Define evolution

[s41nn0n]

Please define evolution for me?

 

[CACTUSJACKmankin]

Please define evolution for me?

change in allele frequency over time.
Evolution is the process by which changes in genetic frequency leads to adaptation and speciation.
In the span of 3.5-4 billion years this process has brought life from the simplest replicators of RNA to highly complex organisms such as ourselves and accounts for all the diversity of life that we see in nature.

 

[Raydon]

There are some good definitions here.

"Biological evolution ... is change in the properties of populations of organisms that transcend the lifetime of a single individual. The ontogeny of an individual is not considered evolution; individual organisms do not evolve. The changes in populations that are considered evolutionary are those that are inheritable via the genetic material from one generation to the next. Biological evolution may be slight or substantial; it embraces everything from slight changes in the proportion of different alleles within a population (such as those determining blood types) to the successive alterations that led from the earliest protoorganism to snails, bees, giraffes, and dandelions." - Douglas J. Futuyma in Evolutionary Biology, Sinauer Associates 1986

Also:

"Evolution is a process that results in heritable changes in a population spread over many generations."

Also:

"In fact, evolution can be precisely defined as any change in the frequency of alleles within a gene pool from one generation to the next." - Helena Curtis and N. Sue Barnes, Biology, 5th ed. 1989 Worth Publishers, p.974

I hope these are good enough for you

 

[lemmings]

The change of traits in a population over periods of time as a result of imperfect replicators being subject to Natural Selection.

It means that over time, random mutations within the DNA will contribute to the creation of new genes that may either help or hinder the organism. Mutations that prove to be beneficial or neutral to the organism’s survival to reproduction will be more likely passed down from generation to generation entering the larger gene pool of the population.

 

[sfs]

The change of traits in a population over periods of time as a result of imperfect replicators being subject to Natural Selection.

It means that over time, random mutations within the DNA will contribute to the creation of new genes that may either help or hinder the organism. Mutations that prove to be beneficial or neutral to the organism’s survival to reproduction will be more likely passed down from generation to generation entering the larger gene pool of the population.

The process of evolution is defined as the change in a population (as stated by others previously), regardless of whether natural selection is involved or not. The theory of evolution, which provides a model for how and why the process occurs, includes natural selection as one causal mechanism; what makes selection notable is that it is the mechanism that produces adaptive evolution.

For the original poster, note that what's being discussed here is a definition that marks out the boundary of what is considered to be the process of evolution. The process of evolution is important in science because it explains the relatedness of all living things and their distribution in time and space.

 

[Jet Black]

evolution is right.

 

[Raydon]

Oh, and don't forget that evolution is a big mafia in worldwide. This is the most important definition in my opinion.

 

[CACTUSJACKmankin]

Oh, and don't forget that evolution is a big mafia in worldwide. This is the most important definition in my opinion.

yes of course we all know that the entire worlds population of scientists, save for a few good christians, is involved in a vast atheist conspiracy to push people away from God.

 

[Gracchus]

yes of course we all know that the entire worlds population of scientists, save for a few good christians, is involved in a vast atheist conspiracy to push people away from God.

SHHHHH!

 

[moogley]

I don't understand how other people can't understand Evolution. It is VERY simple.

An example:
Trait A is better than Trait B; they are both represent 50% of the population. Trait A allows the organism to reach reproductive capability 90% of the time while Trait B only 50%.
(not these are made up and extreme numbers, but the mathematics works with any ammount of difference)

The next generation of the organism will be approx 9/14 Trait A and 5/14 Trait B. (Note: 9/14 > 50% > 5/14)
The second generation will be at a ratio of:
.9*(9/14) : .5*(5/14)
.578 : .179

Or about 75% will be Trait A - in 2 generations...

That is how genes can be distributed.

 

[FishFace]

To the OP: You know, if you don't have a dictionary at home, www.dictionary.com is very useful. It has entries from several different dictionaries.

 

[cerad]

Please define evolution for me?

Minor adaption s that some animals and plants make while always staying within their own kind.

 

[lucaspa]

Please define evolution for me?

change in allele frequency over time.

That one won't work. It won't give speciation. You will find that Ernst Mayr and other evolutionary biologists reject that reductionist definition.

