives (right). If domesticated dogs were discovered today they would be classified as hundreds of different species and considered quite distinct from wolves. Although it is probable that various breeds of dogs were independently domesticated from distinct wild dog lineages, there are no wolf relatives anywhere in the world that look much like dachshunds or collies (below).

These observations demonstrate that selection has profound effects on populations and has the ability to modify forms and behaviors of living things to the point that they look and act very unlike their ancestors. Artificial selection provides a model that helps us understand natural selection. It is a small step to envision natural conditions acting selectively on populations and causing natural changes.

Ecology

The environment affects the evolution of living things.
As predicted by evolutionary theory, populations evolve in response to their surroundings. In any ecosystem there are finite opportunities to make a living. Organisms either have the genetic tools to take advantage of those opportunities or they do not.

House sparrows arrived in North America from Europe in the nineteenth century. Since then, genetic variation within the population, and selection in various habitats, have allowed them to inhabit most of the continent. House sparrows in the north are larger and darker colored than those in the south. Darker colors absorb sunlight better than light colors and larger size allows less surface area per unit volume, thus reducing heat loss — both advantages in a cold climate. This is an example of natural selection acting upon a population, producing micro-evolution on a continental scale.

Experiments

Experiments also show that populations can evolve.
John Endler of the University of California has conducted experiments with the guppies of Trinidad that clearly show selection at work. The scenario: Female guppies prefer colorful males for mating purposes. Predatory fish also "prefer" colorful males, but for a less complimentary purpose — a source of food that is easy to spot. Some portions of the streams where guppies live have fewer predators than others and in these locations the males are more colorful (top frame). Not surprisingly, males in locations where there are more predators tend to be less colorful (bottom frame).

When Dr. Endler transferred predatory fish to the regions with brightly colored male guppies, selection acted rapidly to produce a population of duller males. This demonstrates that persistent variation within a population provides the raw material for rapid evolution when environmental conditions change.

Nested hierarchies

Common ancestry is conspicuous.
Evolution predicts that living things will be related to one another in what scientists refer to as nested hierarchies — rather like nested boxes. Groups of related organisms share suites of similar characteristics and the number of shared traits increases with relatedness. This is indeed what we observe in the living world and in the fossil record and these relationships can be illustrated as shown below.

In this phylogeny, snakes and lizards share a large number of traits as they are more closely related to one another than to the other animals represented. The same can be said of crocodiles and birds, whales and camels, and humans and chimpanzees. However, at a more inclusive level, snakes, lizards, birds, crocodiles, whales, camels, chimpanzees and humans all share some common traits.

Humans and chimpanzees are united by many shared inherited traits (such as 98.7% of their DNA). But at a more inclusive level of life's hierarchy, we share a smaller set of inherited traits in common with all primates. More inclusive still, we share traits in common with other mammals, other vertebrates, other animals. At the most inclusive level, we sit alongside sponges, petunias, diatoms and bacteria in a very large "box" entitled: living organisms.

Evolution Lesson 1

Berkeley has an awesome site to explain all the evidence for the Theory of Evolution called Understanding Evolution. It is a great resource for information on this massive subject. They do a wonderful job in explaining the relevant information in an easy to understand format. I am so impressed with their effort that I will be posting their material here on Skeptic Dave. We should all be thankful to hard working researchers, scientists, and educators who took the time to gather all of this info.

D

Re-posted from: http://evolution.berkeley.edu/evolibrary/home.php


Fossil evidence

Nicholas Steno's anatomical drawing of an extant shark (left) and a fossil shark tooth (right). Steno made the leap and declared that the fossil teeth indeed came from the mouths of once-living sharks. The fossil record provides snapshots of the past that, when assembled, illustrate a panorama of evolutionary change over the past four billion years. The picture may be smudged in places and may have bits missing, but fossil evidence clearly shows that life is old and has changed over time. Early fossil discoveries In the 17th century, Nicholas Steno shook the world of science, noting the similarity between shark teeth and the rocks commonly known as "tongue stones." This was our first understanding that fossils were a record of past life. Two centuries later, Mary Ann Mantell picked up a tooth, which her husband Gideon thought to be of a large iguana, but it turned out to be the tooth of a dinosaur, Iguanodon. This discovery sent the powerful message that many fossils represented forms of life that are no longer with us today. Additional clues from fossils Today we may take fossils for granted, but we continue to learn from them. Each new fossil contains additional clues that increase our understanding of life's history and help us to answer questions about their evolutionary story. Examples include:

Indication of interactions This ammonite fossil (see right) shows punctures that some scientists have interpreted as the bite mark of a mosasaur, a type of predatory marine reptile that lived at the same time as the ammonite. Damage to the ammonite has been correlated to the shapes and capabilities of mosasaur teeth and jaws. Others have argued that the holes were created by limpets that attached to the ammonite. Researchers examine ammonite fossils, as well as mosasaur fossils and the behaviors of limpets, in order to explore these hypotheses.

Clues at the cellular level Fossils can tell us about growth patterns in ancient animals. The picture at right is a cross-section through a sub-adult thigh bone of the duckbill dinosaur Maiasaura. The white spaces show that there were lots of blood vessels running through the bone, which indicates that it was a fast-growing bone. The black wavy horizontal line in mid-picture is a growth line, reflecting a seasonal pause in the animal's growth.

Transitional forms

Fossils or organisms that show the intermediate states between an ancestral form and that of its descendants are referred to as transitional forms. There are numerous examples of transitional forms in the fossil record, providing an abundance of evidence for change over time.

Pakicetus (below left), is described as an early ancestor to modern whales. Although pakicetids were land mammals, it is clear that they are related to whales and dolphins based on a number of specializations of the ear, relating to hearing. The skull shown here displays nostrils at the front of the skull.

A skull of the gray whale that roams the seas today (below right) has its nostrils placed at the top of its skull. It would appear from these two specimens that the position of the nostril has changed over time and thus we would expect to see intermediate forms.

Note that the nostril placement in Aetiocetus is intermediate between the ancestral form Pakicetus and the modern gray whale — an excellent example of a transitional form in the fossil record!

Our understanding of the evolution of horse feet, so often depicted in textbooks, is derived from a scattered sampling of horse fossils within the multi-branched horse evolutionary tree. These fossil organisms represent branches on the tree and not a direct line of descent leading to modern horses. But, the standard diagram does clearly show transitional stages whereby the four-toed foot of Hyracotherium, otherwise known as Eohippus, became the single-toed foot of Equus. Fossils show that the transitional forms predicted by evolution did indeed exist. As you can see to the left, each branch tip on the tree of horse evolution indicates a different genus, though the feet of only a few genera are illustrated to show the reduction of toes through time.

Homologies

Evolutionary theory predicts that related organisms will share similarities that are derived from common ancestors. Similar characteristics due to relatedness are known as homologies. Homologies can be revealed by comparing the anatomies of different living things, looking at cellular similarities and differences, studying embryological development, and studying vestigial structures within individual organisms.

In the following photos of plants, the leaves are quite different from the "normal" leaves we envision.

Each leaf has a very different shape and function, yet all are homologous structures, derived from a common ancestral form. The pitcher plant and Venus' flytrap use leaves to trap and digest insects. The bright red leaves of the poinsettia look like flower petals. The cactus leaves are modified into small spines which reduce water loss and can protect the cactus from herbivory.

Another example of homology is the forelimb of tetrapods (vertebrates with legs).

Frogs, birds, rabbits and lizards all have different forelimbs, reflecting their different lifestyles. But those different forelimbs all share the same set of bones - the humerus, the radius, and the ulna. These are the same bones seen in fossils of the extinct transitional animal, Eusthenopteron, which demonstrates their common ancestry.

Homologies: anatomy

Individual organisms contain, within their bodies, abundant evidence of their histories. The existence of these features is best explained by evolution. Several animals, including pigs, cattle, deer, and dogs have reduced, nonfunctional digits, referred to as dewclaws. The foot of the pig has lost digit 1 completely, digits 2 and 5 have been greatly reduced, and only digits 3 and 4 support the body. Evolution best explains such vestigial features. They are the remnants of ancestors with a larger number of functional digits.

