Through questions you may have ever asked yourself , in this article we will have a first look at the basic principles of evolution and debunk misconceptions about it. But a scientific theory is the explanation of a phenomenon supported by evidence resulting from the application of the scientific method.
So few people sic doubts about the heliocentric theory the Earth rotates around the Sun , or the gravitational theory of Newton, but in the popular imagination some people believe that the theory of evolution made by Charles Darwin and Alfred Russell Wallace is simply a hypothesis and has no evidence to support it. With new scientific advances, his theory has been improved and detailed , but more than years later, nobody has been able to prove it wrong , just the contrary.
We have many evidences and in this post we will not delve into them. Some of the evidence available to us are:. It is a typical example of Lamarck and giraffes : as a result of stretching the neck to reach the higher leaves of the trees , currently giraffes have this neck for giving it this use. They have a necessity , they change their bodies to success. It is what is known as natural selection , one of the main mechanisms of evolution.
It needs three requirements to act :. Over the years these changes are accumulated until the genetic differences are so big that some populations may not mate with others: a new species has appeared. If you thought that this is similar to artificial selection that we do with the different breeds of dogs , cows who give more milk, trees bearing more fruit and larger , congratulations, you think like Darwin as it was inspired by some of these facts.
Therefore , living beings are mere spectators of the evolutionary process , depending of changes in their habitat and their genetic material. Genetic variability allows natural selection act. Changes in the genetic material usually DNA are caused by :. Populations that have more genetic variability are more likely to survive if happen any changes in their habitat. Populations with less variability eg , being geographically isolated are more sensitive to any changes in their habitat , which may cause their extinction.
Evolution can be observed in beings with a very high reproduction rate , for example bacteria , since mutations accumulate more quickly. Have you ever heard that bacteria become resistant to our antibiotics or some insects to pesticides? They evolve so quickly that within a few years were selected the fittest to survive our antibiotics.
Theory of Evolution has various consequences, such as the existence of a common ancestor and that therefore , that we are animals. Even today , and even among the young ones , there is the idea that we are something different between living beings and we are in a special podium in the collective imagination. This anthropocentric thinking caused Darwin mockery and confrontations over years ago. The question has a mistake of formulation: actually evolving pursues no end , it just happens, and the fact that millions of years allows the emergence of complex structures, it does not mean that simpler life forms are not perfectly matched in the habitat where they are.
Bacteria, algae , sharks, crocodiles, etc. Evolution is a process that started acting when life first appeared and continues to act in all organisms , including us, although we have changed the way in which natural selection works medical and technological breakthroughs , etc. We have not evolved from any existing primate.
As we saw in a previous post , human s and other primates share a common ancestor and natural selection has been acting differently in each of us.
That is, evolution has to be viewed as a tree, and not as a straight line, where each branch would be a species. Some branches stop growing species become extinct , while others continue to diversify. Evolution is a very broad topic that still generates doubts and controversies.
In this article we have tried to bring to uninitiated people some basics , where we can delve into the future.
Do you h ave any questions about evolution? By doing so, they can calculate how much time has passed. The atomic clock is a very accurate national timekeeping apparatus calibrated by the precise regularity of radioactive decay. Numerous radioactive isotopes exist. One system that has been very successful in dating the ages of fossils is potassium-argon dating.
Potassium is an extremely common element. Potassium—argon dating relies on the fact that although potassium is a solid, argon is a gas. When rock is melted think lava , all the argon in the rock escapes, and when the rock solidifies again, only potassium is left. The melting of the rock and releasing of any argon present set the potassium—argon clock at zero. As time passes, argon accumulates in the rock as a result of radioactive potassium decay.
When scientists date rocks from our solar system this way, the oldest dates they find are 4. No fossils are present in lava, obviously; anything that was there melted along with the rock.
But by dating the lava flows above and below a fossil find, scientists can put exact boundaries on the maximum and minimum age of that fossil. In this case, the variation in possible ages of the fossil simply reflects the fact that the fossil exists between the dated lava flows. Radioactive dating has been perfected to the extent that scientists can get within a few percentage points of the actual date. Potassium—argon dating has been used to date accurately the age of the eruption of Mount Vesuvius at Pompeii, for example.
