White Tigers and Darwin's Irreducible Complexity

a reply to: Trihalo42

Random cannot happen, because no matter what you are doing "randomly", you are limited by the pool being randomly chosen from. Even random numbers....you are selecting a number from a finite "set" of numbers.

That said...heredity isn't a limit. Mutation is action outside of hereditary traits.

But for the most part, yes....genetic drift has more to do with selection for genes that express an advantagous trait in a competitive environment. Then you get periods of explosive evolution when a new capability is made available. For example, the explosion in diversity of birds once they were able to gain flight. The term is "punctuated equilibrium".

I've always considered both the chicken and the egg came first.

a reply to: Trihalo42

The conspiracy / point of debate being a promotion of "random mutations" and "natural selection" being the entirety of evolution, while side stepping hereditary traits being a limit on how random those mutations can be, as illustrated by Tyson's tweet.

It's genetic mutations, not strictly random ones. They aren't all random, they have many causes. The only thing random is which genes mutate. Hereditary traits are affected by genetic mutations, so it only reinforces that genetic mutations and natural selection do make up the vast majority of evolution. Tyson's tweet was dead on. Hereditary isn't being side stepped and there is no limit.

Your problem with IC isn't a real problem. Creationists have used flagella as one of their primary cases for IC, which is why it has been specifically addressed. When scientists demonstrate that it could indeed be formed in stages rather than all at once, it debunks that concept. The eye is also one of the things that is claimed to be irreducibly complex but that is false as well because models have been designed that show exactly how the eye COULD evolve in stages. The only time people claim IC is when they don't understand the science. To this day, no organism has ever been proven to be irreducibly complex.

Instead of attacking the dumb chicken and egg quote in the OP, I would rather have more discussion about the question he raised about white tigers. How can there be a whole species of white tiger if the gene for it's white coloration is not a dominant gene? If what he says is true, that white tigers bred with other tigers lose their white coloration, how could the white coloration of an entire species be the result of evolution? Interbreeding between the ancestors of white tiger should have eliminated the white coloration entirely.

originally posted by: AnuTyr
yeah kinda but not really. Micro-organisms build the complexity of the world. Not mating. lol.
Enviroment forces the micro-organisms to evolve.

Erm, you can't have genetic mutations without mating (or self replication), so mating does build the complexity of the world, via micro organisms (and others as well).

And when those things change it causes diseases.

Can you be more specific, please? They don't always cause diseases, they cause beneficial changes as well.

I don't think Darwin could of imagined a whole plague could change a species in a couple generations and wouldn't exactly be *gradual* so much as a forced change.

Do you have an example of a plague that could change a species in just a couple generations? A plague could wipe out a whole bunch of species that aren't well adapted to the change, but the change itself via genetics still happens slowly over time. If not there would be no difference between the survivors and the non survivors. A plague may change which species become dominant in an environment, but it doesn't physically change the DNA in most cases, and certainly not just in 2 generations. Yeah it can happen, but it's rarely advantageous so usually the organisms die, although retroviruses have been responsible for certain evolutionary changes.

Niches are created which then breed and carry on their legacy. It's not so much the organisms wanted to change that way it's that the environment becomes hostile forcing everything to change a long with it.

Bingo. It's all the environment changing. The species already have changed prior to the event in question.

Darwin had it sorta right but not exactly.
he put more faith into Cross breeding than understanding how a global temperture change or drop in oxygen would shift all the life that is there. It would be to hard for his brain to come to such a realization several decades ago. I said several. I could of said Dozens i guess but 150 years isn't very long.
It's like a bat of the eye. It's like a sea turtle dying and having it's life flash before it's eyes.

He did pave the wave for genetics tho. Besides that. the dude was not 100% correct.

Darwin was the very first to make the evolutionary ideas public. There were people before him that suspected it as well, but with such opposition from religious folks they had to tip toe around the truth and keep their hypothesis secret for a while. Darwin did have it right, he just didn't have the full picture. Yes, sex is a huge part of natural selection. It's not the only part but a big part of it because conception is when most genetic mutations happen. Darwin was unaware of this mechanism, but was still correct that slight change adds up over time and the better adapted organisms survive.

And don't forget Dawins, * only the strongest will survive* mentaility. He had litte understanding in symbiotic relationships and how they build up the complexity we see today....

Such as ants protecting trees and plants. And plants altering their physical appearance as well as providing all the nutrients the ants would need to survive so the ants can defend the tree lol.

Again, that doesn't make him wrong. It shows he didn't know everything. Today we know significantly more so invoking Darwin is a bit silly to me. It's like invoking Galileo when discussing black holes and Quasars. Survival of the fittest is a fact. Yes some organisms work together to survive. I don't see how that makes him wrong, except in the fact that he thought levels of competition were always greater amongst species that weren't as closely related. This was a lesser known hypothesis that he proposed, but we know now that it isn't completely true.