• People (and apes) have chests that are broader than they are deep, with the shoulder blades flat in back. This is because we, like apes, are descended from an ancestor who was able to suspend itself using the upper limbs. On the other hand, monkeys and other quadrupeds have a different form of locomotion. Quadrupeds have narrow, deep chests with shoulder blades on the sides.

• Hoatzin chicks have claws on their wings, as do some chickens and ostriches. This reflects the fact that bird ancestors had clawed hands.

Homologies: comparative anatomy

Organisms that are closely related to one another share many anatomical similarities. Sometimes the similarities are conspicuous, as between crocodiles and alligators, but in other cases considerable study is needed for a full appreciation of relationships.

Modification of the tetrapod skeleton
Whales and hummingbirds have tetrapod skeletons inherited from a common ancestor. Their bodies have been modified and parts have been lost through natural selection, resulting in adaptation to their respective lifestyles over millions of years. On the surface, these animals look very different, but the relationship between them is easy to demonstrate. Except for those bones that have been lost over time, nearly every bone in each corresponds to an equivalent bone in the other.

Homologies: developmental biology

Studying the embryological development of living things provides clues to the evolution of present-day organisms. During some stages of development, organisms exhibit ancestral features in whole or incomplete form.

Snakes have legged ancestors.
Some species of living snakes have hind limb-buds as early embryos but rapidly lose the buds and develop into legless adults. The study of developmental stages of snakes, combined with fossil evidence of snakes with hind limbs, supports the hypothesis that snakes evolved from a limbed ancestor.

Above left, the Cretaceous snake Pachyrhachis problematicus clearly had small hindlimbs. The drawing at right shows a reconstruction of the pelvis and hindlimb of Pachyrhachis.

Baleen whales have toothed ancestors.
Toothed whales have full sets of teeth throughout their lives. Baleen whales, however, only possess teeth in the early fetal stage and lose them before birth. The possession of teeth in fetal baleen whales provides evidence of common ancestry with toothed whales and other mammals. In addition, fossil evidence indicates that the late Oligocene whale Aetiocetus (below), from Oregon, which is considered to be the earliest example of baleen whales, also bore a full set of teeth.

Again, these observations make most sense in an evolutionary framework where snakes have legged ancestors and whales have toothed ancestors.

Homologies: cellular/molecular evidence

All living things are fundamentally alike. At the cellular and molecular level living things are remarkably similar to each other. These fundamental similarities are most easily explained by evolutionary theory: life shares a common ancestor.

The cellular level
All organisms are made of cells, which consist of membranes filled with water containing genetic material, proteins, lipids, carbohydrates, salts and other substances. The cells of most living things use sugar for fuel while producing proteins as building blocks and messengers. Notice the similarity between the typical animal and plant cells pictured below — only three structures are unique to one or the other.

The molecular level
Different species share genetic homologies as well as anatomical ones. Roundworms, for example, share 25% of their genes with humans. These genes are slightly different in each species, but their striking similarites nevertheless reveal their common ancestry. In fact, the DNA code itself is a homology that links all life on Earth to a common ancestor. DNA and RNA possess a simple four-base code that provides the recipe for all living things. In some cases, if we were to transfer genetic material from the cell of one living thing to the cell of another, the recipient would follow the new instructions as if they were its own.

These characteristics of life demonstrate the fundamental sameness of all living things on Earth and serve as the basis of today's efforts at genetic engineering.

Distribution in time and space

Understanding the history of life on Earth requires a grasp of the depth of time and breadth of space. We must keep in mind that the time involved is vast compared to a human lifetime and the space necessary for this to occur includes all the water and land surfaces of the world. Establishing chronologies, both relative and absolute, and geographic change over time are essential for viewing the motion picture that is the history of life on Earth.

Chronology

The age of the Earth and its inhabitants has been determined through two complementary lines of evidence: relative dating and numerical (or radiometric) dating.

• Relative dating places fossils in a temporal sequence by noting their positions in layers of rocks, known as strata. As shown in the diagram, fossils found in lower strata were typically deposited first and are deemed to be older (this principle is known as superposition). Sometimes this method doesn't work, either because the layers weren't deposited horizontally to begin with, or because they have been overturned.
  If that's the case, we can use one of three other methods to date fossil-bearing layers relative to one another: faunal succession, crosscutting relationships, and inclusions.
  By studying and comparing strata from all over the world we can learn which came first and which came next, but we need further evidence to ascertain the specific, or numerical, ages of fossils.