The scientists knew that the technique worked because the age their equipment indicated matched the age noted in historical Roman records. They form when molten lava from volcanoes cools and solidifies. Basalt and obsidian are examples of igneous rocks. Sandstone is an example of sedimentary rock. Understanding these rock types helps biologists understand the fossil record. Fossils are found only in sedimentary rocks.
Today, scientists know quite a bit more. Scientists also know that life has existed on Earth for at least 3. By knowing the actual age of the Earth and how long life has been present, scientists can ask whether enough time has passed for simple creatures such as the ones they see in the oldest rocks to evolve into more complex creatures, such as the ones that can write and edit books.
The quick answer: Yes. The total of all fossils is called the fossil record. The earliest organisms that scientists can identify were single celled; now complex creatures exist.
The fossil record, incomplete though it may be, is a record of change through time. This record gives us clues to the progression of the development of life on Earth: Small single-celled organisms evolved into more complex ones; life started in the oceans and only later moved onto dry land.
The fossil record provides a rough draft of the tree of life. Head to Chapter 9 for a detailed explanation of the role that the tree of life — code word phyolgenetics — plays in evolution. The following sections explain what modern science says about these issues.
Today, scientists have the advantage of a much more thorough search of the planet for older fossils and, more important, far more sophisticated techniques for identifying microscopic fossils in rocks. The earliest fossils that scientists find are single-celled organisms, which Darwin lacked the ability to see physically. Today, scientists know that life has existed continuously on Earth for about the past 3.
But today, people know something even cooler: Some of the biological material can survive this process and persist for a very long time.
Scientists have been able to isolate DNA from organisms, like mammoths and cave bears, that died tens of thousands of years ago. In retrospect, this feat is not as surprising as it first sounds. DNA is awfully tough stuff; your survival depends on it, after all. Also, techniques for isolating DNA are becoming more and more precise, allowing scientists to work with smaller and smaller quantities. Even more amazing, scientists recently showed that soft tissue can survive for at least 68 million years inside fossilized Tyrannosaurus rex bone.
Tyrannosaurus rex proteins show considerable similarity to the proteins of modern birds — it turns out that T. Now scientists have biochemical evidence supporting the same connection.
What seemed like science fiction a little while ago is now something that science can routinely observe and measure. Submarines can dive to the depths of the ocean where plates are separating so researchers can measure the process. Very accurate markers can be placed in different locations across fault lines and their relative movements can be tracked with satellites and lasers. Scientists know, for example, the rate at which parts of California are moving apart and mountain ranges are pushing higher.
The fact that continents move explains why fossils turn up in the unlikeliest places: tropical fossils in Antarctica, for example biologists have every reason to believe that Antarctica was once in the tropics , or seashell fossils on mountaintops rocks that were once at sea level can be pushed upward over long periods to form mountain ranges.
By understanding more about geological processes and time scales, the fossil record is more comprehensible. They are better at knowing where to look and they have more people looking, but they still struggle to find them. If the transitional period was brief, the chance that such forms would have been fossilized is even more dicey. The organism not only has to die, but it also has to be buried intact and remain undisturbed in conditions hospitable to the mineralization process that preserves the remains.
Then, possibly millions of years later, someone stumbles across it and calls in the news cameras. Biogeographic patterns, or location, location, location Darwin carefully studied the biogeographical patterns of existing species. Biogeography is the study of the locations of different species through space. Biogeography reveals that species that appear to be closely related tend to be geographically close as well, as though groups of species had a common origin at a particular geographic location and radiated out from there.
Darwin was especially interested in the study of species on islands, and he observed that they seemed to be most closely related to species found on the nearest mainland. Darwin was interested in what, if anything, these biogeographical patterns revealed about evolutionary history. In developing his ideas, Darwin focused on finches that lived on the Galapagos Islands, an archipelago in the Pacific Ocean off South America. Several species of finches live on the Galapagos, each species inhabiting a different island.
The species seemed quite similar to one another and to a species on the mainland, leading Darwin to hypothesize that the different species of Galapagos finches were descended from individuals in the mainland species that had reached the islands sometime in the past. Because conditions on the islands differed from conditions on the mainland, the selective pressures acting on the finches also differed, resulting in new traits being favored in the new environment.
