EvC Forum: Should the term species be used?

Hi wolfwing

The term species works, but in reality looking at long time, it doesn't exist. We've found many fossils of various animals, and call some species like T-rex, triceratops and so on, but in reality what were seeing is a snapshot of a continual line of animals. We have species today, but what were seeing is a snapshot of the animal lines that exist today.

One of the things to consider is the difference between species identified by speciation events - where a parent population divides into two or more daughter populations that have become reporductively isolated - and species identified by arbitrary comparison of traits - as in the gradual change of species along a lineage.

Or even a line, say mine all the way back to the common ancestor of chimps ...

That would be a speciation event that divide the populations between chimp ancestors and human ancestors.

... and us, taking a section of the timeline you could say this was say aferensis, and this section past it is the next species.

That would be the arbitrary speciation designations along a lineage.

A good visual example of this difference is found in Pelycodus evolution:
A Smooth Fossil Transition: Pelycodus

quote:
The dashed lines show the overall trend. The species at the bottom is Pelycodus ralstoni, but at the top we find two species, Notharctus nunienus and Notharctus venticolus. The two species later became even more distinct, and the descendants of nunienus are now labeled as genus Smilodectes instead of genus Notharctus.

As you look from bottom to top, you will see that each group has some overlap with what came before. There are no major breaks or sudden jumps. And the form of the creatures was changing steadily.

The division shown is a speciation event, and as you look at the lineage you will see several arbitrary speciation designations to differentiate the morphological changes (including size) as they trend from the bottom to the top.

You will also see that the overall trend from Pelycodus ralstoni at the bottom to Notharctus venticolus at the top right has a gradual "trendency" of increasing size with time, but that the divergence of Notharctus nunienus from that trendency occurs at a greater rate of change. This likely occurs for two reasons: (1) the original ecological niche of Pelycodus ralstoni still exists, providing an open opportunity for a smaller species, and (2) the separation in habitat\ecology is necessary to reduce competition between the daughter species (without it one species will likely drive the other to extinction or being reabsorbed - as you can see occurred between Pelycodus trigonodus and Pelycodus jarrovii when an earlier shift to the left shows up, then dissappears).

Reason I say this is that as we keep finding with animals alive now, there really isn't any easily defined definition of species even using animals alive, what many would consider a species, like lions/leopards/tigers can still interbreed and ocasionally produce reproductive capable offspring.

There is a difference between animals that can be made to interbreed in captivity, and what animals chose to do in the wild. If the mating signals are all wrong between daughter populations, they will not chose to mate whether they are capable of doing so or not.

A good example of this is the ring species, the Asian Greenish Warbler:
Greenish warblers

quote:
Greenish warblers (Phylloscopus trochiloides) inhabit forests across much of northern and central Asia. In central Siberia, two distinct forms of greenish warbler coexist without interbreeding, and therefore these forms can be considered distinct species. The two forms are connected by a long chain of populations encircling the Tibetan Plateau to the south, and traits change gradually through this ring of populations. There is no place where there is an obvious species boundary along the southern side of the ring. Hence the two distinct 'species' in Siberia are apparently connected by gene flow. By studying geographic variation in the ring of populations, we can study how speciation has occurred. This unusual situation has been termed a 'circular overlap' or 'ring species'.

The mating songs and the plumage are sufficiently different at the overlap that the two populations remain reproductively isolated, yet the hybrid zones between each of the pairs of varieties as you go around the ring from one end to the other show that in these zones the mating songs and the plumage do not prevent or inhibit interbreeding, because they are still recognized as being potential mate material.

Also see Definition of Species

Plus it gets hung up on the creationists term Kind and get into semantic arguments.

In my humble (or not so much) opinion, the best comparison with the creationist "kind" is with clade, from cladistics, as all descendants are members of the same clade\kind.

Species is useful in clarifying what we are talking about, but should also be taken with a grain of salt.

Enjoy.

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