However Darwin bought up some trouble for us by making it seem like we can just slay things and the enviroment will just cope with it.

He did? Can you give me some examples? From what I remember, it was the BIBLE that gave humans the idea that all plants and animals on the planet belong to them and their lives aren't as valuable as humans. If we indiscriminately just "slay things" we can cause extinctions. Yes, the environment will overcome it in most cases, but that doesn't give us the green light to go around killing everything we see.

originally posted by: peskyhumans
How can there be a whole species of white tiger if the gene for it's white coloration is not a dominant gene? If what he says is true, that white tigers bred with other tigers lose their white coloration, how could the white coloration of an entire species be the result of evolution? Interbreeding between the ancestors of white tiger should have eliminated the white coloration entirely.

I don't understand the problem. The white fur trait of those tigers probably emerged during one of the last glacial periods because it helped them blend in and hunt in cold snowy environments. It not just all interbreeding, it's also natural selection. And yes, the white fur gene IS dominant amongst the white tiger species, although I'd bet that a certain percentage are still born orange. The white ones just stuck to the snowy environment while the orange ones kept to the jungles and plains with vegetation that helps camouflage them. Just look at where these 2 species live.

It seems logical that Bengal tigers were split up at some point and a bunch of them had to migrate to a different environment. Over hundreds of thousands of years they adapted to it because white fur was very beneficial. If a regular bengal tiger was born with white fur in Africa, it probably gets killed. This is why the traits are not dominant at first. You might start out with just 1 out of 100 tigers are born with white fur, because orange is dominant. But after the environment shift, the birthrate of the white furred tigers increased because they survived more often than orange in the new environment and passed down more genes. Given enough time, that could change it enough so that only 1 out of 100 are now born orange within the species or sub-species. The white fur becomes dominant in the given environment.

I don't think it's coincidence that the last glacial period ended 10.000-12,000 years ago, and that white tigers are becoming extinct. Part of it is humans hunting them as well, but they just don't blend in like they used to and now, the only known ones left are in captivity. There could still be some out there somewhere, but they haven't been seen in the wild since 1958. Perhaps when the next glacial period comes, they will rule again.

I hope I explained that thoroughly enough.

originally posted by: peskyhumans
Instead of attacking the dumb chicken and egg quote in the OP,

Actually, it's not a dumb quote at all. it's simply abbreviated. I mean you can only fit so many words into a tweet, and he actually nailed it down with what he had at hand.

I would rather have more discussion about the question he raised about white tigers. How can there be a whole species of white tiger if the gene for it's white coloration is not a dominant gene?

well, there's not a "whole species" of white tigers, any more than there's a "whole species" of siamese cats. They're a color variation, nothing more. Specifically they are a color variation in the bengal tiger, which is a subspecies of the one tiger species on earth, Panthera tigris .

And there are (roughly) two kinds of genes. Dominant, and recessive. in the case of tigers, let's say htey have one dominant gene for fur color (orange, your 'typical" tiger color) and a number of recessive genes for fur color (white, melanistic, 'golden,' spots instead of stripes, that sort of thing). Each offspring receives one gene from each of its parents for fur color, for a total of two genes for that particular trait.

if the tiger has two copies of the dominant (orange) gene, he has orange fur, and no chance of passing on a color varietal recessive gene to its offspring.

if hte tiger has a dominant (orange) gene and a recessive (whatever else) gene, then he will be orange, but can still pass the recessive gen on to his descendants.

if the tiger has two matching recessive genes, hew will express that gene's information in his phenotype, and will not be able to pass on the dominant gene to his offspring.

This is all sort of "basic outline" stuff, there's a lot of in-betweens and variables - between two recessive genes, for instance, one will act as dominant, (melanism is usually dominant over white fur in felines). Certain mutations could create a situation where both the "normal" color and the varietal act as domiannt, resulting in a weird patchwork or blend... but generally, it works like..

D/D - Animal expresses domiannt gene, can only pass on that gene.
D/r - animal expresses domiannt gene, but can pass on either dominant or recessive genes.
r/r - animal expresses recessive genes, and can only pass on recessive genes.

If what he says is true, that white tigers bred with other tigers lose their white coloration, how could the white coloration of an entire species be the result of evolution? Interbreeding between the ancestors of white tiger should have eliminated the white coloration entirely.

Yup, because white coloration is recessive against orange, as far as tigers are concerned. if you breed a white tiger (r/r) with a "normal" tiger with no white ancestors (D/D), all the offspring are going to be D/r - they will be orange-furred, but all will carry the recessive gene.