This early birdlike creature had many characteristics in common with some dinosaurs, yet it also had wings and feathers. Most obvious to the casual observer, Archaeopteryx had jaws full of sharp teeth, rather than the beak structure of birds. Archaeopteryx was clearly more toward the bird end of the transition to flight. Recently, paleontologists have discovered feathered dinosaurs that did not have wings.
Another interesting creature, Tiktaalik, had a skeletal structure intermediate between fish and tetrapods critters with four legs and had both gills and lungs.
This skeletal structure was sufficient to have allowed the organism to support itself, at least briefly, out of water. When the first creatures crawled onto the land, they might have looked like Tiktaalik.
You can read more about these and other fossil finds in Chapter As a result of the different evolutionary tracks between the mainland finches and island finches, the gradual changes accumulated to the point where the island finches were different enough from the mainland finches to be considered a new species.
Head to Chapter 8 for the details. This process occurred on the various Galapagos Islands, which are far enough apart that travel among them by finches is uncommon. After those rare events when finches did make it to a new island — perhaps as a result of being blown there by a storm — they evolved separately from the population on the island from which they came, in response to whatever novel environmental factors were present in their new home. When Darwin proposed that the Galapagos Islands had become inhabited by so many different but apparently related species of finches through the process of evolution, he had only his observations of existing variation to rely on.
Natural selection and speciation As the preceding section explains, Darwin hypothesized that natural selection operating over a long period accumulates enough small changes in a population to make that population so different that it would be its own species, no longer able to interbreed with other populations of the species it had previously been a member of. Once again, Darwin turns out to have been right.
Scientists have evidence that such small changes can have such large consequences over time. Scientists have a reasonably good handle on what constitutes an animal species; determining what differentiates plant and microbial species such as viruses and bacteria is a bit slipperier.
For animals, though, differentiating one species from another is fairly clear cut. A species is a group of organisms that can breed with one another but not with organisms in different species.
In other words, reproductive isolation is the key to differentiating species. Given the way evolution works small changes over time produce enough changes to create a different species , researchers should be able to find all intermediate forms in nature.
You can find out more about these patterns in Chapter 8. Origin of life This book concerns itself with the evolution of organisms that are already present, not with the question — fascinating as it is — of where organisms came from in the first place.
Although no one has succeeded yet with an experiment that involves mixing a bunch of things in a beaker and waiting for something to crawl out, some very clever experiments have been conducted that show how complex biochemicals can arise spontaneously out of simple mixtures under conditions thought to be present on Earth more than 3 billion years ago. Darwin imagined that such things might happen in a warm pond. Chemists Harold C. Urey who won the Nobel Prize for discovering heavy water and Stanley L.
Miller actually made the pond. They combined water hydrogen, methane, and ammonia in a sterile glass system; heated the flask to produce a humid atmosphere; and then sent electrical shocks though the mixture to simulate lightning. They repeated this procedure for a week and then analyzed the contents of the flask.
By using this simple procedure, they were able to produce DNA, RNA, amino acids, sugars, and lipids — all the building blocks of life from four very simple molecules. The answer is simple. Evolution involves genetic changes over time, so to understand evolution, you need to know a little bit about genetics: what it is, how it works, and what parts are particularly important to the study of evolution.
What Is Genetics? For most of human history, people have understood that offspring tend to resemble their parents. Only relatively recently, beginning in the late s, have we begun to understand how the genetic process works. An easy way to think about genetics is to think about it in terms of information. In every cell of your body is a complete instruction manual for making a person, and somehow, these instructions get passed on to your offspring.
The instruction manual is your DNA — basically a repository for all the instructions that make you, you. Molecular genetics is important to evolution because it helps clarify the process of mutation — that is, the errors that occur when something in the replication process goes awry. Most of these mutations are bad, but every so often, one of them results in something good. Mutations are the initial sources of the variations on which natural selection can act.
Comparing the genomes of different organisms gives us a better idea of how, for example, humans can be so different from chimps when they have most of the same DNA sequences. Looking at major genome-wide differences between people can help us understand the health implications of these differences. By studying large groups rather than individuals, scientists can observe the evolutionary process — some genes become more common, and others go extinct — to determine whether natural selection is involved.
