I came across this picture many times while doing some reading. This picture states the facts that a recessive deleterious allele will become dominant in offspring born of 2 carriers of the deleterious allele. But it seems to have removed the other possible outcomes.
Aa + AA = { AA, Aa, Aa } the assumption is that the deleterious allele is more likely to be passed on rather than the dominant beneficial allele? According to probability shouldn't the chances of offspring with AA and Aa be equal?
Aa + Aa = { aa } and where have the other possible outcomes gone? Aa + Aa = { AA, Aa }. Yet again in terms of probability the chances of producing offspring with Aa should be higher than aa and AA.

Now lets define a new diagram: (only inbreeding, no crossbreeding)

First Stage :
AA + Aa = { AA, AA, Aa, Aa }

Second stage :
AA + AA = { AA, AA, AA,AA }
Aa + Aa = { AA, Aa, Aa, aa }

Third stage :
AA + aa = { AA, Aa, Aa, aa } but if natural selection were to be present aa wouldn't get a chance to reproduce no? **
Aa + aa = { Aa, aa, aa, Aa }


**Over time, natural selection weeds deleterious alleles out of a population — when the dominant deleterious alleles are expressed, they lower the carrier's fitness, and fewer copies wind up in the next generation

Already by the 3rd generation we see that the AA individuals are more abundant than individuals with Aa and aa.
I am assuming that we can compute the outcome of genetic drift using probability.

Another point to ponder : what if there were a recessive beneficial allele? What outcome would we get then?

What is the basis of your assertion that male preferences have shifted from plump women to slim women?

Also if the time period of human history up to the present and five hundred years in the future is too short to produce any meaningful results in human evolution, then what's all the fuss about humans not evolving anyway? The time scale we are talking about would still be too short despite the technological advances and changes in human lifestyle.

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Added on January 12, 2010, 6:08 pmI'll make this simple, Mesos.

I can point out the flaws and mistakes in your reasoning.

But what are you going to pay me for it? What do I get out of it?

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Added on January 12, 2010, 6:09 pmOn the other hand I could perform a psychoanalysis of your writing for absolutely free!



This post has been edited by Dickson Poon: Jan 12 2010, 06:09 PM

I still disagree. Humans have used medicine to treat themselves for thousands of years, possibly millions. Other animals have shown similar traits as well (dogs eating grass). Now, although Lamarckism is distinct from Natural Selection, it does play a significant role in a species's survival.

It is true that genetically our genes might not be "better" due to medicine, but the use of modern medicine can be equated to similar traits demonstrated by other primates, such as calling out when they see danger so that their entire group can flee. Thus, both forms can be said to provide evolutionary advantage to a species, but Darwin's evidence seem to suggest team work is more important. In The Descent of Man, he noted that tribes that demonstrated better team work usually triumph over those that do not.

A being the dominant allele will suppress the recessive a. so Aa while carrying bad genes, the bad quality is not express and the individual live a healthy life.

so as far as quality of life is concern, Aa and AA has no difference. while aa is catastrophic. in case of a large population, the chance of aa being expressed is significantly lower than AA or Aa as opposed to a small sample size of inbreeding.

as shown in the your example, by the third generation, 3/8 has aa. (1/8 at 2nd)

comparatively in crossbreeding, the chance of aa being expressed is significantly lowered.

not not neccessary all a is bad, there is a possibility that ou have some recessive genes that are good. but life prefer to err on the side of safety. its basic instinct. you prefer to take a risk if its to protect something you already have rather than to take a risk to get something that may benefit you.

