WEIT Chap1

What is evolution?

Evolution consists of physiological changes in organisms of a generation compared to previous generations of the same organism. These changes can appear in many different forms. The main aim is to give the evolved organism a physical advantage compared to its ancestors. This advantage may affect the everyday life of the organism or be a very specific change for a very specific situation.

it occurs in all species: plants ,animals ,viruse

It is a sort of adaptation to a changing surrounding world and changing living conditions. It gives an organism tools to survive more easily in its environment.

The 6 components of evolution: evolution, gradualism, speciation, common ancestry, natural selection, nonselective mechanisms

Some of these parts go tightly together, one being inevitably linked to the other. <<If speciation is true, for instance, then common ancestry must also be true.>> Others are independent. Together, they make up the system of Evolution.

What is gradualism?

Gradualism don't evolve at an even pace. It means that it can take 20 minutes as certain microbes or it can take over hundreds or thousands even millions of generations.

When natural salection is strong, as when an animal or plant colonizes an new environment, evolutionary change can be fast. Once a species becomes weel adapted to a stable habitat, evolution often slows down.

The time it takes to evolve

It takes many generations to produce a evolutionary change. Mutationists in the 2oth century tought that evolutionary change can occur from one single individual. This individual would be bearing a strong mutation and by passing it on to its offspring, a new species could arise. However, the examination of fossils has taught the scientists that this is not true. Evolution occurs gradually and takes time.

eg: evolution of birds from reptiles... page 4

Often, many generations are needed for one trait to conquer a whole population and this might take several million years. Depending on the species, this progress might be slower or faster and the evolution speed inside a species is not always constant, because it depends on the environmental pressure to which the species is exposed. Some bacteria have generations that last only a couple of minutes and so, their populations evolve very quickly. This causes rapid mutations and explains why some bacteria become drug-resistant so rapidly. In fact, the species just evolves and adapts to the hostile drug, making it inefficient.

Over a long period of time (several millions of years), a species might evolve so much that there are more evolved characteristics than original ones. Furthermore, several types of organisms that have different characteristics may arise from one single species.

What is speciation?

<< Speciation simply means the evolution of different groups that can't interbreed/can't interchange genes >> p.6 Why evolution is true

For example, a population of an organism might divide, one fraction going to a region and the other fraction to another region. The two fractions might evolve differently from each other depending on the conditions of the environment surrounding them. It is thought that all existing species have a common ancestor that gave rise to all others in this way.

This phenomen can be observed in places where populations have been divided by natural barriers such as water (islands), canyons or mountains. In such places, we can often see how the different fractions of the populations have evolved independently from each other and formed astonishing diversity from each other.

This is due to the fact that some genes may not be present in one of the separated subgroups and so, they can't be passed to the offspring of that subgroup while the gene will be present in the offspring of the other subgroup, resulting in different characteristics between the two new populations over time.

The elements separating a population are called barriers to gene exchange as they physically prevent the exchange of genes between two groups or two individuals.

what is common ancestry?

It is the idea that all species living on earth today are descendants of one primary common ancestor. Proof for this theory can be found in all species : All species << share some fundamental traits ; biochemical pathways to produce energy, a standard four-letter DNA code, and how that code is read and translated into proteins >> e.g. p.4 Why evolution is true

<<Creatures with recent common ancestors share many traits, while those whose common ancestors lay in the distant past are more dissimilar.>> e.g. p.9 WEIT

Common ancestry is studied comparing the DNA codes of different species. We assume that the more the DNAs of two species have in common, the more closely they are related. It is therefore difficult to find a common ancestor for every species as it is very difficult to analyse the DNA of animals that have lived million years ago. One has to find fossils and then be able to extract DNA from them.

what is natural selection?

Evolution creates diversity. This diversity then allows natural selection, meaning that the organisms that are best fitted for survival will produce offspring that will survive more easily thanks to its inherited traits. The organisms that are less well fitted will survive more difficultly. Their offspring will be weaker and they will dissappear after a certain time. More of the genes that confer the good characteristics will be passed on to later generations because more of the individuals carrying them survive and can then reproduce. The not so good genes are less likely to subsist on the long-term as the individuals carrying them can seem less attractive to others and more of them will die before being able to mate with others.

It is <<the only process that can produce adaptation>> e.g. p.13 why evolution is true

what is nonselective mechanisms of evolutionary change?

There are several of these processes. They lead to random evolutionary change rather than adaptive change.

For example <<Different families have different numbers of offspring. This leads to evolutionary change that, being random, has nothing to do with adaptation.>> Furthermore, << The influence of this process on important evolutionary change, though, is probably minor, because it does not have the molding power of natural selection.>> e.g. p.13 WEIT

<<Genetic drift>> may also <<play some evolutionary role in small populations and probably accounts for some non-adaptive features of DNA.>>

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