چكيده فارسي :
Since the description of Darwin theory in 1859 for speciation and divergence
of species from common ancestors, several other theories have been proposed to detail
or complete it, all of which were based on modifications of traits and natural selection
for/against them. The existence of shared organs, tissues, processes, molecules and
genes as well as a consensus on trends of changes among methods of phylogenic
analysis were all in favor of such theories. At molecular level, there are many genes
shared among species with similar sequences that, of course, have been mutated
throughout the time by substitutions and insertions/deletions. Consequently, their
structures and functions have been modified so that the mutations were reflected at
phenotype level and subjected to natural selection. However, deposition of a mass of
genetic data- particularly through genome projects- has introduced new aspects. For
instance, over five percent of genes are new and even unique in certain species.
Proposed theories such as horizontal gene transfer, gene duplications,
neofunctionalization of existing genes, and formation of new genes via recombination
or exonation, gene losses and so on do not adequately describe such realities. Indeed,
these data led to postulations such as (1) the shared (homologous) traits are indicative
of common ancestors; (2) vital needs dictate having common (analogous) traits; or (3)
a combination of both is true. In this presentation, I will review current theories
including divergent evolution, radiation evolution and convergent evolution with
referring to examples of lineage specific genes. Also, the evolution of plant acid
phosphatases will be pointed out as a case for which a combination of theories works.
