Natural Selection

The 3 types of selection pressure on a population:

1) "Stabilizing selection" = intermediate phenotypes are favored and extremes on both ends are eliminated.

2)"Directional selection" = is a mode of natural selection in which a single phenotype is favored, causing the allele frequency to continuously shift in one direction.

3) "Disruptive selection/ Diversifying selection" = describes changes in population genetics in which extreme values for a trait are favored over intermediate values

A nominated COR frequently is asked to write evaluation factors during the source selection process.

Natural selection doesn't reduce variation. Variation is regulated by the rate of mutation.

Natural selection reduces the chance of bad variation from being passed on and increases the chances for good variation to be passed on.

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Natural Selection is driven by random mutations and sexual reproduction. Organisms produce more offspring than can survive. These offspring compete for resources for food and water and who can aviod stuff such as predators and disease. Sexual Reproduction allows a population to have variation. If all of a population was the same, then it could easily die out if it had a adaptation that decreased its chance of survival. With sexual reproduction, all of a population has some sort of variation. Random Mutations allow organisms to gain new adaptions to help them survive in their environment. Together, Random mutations and sexual reproduction allow organisms that can survive in their environment survive and pass on their genes to their offspring.

Fitness is a measure of the ability to survive and produce more offspring relative to other members of the population a given environment. Natural Selection is is a mechanism by which individuals that have inherited beneficial adaptations produce more offspring on average than do other individuals.

So how does these two things relate? But the offspring must survive to contribute to the following generation, so fitness as a generational value. An individual's fitness became defined as to how well that individual contributed its genes to the next generation. The bottom line is still how many successful offspring an individual has.

The basis for all science, be it evolution or the study of how squeaky noises annoy people, is evidence. Darwin's primary evidence for evolution by natural selection was morphological homology; physical similarities between species. Modern evidence for evolution by natural selection is vast and includes a rich fossil record, well understood geologic evidence, radioisotopic evidence, as well as a host of genetic evidence from protein homologies to complex molecular systematics. All evidence for evolution converges on the singular observation that all organisms can be organized in a nested hierarchy much like a family tree; a Tree of Life.

Natural selection works on a simple premise that the better equipped have more chance of survival and reproduction. The fact that the 'better' animal has more chance of producing offspring means more of his or her genes reach the next generation than his or her weaker rivals, thus weakness is filtered out. Although luck and chance can come into the equation (a 'weaker' animal may get lucky) in the long run over generations and generations, luck is no match for 'good' genes which enable advantages in the fight for survival. The chemical process of reproduction is slightly different. When cells are creating copies of themselves to make the new being, they are essentially copying enormous sets of instructions that their parents cells followed to create them, and the offsprings cells will use to build them. As the instructions are so huge, the number of cells involved is so colossal, the number of animals involved in reproducing is vast, and the number of generations and generations, and millions and millions of years… the opportunity for 'mistakes' is likewise gigantic, no matter how accurate and efficient the cells involved are supposed to be. These 'chance' mistakes are actually something like 1 in a giga-mega-godzillion (not an official statistical measure I might add!) but because the process happens more than a giga-mega-godzillion times, mutations are seen to occur. These mutations can either improve the animal slightly, or hinder it. The mutations are never that huge as the new being would be unable to survive or find a mate if it drastically differed from the species as a whole. Of course, any improved instructions which give the being a slight advantage, have more chances of being copied in the future - the mutation is now the new standard. An interesting position on this is that cells actually evolved with this chance of mutation. Cells which were 100% accurate in their reproductive instruction copying never hit upon anything new, or advantageous to the species while the world changed around them. What was a good design then, perhaps isn't so good in today's world. Meanwhile, cells which had a 99.999999…..% accuracy were actually more successful in the fight for survival as they enabled the opportunity for mutation, and thus the opportunity for improvement - a species which can change with time is far more likely to survive in a world that too changes with time. With this in mind, you could argue randomness in cell mutation was actually naturally selected by a non-random process!

Because one cannot understand evolution without it. It is the primary driving mechanism of evolution; the mechanism that gives evolution its direction. If one is to learn about biology at all, one must have at least a basic understanding of the mechanism that produced all of today's biological variety.

Natural Selection is the process of organisms adapting and evolving with their surroundings. The weaker ones who cannot adapt die off while the adapting ones stay alive.

"The excess fecundity, and consequent competition to survive, in every species provides the precondition for the process Darwin called natural selection. Natural selection is easiest to understand as a logical argument, leading from premises to conclusion. The argument requires the four conditions listed below.