Here is the defintion given by Douglas Futuyma in Evolutionary Biology, which is the most common college textbook for evolution:

"Thus, evolution, in a broad sense is descent with modification, and often with diversification. Many kinds of systems are evolutionary ... In all such systems there are populations, or groups, of entities; there is variation in one or more characteristics among the members of the population; there is HEREDITARY SIMILARITY between parent and offspring entities; and over the course of generations there may be changes in the proportions of individuals with different characteristics within populations. This process consitutes descent with modification. Populations may become subdivided so that several populations are derived from a COMMON ANCESTRAL POPULATION. If different changes in the proportions of variant individuals transpire in te several populations,the populations DIVERGE, OR DIVERSIFY. ... All these properties of an evolutionary process pertain to populations of organisms, in which there is hereditary transmission of characteristics (based on genes, composed of DNA or, in a few cases, RNA), variation owing to mutation, and sorting of variation by several kinds of processes. Chief among these sorting processes are CHANCE (random variation in the survival or reproduction of different variants), and natural selection (consistent, nonrandom differences among variants in their rates of survival or reproduction). It is natural selection that causes adaptation -- improvement in function. Thus biological (or organic) evolution is change in the properties of populations of organisms , or groups of such populations, over the course of generations. ... Biological evolution may be slight or substantial; it embraces everything from slight changes in the proportions of different forms of a gene within a population, such as the alleles that determine the different human blood types, to the alterations that led from the earliest organisms to dinosaurs, bees, snapdragons, and humans." Douglas Futuyma, Evolutionary Biology, (1999) pg 4.

 

[Loudmouth]

That one won't work. It won't give speciation.

It's nice to find someone who thinks like I do. Speciation is a very, very important mechanism because it produces divergence. Evolution is a theory that is meant to explain biodiversity. The only way to get diversity is through speciation.

I have always preferred to define Evolution by it's mechanisms. Those mechanisms are random mutation with respect to fitness, differential reproductive success (which also encompasses genetic drift), and speciation. That is what evolution is. What these mechanisms produce is change in allele frequency over time.

 

[Aron-Ra]

Please define evolution for me?

The Definition:
Biological evolution, simply put, is descent with modification. This definition encompasses small-scale evolution (changes in gene frequency in a population from one generation to the next) and large-scale evolution (the descent of different species from a common ancestor over many generations). Evolution helps us to understand the history of life.
--University of California at Berkeley

But I don't know that definining evolution alone is really enough. Perhaps you should know the definitions of other immediately-relevant concepts as well.

 

[lucaspa]

It's nice to find someone who thinks like I do. Speciation is a very, very important mechanism because it produces divergence. Evolution is a theory that is meant to explain biodiversity. The only way to get diversity is through speciation.

Well, actually the only way to get diversity is thru cladogenesis -- a species splitting into 2. If one species simply transforms into another species (anagenesis), you still only have 1 species and you don't get diversity.

I have always preferred to define Evolution by it's mechanisms.

Why don't you look at the definition Futuyma gives and use that one.

Those mechanisms are random mutation with respect to fitness, differential reproductive success (which also encompasses genetic drift), and speciation. That is what evolution is. What these mechanisms produce is change in allele frequency over time.

These are really poor mechanisms. They are going to get you into trouble.

1. You have put genetic drift in with natural selection. Please don't do that. Apples and oranges.
2. Speciation is reproductive isolation.

Speciation is more the RESULT of changes in allele frequency, not the cause of change in allele frequency.

However, I will put up Mayr's argument:

" 'Evolution' implies change with continuity, usually with a directional component. Biological evolution is best defined as change in the diversity and adaptation of populations of organisms." pg. 47

"No Darwinian I know questions the fact that the processes of organic evolution are consistent with the laws of the physical sciences, but it makes no sense to say that biological evolution has been "reduced" to physical laws. Biological evolution is the result of specific processes that impinge on specific systems, the explanation of which is meaningful only at the level of complexity of those processes and those systems. And the classical theory of evolution has not been reduced to a "molecular theory of evolution," an assertion based on such reductionist definitions of evolution as "a change in gene frequencies in natural populations." This reductionist definition omits the crucial aspects of evolution: changes in diversity and adaptation. (Once I gave a lump of sugar to a racoon in a zoo. He ran with it to his water basin and washed it vigorously until there was nothing left of it. No complex system should be taken apart to the extent that nothing of significance is left.)" Ernst Mayr, Evolution, Scientific American 239: 47-55, Sept. 1978.

 

[Atheuz]

Evolution is when minor mutations in genetic codes accumulate over time to make new traits - if these traits do not work in the environment the creature is currently living in it is more likely to die and thus the mutation does not get carried on to the next generation - thus the favorable mutations get carried on to the next generation.

