Why do functionally \"anomalous\" characters (e.g., the whale\'s non-functional

Question

Why do functionally "anomalous" characters (e.g., the whale's non-functional hip and leg bones) support Darwin's inferred evolutionary relationships between certain groups (e.g., the whales and other land mammals)?

What is the modern notion of fitness? What did Darwin mean by the phrase "Survival of the Fittest?"

What is the purpose of using a population genetic model such as the Hardy-Weinberg-Equilibrium Principle?

What is Overdominance? How can it lead to a stable equilibrium frequency of an allele in a population?
What is Underdominance? What is likely to happen to an allele under these conditions? Why?

What is Genetic Drift? How can it influence the gene pool of a population?

What is the Founder Effect? Give an example of a population that has experienced a Founder event in the recent past.

How does inbreeding affect a population? Does it cause the population to evolve? What does it do?

How could you tell if an allele was under selection?

Explanation / Answer

There are three basic terms you need to know: Vestigial structures, homologous structures, andtransitional fossils. These three sum up the anatomical evidence for evolution

Vestigial structures are physical components that are either useless or do not serve the same use as they once did. Structures do not have to be nonfunctional to be considered vestigial; they may retain lesser functions or develop minor new ones, but nevertheless be in a degenerated state. If evolution is true, then "imperfect design" is expected, because natural selection works to make an organism well-adapted, but not perfectly adapted, to their environment. There are countless examples of vestigial structures found throughout many animals. Here are just a few:

In humans the vermiform appendix is almost useless and does more harm than good, and it is sometimes removed. It is a vestige from our primate ancestors who had larger intestinal tracts. Wisdom teeth are vestigial and are often removed. Our ancestors ate different foods so they required extra teeth. We also have a vestigial tail bone (coccyx), because we evolved from primates that had real tails. In rare cases a human is born with a partial tail.

In flightless birds such as ostriches or penguins the wings are considered vestigial structures because they are no longer used for flying, even though they may still have some other purpose (in penguins they are used for swimming). Flightless birds evolved from birds that could fly, but for one reason or another lost their flight ability.

The vestigial hind limbs and pelvic structures in whales and other cetaceans serve little use and are detached from the spine, remaining inside the body. Whales evolved from land mammals that actually used their hind legs, but as they became adapted to the ocean the legs and pelvis shrunk from disuse to their present degenerated state.

Homologous structures are physical parts that have a similar composition throughout many animals, although they might have different shapes and sizes. For example, almost all vertebrates share homologous bone structures. Among amphibians, reptiles, and mammals (including humans) the front limbs always contain a humerus, ulna, radius, carpals, metacarpals, and phalanges. While these structures will come in radically different shapes and sizes between all kinds of animals, they are still there. This shows a strong relationship among vertebrates and is highly suggestive of common ancestry. These animals all evolved and diversified from a common ancestor that had these basic components, but as the animals differentiated and adapted to their way of life, the shapes and sizes of the components changed.


Transitional fossils show the anatomical similarities of organisms that lived in the past to ones that live in the present. These fossils reveal the transition from one type of animal into another because they contain anatomical features of both groups. In order for a fossil to be transitional, it must be located at the right point in time between two groups of animals. Numerous transitional fossils have been found that trace the lineage of all kinds of animals. While the fossil record is incomplete it provides sufficient evidence of evolution that occurred in the past. Here are two famous examples:

Tiktaalik represents one stage in the transition from fish to amphibians. It had fins, scales, and gills like a fish. However, its fins were bony and weight-bearing, it had a flat head attached to a mobile neck, tetrapod lungs, and a wide ribcage, characteristics of tetrapods. It is also found in the right rock layer, which is crucial for it to be a transitional form.

Archaeopteryx is another famous transitional fossil that represents one stage in the transition from dinosaurs to birds. It was a mosaic, being more dinosaur-like than bird-like. Its most prominent bird-like feature was feathers that were most-likely used for short-term flight. It also had an opposable claw that was probably used for perching, and better eyesight like modern birds. Like a dinosaur, it did not have a beak, instead possessing a scaly snout full of sharp, cone-shaped teeth. It had a long, bony tail, claws, a saurischian pelvis, an S-shaped neck, and the spine was attached behind the skull, rather than below as in modern birds.
Answer Humans aren't the best place to look for this. Until relatively recently in our history we were a small population species that lived in areas that were not very good for fossilization. The best place to look is through the layers of dirt that were once oceans. Here you can find great places where you can almost see evolution occurring layer by layer much as you would see a series of drawings as a moving picture if you flipped through them fast enough.

