18 Apr 07
Originally posted by TheMaster37Could you explain this better? I don't remember my biology all that well. True, some subcellular structures do fix some mutations, but they miss some (otherwise no mutations/evolution would ever occur)...
Any flaws in the DNA of one parent are "fixed" by the corresponding DNA frmo the other parent.
18 Apr 07
Originally posted by PBE6This isn't my subject, but in the spirit of most of the other posts in the thread I'll go ahead and talk about it anyway 😉
I agree. There may be some short-term detriment to some of the organisms who express the deleterious recessive traits (i.e. death, or inability to pass on genetic material to descendants), but overall the group will eventually be purged of these deleterious traits to a workable degree provided the group has indeed survived.
So why does inbreeding appear to ...[text shortened]... , cats, pigs, cattle, etc...) are often subject to extreme inbreeding, but they seem just fine.
In humans inbreeding tends to hit intellegence very hard and this is something we think is important, so I think we regard the short term problem as unacceptable. Unless the cost to the individual is high enough to prevent reproduction the faulty gene isn't wiped out. If we were a species of loners then the hit on intellegence would be enough to prevent individual survival, but we are social creatures so inbred individuals survive and potentially reproduce, although you'd imagine that sexual selection would slowly marginalize the gene.
There's been some mathematical work done on this which you can read about here: http://en.wikipedia.org/wiki/Price_equation
18 Apr 07
The explanation I always had was as follows.
Within every person is a set of genetic characteristics, most of which benefit us, some of which may be counterproductive to our survivability (most of which are probably recessive, or else they would inhibit their own ability to survive several lines).
Under normal circumstances, the child will have DNA from 2 fairly diverse parents, and the chances of both having the same genetic defect are fairly minimal, and the child will tend to only exhibit minor defects if that. The reason is that one parent's dominant good genes will tend cover the other's recessive defect, although this isn't an absolute certainty.
However, inbred children will have 2 parents whose DNA matches to a much higher degree, which means any defect found in one parent has an increased chance of being found in the other as well. The closer the parents, the greater this risk.
18 Apr 07
Originally posted by geepamoogleYes, but then the question is why is inbreeding less of a problem for some species and why does a restriction on the gene-pool, for example with cheetahs, not always cause big problems for them. Around 70,000 years ago a supervolcano erupted in what is now Indonesia. The world wide population of humans dropped to about 1,000. This means that inbreeding was more or less compulsory at that time, so how come we survived?
The explanation I always had was as follows.
Within every person is a set of genetic characteristics, most of which benefit us, some of which may be counterproductive to our survivability (most of which are probably recessive, or else they would inhibit their own ability to survive several lines).
Under normal circumstances, the child will have D ...[text shortened]... d chance of being found in the other as well. The closer the parents, the greater this risk.
18 Apr 07
Originally posted by PBE6PB, I'm thinking you've got a sister who's been looking pretty hot lately.
So my question is: why does inbreeding cause an increase in the number of mental/physical defects? Does anyone who studied biology have a simple explanation? Kissing your sister might make you disgusting, but how does it make your kids crazy?
I've got three words for you... ..British royal family.
So don't do it you fool!
Kidding aside, I remembered this term from first grade biology class: http://en.wikipedia.org/wiki/Hybrid_vigor
I'm thinking this is sort of the opposite effect.
18 Apr 07
Originally posted by DeepThoughtI think that inbred populations will be outcompeted by non-interbreeding populations due to increased expression of recessive genes. However if there is only one population, it can inbreed and make it because there's no competition.
Yes, but then the question is why is inbreeding less of a problem for some species and why does a restriction on the gene-pool, for example with cheetahs, not always cause big problems for them. Around 70,000 years ago a supervolcano erupted in what is now Indonesia. The world wide population of humans dropped to about 1,000. This means that inbreeding was more or less compulsory at that time, so how come we survived?
19 Apr 07
Originally posted by AThousandYoungThe thing is that a population's viability doesn't just depend on pressure from other species, but on intrinsic factors as well. If your gene pool has become so small you are looking at a world wide population smaller than the average village you can expect real problems without "having to compete with" other species. The Easter Islanders became extinct (but probably not due to genetic problems except towards the end) without the presence of competing groups of humans.
I think that inbred populations will be outcompeted by non-interbreeding populations due to increased expression of recessive genes. However if there is only one population, it can inbreed and make it because there's no competition.
As an aside to the main debate I feel that this notion that species are in a continuous, competetive struggle to survive falacious. The average herbivore eats grass and frankly there's tons of the stuff. How are whales going to compete with each other over plankton? With carnivores you'll get more powerful species taking prey off smaller ones - losing the catch is a particular problem to cheetahs as after their sprint it takes them half an hour to get their breath back to the point that they can eat. But this doesn't particularly imply that they are in a state of competition, just that some species will opportunistically take the kills other species have made. In general there isn't any competition between animal species, just resources that become scarce due to whatever reasons, generally climatic changes, and drive those less able to exploit them into extinction.
