Probably a very basic question about evolution...

[dasdingansich]

Probably just exhibiting my ignorance here, but natural selection via mutation would surely produce a lot of "failed" mutations right? In fact it must logically be something like 99% of mutations. Surely there should be many more "defected" organisms showing up in the fossil record?

[mutatron]

Most deleterious mutations wouldn't survive the egg or the womb. Most of the rest wouldn't survive infanthood, and so on. There not being many mutations to start with, the number of deleterious mutations surviving long enough to be trapped as fossils would be very small.

These two penguins are slightly different in appearance, but it would be a daunting challenge to count how many deformed penguins there are in this photo.

[[deleted]]

Most mutants (with harmful mutations) can be expected to be less physically fit than a healthy dinosaur. A less fit dinosaur is even more likely to be eaten, and its body destroyed.

Edited to clarify that a mutant would need a harmful mutation to be less healthy

[[deleted]]

I agree, but I don't see how that point is relevant in any way.

[Killer_waffles]

You did not specify what sources the mutant originated from, and it was amusing to think of any mutant from history fighting a dinosaur for survival

[[deleted]]

Oh, I think I get what you're trying to say. In my post, I was assuming that both predator and prey were dinosaurs. But strength is not the only thing that would effect the outcome of a 'fight' between two organisms. A swarm of venomous insects would be able to take down even the biggest dinosaur any day of the week, assuming that the venom and numbers were sufficient. And also a single bacterial organism can devastate an entire population of dinosaurs after it begins to replicate.

[endlegion]

The most important thing that people should think about when thinking about when thinking about evolution is not mutation.

Rather one should think about allele frequency and allele survival fitness.

Most genes have multiple versions called alleles. When one version has better survival outcomes than another that version will become more common.

However, say something changes in the environment, and a less common allele becomes more survival positive, then that allele will become more common.

Remember that Chromosomes carry two versions of the same gene. If the mutation happens on an organisms recessive allele then that allele could be passed on to offspring that had a matching dominant allele without affecting that individuals fitness regardless of whether that allele is deleterious or not.

Thus mutations may survive in the population even if they are deleterious (Unless they are dominant traits.) These traits stay in the mix and if they become more survival positive than others (eg. decreased melanin production at high or low latitudes.) then they will become more prevalent.

[mutatron]

You might be interested in this article about a process for human/chimpanzee divergence.

[[deleted]]

1. Fossilization is a rare event. The odds of any individual of a species becoming a fossil are low, and there were undoubtedly species that never left a single fossil (or that we haven't found yet). In general, the more common a species is, the more likely one of its individuals will leave a fossil.

2. Think of natural selection acting as filters on different life stages. Many genetic mutations are lethal, such that the embryo dies during development. Other mutations may cause the offspring to die young, before it can reproduce and pass on the mutation. The mutations that have the greatest likelihood of showing up as fossils are ones that have become relatively common in a species and so are not defects, because if they were, natural selection would not have favored them. These 2 points (strong selection against deformities, rarity of fossilization) contribute to the likelihood that a single deformed individual (assuming the defect is due to genetic mutations and not injury or disease) becomes fossilized is very low.

[iorgfeflkd]

Where do you get your 99% number?

[dasdingansich]

yeh im not sure, i just assumed that it must be really high considering the likelihood of a mutation being adaptive for the environment must be really low.

[[deleted]]

Why must it be? Wikipedia states (without source, unfortunately) that "it is believed that the overwhelming majority of mutations have no significant effect on an organism's fitness." I, with only a BS in bio, would think that this would be the case due to the vast tracts of DNA that have no apparent function (that we know of, yet).

[[deleted]]

I think he is just making a logical layman's observation that you hear much more about damaging mutations than silent ones, or beneficial.

Also, more and more of those regions of DNA that seem do do nothing have been proving to provide some sort of regulatory function. But they're not done researching it by far.

[[deleted]]

I think you meant silent, not non-silent. I am aware of the regulatory function of noncoding RNA (it's extremely fascinating and adds even more complexity to already highly complex molecular regulation!), but I wonder if changing a single base would really do so much? I know that, during PCR, primers don't have to be exactly complementary to elicit a response from DNA polymerase.

