Question

Evolution:

What are the issues about the classification of the hagfish and of the birds? Explain the controversy (or disagreement) which has involved each of these groups.

Answer 1

In the case of hagfish, the sontroversy is caused by the fact that hagfish do have a skull but no vertebral column, and its proximity to lampreys and lancelets, evolutionary speaking.

On one hand, scientists hypothesize that hagfish are a kind of degenerate species; menaing that they had a spine, but lost it over tie due to evolutionary forces, which would relate them to lampreys. On the other, it is believed that they never had a vertebral column to begin with; which places them in a more primitive spot when it comes to the evolution of vetebral columns (they precede the existance of spines), along with lancelets.

Beause of these characteristics of the hagfish, there is much disagreement as to where in the tree of life they belong, and arguments can be made for both of the theories. However, recent research into microRNAs (miRNAs) suggests that hagfish did have a vetebral column before, but lost it at some point in time. This is only suggestive information, so the debate is still open.

The case of birds is much, much broader. Classification of them has always been an issue in taxonomic societies. Epecially when it comes to songbirds living in forests and jungles. This arises because birds who are pressumably of the same species, might have different communication (song) patterns, which might entiltle them to be classified on their own species. This is a taxonommical nightmare due to the fact that the concept of "species" is not even well defined. In ANY species. Classifying a bird in a new species due to the song they make alone would be like classifying the French as a new speeces because they do not speak English.

Thus, many cryteria are taken into account to classify a species. But in birds it can be a mess due t the sheer variety there can be in a "single species" (various colors, behaviors, sizes, songs, etc.). The usual definition of species used in these cases is the biological one: a species is a grpup of individuals that can breed with each other. This has its own caveats. For instance, donkies and mares, and lions and tigers can be bred to yield mules and ligers, respectively. does this mean that horses and donkies, and tigers and lions are the same species? Off course not. So,you might see what the controversy is about. In my opinion it is not so much abut birds, nut about the conept of species.