Now, here's where you get white tigers - inbreeding. massive, massive amounts of inbreeding. It's like how you 'set" a breed of dog or cat, basically, you breed offspring back to parents, siblings, close relatives that you KNOW have the genes for the trait you want. As progressively more and more animals are born with the recessive trait, you are "isolating" it, until you have a lineage of animals that have nothing but the recessive trait floating around in their genome.

it has nothing to do with natural selection - in fact white tigers are selected against by natural selection. it's just that every now and then, a mutation appears in the tiger genome that causes white tigers to pop up - and htne very quickly fade away, if nature is left to its own devices... Which is why every single white tiger you see today is bred by humans, from lineages bred by humans for generations, tracing themselves all the way back to a pair of animals held by some Indian prince or other back when the British took over the subcontinent.

They are greatly inbred, especially since - unlike dogs - there wasn't a large pool of material to work with. You can create and "fix" a dog breed that has enough genetic variability to still be healthy, by collaborating with other breeders to all follow the same guidelines, using different pools of dogs to start with. but tigers are... rather less common than dogs, obviously and so limited supplies meant a lot of direct offspring-to-parent matings... And let's just say that white fur isn't the only recessive trait that can get isolated this way. Essentially any and every recessive gene the parents possess can be distilled down in this way, which is how you get blind, deaf, deformed tigers with white fur so often.

a reply to: Trihalo42

Any complex multicellular organism that reproduces sexually is governed by hereditary traits. An organism that has a trait that is not shared by the general population that then breeds with the general population will produce hybrids, provided the variation in genetics is not great enough to prevent viable offspring, and will eventually see that trait "bred out of the line". We see this effect in White Tigers. To preserve the trait that gives them their coloration, they must be in-bred, which has been declared inhumane and banned in most countries. If they are bred with the general population, they produce off colored hybrids and the next few generations see the trait suppressed / eliminated.

You are abusing the term "hybrid" here. The offspring from two parents are not called "hybrid"; they are called "children".

Please refer to the Wikipedia article: Hybrid (biology)

If a parent has an allele that is advantageous to its breeding cycle, that parent will have more chance to pass that allele to its descendants. "Recessive genes" do not get "bred out of the line" - the idea is absurd. If recessive genes got bred out of the line" then recessive genes would not exist.

Please refer to the Genetic Science Learning Center article: What are Dominant and Recessive?

Animals that are bred 'unnaturally' (say lions and tigers) produce "children" who are considered "hybrids" because they are from different species that do not interbreed naturally. There are several different methods of producing hybrids. Not all hybrids are mules - this fact is a major reason that biologists no longer attach much meaning to the term 'species'. It is still a useful term as a general descriptor, but the old definition is no longer valid and no satisfactory new definition has been found.

Animals that breed 'naturally' do not produce children that are hybrids; they produce children who are slightly genetically different than themselves because the DNA replication is never perfect. The imperfect DNA replication is called 'random mutation'. One mutation does not make a different species. One mutation makes a child with a slightly different DNA profile. If that one mutation helps the child reproduce better, then the mutation will spread into the population. The spread into the population is called 'natural selection' and the population is said to evolve. Repeat: the term "evolution" refers to the change in the population, not the individual.

White Bengal Tigers occur naturally in the Bengal Tiger population, however they have not been seen in the wild for many decades (at least in part because the population is so small now - less than 2500 individuals). They are not the result of hybridization, though some people have cross bred White Bengals with Sumatrans to produce White Tigers which are highly prized zoo specimens, but the gene pool remains exceedingly small.

White Tigers are certainly bred with "the general population" in a process known as 'outcrossing'. Outcrossing is a way of bringing fresh blood into the white strain to avoid the problem of inbreeding (breeding closely related individuals). In such a breeding program, some of the cubs will be 'normal' orange and some will be white. However, because the gene pool is still quite tiny there are continuing problems as a result of inbreeding and the Association of Zoos and Aquariums directed its members to stop breeding certain animals including the White Tiger.

Inbreeding causes many genetic problems in Tigers, white or not, just as it does in most other animals, including Humans. Every human population everywhere on the planet has taboos against inbreeding. The White coloration itself has nothing to do with inbreeding. Inbreeding problems occur because of breeding programs designed to produce White Tigers for display to the public in zoos (and Magic Acts in Las Vegas).

Finally, a complete scan of the genome led to the discovery that the white tiger’s distinguishing characteristic arises from a single naturally occurring mutation, the substitution of one amino acid for another—valine for alanine—in the protein identified as SLC45A2. The implication of this discovery means that white tigers can be bred from any colored Bengal tiger pair possessing the unique but naturally occurring recessive gene. So White Tigers can be bred without resorting to incestuous crosses - just modifying the protein will do the trick.

Please refer to the Wikipedia article: White tiger and the Wikipedia article Inbreeding.

a reply to: rnaa

Actually, "hybrid" is a perfectly valid term. It doesn't just mean "offspring of two species." it means any offspring generated by a combination of two different things in general. So yes, the outbred offspring of white and non-white carriers are hybrids between the two color variations.