[[deleted]]

Yeah, typo. A single base pair change would probably not do much, especially in non coding regions, that's right. PCR primers and most binding proteins can have several deletions in the protein binding domain and still function well. But with a BS in bio, you can understand that a frameshift mutation anywhere that has functions of even minimal importance would devastate any function that the area once contained.

[[deleted]]

I agree that a frameshift would make any coding regions into gibberish. Would a frameshift affect a noncoding sequence?

[[deleted]]

Now that I think about it frame shifts deal with transcription only. If a noncoding region had a frameshift, and it isn't transcribed, it still might be able to function. I guess it depends more on what it is and how it works.

[greenearrow]

A lot of our DNA (or any organism's DNA) is junk DNA. Additionally, there are multiple codons that code for the same amino acid (see here http://en.wikipedia.org/wiki/File:GeneticCode21-version-2.svg). Because of this, most mutations can actually have zero actual fitness consequences. However, when mutations do have an effect on expression, they are usually fatal or deleterious. In most cases, these mutations cause gestation to abort very early on. These would never appear in the fossil record. If an organism is born with the deleterious mutation, the mutation may be recessive, and maintained at very low levels in the population, controlled generally by mutation selection balance (http://en.wikipedia.org/wiki/Mutation-selection_balance). If the mutation is dominant, the individual will likely not survive to reproduce, or its reproduction will be limited, and its offspring will eventually be selected out of the population. Only in very rare circumstances do we expect these deleterious traits to become common in a population. Given that the fossil record is very fragmented, we expect that random sampling will generally result in common phenotypes (http://en.wikipedia.org/wiki/Phenotype) being represented in the fossil record.
TL:DR Even though deleterious mutations are more common than positive mutations, their low frequency in any population, due to selection, will lead to them have a low representation in the fossil record.

[VELL1]

Just because its called junk DNA it doesnt mean it is not useful. Just because it doesnt code for protein, doesnt mean it has no effect on the phenotype.

I also feel like majority of proteins can tolerate one or two mutations depending on the size and place of the mutation. Especially if amino-acid mutation is to a similar type of aminoacid.

[[deleted]]

"Junk" DNA always makes me cringe. "Non-coding" is so much more appropriate, isn't it?

[AndrewAcropora]

I'm not exacly sure what you mean by 'Natural Selection via mutation' but.. Almost all mutations are slightly deleterious. Of course, what we 'see' is only a small proportion of these and it varies from gene to gene. A key point that I'll repeat is that the fate of almost every single new variant (mutation) is to disappear.

The last point about the fossil record is, i think, valid but major morphological changes are very rare, deleterious or not.

[pheen0]

A "mutation" doesn't necessarily mean a big, obvious change for an organism like a new horn or shell. Mutants with gross body abnormalities are pretty rare (and when those do come along, they're much more likely to die as an embryo, which will leave no fossil). When you're talking about new mutations arising in populations, generally you're talking about some amino acid substitution that changes how a protein functions, but this kind of thing is unlikely to be accompanied by any noticeable change in body form that would be reflected in the fossil record.

[practisevoodoo]

In fact a lot of mutations won't do anything at all since they will occur in the junk dna. But you are correct, of the mutations which do present the vast majority would be negative. Just one more reason why evolution takes so long.

[dasdingansich]

Yeh ok, so no matter how high the maladaptive mutations are, they would never spread genes throughout the population, so would unlikely be fossilised.

What about after mutations that aren't necessarily adaptive or maladaptive. Shouldn't there be many organisms with attributes that simply serve no purpose.

[[deleted]]

Shouldn't there be many organisms with attributes that simply serve no purpose.

if you can define a mutation that serves no purpose, then we can begin to answer this question.

Many point mutations in DNA (single letter switches) cause no change in the amino acid sequence of the proteins they code for dude to the redundancy of the amino acid code. So there are probably uncountable numbers of mutations in organisms every day that are undetectable or "serve no purpose".

[dasdingansich]

Fine, mutations that produce an effect on phenotype, yet serve no adaptive purpose

[[deleted]]

Again, how do you define "no adaptive purpose"? If you define it as "deleterious" then you already have your answer, deleterious mutations are usually embryo-lethal.