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Added on January 13, 2010, 12:51 amsee difference from renaissance to present day

also

some article

now, i am not saying plump women are unattractive or vice versa, but society in general views slimness (hour glass) as the ideal female figure now, versus the plumpier version as the ideal 500 years ago.

there are numerous psychological and economical reasoning into why this happened, if you are interested in learning more.

yes, current age with medicine and technology is too short to produce any significance in evolution pressure, but if the current trend continues, we will see human as a species rely more and more on technology and medicine, and less on any evolution that occur (ie, the one that is more susceptible to illness get more or less the same chance to reproduce as the healthy one)

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Added on January 13, 2010, 1:04 amnaturally occuring medicine dont usually have as wide and deep effect as artificial medicine. and knowledge of medicine is not genetically passed on (at least not for human)

lamarckism does not play any role in species survival, because it does not happen. it is not an "alternative" path of evolution, it is a mistaken path of evolution.

you have thick pads on your fingers and feet because your body has the ability to develop harder skins at places where more stress is applied. your fingers are more flexible because you practise it more and your muscle and tendons did not harden. these are naturally occuring adaptation that you as an individual can perform. at no time is this information passed on to your offsprings. a baby is always born is soft smooth soles even though their parents are hard laborers with calloused feet and hands.

AND, grass is not "medicine" to dogs, at least not in the sense you are implying.
dog eat grass


This post has been edited by lin00b: Jan 13 2010, 01:11 AM

@lin00b
Just pointing out something regarding my example that I did not mention previously. My diagram was intentionally flawed because I left out similar outcomes. But if the frequency of allele is calculated :
Assumptions
- each pair of parents produces 4 offspring
- offspring consist of equal number of male and female (for reproduction purposes)
- and that the cumulative number of each type of allele in the offspring is double the number of each type of allele in the parent
- each offspring mates with both of the offspring of opposite sex



The frequency of recessive allele doesn't change. But applying this theory:
Over time, natural selection weeds deleterious alleles out of a population — when the dominant deleterious alleles are expressed, they lower the carrier's fitness, and fewer copies wind up in the next generation
Offspring with aa will not be able to reproduce, thus the frequency of the recessive deleterious allele will be reduced by 5%.

It's true that through crossbreeding the chances of aa being expressed is significantly lowered, but only if we assume that the current population is comprised of more AA than Aa. If the opposite was true and there is more Aa than AA the chances of producing aa is increased rather than decreased. (Does this make sense? I'm a little bit confused)

Regarding your final statement. I totally agree that our current human population poses this instinct of protecting what we have. This is probably why natural selection doesnt work very well when human beings are concerned. While in the animal population, a weak lion cub which cannot cope with the harshness of the environment is regrettably left behind. Even though I want to accept the fact that it is natures way of functioning I cant help but to pity the ones left behind. And I think this is where we distinguish ourselves from the animal kind, even at the cost of evolution.

result of evolution is not to reduce bad genes, it is to reduce the expression of bad genes.

if bad genes are dominant - hence frequently expressed, that particular community will eventually be dead. if the bad genes are recessive, hence seldom expressed, the community will survive. if this surviving community resort to interbreeding, the odds of these bad genes being expressed is increased, and that is bad.

an interesting point is that majority of our genes are actually not expressed in any way. they may be junk, or extremely recessive

while you are referring to protecting the individual, i'm referring to protecting the species and community. the whole community suffer if the quality of the offspring produced is of frequently low quality. it is arguably better to allow only the better/fitter individual to reproduce and increasing the quality of the output. at least that's nature's way.

My point isn't about the differences between the effects of natural and modern medicine. The point is that humans have the unique ability to use tools. Modern medicine can be seen as one of humankind's greatest tools. Arguing medicine is counter productive to evolution would be similar (perhaps the same) as arguing the invention of guns have made the weak able to hunt for food, when in fact they should be left to die. Or the use of clothes have ensured the survival of those with less adipose tissues.

The use of tools is part of our evolutionary history and since we still exist, it can be said that it has served us well so far.

I was not referring to Lamarckism in its traditional sense. Genes cannot be altered, I know that. I was referring to the passing on of knowledge. We do not pass on knowledge of medicine genetically, but we do so in the form of books, lectures and teachings. In a sense, this is not Lamarckism, but it is close. We acquire that knowledge throughout life and pass it on. This ability to pass on knowledge is immensely significant in many species's survival.

