Natural Selection

The europeans used Social Darwinism to justify their increase in emprie building with the justification that all creatures have and will still continue to evolve, and as such, there needed to be new accomodations met.

Volcanic eruptions, changes in earth's orbit, changes in the sun's intensity, and changes in ocean currents are some examples of what natural events affect climate.

Advantages:

* determines the fitness of an organism by direct application. * employs a wide range of criteria * provides for opportunism Disadvantages:

* involves a lot of chance. * some organisms escape the full range of possible criteria * is under employed in boom times, over-employed in lean times. * recessive traits 'hide' from the process. *

Natural selection is a direct product of the environment.

A couple of simple examples are:

In a cold environment the only plants and animals that will survive will be cold tolerant plants and animals.

In a forest of Bears the only animals to survive will be animals that are faster or bigger than Bears.

A sudden change in environmental conditions, such as an Ice Age, will see whole populations of some species disappear while only remnants of some species will survive.

Those remnants will display either cold tolerance or the ability to withstand the cold by other means ie: clothing or fire.

One part of the theory of evolution by natural selection is that only the best-adapted animals in a population survive.

Small changes add up over many generations.

Lets say you have two bunnies. One has a long tail, the other has short tail. The one with the long tail died because a predator was able to catch onto the long tail and eat it. Therefore, the long tailed bunny can't pass on the characteristic of a long tail and that trait is no longer seen in bunnies. However, the bunny with the short tail isn't caught by predators as easily, and as a result, passes on the trait of a short tail to its offspring. After a long amount of time, no bunnies will have long tails because all the bunnies with long tails were killed out, and as a result, can't pass on the characteristic of a long tail. Bunnies then evolve to always have short tails.

this is where the genes are mixed up, and it allows genes to be exchanged across chromosomes and randomizes the assortment of chromosomes to the offspring.

Previewing is important because it gives you some information about what you will be reading before you actually read the story.

according to Darwin's theory of evolution, species go through a natural selection over long periods of time. meaning that only the fittest of a species survive as it is the organisms of a species who are the most fit, that have the greater capability to hunt or gather food versus weaker organisms of that species who die out as the fitter organisms out-compete them for food or resources. for example, giraffes who have longer necks are considered to be more fit as they can more easily reach tall trees and gain access to food, as opposed to giraffes with shorter necks who can't reach enough food and therefore die out. it is considered natural selection as certain animals are "fitter" than others because of a mutation they have (like longer necks) that put them at an advantage.

Natural selection is the nonrandom survival and reproductive success of randomly varying organisms.

Evolution is the change in allele frequency over time in a population of organisms.

So, the individual naturally selected will leave more decedents in the population and his descendents will have the traits that made him survive and reproduce better and this will change the allele frequency of the population, the population's gene pool, and lead to evolution in this population.

Charles Darwin is credited with this theory in his book, The Origin Of Species. ---> Actually... Jean-Baptiste Pierre Antoine de Monet, Chevalier de la Marck (AKA Lamarck) was the first to propose the hypothesis that species change over time.

An organism with a charecteristic that is more helpful to its survival will be more likely to survive and breed than one without that characteristic.

External selection forces that make survival hard.

To get the fastest rate of evolution these forces should kill or disable 50% to 90% of the individuals in each generation before they are able to reproduce. But these forces should not kill so many as to make the species go extinct. In most cases these forces only kill or disable less than 10% of the individuals in each generation before they are able to reproduce.

Genetic relatedness

It is meant to indicate the Darwinian model for evolution, as opposed to for instance the Lamarckian model. It would be true that evolution occurs and has occurred even without Darwin; but until Darwin, various explanations would have been possible for why and how it happens. Darwin first formulated the thesis that evolution is directed by differential reproductive success.

Assume you have a population of people of various genetically influenced heights; they all varied in height potential. They all were raised in an environment that was deprived of basic nutrients and all were somewhat stunted in growth. A person that would have been tall in a normal environment passes on those genes for tallness in his deprived -of -nutrients environment, so his sons/daughters, if properly feed, would grow tall. So you see, natural selection must work on the genetic/individual variation and not variations that are not inherited.

Natural selection is differential reproductive success. It occurs when a population consisting of multiple variants exist in a limited environment. Some variants will be more successful - in terms of producing offspring - than other variants. The term used to indicate the measure of reproductive success of a variant is 'fitness'. The alleles (variations of a gene) of a 'fitter' variant will have a larger representation in the next generation than the alleles of a less 'fit' variant, and so the 'fit' alleles spread throughout the population at a greater rate than less 'fit' alleles. Eventually, less 'fit' alleles may even vanish from the population entirely. When an allele is so successful that it becomes the only variant for a given gene, we say that the allele has become 'fixed'.

Note that the term 'fitness' has no direct relation to the health, strength, intelligence or speed of the variant: the only measure of 'fitness' is the reproductive success of the variant.

Because in natural selection heritable traits will be passed down allowing those species to have a better chance at survival, thus making speciation a reality.

Humans are the only cause of artificial selection. Humans take organisms that they think are useful, or may become useful and they breed them true for traits they want in the organism and they cull the organisms that do not possess traits that humans find useful. not all animals can be artificially selected though.

Right from the start, the terms "strong" and "favors" should be defined. Natural selection "favors" simply in that the mechanism allows the continuation of those who are better suited to their environment. "Strong" and "fittest" are synonymous in this regard, because it's not referring to physical strength.

Natural selection only favors those who are able to survive long enough to reproduce and thus pass on their genes. That's all there really sis to it.

They are the selective agent in natural selection ;)

Notably, the phrase 'survival of the fittest' is a particularly poor choice of words for describing natural selection, in my opinion. Mainly because, in the perception of the layman, it might be taken to mean that natural selection is a black-and-white phenomenon, always favouring more able variants, and that ability (fitness) is measured in terms of health, strength, intelligence, rather than ability to produce offspring.

A far more accurate phrase would be: differential reproductive success - meaning the difference in numbers of surviving fertile offspring between variants.

That more organisms are born than the available resources can support leading to a struggle for existence. That all these organisms are variants and that some variants are better adapted to the immediate environment and will survive and reproduce better that the other organisms in that environment. That these beneficial traits that organisms posses are heritable, passed on to progeny and change the allele frequency in populations of organisms over time leading to evolution.