 

[sfs]

Evolution is when minor mutations in genetic codes accumulate over time to make new traits - if these traits do not work in the environment the creature is currently living in it is more likely to die and thus the mutation does not get carried on to the next generation - thus the favorable mutations get carried on to the next generation.

That's natural selection, which is one of the mechanisms of evolution. Evolution includes inherited changes that are not favorable, not just favorable ones.

 

[lucaspa]

Evolution is when minor mutations in genetic codes accumulate over time to make new traits - if these traits do not work in the environment the creature is currently living in it is more likely to die and thus the mutation does not get carried on to the next generation - thus the favorable mutations get carried on to the next generation.

Let me reinforce SFS: you are attempting to describe natural selection, not evolution. Please go up and read Futuyma's definition in one of my earlier posts. Evolution is SO much more than natural selection.

Evolution is "descent with modification" and that modification can come from mechanisms other than natural selection: genetic drift, for instance.

Natural selection is how the designs in living organisms arise.

BTW, you might want to look at Darwin's definition of natural selection -- and use it.

"If, during the long course of ages and under varying conditions of life, organic beings vary at all in the several parts of their organization, and I think this cannot be disputed; if there be, owing to the high geometric powers of increase of each species, at some age, season, or year, a severe struggle for life, and this certainly cannot be disputed; then, considering the infinite complexity of the relations of all organic beings to each other and to their conditions of existence, causing an infinite diversity in structure, constitution, and habits, to be advantageous to them, I think it would be a most extraordinary fact if no variation ever had occurred useful to each beings welfare, in the same way as so many variations have occured useful to man. But if variations useful to any organic being do occur, assuredly individuals thus characterized will have the best chance of being preserved in the struggle for life; and from the strong principle of inheritance they will will tend to produce offspring similarly characterized. This principle of preservation, I have called, for the sake of brevity, Natural Selection." [Origin, p 127 6th ed.]

 

[Loudmouth]

Well, actually the only way to get diversity is thru cladogenesis -- a species splitting into 2. If one species simply transforms into another species (anagenesis), you still only have 1 species and you don't get diversity.

Thanks for the clarification. That's what I meant to relate, and you have stated it very succinctly here.

Why don't you look at the definition Futuyma gives and use that one.

It's a bit clunky, but it's a very good definition. The problem with these types of forums is that complicated and long definitions will probably be ignored or glossed over.

These are really poor mechanisms. They are going to get you into trouble.

1. You have put genetic drift in with natural selection. Please don't do that. Apples and oranges.

Both are stochastic processes that filter alleles. Why can't they both fit under the heading "differential reproductive success"? Whether reproductive success is due to negative, neutral, or positive selection it is still differential reproductive success. Or am I missing something?

2. Speciation is reproductive isolation.

Speciation is more the RESULT of changes in allele frequency, not the cause of change in allele frequency.

Reproductive isolation can also be due to geographic isolation which is not driven by changes in allele frequency.

However, I will put up Mayr's argument:

" 'Evolution' implies change with continuity, usually with a directional component. Biological evolution is best defined as change in the diversity and adaptation of populations of organisms." pg. 47

"No Darwinian I know questions the fact that the processes of organic evolution are consistent with the laws of the physical sciences, but it makes no sense to say that biological evolution has been "reduced" to physical laws. Biological evolution is the result of specific processes that impinge on specific systems, the explanation of which is meaningful only at the level of complexity of those processes and those systems. And the classical theory of evolution has not been reduced to a "molecular theory of evolution," an assertion based on such reductionist definitions of evolution as "a change in gene frequencies in natural populations." This reductionist definition omits the crucial aspects of evolution: changes in diversity and adaptation. (Once I gave a lump of sugar to a racoon in a zoo. He ran with it to his water basin and washed it vigorously until there was nothing left of it. No complex system should be taken apart to the extent that nothing of significance is left.)" Ernst Mayr, Evolution, Scientific American 239: 47-55, Sept. 1978.

I agree that reductionism ruins much of biology. It's a problem that I run into in my own research. I am leaning more and more towards the attitude that evolution is an emergent process. I think this can best seen in the popularity of evo-devo over the last 15 years. In the same way that morphology is an emergent property of dna regulation, so too might evolution be an emergent property of many different mechanisms that affect populations. Just a thought.