Sure, it takes some of the glamour out of the headlines, but the findings are still pretty amazing to geneticists, anyway. Because we now have a better understanding of the nuts and bolts of genetics and heredity, we are able to understand the evolutionary process in ways that Darwin could only dream of.
Some organisms have all their DNA on one chromosome, while other organisms have their DNA spread across several chromosomes. The DNA of sexually reproducing organisms, like animals and humans, is arranged on pairs of chromosomes.
When these organisms make offspring, the offspring get one set of chromosomes from each parent. Humans, for example, have 23 pairs of chromosomes. And every cell has a copy of the chromosomes. DNA is made up of just four different building blocks that are called nucleotides, or bases. All the instructions needed to make you can be written with just four letters!
The structure of DNA is a double helix consisting of two strands winding around each other see Figure One strand is an inverted version of the other, so if you know the sequence of one strand, you know the sequence of both strands. You may wonder how four nucleotides could possibly be the basis of all life in all its complexity.
What scientists discovered is that these four letters actually appear in groups of three, called codons. It turns out there are 64 codons. DNA is so tough, in fact, that scientists have been able to isolate intact DNA from extinct mammoths found buried in Siberian ice and even, in some cases, from fossilized bones. This produces two double helix molecules. Each is an exact copy of the original.
If you want to see DNA rather than just read about it, the following recipe for a DNA cocktail shows you how to do so. The chemistry is simple. Freeze the strawberries. A tall narrow glass works best. Strawberries contain DNA. Blending them with pineapple juice allows the enzymatic activity in the juice to free the DNA from all the other bits of the strawberry that it hangs onto. The fresher the pineapple juice, the more enzymatic activity it will have, allowing the experiment to work even better.
Layer the strawberry-pineapple mixture on top of the gin. When the now-dissolved DNA comes into contact with the cold gin, it precipitates out of solution that is, turns into a solid due to the chemical reaction , and you see little white wisps floating in the gin layer.
Those white wisps are the actual DNA molecules, and they contain all the information that makes the strawberry plant what it is. Proteins comprise most of the basic machinery that makes an organism work. Proteins are composed of 20 subunits, called amino acids. The exact translation from codons to the amino acids is called the genetic code.
They wondered how something with only four different letters could code for all the complexity of an organism. Thus, at one point, proteins were considered to be good candidates for the material used for information storage because they had 20 amino acids — or 20 different letters available in their alphabet. The breakthrough in understanding came when scientists determined that the 4 nucleotides were read in groups of 3, meaning that instead of containing 4 individual letters, DNA has an alphabet of 64 triplet letters, called codons.
That discovery raised another question. Instead of wondering how to code for 20 amino acids with only 4 letters, people questioned how you would code for only 20 amino acids when you have 64 codons. The answer is that there is some redundancy in the translation of DNA into proteins.
Figure shows all 64 codons of the genetic code. Most of the amino acids correspond to multiple codons, as you can see from the figure the notations Phe, Leu, and so on. These codons are called stop codons. They tell the protein-producing machinery to stop adding amino acids to a growing protein, and their presence indicates that the protein is finished. These other RNAs fall into several categories. All you need to remember is that the most important category for evolution is ribosomal RNA.
Take eyes, for example. Few things have eyes. As a result, comparing a human with, say, a stalk of broccoli and a mushroom based on similarities and differences in the structure of the eye is impossible. But humans, mushrooms, and stalks of broccoli do all have ribosomal RNA. In other words, it can help clarify which branch of the tree of life an organism belongs to.
You can read more about the tree of life in Chapter 9. The other categories of noncoding RNA are transfer RNA abbreviated tRNA , which is involved in assembling the amino acids that make a protein, and a growing collection of small RNA molecules we keep discovering new ones that seem to be involved with the regulation of gene expression — a fancy way of referring to the process of deciding which genes get turned on and off in any given cell. It has fallen mightily from its halcyon days of being defined as the fundamental unit of heredity.
Back then, it was clear that somehow, some way, specific bits of information were passed from parent to offspring. No one had any idea exactly what these bits were, but it was clear that they existed, and we called them genes. Of alleles and loci When most people think about heritable traits, they think about genes. Unfortunately, the term gene is a little too general for a discussion of evolution.
