shinbits said:
Okay.
Okay. But then, doesn't this make it even more difficult, and make it take even longer for evolution to happen? That's even less feasable then the the theory that there's a minute mutation with each passing generation. If it turns out, as you say, that this isn't even the case, but rather, mutations are very infrequent---that makes evolution that much harder to swallow.
When it is said that a mutation is rare, one needs to look at the context. A human cell contains some 60,000 genes, each of which is composed of hundreds, even thousands, of base nucleotides. It is estimated there are about 6 billion base nucleotides in a human cell. A change to just one of these 6 billion nucleotides counts as a mutation.
The estimated average number of mutations in a new human cell is 120. And insertion or deletion or duplication may affect more than one base nucleotide, but most affect less than 5. It is rare to have the duplication of a whole gene.
So in terms of the % of the genome affected, mutations are rare indeed. Like 100-200 people out of all the 6 billion on the face of the planet. Hardly noticeable at all.
Yet, the extent of the genome is such that there will probably be some mutations in every cell, including the germ line cells which transmit evolutionary changes.
As would any "beneficial" mutation. Right?
But a beneficial mutation would not cause early death. If the host of a beneficial mutation died before reproducing, it would be due to a factor other than the mutation.
Wouldn't even the "detrimental" mutations it may have get passed along as well? If so, that would just hinder evolution. That's a sort of "catch 22" of evolution, which makes it hard to believe.
Yes, but it is not as much of a "catch 22" as you might think. Every organism will have a mix of neutral, beneficial, and detrimental traits. This gives it an overall fitness level. Natural selection acts on the overall fitness level, not each trait individually.
Below is an excerpt from a formal debate I had with mark kennedy. It shows mathematically how natural selection impacts various groups in a population when a beneficial mutation and two detrimental mutations are randomly spread through the population over a number of generations.
Finally, let's look at one last hurdle. What if the number of harmful traits outnumbers the beneficial traits? Won't the harmful traits "gang up" on the beneficial traits rendering the beneficial trait useless to the species? Well, let's see.
Let us assume a population with one beneficial and two harmful genes in its gene pool. We will designate the beneficial gene (b), the less harmful gene (h) and the more harmful gene (d) (for "deleterious"). We will also assume the possibility of individuals who have none of these genes. Let's call them (n) for "normal" From this we can derive eight types of individuals:
No gene subject to selection: nnn
One gene subject to selection: bnn nhn nnd
Two genes subject to selection: bhn bnd nhd
All three genes subject to selection: bhd
Next we need to assign a selection factor to each of these groups.
nnn will have the neutral factor of 1
bnn = positive selection factor of 1.15
nhn=negative selection factor of 0.9
ndn=negative selection factor of 0.7
From these we can calculate the selection factor when two or three genes subject to selection pressure are present.
bhn = 1.15 x 0.9=1.04 (positive)
bnd=1.15 x 0.7=0.81 (negative)
nhd = 0.9 x 0.7=0.63 (negative)
bhd = 1.15 x 0.9 x 0.7 = 0.73 (negative)
Finally, let's begin with a population in which each of these possibilities is equally represented, i.e. each forms 12.5% of the population. The chart below shows the results (arranged in order of increaing negativity) of these selection pressures.
bnn (1.15) F2 16.5 F3 21.0 F4 25.8 F5 30.8 F6 35.7 F7 40.4
bhn (1.04) F2 15.0 F3 17.2 F4 19.1 F5 20.6 F6 21.6 F7 22.1
nnn (1) F2 14.4 F3 15.9 F4 17.0 F5 17.6 F6 17.7 F7 17.4
nhn (0.9) F2 12.9 F3 12.8 F4 12.3 F5 11.5 F6 10.4 F7 9.2
bnd (0.81) F2 11.6 F3 10.4 F4 9.0 F5 7.6 F6 6.2 F7 4.9
bhd (0.73) F2 10.5 F3 8.5 F4 6.6 F5 5.0 F6 3.7 F7 2.7
ndn (0.7) F2 10.1 F3 7.8 F4 5.8 F5 4.2 F6 3.0 F7 2.1
nhd (0.63) F2 9.1 F3 6.3 F4 4.2 F5 2.7 F6 1.7 F7 1.1
At F7 the total representation of all five groups experiencing negative selection is only 20% instead of the 62.5% they were in the P generation. Meanwhile the two groups benefitting from positive selection pressure now represent over 60% of the population up from the original 25%.
If you want I can pm the whole post to you. It goes more in depth into the math behind those results.
And I know you'll say that only beneficial mutations get passed along. But then I ask you, what keeps detrimental mutations from getting passed along with beneficial ones?
It is a combination of natural selection and independant assortation of characters. The latter was discovered by Gregor Mendel.
How much highschool genetics do you remember? You know about having 2 sets of chromosomes, right? Half from mum and half from dad.
And you remember that before an egg or sperm is created, you have to get the double set of chromosomes reduced to a single set. That is why each of your children gets only half of your chromosomes, and gets the other half from their mother.
Furthermore, when a mutation occurs, it only occurs on one of your two homologous chromosomes i.e. either on the one your inherited from your mother or the one you inherited from your father, not both.
Since each of your children will get only one of these chromosomes, each has only a 50% chance of inheriting the one with the mutation. And unless the beneficial and harmful mutation occur on the same chromosome, there is only a 1 in 4 chance that a child will inherit both of them. There is also a 1 in 4 chance that a child will inherit neither of them.
In short, reproduction splits up the mutations so that they are seldom inherited as a set. And this means each of your children will have a different fitness profile and a different opportunity for reproductive success.
btw, this again is why you have to look at population and not just individuals. Reproduction is the mechanism for spreading the mutations through the population--but not as fixed sets. And natural selection means that each of the various sets enjoys a different rate of reproductive success that does weed out harmful mutations while distributing beneficial ones more widely in the population.