I think that the "species in competition" model has more to do with our tendency to be unable to think outside the frames of reference of our economic system than what is actually going on in nature.
22 Apr 07
Originally posted by wittywonkaAh, I was referring to the dominant/recessive part of DNA 🙂
Could you explain this better? I don't remember my biology all that well. True, some subcellular structures do fix some mutations, but they miss some (otherwise no mutations/evolution would ever occur)...
It's been too long for me to make a very detailed description 😉
23 Apr 07
Originally posted by DeepThoughtSpecies are definitely in competition if they occupy the same niche, though. Two organisms with only enough resources for one will definitely spark competition. And don't forget, organisms in the same species compete against each other all the time.
The thing is that a population's viability doesn't just depend on pressure from other species, but on intrinsic factors as well. If your gene pool has become so small you are looking at a world wide population smaller than the average village you can expect real problems without "having to compete with" other species. The Easter Islanders became extinc ...[text shortened]... e frames of reference of our economic system than what is actually going on in nature.
23 Apr 07
Originally posted by PBE6Give some examples then. You may as well say species cooperate. We wouldn't exist if it weren't for archaic species cooperating and then merging into subsets of the same organism. A better model than "nature red in tooth and claw" is a game theory approach where different strategies work depending on the environment. We most certainly are not in competition with our gut bacteria. Two species occupying the same niche are only likely to "compete" if resources become scarce, and if that happens the most likely outcome is mutual extinction. All this competition stuff is nonsense born out of a desire to justify the prevailing economic system by claiming that nature follows it - for example in Aristotle's cosmic theories, which were official church doctrine all through the feudal era, everything had a place and everything was in it's place.
Species are definitely in competition if they occupy the same niche, though. Two organisms with only enough resources for one will definitely spark competition. And don't forget, organisms in the same species compete against each other all the time.
24 Apr 07
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Originally posted by DeepThoughtThe Easter Islanders never became extinct. They were humans, and humans are still here. In addition, I don't think Easter Island ever went from populated to not populated. Once people arrived there (somewhere between 300 CE and 1200 CE) there were always people there, and there still are.
The thing is that a population's viability doesn't just depend on pressure from other species, but on intrinsic factors as well. If your gene pool has become so small you are looking at a world wide population smaller than the average village you can expect real problems without "having to compete with" other species. The Easter Islanders became extinc e frames of reference of our economic system than what is actually going on in nature.
How are whales going to compete with each other over plankton?
The whales will eat lots of plankton and have lots of babies. Next generation there will be more whales due to the tremendous amount of food. Then those whales will have babies. Eventually there will be so many whales that plankton becomes scarce. At this point some whales will be able to get lots of food and some will not due to genetic differences; for example, variations in the shape of the baleen or variations in the shape of digestive enzymes.
If a population is inbred for a long time and then meets whales that were not inbred, the best of the non-inbreds will be more effective than the best of the inbreds.
In general there isn't any competition between animal species, just resources that become scarce due to whatever reasons, generally climatic changes, and drive those less able to exploit them into extinction.
Resources become scarce because any population will increase and the resource does not. You don't need climatic changes. All you need is to let the organisms breed. Eventually there will be too many of them.
24 Apr 07
Originally posted by DeepThoughtWow, that's not paranoid in the slightest. 😕 Competition in nature was not invented to explain the free market system, rather the economists co-opted it as a useful analogue. And they may try to use it to justify the dog-eat-dog world of economics, but they shouldn't as they run headlong into the "is/ought" problem.
Give some examples then. You may as well say species cooperate. We wouldn't exist if it weren't for archaic species cooperating and then merging into subsets of the same organism. A better model than "nature red in tooth and claw" is a game theory approach where different strategies work depending on the environment. We most certainly are not in comp ...[text shortened]... ine all through the feudal era, everything had a place and everything was in it's place.
I agree that species also cooperate, but you have to see that competition is the basis of evolution. Within a niche, organisms will compete with each other to gather resources and create offspring. The more offspring you produce, the better the chances that your genes will end up dominating that niche. For example, many animals including apes have a male hierarchy when it comes to sexual selection. Alpha male apes mate with the females and try to exclude others from doing the same - competition for limited resources between organisms in the same niche, and extinction is not the result. It also happens when human males go to the bar. But the net result is that the organism that out competes its neighbours will leave a larger imprint on the next generation (barring random infertility, environmental catastrophes, etc...).
Now, cooperation also occurs. The other apes will gather food or protect a resource in an effort to make sure they and their relatives survive long enough to produce offspring, and human males will take wingmen with them to the bar in a cooperative effort to get some in the hopes that the favour will be returned in the future - both examples of organisms in the same niche cooperating. With regards to human intestinal bacteria, there is a cooperative interaction (humans provide food for the bacteria, the bacteria aid in human digestion), but these organisms occupy different niches. However, each of these cooperative actions must have a net positive impact on the fitness of the respective organisms or the cooperative behaviour would not be selected for. This is the competitive nature of evolution. To say that "different strategies work depending on the environment" is true, but it's also a tautology.