Instead, you need to know a little more about how the DNA strand is put together. The different instructions for different genes are located in different places along the DNA sequence. These different sequences are called alleles. Take the locus that stores the information to make the blood type protein. When scientists examine this locus in several individuals, they find variations; some alleles code for type O blood, some for type A blood, and so on.
The exact sequence of the ACTG alphabet is different, and this is why people have different blood types. At the locus where the eye-color trait resides, for example, you find alleles representing the different colors: blue, green, brown, and so on.
Imagine a single locus with two alleles, A and a, each representing a different manifestation of a particular trait. Because the locus has only two options, you can figure out pretty easily what individual combinations you may find in the population. In this case, some people would have AA having received A from both parents , Aa having received A from one parent and a from the other , and aa having received a from both parents.
Whether the alleles are different or the same is an important factor in how, when, or even whether the heritable trait manifests itself, as the following sections explain. Dominant, recessive, or passive-aggressive? Maybe AA makes red flowers, aa makes white flowers, and Aa makes pink flowers — an easy-to-understand example if you know that the A allele codes for a redpigment protein, and the more of that protein the individual makes, the redder the pigment is.
When a recessive allele is paired with a dominant allele, the phenotype is the same as for an individual with two dominant alleles. Studying the genome can reveal quite a bit. Scientists know, for example, that a gene exists for a trait like eye color. From an evolutionary point of view, the genome is intriguing because it presents evolutionary scientists with a bunch of deep questions to ponder like, if genome sizes are different for different organisms and some in ways that make no obvious sense , then how did that happen?
Or why does so much of the genome seem to be junk and why is this the case in some species but not others? Any why are similar genes in different places on the genomes of different species?
You have a much bigger genome than a bacterium or a mushroom does, and at first, that seems to make a lot of sense. After all, humans certainly appear to be more complex than bacteria or mushrooms. We have a lot more parts — arms, eyes, complicated nervous systems, and so on — so it seems reasonable that our genome would be bigger.
The range of genome sizes varies among several major groups of organisms. Your genome is much bigger than the genome of yeast or Escherichia coli E. Poplars, for example, have twice as many genes as people do. For details about genome size and coding and non-coding DNA, head to Chapter Base pairs The unit of genome size is the number of base pairs abbreviated bp.
Why base pairs? Because of the paired structure of DNA A always pairs with T, C always pairs with G, and so on , when you know the 6 billion on one strand, you automatically know the 6 billion on the other strand.
From an information standpoint, only 6 billion independent bits of information exist. As a result, scientists refer to the size of the human genome as 6 billion bp.
Some junk DNA consists of long sections in which short sequences of nucleotides repeat over and over and over. Both plants and mammals have lots of junk DNA, but plants seem to have more which explains why the fern hanging in your kitchen has more DNA than you do. And just how much junk do we have? Researchers are still trying to figure out why so much of human DNA is junk — a problem that I discuss in Chapter Number of genes Scientists have determined the DNA sequence of the entire human genome a fact you may already know from the various news stories that accompanied the completion of the Human Genome Project.
Are they lazy or just unmotivated? As it turns out, neither. As researchers keep refining their techniques for identifying genes in this big sea of DNA, they end up revising their numbers progressively downward.
Currently, they think they have a good handle on the situation and are reasonably certain that the human genome contains about 25, genes.
Is that a lot? Common intestinal bacteria have about 5, genes; yeast has about 6,; the common laboratory roundworm has around 18,; and the fruit fly Drosophila has 14, And many plants seem to have as many genes as human do, and some have far more. The human genome is not the only one that scientists have sequenced in its entirety. Initial genome sequencing projects concentrated on smaller creatures, such as bacteria, and it turns out that very little of those genomes is junk.
Humans, however, are not in such a hurry all the time, and the energy it takes to copy human DNA is a very small part of our total energy budget. When scientists look at a sequence of DNA and identify genes, they have techniques for determining that a particular piece of DNA makes something and can use the genetic code to determine the amino-acid sequence of the protein that piece of DNA makes.
If the protein looks like something else whose function scientists understand, they have some clues. Genome organization: Nuclear, mitochondrial, or free floating? Where in the world is your genome, anyway?