1. Reproduction. Entities must reproduce to form a new generation.

2. Heredity. The offspring must tend to resemble their parents: roughly speaking, 'like must produce like'. This condition is provided by Mendelian inheritance.

3. Variation in characteristics of the members of the population.

4. Variation in the fitness of organisms associated with these characteristics.

Provided these conditions are met for any property of a species, natural selection automatically results, as in the case of the peppered moth. If any are not, it does not. Thus entities, like planets, that do not reproduce cannot evolve by natural selection. But when the four conditions apply, the organisms with the property conferring higher fitness will leave more offspring, and the frequency of that type of organism will increase in the population."

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Which does not add new alleles to a population gene pool?

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"Darwin's finches are an excellent example of the way in which species' gene pools have adapted in order for long term survival via their offspring." See http://www.biology-online.org/2/11_natural_selection.htm.

Actually, all the religious people believed God created this world, and put them on this world for a reason. They believed that they had purpose in life.

But when Charles Darwin came along and said that we're related to monkeys, people got very upset. BEcause if you question one part of the bible, you're questiong the entire bible, and that's what Darwin did.

After he released his book, people found it upsetting to know that we are here by chance, and that we don't actually have a purpose on earth.

but honestly, if that's teh case, then we should be happy we're here by chance and live it up while it lasts.

Natural selection leads to evolution by giving the organism that is best suited for the area to thrive. Thus those who not suited for the area die off and evolution moves forward.

Genetic drift has reduced the polymorphism of the cheetah population. The cheetahs probably underwent a "genetic bottleneck" a few thousand years ago, when the population was reduced to just a few individuals. Then as they reproduced, all surviving cheetah offspring were closely related.

The principles of natural selection are:

That life reproduces with variation.

That variant features are inherited by offspring.

That organisms always produce more offspring than can comfortably be sustained by the environment they inhabit.

That variant offspring therefore must compete for resources and mating opportunities.

That this competition results in the differential reproductive success of variants, and therefore in changing frequencies of variant traits in the population.

Camouflage is such a good adaption because it allows creatures of all kinds to 'hide in plain sight' from predators. One of the simplest examples of how this works is the dappled coat of the fawn (baby deer), necessary because the mother must leave the baby alone, hidden in the tall grass or bushes while she gets enough to eat. The dappling mimics the spots of sunlight passing between the tall grasses or leaves of the bushes. The fawn also sits very still as part of the deception because movement would attract the eye of a predator. The coloring and the ability to stay motionless are two very common forms of camouflage. Without these elements, far fewer baby deer would survive to maturity and continue the deer population.

Not all camouflage is for the purpose of hiding from predators; another form is designed to confuse predators, sometimes called 'dazzle camouflage'. Some examples of this type are zebra stripes, water birds like flamingos that flock in great numbers with bright feathers, and silvery fish who live in large schools (groups). The purpose of this adaption is when danger is detected, the large group will all move at once creating a flurry of stripes, flashing, or color that makes it difficult for a predator to pick out an individual to strike.

Another type of camouflage is designed to help predators be more successful. This type also uses coloring and the ability to remain motionless; some examples of this are lions, tigers, and snakes. Their ability to blend into their background and stay still allows them to wait without being noticed for the best moment to strike their prey. This helps that species to obtain food and survive.

Most species of bird, fish, or mammal have predators, and predators have the need to successfully catch prey. Each species has developed (evolved with) what works for them, allowing them to survive and produce the next generation of the species.

1. Overproduction - more offspring are born than survive

2. Genetic Variation - there is variation in the population

3. Struggle to Survive - organisms with suitable variations will survive and reproduce

4. Differential Reproduction - suitable variations are passed on to offspring

Genes are the medium by which inherited traits are passed on to offspring. It is inherited traits, and thus genes, that receive positive or negative selection.

Absolutely. We have "moderated" its effects some with our technology (especially in the last 100 years, but that is too short a period to make much difference) but you can't stop it.

Being hit and killed by a bus because of inattentiveness is as effective a means of selection as being killed and eaten by a predator because of inattentiveness was thousands of years ago.

Wegener proposed the continental drift theory, and provided scientific evidences for such, but couldn't explain the mechanism or processes behind the movement of continents. It wasn't until the mid-twentieth century with the discovery of the Mid-Atlantic Ridge that the processes causing plate movements began to be understood and led to the science of plate tectonics.