Re: What causes the special alignment of chromosomes during metaphase I ?

The point of meiosis is to produce haploid sex cells, the eggs (oocytes) and sperm.  The point of 
mitosis is to produce daughter cells identical to the parent cell (diploid cells).  Therefore, the way 
the chromosomes align in meiosis and mitosis is different.  I will take a shot at describing the 
differences to you briefly here.

In meiotic metaphase I, the bivalents align at the metaphase plate. The bivalent is composed of 2 
homologous chromosomes, each of which contains 2 sister chromatids. The homologous 
chromosomes (they look like the letter X in most diagrams) undergo recombination (crossing 
over) at the chiasmata in meiotic prophase I, and the chiasmata remain and help the bivalents 
line up correctly at the metaphase plate in metaphase I.  In anaphase I, the bivalent separates 
with each homologous chromosome (composed of 2 sister chromatids) going to a separate cell 
(or in an oocyte to the polar body).  Therefore, in meiosis II, there are no bivalents, and no 
chiasmata.  The two sister chromatids line up a the metaphase II plate and separate from each 
other during anaphase.  The result of meiosis is 4 haploid cells (one copy of each chromosome in 
the case of human sperm).  

In mitosis, two daughter cells identical to the parental cell are produced.  The homologous 
chromosomes do not find each other and form bivalents.  No chiasmata are formed. Mitotic 
metaphase is most similar to meiotic metaphase II in that the sister chromatids separate at 
anaphase.  

This is all much easier to describe with a diagram.  Wikipedia has  good ones.  http://en.wikipedia.org/wiki/Mitosis http://en.wikipedia.org/wiki/Meiosis

I also like Brooker's Biology textbook. The diagrams and explanations are quite good.

As to the evolution of mitosis and meiosis, I am not an expert on that at all!  But, since bacteria 
replicate essentially by mitosis, I think meiosis must be a "later" invention building on mitosis.  
The evolution of sexual reproduction is a fascinating topic full of interesting why and how 
questions.  At the bottom of the following web page, several good links with information about 
this topic are listed: http://www.dorak.info/evolution/sreprod.html 

Thanks for your question!