Answer Humans have an inside-out retina giving us a blind spot that we have to compensate for by constantly moving our eyes. All mammels (except manatee and sloth) have seven cervical vertebrae. You, me, giraffes and mice. Why? Wouldn't it be handy for a giraffe to have a few more? Well, making new vertebrae is complicated from in evolutionary standpoint. Making structures, like stronger muscles, to compensate is easier. The spine of humans, as well as the leg joints, are poorly designed for standing upright. The redundant fat on female humans mammaries attracts mates but is hard on her health. Also, baby humans are too big for the human birth canal compared to other animals. Other animals show signs too. Why are there fish with lungs? Why do animals that live in complete darkness have eyes, eyes that don't even work? Why are animals on islands most similar to the animals on the nearest mainland, even if the climate is totally different? The list goes on and on. We discover new elements of anatomical evolutionary evidence all the time. Next time you are shaving your legs, think about why you would have that useless short hair there. Guys, you might want to think about your nipples and their purpose. Or, why you can't directly make estrogen without ovaries even though you need it to survive. Your bodies have to manufacture it from excess testosterone. (All the extra testosterone causes higher cancer rates, shorter temper, more hair and potentially might be shown to show a shorter attention span. Great design, huh?) We are all full of these "shortcuts", "leftovers" and flaws. Evolution guarantees "brilliant" solutions to adapting to a niche. But, not perfectly designed ones. The first one to work will be the one that takes hold. A slightly more elegant design won't give enough of an advantage to make a difference. Plus, the easiest design to get from a mutation will obviously be one that changes the existing structure to be something else. So, we get these jury-rigged solutions like inside-out retinas. Every "flaw" can be traced back to a previous structure that laid the groundwork for the structures we have now. It's pretty amazing and fascinating to think about.

A scientific theory is based on an observable phenomena, IE gravity. The phenomena is not in question, the how of it is the theory. A theory is the result of a positive test result, and accumulated positive test results that creates the sound basis for how something occurs. If there is no positive test result, it remains an unsubstantiated idea.

Evolution is the process of physical change, over an extended period of time, that has been slowly accumulating positive test results, to the point where it can now be declared as fact.

Most populations have some degree of variation in their gene pools. By measuring the amount of genetic variation in a population, scientists can begin to make predictions about how genetic variation changes over time. These predictions can then help them gain important insights into the processes that allow organisms to adapt to their environment or to develop into new species over generations, also known as the process of evolution.

Genetic variation is usually expressed as a relative frequency, which means a proportion of the total population under study. In other words, a relative frequency value represents the percentage of a given phenotype, genotype, or allele within a population.

Relative phenotype frequency is the number of individuals in a population that have a specific observable trait or phenotype. To compare different phenotype frequencies, the relative phenotype frequency for each phenotype can be calculated by counting the number of times a particular phenotype appears in a population and dividing it by the total number of individuals in the population.

Relative genotype frequency and relative allele frequency are the most important measures of genetic variation. Relative genotype frequency is the percentage of individuals in a population that have a specific genotype. The relative genotype frequencies show the distribution of genetic variation in a population. Relative allele frequency is the percentage of all copies of a certain gene in a population that carry a specific allele. This is an accurate measurement of the amount of genetic variation in a population.

Examining allele frequencies

A gene that can occur in two forms is said to have two alleles. Body color in fruit flies is an example of a gene with two alleles: a dominant allele for brown body color, and a recessive allele for black body color. The brown body color allele can be represented as "B" and the black body color allele as "b." The allele frequencies for a gene with two alleles are usually represented by the letters p and q, where the relative frequency of the B allele is p and the relative frequency of the b allele is q.

This definition of evolution was developed largely as a result of independent work in the early 20th century by Godfrey Hardy, an English mathematician, and Wilhelm Weinberg, a German physician. Through mathematical modeling based on probability, they concluded in 1908 that gene pool frequencies are inherently stable but that evolution should be expected in all populations virtually all of the time. They resolved this apparent paradox by analyzing the net effects of potential evolutionary mechanisms.

