What measure is microevolution?

[Ngakunui]

It's a simple question, and don't dumb it down or just respond with an "because it is". Things like this tend to have more depth than that. Everything I read here involving micro/macro evolution is rather assertive and not the most informative; being cited for the sake of trying to quickly "solve" and argument.

But I'm not asking for a debate, or arguments; I'm asking for information, preferably from different sides that is neither assertive, brief, nor disingenuous. I'm asking for you all to humble yourselves and not derail this into an argument.

What measure, when it comes to adaption, is the difference between micro-evolution, and macro-evolution? How much or how little of a strain is it for a creature's offspring to become a different species, and why? What are the natural examples of either both or either, and how is this supported beyond simply stating that it's by "years and years of research and lots of people believe it"?



If you can give me very to-the-point, humble, and neutral answers, you have my thanks.

[Canuckster1127]

Microevolution is relatively short-term and is supported by genetic research that examines the genes and allules and can demostrate the modification and adaptation of a particular species.

Macroevolution is the extension of microevolution back over great periods of time by inference to explain speciation and the modification and changes of life through the process of natural selection.

The terms microevolution and macroevolution are not commonly used in the scientific community. The terms are used more on a philosophical level by those (and I'm among "those") who want to differentiate between those elements of evolutionary theory that are based on direct observation and measures, versus those that extrapolate back.

So in that regard, in terms of measure, the general difference is that microevolution is directly observable and provable, while macroevolution is based on inference and is not provable to the same degree. Most christians who do not hold or believe in evolution as it is taught or understood at a large scale, accept microevolution and recognize that there is a process of change and adaptation that over time impacts the genetic makeup of species.

[kmr]

Yes, as Canuckster1127 said. Also I might add that microevolution deals with the same alleles, just different combinations and no new dominant genes produced (usually), while macroevolution deals with the increase of dominant alleles for different functions in chromosomes over time.

[zoegirl]

i'm struggling with a virus right now but i will add my .02 ...just need to get over this awful-ness

[zoegirl]

It's a simple question, and don't dumb it down or just respond with an "because it is". Things like this tend to have more depth than that. Everything I read here involving micro/macro evolution is rather assertive and not the most informative; being cited for the sake of trying to quickly "solve" and argument.

But I'm not asking for a debate, or arguments; I'm asking for information, preferably from different sides that is neither assertive, brief, nor disingenuous. I'm asking for you all to humble yourselves and not derail this into an argument.

What measure, when it comes to adaption, is the difference between micro-evolution, and macro-evolution? How much or how little of a strain is it for a creature's offspring to become a different species, and why? What are the natural examples of either both or either, and how is this supported beyond simply stating that it's by "years and years of research and lots of people believe it"?



If you can give me very to-the-point, humble, and neutral answers, you have my thanks.

Bart is correct when he says that the two terms aren't in usage now; however, they have been rather recently (my previous AP bio text used them and that was only 4-5 years ago when the term was used in science texts).

In evolutionary terms, often reproductive isolation is a measure of how much two populations have diverged genetically. Essentially this is looking at the process of speciation. Anything that blocks reproduction from two populations is, in essence, allowing mutations to build up that, in theory, would then lead to reproductive isolation even when the two populations have access to each other.

Prezygotic barriers would include anything that is preventing egg and sperm from coming together, hinders fertilization...

This would include
1. Habitat isolation-they are separating from coming together
2. Temporal isolation- northern variations may bloom later, or come out of hibernation later
3. behavioral isolation- anything that might change courtship behavior could prevent males form successful mating
4. mechanical isolation- snails can have two different "spirals" and these two variations then cannot mate
5. Gametic isolation- mating can occur, but the sperm either cannot survive or lack the proper protein receptors that signal fertilization

So any of these changes would prevent sperm from getting to the egg (preventing mating, preventing pollination, etc) and that can lead to reproduction isolation and therefore potentially leads to two species (or at least two populations that do not interbreed)

Some species can interbreed but have post-zygotic barriers...some offspring are sterile (mules) or the hybrid have reduced viability or reduced fitness (the phenotype means that they do not fit with either of the parental habitats)...

In some cases with plants (and a very few cases with animals), we do see speciation that occurs because the entire genome replicates and we see a tetraploid cell (with 4 copies of the chromosomes) instead of 2. In this case the sperm and the egg cells would not fertilize.

In historical context, macroevolution has been used to refer to accumulations of changes that lead to different species over time....it also sometimes refers to those changes that we do not observe or test in real-time but use genetic histories or morphological changes (fossils or DNA changes) to infer changes.

With regards to experimental evidence, there is plenty of evidence for plant speciation (with the examples above with tetraploids) and also for changes in morphology leading to differences in pollinators or timing. In a classic experiment with fruit flies, after 40 generations with different diets, some fruit flies only mated with those that were raised with the same diets....it showed a *preference* for mating which, in theory, could lead to a more solid reproductive isolation. Sexual selection can also affect mate choice and therefore potentially leading to isolated populations.

All of these are intriguing but we are still left with a big gap that must be filled with "accumulations over time"...since we are limited to lifetime studies. There are clear lines and blurred lines and we are left with trying to piece together genetic puzzles.

An interesting book to read is Behe's new book on limits of microevolution called "The Edge of Evolution".

I'm not sure if these have answered some of all of your questions....what else would yoiu like to know?

[Jad]

I too am curious about this because I am in discussions with an evolutionist who sees macro/micro evolution a lot different to what I do. This person believes that given enough time macroevolution can occur and that makes all the difference in the world concerning the two. Whereas I am saying you can have all the time in the world and still there is no genetic mutation or evolutionary process that increases the information in the genome, and that to me makes all the difference in the world. Time is not a necessity for me on this issue because it all comes down to the increases of information in the genome and whether or not that is possible. That is where I place the difference between macro and micro. This person places the difference in the time it takes, that given enough time macroevolution can occur.

Would it be correct to say that time is not the deciding factor between the two, that time is not necessarily the primary factor here?

[zoegirl]

well, time would certainly influence the process, but as you say, one would have to see whether mutations can really provide the necessary changes. Behe's new book has some interesting examples that show some of the limitations.

[kmr]

I am in a similar place as Jad. If mutation occurred in an allele, it usually would create a non-functioning allele, often would create a recessive allele, but rarely would create a new dominant allele, and even so this would just replace the old one, with no new amount of DNA. Is there some way that new dominant genes can be produced without just replacing or destroying the old ones?

[zoegirl]

Mutations have no inherent drive to produce dominant or recessive alleles. There are diseases or mutations that are dominant...polydactyli being a good example. It produces the six-fingered condition and it is dominant. SO is Huntington's disease but because it is not expressed until later in life, the allele is passed down during the reproductive time of life, so it is not selected against.

Chromosomes can be duplicated as well, both pieces as well as entire chromosomes. In this case you have an extra copy of the gene and mutations here would have no bearing on the original gene.

[proxious]

wonderful cogent thoughts here

[rajanpunj]

thanks to zoegirl for answer rarely seen on this site.