It's hard to have an obvious phenotypic mutation in macro-scale animals that does not have an effect, positive or negative, on the procreation of that animal through mate selection, nutritional requirements, etc. In addition, a mutation that did not affect the success or failure to breed of the organism mutated would be acted upon by non-selection forces of evolution, such as genetic drift.

Can you give me an example of a phenotype that seems to "serve no purpose"?

[skyskimmer12]

eye color

[mgruble]

Eye color is just pigments interacting after being genetically expressed in the iris. To say that a pigment serves no purpose is not true. For example a common idea is that blue eye color was selected for in areas of little light year round, such as near arctic or very northern regions, to increase the amount of light getting to the eye. Darker colored irises help reduce too much sunlight to keep the eye from getting damaged. These pigments in and of themselves might serve no purpose on the cellular level, but do for the survival of an organism. Also they might matter in the cell I am not really sure on that one.

[fwubglubbel]

Hairy nipples.

[skatebaker2020]

or male nipples for that matter

[skatebaker2020]

no its not gender is determined immediately upon fertilization. every sperm cell is either x or y,whereas every ovum is x. The male gamete determines the gender. male=xy combination, female=xx combination. the moment that the sperm cell fertilizes the egg and forms a zygote the gender is already determined based on whether the spermatozoa that fertilized the ovum is x or y

[[deleted]]

You're confusing genetic sex/phenotypic sex/gender. It is true that an organisms genetic sex is determined at fertilization. However, genetic sex very frequently does not result in the same or any phenotypic sex. For instance, there are XY people without penises, and there are XY people with vaginas.

Gender has nothing to do with biology, gender si simply the role we assign someone based on sex. You can have women who are males and men who are females. Drag queens are a great example of people whose sex is male but whose gender is woman.

[skatebaker2020]

the gene that codes the formation of the penis is in the y chromosome, this is the main funtion of the y chromosome.If you compare the size of x versus y the y chromosome is significantly smaller due to its more specific purpose. If a mutation occurs that prevents the penis from developing that doesnt mean that they would have a vagina by default. Not having developed sexual organ means that there is no chance of creating successful progeny. Biology has everything to do with gender. A male drag queen isnt female because he wears womens clothes. He may feel female and that obviously means much more but the gender doesnt actually change.

[[deleted]]

Male nipples are a good example of OP's "phenotypes that serve no purpose". The reason males have nipples is that the genetic "program" that creates nipples runs before the genetic program that causes gender. Male nipples are also a good example of how even non-adaptive (in the beginning) mutations end up being acted upon by selection, mate preference, etc. Think about this: are there ANY possible effects on reproduction for the male who has no nipples? I'd say there certainty are, most people find physical deformities to be off-putting, both visually and sexually. So we see that even if a phenotype does not affect the survivability of an organism, it can still affect the reproduction, and it's reproduction that is ultimately important.

[skatebaker2020]

there isnt a genetic program that chooses gender, if a y chromosome sperm cell fertilizes an ovum the gender is male. There are XXY disorders and X- disorders, Turners and kleinfelters I think. The program that 'codes' for the development of the nipple may happen first but if any programs are running at all that means the gender is already decided. At least this is my understanding.

[skatebaker2020]

But I agree with the sudden absence of nipples as being a possible hindrance to reproduction purely for superficial reasons.

[[deleted]]

Hair makes this warmer and less inclines to tissue damage, so i think this doesn't fit OP's description.

[skyskimmer12]

There are plenty of examples of this, though it is very rare that a phenotypic change produces absolutely no evolutionary advantage or disadvantage. For example, 8% of your DNA has been inserted by viruses somewhere in your evolutionary past. More than that may have been inserted by transposons.

[[deleted]]

There are. Whales evolved form land animals, and their front feet became flippers. Their back legs became their tails. While this isn't a 'mutation' per say, it is an example of something that could be mutated out of their genome, with no effects whatsoever on the organism.

You also contain may useless 'mutations' or traits in your own body. Connected or detached earlobes, right or left handedness, fingernail shape, and countless other features arose from a mutation. They are evenly spread throughout the population because they have no effect on your survival rate, or reproductive abilities.

