gmacrider

Ah yes! Now it's starting to make sense. I hadn't made the connections between mutations, sister chromosomes, cell division, gene expression, and Mendel's laws of genetics. Amazing stuff. Thanks for the help!

Interesting - I think I'm learning something here. It appears that a mutation can occur without being expressed in the phenotype (why wouldn't a mutated gene be expressed?). Until it's expressed I assume Natural Selection would "treat it" as a neutral mutation, so it would continue to migrate through more of the population. Eventually something would cause the gene to be expressed in some members of the population and Natural Selection would come into play. What would cause a gene to suddenly be expressed? An external factor like changes in the texture of foods? Thanks for all the info.

Sorry, I'm confused. If the mutation (genotype) occurred way back in our evolutionary history, then why is the smaller jaw (phenotype) only becoming prevalent in recent generations? I may be making a faulty assumption here about the smaller jaw only becoming prevalent in recent generations. I'll do some research on that. I thought the jaw changes were because recent generations were eating softer, processed foods.

Thanks for the replies. Some good ideas. But isn't it odd that the same mutations (resulting in smaller, weaker jaws) are occurring many times in the population simultaneously?

I understand that the human jaw and teeth are becoming smaller and weaker over recent generations because modern food is soft and mushy and easy to eat (please correct me if I'm wrong in this premise). What is the process that is causing our jaws to diminish? It can't be evolution can it? Evolution would be where a single individual was born with a mutation resulting in a smaller jaw. If the smaller jaw gave the individual an advantage over others, then this trait would be passed on to subsequent generations. But I can't imagine that is what is happening with our jaws. Please enlighten me. I don't understand how reducing the use of a characteristic would cause that characteristic to "devolve" over generations. Thank you!

Thanks all for the info. I was just trying to understand how mutation drives evolution. So it sounds like any new heritable characteristic in a population can be trace back to a mutation in the gametes of a SINGLE individual. I hadn't thought it through before and was under the impression new (similar) mutations would occur in several members of the population at the same time, but now that sounds highly unlikely.

What are the odds of the same heritable mutation occuring in more than one individual during a period of time that spans roughly a couple of generations? I guess that's tough to answer. I just find it odd that several individuals in a population would have the same mutation at the same time, resulting in numerous offspring that have an advantage over the rest of the population.

When I think of a computer I think of work, work, work.

Your theory may run into problems because it conflicts with the apparent DISTRIBUTION of the dark matter. Measurements indicate the missing matter is spread throughout a huge dark halo much larger than the visible halo of typical whirlpool galaxies. There should be about TWICE as much galactic mass OUTSIDE of the visible halo compared to what's inside it. So more black holes within the visible halo would be in the wrong location to explain the missing mass. Could there be a huge number of smaller black holes distributed in a large halo surrounding a galaxy? I'm not sure about that question, but I suspect there would be a problem explaining how such black holes would have evolved.

Nice statement. It made me think. Personally, I would prefer re-wording it something like: Natural Selection is a stochastic sorting algorithm, processing life in a massively parallel random walk through an endless variety of constraints and opportunities. The result is evolution (or extinction). Just thinking out loud. Good stuff.

There's the rub. The proposed existence of Dark Matter is due to the unexpected high orbital velocities of objects far from the Galactic Centre (in the halo). But if those orbits are highly eccentric, does that not mean that the calculations have assumed an incorrect semi-major axis? And that not quite so much Dark Matter is required? I must be missing something...

Yes, exactly. I thought they'd need at least 2 points to plot the orbit. How do they get the 2nd point when everything is moving so slow?

I mean Kepler's 3rd Law as revised by Newton.

Using Newton's 3rd Law, we can calculate the total galactic mass within the orbit of an object if we know the rotational velocity of the object and it's distance from the galactic centre. Apparently this is done routinely and the results indicate there must be a huge halo of dark matter extending well beyond the halo of visible galactic matter. My question is: The "distance" in Newton's 3rd Law is the semi-major axis. When we establish the distance of an object from the galactic centre, how do we know that distance is also the semi-major axis? Could not the object in question have an orbit that brings it much closer to the galactic centre than it is "now". In that case the semi-major axis would be smaller and the resulting calculations would be quite different. Enlightenment would be most welcome. Thanks!

So, even though in Newtonian physics the "test particles" have mass, does the above statement mean the gravitational force of the "test particles" is ignored in Newtonian calculations? If so, wouldn't Newtonian calculations of Jupiter's motion be slightly off because they don't take into consideration it's large gravity well? I'm no expert (and I probably just proved it), but I'm having trouble understanding the new theory. Thanks for the link BTW - very interesting.

It just amazes me that in our society alcohol is fine, but pot is illegal. What an absurd situation.

Thank you! I also found this in Wikipedia (hilites are mine): Mutations are permanent, sometimes transmissible (if the change is to a germ cell) changes to the genetic material (usually DNA or RNA) of a cell. Mutations can be caused by copying errors in the genetic material during cell division and by exposure to radiation, chemicals, or viruses, or can occur deliberately under cellular control during the processes such as meiosis or hypermutation. So the germ cells are also called gametocytes and, via meiosis, create gametes. I can see how mutations in those cells could be heritable. I'm also curious about the impact of DNA mutations in other cells. Even if they are not heritable, can they change the phenotype of the individual? This is cool stuff.

I think I'm missing a key concept here. Do DNA mutations have to occur in gamete cells in order to be passed on to offspring? For example, if a cosmic ray tweaks the DNA in a cell on the end of my elbow - how could it possibly be passed on to future generations? When scientists speak of DNA mutuations that are inherited, they must be talking about mutations that occur in very specific cells, yes? I'm confused.

Thank you Mokele, for that excellent explanation.

Surely not all heritable variations in a population are caused by mutation, are they? I'm slightly different than my brother for example - different eye colour, different nose, much better looking, etc. What is the correct term for the cause of this type of heritable variation? Are there other causes of heritable variation?

Keep in mind I'm a complete non-scientist. According to Carl Sagan in his book "Cosmos" (from 1980 or so) a single human cell contains about 5 billion bits of genetic information. I'll simplify it a bit and call it 5 Gigabits (not Gigabytes!). He also says our brains have about 100 trillion neural connections, which would translate into about 100 Terabits of memory. So, 5Gb of genetic information and 100 Tb of human RAM. Being a computer geek, I can get my head around those numbers. But are they accurate numbers? I'm most curious to see if any of you have opinions on that. Thanks. (my apologies if this has been discussed before...I'm new to the board)