• Numerical dating relies on the decay of radioactive elements, such as uranium, potassium, rubidium and carbon. Very old rocks must be dated using volcanic material. By dating volcanic ash layers both above and below a fossil-bearing layer, as shown in the diagram, you can determine "older than X, but younger than Y" dates for the fossils. Sedimentary rocks less than 50,000 years old can be dated as well, using their radioactive carbon content. Geologists have assembled a geological time scale on the basis of numerical dating of rocks from around the world.

Geography

The distribution of living things on the globe provides information about the past histories of both living things and the surface of the Earth. This evidence is consistent not just with the evolution of life, but also with the movement of continental plates around the world-otherwise known as plate tectonics.

Marsupial mammals are found in the Americas as well as Australia and New Guinea, shown in brown on the map at right. They are not found swimming across the Pacific Ocean, nor have they been discovered wandering the Asian mainland. There appear to be no routes of migration between the two populations. How could marsupials have gotten from their place of origin to locations half a world away?

Fossils of marsupials have been found in the Antarctic as well as in South America and Australia. During the past few decades scientists have demonstrated that what is now called South America was part of a large land mass called Gondwana, which included Australia and Antarctica. Click on the map below for a short animation that shows how Gondwana split apart 160 to 90 million years ago. Marsupials didn't need a migration route from one part of the world to another; they rode the continents to their present positions.

Evidence by example

Although the history of life is always in the past, there are many ways we can look at present-day organisms, as well as recent history, to better understand what has occurred through deep time. Artificial selection in agriculture or laboratories provides a model for natural selection. Looking at interactions of organisms in ecosystems helps us to understand how populations adapt over time. Experiments demonstrate selection and adaptive advantage. And we can see nested hierarchies in taxonomies based on common descent.

Creationist Science Fair Cartoon

I found this on the Richard Dawkins forums. I had to post this because it's sooooo funny. It's funny because it's true.

D

Dr. Dino's Son And Population Growth

Bad news from P.Z. Myers today, Eric Hovind (son of tax dodger and creationist Kent Hovind) has picked up where Daddy left off. Eric uses new slick and up to date graphics and web technology to lure in the ignorant masses. He may be using new technology, but he is still using the same old arguments. All of these have been thoroughly debunked and explained ad nauseum. But being a masochist I just had to wonder over to his site and take a peek.

Eric Hovind's website ( http://www.drdino.com/read-article.php?id=137) asks:

How could population levels be minimal for millions of years and then suddenly explode in the last 2,000 years?

Here's the short answer. Actually the world's population didn't really "take off" until the 1950s. The world's population had been on an upward trend from 1750 to 1950 (see the graph below). But because of industrialization and the rise of technology, we were able to dramatically change the quality of life around the globe, thus increasing the world's population.

D

Another Creationist?

Do we have another creationist on the blog? This one is a bit tougher to decifer. This person does pose an interesting question (see below).


Mynym wrote:
..and every fact that has something to do with evolution confirms its truth.Interesting... so what type of biological observation would not confirm "evolution," whatever it may be?

Actually there is a few answers to this but I think I will take HIV for two-hundred Alex.

Berkley University has a website dedicated to understanding evolution. One of their web pages lists in detail how the HIV virus evolves. I will re-post their findings below. You can also see this example in the PBS Evolution series which can be found here. I warn you, it is long but well worth the time.

D

Re-posted from: http://evolution.berkeley.edu/evolibrary/article/_0_0/medicine_04

HIV: the ultimate evolver

Evolutionary biologists can help uncover clues to new ways to treat or vaccinate against HIV. These clues emerge from the evolutionary origins of the virus, how human populations have evolved under pressure from other deadly pathogens, and how the virus evolves resistance to the drugs we've designed. Controlling the disease may be a matter of controlling the evolution of this constantly adapting virus.

The human immunodeficiency virus (HIV, shown here budding from a white blood cell) is one of the fastest evolving entities known. It reproduces sloppily, accumulating lots of mutations when it copies its genetic material. It also reproduces at a lightning-fast rate — a single virus can spawn billions of copies in just one day. To fight HIV, we must understand its evolution within the human body and then ultimately find a way to control its evolution.