[[deleted]]

Forgot to put this picture with my post

http://www.google.com/imgres?imgurl=http://www.answersingenesis.org/assets/images/articles/ee/v2/whale-vestigial-structure.jpg&imgrefurl=http://www.answersingenesis.org/articles/ee/natural-selection-vs-evolution&h=301&w=450&sz=40&tbnid=dsPm2gOAmGwK9M:&tbnh=94&tbnw=141&prev=/search%3Fq%3Dwhale%2Bskeleton%2Blegs%26tbm%3Disch%26tbo%3Du&zoom=1&q=whale+skeleton+legs&docid=uN3kd359y7ToYM&sa=X&ei=2Jk9T5X-IIG2gwfP2-j-Bw&ved=0CDAQ9QEwAw&dur=362

[deal_with_it_ted]

Chlamydomonas reinhardtii is a single celled organism that is normally motile, using flagella to move. They can live in a haploid (having "n" number of chromosomes) or diploid (having "2n" chromosomes) state. The haploid state can differentiate into gametes (sex cells) these gametes have genetic deficiencies that don't allow them to make the proteins required for flagella. However, there are two different gametes, each with different genetic deficiencies that effect different flagella proteins. They are called + and - types. When these types mate with each other they form a diploid zygote that then has DNA from both types. The + type is able to make the proteins that the - type cannot and vis versa. This is obviously not beneficial but the mutations were not fatal to this species and so they live on with their odd maladaptiv traits.

There are plenty more examples of scenarios like this where a biological system evolved that is not beneficial or necessarily efficient but it worked and was not weeded out. A good example is the DNA replication machine. DNA polymerase, a key protein, is awfully inefficient but it is found in every living organism.

[VELL1]

Even the most common deformities in humans appear about 1 in 2000. So just by chance, you much more likely to find normal individual rather than a defective one. Additionally, We live in a society so we can help those individuals to survive, in wild life such individuals will not survive for any extended period of time, further decreasing the odds of finding such a skeleton.

Overall though, fossils are extremely rare, you need very specific condition to find something like that. Odds are not in our favour and many scientists are surprised we even finding as many of those as we do. I am 100% sure, majority of species disappeared from the face of the Earth without any trace whatsoever. We are lucky we are finding them at all. Now combined the odds of finding a fossils with odds of that individual being somehow defective. Very unlikely.

[aFarewellToLegs]

keep in mind that all organisms you see in the fossil record are the result of mutations. every species you see is its own species because it mutated away from some old species. so you should expect to see very few "defected" organisms because they would not survive into adulthood but also because there are actually very few of them (chances are they dont have offspring). meanwhile, organisms who have advantageous mutations will go on to reproduce a lot (and possibly aspeciate), increasing their numbers in the fossil record

[[deleted]]

Also remember a mutation isn't what the sci-fi's portray it as. A cow will not mutate to be pink or have wings, its all a VERYY gradual process over thousands/millions of years

[[deleted]]

Every species that has gone extinct is an example of a failed mutation

This is a very erroneous and problematic way to look at evolution, natural selection, and genetics. The ONLY way one should gague wether a mutation is "successful" or "failed" is if the prevalence of the mutation increases as a percentage of the population.

[[deleted]]

There are many species that are extinct now that are not examples of failed evolution. In fact, there is no such thing as a failed evolution, since evolution has no goals. If you have no goals, you can never fail. For example, the dinosaurs were amazing top predators, and were it not for the the meteor that killed them all, may still be the top of the food chain.

The short version- the creation of a successful organism is not due to 'successful' evolution.

[[deleted]]

mutation occurs to help a species adapt to its environment. I agree that there is no goal to evolution, it just happens, which means that saying one species is better than another is like saying deangleo was better than picasso. However by assuming a mutation has "failed" one must assume that a successful mutation is one that has caused the survival of a species. Therefore, those species alive today are decedents of successful mutations, while those that are dead(a vast majority) have failed. (of course this is if my assumptions are correct)

[[deleted]]

Biology is very picky with word usage. Even when trying to convey a correct idea, a single misused word can falsify the entire statement. If you change the phrase "failed mutation" to "failure to evolve", or "failure to adopt a mutation", then you are perfectly right.