Perhaps this is more akin to the Meme theory. If it is, then that further supports my point as modern medicine has grown and flourished.

all those other "counter point" you use are actually true. although the exact line can be blurred. whatever artificial tools we make is not a result of our evolution. and by continuing to use them, we are in a sense limiting whatever natural selective pressure on use to be better biologically.

not to say tools are bad, but looking at a strictly evolution point of view, it is creating a weaker species biologically.

passing of knowledge is not lamarckism in any sense. say engineering parents, son may grow up to a profession that does not use engineering skills at all. whatever skill that the parents frequently use and depend upon is not transferred on to offspring

the passing of community-wide knowledge is good, but is fragile. knowledge is easily lost during catastrophes. after which the community has to start from a lower knowledge level, this is because those information is not guaranteed to pass on to future generation, unlike evolutionary genetic information.

Even if humans were to cross-breed, wouldn't we one day all posses the same recessive genes? And when that happens, won't the same effect of inbreeding be shown in those who cross-breed? So are we just trying to avoid the inevitable?

Medicine, weapons, and even clothes hinders evolution, in some way. Because these tools allowed unfit individuals(in the physical sense) to survive and reproduce. Which would not happen if nature had her way. But looking at it from a different point of view, it is probably because those unfit individuals(who were not strong physically but posses mental strength) were able to survive, that we are able to enjoy the luxuries of technology in this age and time. In which case Steven Hawking would make a perfect example.

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I feel obliged to include this here. I read an article here. The article states :

That statement there confuses me greatly. So far in my reading, I've noted that the only way harmful DNA mutations / deleterious allele were able to be eliminated or suppressed is by removing the particular individual that carries the deleterious allele.

What my whole thread was based on was the fact that inbreeding lead to deleterious traits to be expressed thus individuals with those traits were left unable to reproduce. Thus removing the particular deleterious trait from the gene pool. And allowing only those with seemingly perfect genes to continue populating the earth. Or the other way around where previously recessive beneficial traits are expressed allowing them to aid the evolution of mankind. But if cross-breeding removes deleterious traits from the gene pool, then the whole point of this thread has been nullified.

This post has been edited by Mesosmagnet: Jan 13 2010, 10:51 PM

There are no "perfect" genes. That simply defies the logic of having a genetic algorithm in the first place. If it's all towards reaching perfection, then all we need is an optimizing algorithm.

My point is, genetic algorithm interacts with a constantly changing environment to maximize the species survivability. And when the environment changes, so must the set of "good" genes as they are no longer as "good".

From the algorithm point of view, it's always better to keep as rich a gene pool as it can manage, and to create as many offspring variations as possible in order to maximize the species survivability.

Not necessarily. Evolution did not end when humans started using tools. Because of our use of tools, more importance have been placed on intelligence. And as such, our brain size have increased. The tools only hinder our evolution if you do not consider all the "tools" we invented as part of our lives. Artificial or not, it is now part of humanity. Taking away houses from humans is similar to taking away trees from monkeys. We have evolved such that the essential tools we have created are part of humanity, part of our species. Of course, not all tools are essential, like iPhones. Natural or not, we have thrived with it, just like monkeys have thrived on trees.

A catastrophe can wipe out human knowledge which would set back humanity. True. But the same can happen if a catastrophe wiped out all the trees. Monkeys would then have to evolve to adapt to life on land (non-tree land. What's the word? Terrestrial?), or face extinction. That is what humans would have to do should that happen, regardless of whether we live in houses or in caves.

http://en.wikipedia.org/wiki/Lamarckism#La...societal_change
Knowledge can be considered part of our culture. Your example presupposes that all knowledge is passively transferred. Knowledge is more often actively transferred than passively transferred (that is until they invent that Dexter-learning-French-in-his-sleep device). Cultures are very often passed down from one generation to another.

Catastrophe, refer above. Also, with the increase in intelligence, I would presuppose that humans will return to where they were before in a shorter time than it took them the first time. Though I admit, that does not mean it will not take millions of years, just shorter. Hopefully some books survive.

EDIT: Grammar.

This post has been edited by thesupertramp: Jan 14 2010, 10:55 PM