Friday, October 10, 2014

Convergents and Parallels



Organisms evolved to complement each other in a working system (therefore there cannot be one single best fit for an environment) they specialize each playing a different complementary role in the system: ex: climbing plants and trees.


Did paradise, that Adam and Eve staying in at first, contain a wide diversity of plants (and animals) or was the variety of species around them relatively limited?



  • Similarity in form and behavior between organisms living in a similar environment, but belonging to different different branches of the evolutionary tree, illustrates the match between the nature of organisms and their environment.
  • The idea that there is only one perfect organism for every environment is proven wrong by such similarities.
  • Convergent evolution takes place when the phyletic lines are far removed from each other, and when similar roles are played by structures are analogous but not homologous.
  • Many plants use the support of others to climb up to gain access to more light.
  • Analogous structure:
    • Different evolutionary origins, similar in superficial form or function
    • "The ability to climb has evolved in many different families, and quite different organs have become modified into climbing structures: they are analogous structures but not homologous."
    • Analogous plants having structural features that are derived from modifications of quite different organs: leaves, petioles, stems, roots and tendrils.
  • Homologous structure:
    • Derived from an equivalent structure in a common ancestry.
    • "In other plant species the same organ has been modified into quite different structures with quite different roles: they are therefore homologous, although they may not be analogous."
    • Homologous plants having structural features that are derived from modifications of a single organ: the leaf
  • The radiation amongst the placental and marsupial mammals is a classic example of parallel evolution (evolutionary pathways within separate groups that have radiated after they were isolated from each other).
  • Similarities between parallels in both the form of the organisms and their lifestyle is so striking suggesting that the environments of placentals and marsupials provided similar opportunities to which the evolutionary processes of the two groups responded in similar ways.
Cobaea scandens flower
Cobaea scandens


Is it possible that two species would have evolved separately in similar but separate environments to become more or less similar to one another?