In two different places within your cells: the nucleus and the mitochondria. This is where most of your genetic material resides. This structure is called mitochondria, and each of your cells contains several dozens to hundreds of these structures.
Why do these small things inside your cells have their own genome, and how did they get there? In later chapters, I get back to mitochondria, examining how they evolved and looking at what various studies of mitochondrial DNA tell scientists about human history.
For now, just remember that you have some mitochondria and that your mitochondria have some DNA. Not all organisms have cells with nuclei. Furthermore, bacteria tend to keep their genome in one piece. It probably would be biochemically complicated for humans to have their entire genome in one segment, as the DNA would be extremely long.
Bacteria can get away with keeping their genome together only because their genomes are much smaller. How many copies? Some organisms have more copies of their genome than others do.
At first, you may think it would be good to have extra copies of your own personal blueprints, just in case you lose one of the instructions. Although having an extra copy has obvious advantages, it also may have some costs, including the additional time it takes to replicate two copies of your genome before cell division. Biologists think that these costs must outweigh the benefits for most bacteria, which is why many bacteria have only a single copy of their genome. Sometimes, when the benefits of having a backup copy outweigh the costs of growing more slowly, an organism has an extra copy of its genome.
These cases include organisms that really need multiple spare genomes to fix errors. One such organism is the bacteria species Deinococcus radiodurans. This little critter has not one extra copy of its genome, but several copies, probably due to the fact that it lives in extremely harsh environments where DNA damage is more likely to occur from such factors as extreme drying.
As a result of having these extra copies of its genetic material, Deinococcus radiodurans is the most radiation-resistant organism known. This little fellow can handle times more radiation than you can. Instead, each locus on the genome is comprised of two sets of alleles.
When a sexually reproducing organism — such as a person — produces offspring, it first must make gametes in the case of a human, eggs or sperm. Each of the gametes gets one copy of the DNA segments. When one set comes from Mom and one set comes from Dad, the sets may be slightly different. This situation makes for some interesting genetic questions.
Dominating issues Consider the snapdragons. Snapdragons are diploid, just like you are, though they make ovules and pollen rather than eggs or sperm.
Two possible alleles appear at this locus; call these alleles W and R. Alleles are often referred to by letters. Plants with two copies of the W allele are white; plants with two copies of the R allele are red. How about plants that have one copy of each allele? In the case of snapdragons, the plants with one W allele and one R allele are pink, which seems to make sense. In the pea plants that the famous geneticist Gregor Mendel worked with, there are two possible alleles at the locus responsible for flower color: one that codes for purple flowers P and one that codes for white flowers w.
If a plant has two alleles that code for purple, then it has purple flowers. If it has two alleles that code for white, then it has white flowers. But because the purple allele is dominant, a plant with one purple and one white allele turns out just as purple as a plant with two purple alleles. If the pea flour is white, you know that it has two of white alleles ww. But if the pea flour is purple, it may have two purple alleles PP or one purple allele and one white allele Pw.
This situation leads to the topic of genotype and phenotype, which very conveniently comes next. Genotype and phenotype Genotype refers to the alleles that a particular organism has — the actual sequences of DNA in its genome, such as a gene for growth hormone. Genotype and phenotype are often connected, but the important thing to remember is that the connection is not always absolute.
Organisms with the same phenotypes may have different genotypes; similarly, organizations with the same genotypes may have different phenotypes. Grasping this concept is especially important when you think about evolution by natural selection. Imagine a pack of cheetahs chasing a gazelle across the African plains.
One by one, the cheetahs get tired and give up. But one cheetah keeps at it and eventually catches the gazelle. Why this cheetah captured the gazelle while the others fell away, I have absolutely no idea. Are her genes especially good? Does she have different genes that make her go extra fast? It could be that all the cheetahs have the same genes, but this particular cheetah was lucky enough to have been very well fed when she was a cub and, as a result, grew up to be faster and stronger.
Consider the human blood-type alleles A, B, and O. Each of us has two of these alleles, receiving one from each parent. How does that work? To understand the others, you need to know that A and B are dominant over O, but neither is dominant over the other. Knowing the phenotype sometimes gives you complete information about the genotype, such as the phenotypes for type O blood and type AB blood. But in the cases of blood type A and blood type B, two possible genotypes could bring about each phenotype.