Hardy, Weinberg, and the population geneticists who followed them came to understand that evolution will not occur in a population if seven conditions are met:

When a population interbreeds, nonrandom mating can sometimes occur because one organism chooses to mate with another based on certain traits. In this case, individuals in the population make specific behavioral choices, and these choices shape the genetic combinations that appear in successive generations. When this happens, the mating patterns of that population are no longer random.

Nonrandom mating can occur in two forms, with different consequences. One form of nonrandom mating is inbreeding, which occurs when individuals with similar genotypes are more likely to mate with each other rather than with individuals with different genotypes. The second form of nonrandom mating is called outbreeding, wherein there is an increased probability that individuals with a particular genotype will mate with individuals of another particular genotype. Whereas inbreeding can lead to a reduction in genetic variation, outbreeding can lead to an increase.

Random forces lead to genetic drift

Sometimes, there can be random fluctuations in the numbers of alleles in a population. These changes in relative allele frequency, called genetic drift, can either increase or decrease by chance over time.

Typically, genetic drift occurs in small populations, where infrequently-occurring alleles face a greater chance of being lost. Once it begins, genetic drift will continue until the involved allele is either lost by a population or is the only allele present at a particular gene locus within a population. Both possibilities decrease the genetic diversity of a population.

Genetic drift is common after a population experiences a population bottleneck. A population bottleneck arises when a significant number of individuals in a population die or are otherwise prevented from breeding, resulting in a drastic decrease in the size of the population. Genetic drift can result in the loss of rare alleles, and can decrease the size of the gene pool. Genetic drift can also cause a new population to be genetically distinct from its original population, which has led to the hypothesis that genetic drift plays a role in the evolution of new species.

Distribution

How does the physical distribution of individuals affect a population? A species with a broad distribution rarely has the same genetic makeup over its entire range. For example, individuals in a population living at one end of the range may live at a higher altitude and encounter different climatic conditions than others living at the opposite end at a lower altitude. What effect does this have? At this more extreme boundary, the relative allele frequency may differ dramatically from those at the opposite boundary. Distribution is one way that genetic variation can be preserved in large populations over wide physical ranges, as different forces will shift relative allele frequencies in different ways at either end.

If the individuals at either end of the range reconnect and continue mating, the resulting genetic intermixing can contribute to more genetic variation overall. However, if the range becomes wide enough that interbreeding between opposite ends becomes less and less likely, and the different forces acting at either end become more and more pronounced, and the individuals at each end of the population range may eventually become genetically distinct from one another.

Migration

Migration is the movement of organisms from one location to another. Although it can occur in cyclical patterns (as it does in birds), migration when used in a population genetics context often refers to the movement of individuals into or out of a defined population. What effect does migration have on relative allele frequencies? If the migrating individuals stay and mate with the destination individuals, they can provide a sudden influx of alleles. After mating is established between the migrating and destination individuals, the migrating individuals will contribute gametes carrying alleles that can alter the existing proportion of alleles in the destination population.

How do populations respond to all these forces? As relative allele frequencies change, relative genotype frequencies may also change. Each genotype in the population usually has a different fitness for that particular environment. In other words, some genotypes will be favored, and individuals with those genotypes will continue to reproduce. Other genotypes will not be favored: individuals with those genotypes will be less likely to reproduce. What type of genotype would be unfavorable? Unfavorable genotypes take many forms, such as increased risk of predation, decreased access to mates, or decreased access to resources that maintain health. Overall, the forces that cause relative allele frequencies to change at the population level can also influence the selection forces that shape them over successive generations.

For example, if moths with genotype aa migrate into a population composed of AA and Aa individuals, they will increase the relative allele frequency of a. However, if the aa genotype has a clear disadvantage to survival (e.g. vulnerability to predation), eventually the changes brought about by the initial migration will be reversed.

1. mutation is not occurring 2.   natural selection is not occurring 3.   the population is infinitely large 4.   all members of the population breed 5.   all mating is totally random 6.   everyone produces the same number of offspring 7.   there is no migration in or out of the population

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