Taking an evolutionary perspective on HIV has led scientists to look in three new directions in their search for treatments and vaccines:

• What are the evolutionary origins of HIV?
• Why are some people resistant to HIV?
• How can we control HIV's evolution of resistance to our drugs?

1. What are the evolutionary origins of HIV? HIV, like any evolving entity, has been deeply marked by its history. Scientists studying the evolutionary history of HIV found that it is closely related to other viruses. Those viruses include SIVs (simian immunodeficiency viruses), which infect primates, and the more distantly related FIVs (the feline strains), which infect cats. However, studies of these related viral lineages showed something surprising: primates with SIV and wild cats with FIV don't seem to be harmed by the viruses they carry. If scientists can figure out how non-human primates and wild cats are able to live with these viruses, they may learn how to better treat HIV infections or prevent them altogether. The diagram shows some of the evolutionary history of HIV as we know it today. An ancestral virus (bottom) evolved into strains that infected chimpanzees (SIV). Over time, new strains began to infect humans (HIV).

2. Why are some people resistant to HIV?
HIV is by no means the first plague that human populations have weathered. Many pathogens have deeply affected our evolutionary history. In fact, the human genome is littered with the remnants of our past battles with pathogens — and one of these remnants, a mutation to a gene called CCR5, may lead researchers to a new treatment for HIV.

The mutant CCR5 allele probably began to spread in northern Europe during the past 700 years when the population was ravaged by a plague. (It may have been bubonic plague or some other pathogen; research on this topic continues.) The mutant CCR5 probably made its bearers resistant to the disease, and so its frequency increased.

In some parts of Europe today, up to 20% of the population carry at least one copy of the protective allele. However, the populations of Asia and Africa were not exposed to the same epidemics; very few Asians and Africans now carry the allele (see map above). Thus, CCR5 is fairly common in northern Europe but its frequency diminishes as one moves south, and the mutation is rare in the rest of the world.

We now know that the mutant CCR5 allele has an unexpected side effect: it confers resistance to HIV. Scientists hope that studying this by-product of past selection will help them develop new treatments for the HIV epidemic ravaging human populations today.

3. How can we control HIV's evolution of resistance to our drugs?
HIV evolves so quickly that it evolves right out from under our treatments. When a patient begins taking an HIV drug, the drug keeps many of the viruses from reproducing, but some survive because they happen to have a certain level of resistance. Because of HIV's speedy evolution, it responds to selection pressures quickly: viruses that happen to survive the drug are favored, and resistant virus strains evolve within the patient, sometimes in just a few weeks. However, basic evolutionary theory points out a way that this evolution of resistant viral strains can be delayed. Patients are prescribed "drug cocktails" — several different HIV drugs taken together.

When taking any single drug, it is fairly likely that some mutant virus in the patient might happen to be resistant, survive the onslaught, and spawn a resistant lineage.

But the probability that the patient hosts a mutant virus that happens to be resistant to several different drugs at the same time is much lower. Although multiple-drug-resistant HIV strains do eventually evolve, drug cocktails delay their evolution.

An evolutionary trade-off
If a patient is already infected with a drug-resistant HIV strain, basic evolutionary theory has also pointed out a way to make the drug useful again. Studies of the evolution of resistance often show that you don't get something for nothing. Specifically, it "costs" a pest or pathogen to be resistant to a pesticide or drug. If you place resistant and non-resistant organisms in head-to-head competition in the absence of the pesticide or drug, the non-resistant organisms generally win.

Consider a patient who takes a particular drug and winds up with viruses resistant to the drug. If the patient stops taking the drug for a while, evolutionary theory predicts that her viral load will evolve back towards a non-resistant strain. If she then takes very strong doses of the drug, it may be able to halt the replication of those non-resistant viruses and reduce her viral load to very low levels.

This therapy has shown early, promising results — it may not eliminate HIV, but it could keep patients' virus loads low for a long time, slowing progression of the disease.

Ultimately, understanding the evolutionary history of HIV and its pattern of evolutionary change may help us control this disease.