What this has to do with natural selection Natural selection — the process by which organisms with favorable traits are more likely to reproduce and pass on their genes see Chapter 5 for more indepth info — acts on phenotype, not genotype. Think about it. Some phenotypic variation existed in the cheetah population, and as a result, some cheetahs did better than others.
But is it evolution? The difference in speed has to be a heritable one — one that can be passed on genetically from parent to offspring.
If the faster cheetahs have different genes than the slower cheetahs, then the next generation will have a higher proportion of those genes because the cheetahs that had them eat more antelope and made more baby cheetahs. Even in evolutionary terms, most mutations are bad.
But some mutations give an organism a fitness advantage resulting in its being able to survive and reproduce. The result? More of the genetically advantaged organisms in future populations. Genetic drift a fancy way of saying random events can affect gene frequencies, too. If a mudslide wipes out a large portion of a wildflower that just happens to bloom pink in a particular area, then there will be fewer pink-flowering plants in later generations.
This part tackles the mechanisms of evolutionary change variation, mutation, selection — both natural and artificial — genetic drift, and so on ; their results loss of genetic variation, change in genetic variation, and speciation ; and how to retrace past evolutionary events and see the relationships among species through phylogenetic trees. It must be heritable variation — that is, variation that gets passed genetically from parent to offspring.
But some evolutionary forces, such as natural selection and genetic drift covered in Chapters 5 and 6, respectively , actually cause a reduction in genetic variation over time. Fortunately, mutations — random errors in the genetic code — generate the very kind of variation that evolution needs. Variation and mutation go hand in hand, so this chapter examines both topics. Understanding Variation In evolutionary terms, variation simply refers to the differences you see among individuals.
Look around a room full of people, and you notice that all of them look different. You can see how heritable changes — hair color, eye color, facial structure, height, and so on — manifest themselves outwardly. If every individual in one generation were the same, every individual in the next generation would be the same.
Key concepts in variation As stated previously, for evolution to occur, the variation has to be heritable. Just thinking of the variations within our own species is a good place to start. It would take at least books this size to list all the ways that people are genetically different from one another.
For example, a species may contain individuals of many different heights, but not all populations within that species will have individuals of all heights; some populations may be made up of, on average, taller individuals than others. Take the finches in the Galapagos. Within one finch population that was studied, there was existing variation in beak size. When other birds arrived on the island and began eating the food these finches relied on, this existing variation allowed that species to evolve to better utilize a smaller seed resource.
If two populations continue to become genetically different, they can become too different to interbreed, a topic addressed in Chapter 8. This work covers two often antagonistic fields: biology and the social sciences.
It seeks to develop a seamless transition from genes to human motivations as bio-electric brain processes emotional-cognitive processes , to human nature propensities various constellations of emotional-cognitive forces, desires and fears to species typical patterns of behavior. It should be of strong interest to anthropologists, sociologists, sociobiologists, psychobiologists and psychologists who are interested in the question of human nature influences on social behavior.
Its effects on our view of life have been wide and deep. Wallace, T. Huxley, August Weismann, Asa Gray—better than Ernst Mayr, a man considered by many to be the greatest evolutionist of the century?
Here we have an accessible account of the revolutionary ideas that Darwin thrust upon the world. He proposed the idea that humans were not the special products of creation but evolved according to principles that operate everywhere else in the living world; he upset current notions of a perfectly designed, benign natural world and substituted in their place the concept of a struggle for survival; and he introduced probability, chance, and uniqueness into scientific discourse.
Here is a book by a grand master that spells out in simple terms the historical issues and presents the controversies in a manner that makes them understandable from a modern perspective. Cooper Publisher: Cambridge University Press ISBN: Category: Science Page: View: The formal systems of logic have ordinarily been regarded as independent of biology, but recent developments in evolutionary theory suggest that biology and logic may be intimately interrelated.
He examines the connections between logic and evolutionary biology and illustrates how logical rules are derived directly from evolutionary principles, and therefore, have no independent status of their own. This biological perspective on logic, though at present unorthodox, could change traditional ideas about the reasoning process.
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