Actually, "hybrid" is a perfectly valid term. It doesn't just mean "offspring of two species." it means any offspring generated by a combination of two different things in general. So yes, the outbred offspring of white and non-white carriers are hybrids between the two color variations.

a reply to: TheTengriist

No, you are wrong. Offspring between two Bengal Tigers, one white and one orange are Bengal Tigers through and through, they are merely natural children. However, a cross between a Bengal Tiger and a Sumatran Tiger could be called a hybrid and since it is fairly common to make such crosses, you are fair to use the term in that sense, however that is not the sense you are using it, and that is the part I am objecting too.

Since you obviously failed to read or comprehend the link I provided, I'll repeat the definition here:

In biology a hybrid is an offspring of two animals or plants of different breeds, varieties, species, or genera.

White Bengals are not a different breed, variety, species, or genera than orange Bengals anymore than brown eyed humans are a different breed, variety, species, or genera than blue eyed humans. You are not a biologic hybrid of your parents, that would be an abuse of the term.

Furthermore, I am also objecting to your understanding of the concept of recessive and dominant genes and this is a much more important error. Recessive genes do not necessarily breed out of the gene pool, else there would not be any such thing as a recessive gene in any population (except those that result from 'recent' random mutations).

If your OP actually had a point other than to ask for clarification of these two biological concepts, I missed it. Could you try again with clarity?

a reply to: Trihalo42

On rereading your OP, maybe I found the point you were trying to make:

There is still quite a bit of confusion in the general media and among some media icons about this. Neil deGrasse Tyson tweeted, "Just to settle it once and for all: Which came first the Chicken or the Egg? The Egg -- laid by a bird that was not a Chicken". To which several of us replied that you cannot breed a not-a-chicken with a chicken, so there would be no way to produce offspring. If you were to have an almost-a-chicken and breed it with a chicken, you'd still get hybrids, which could result in the new traits being bred out of the line.

This statement, while a clever rejoinder seemingly hoisting a scientist by his own petard for the benefit of non-thinking readers actually just exposes your misunderstanding of evolution, biology, sex, and possibly the English language.

First and most obvious, Tyson did not suggest breeding a 'not-a-chicken with a chicken'. English is perhaps not your first language, I'll give you a pass in that case. You repeat your misunderstanding of recessive traits being 'bred out' of the gene pool, but I discussed that above so I won't repeat it.

What Tyson said in his little tweet is:

• a not-a-chicken bred with another not-a-chicken and produced a slightly-different-not-a-chicken
  
• that not-a-chicken bred with yet another not-a-chicken and produced a slightly-different-not-a-chicken that was a bit further different from the original not-a-chickens
  
• that went on for many generations and the original population of not-a-chickens have changed from not-a-chickens into no-longer-a-not-a chickens and beyond to 'almost-a-jungle fowl' (this does not preclude that another population of not-a-chickens is going merrily on its not-a-chicken way somewhere else - we're are only talking about 'this' population of what used to be not-a-chickens and are now almost-a-jungle-fowls).
  
• a almost-a-jungle-foul bred with another almost-a-jungle-foul and produced a slightly-different-almost-a-jungle-fowl
  
• this continued for many more generations until the population was became jungle-fowl.
  
• then man got involved and noticed that when they put nice fat jungle fowl in a cage they produced nice fat jungle fowl chicks and when their neighbors used skinny ones they got skinny chicks.
  
• so they kept selected nice fat jungle fowls to breed and ate the skinny ones first
  
• pretty soon they were getting consistent results with their captive starting-to-be-different-than-jungle-fowl that were much nicer to eat than the wild jungle fowl.
  
• other breeders probably found a similar way to improve the egg laying process. Maybe they were neighbors or nearby villages and they traded breeding birds
  
• after many generations of human selective breeding of the jungle-fowl they had changed the population of birds they were working on to the point that they were almost-a-chicken and after even more generations they had - you guessed it - chickens
  
• a few more generations and they had Rhode Island Reds and Silkies and Australoops and on and on and on
  

It isn't a question of breeding a not-a-chicken with a chicken. It is a question of the evolution (via natural selection or selective breeding) of populations.

Anyway, Tyson is saying that there were eggs before there were chickens which is undeniably true, no matter how you try to twist his words or try to make silly retorts.

a reply to: rnaa

There's no need for the hostility.

I would certainly argue that white bengal tigers are a "breed" or "variety" - at least as much as any breed of domesticated animal. After all, their continued existence and prevalence is wholly dependant on the selective breeding by humans for reasons of aesthetic quality.

And yes, I'm aware that my writing on how genes work wasn't 100% absolutely thorough - I was writing a forum post on the internet, not a college thesis. I went with a basic (text-based) punnet square example for brevity and ease of access for someone who seems to have not had it down quite so much.