n talk.origins Lori Malt <malt@gramana.com> wrote:

So what? The lizard legs got shorter. This is just variation within a kind. It's not as if a dog gave birth to a cat.

This is undoubtedly a troll. However, it does bring up an important point - and even more importantly, allows me to recycle some email as a post :-)

The relevance of this finding is the speed at which stabilising selection breaks down in response to environmental change. Here, as in the case of the Galapagos Finch species, there is a rapid response to a changing environment whereby clear morphological differences are seen to emerge (caveat - I haven't read the report yet so I do not know if the morphology of the new lizards exceeds the normal morphological variation of the original group. This is an important point as Clark pointed out - by the way Dorman, where is my video?!!). The island lizards are now morphologically different from the original population of lizards from the main island.

Now as has been pointed out (however tongue in cheek), this is not speciation. Or is it?

Certainly it is not biological speciation. The morphological changes have not resulted in reproductive isolation (provided the short-legged lizards get a helping . . umm, err, . . leg up) and so, using the biological species concept, the two groups of lizards are still the same species.

But, palaeontologists cannot use the biological concept of the species, nor DNA studies, in identifying fossil species. The only criterion we are left with is morphological comparison. Not that this is a problem by and large, since virtually all taxonomy is based primarily on morphological comparison. However, palaeontologists are further restricted in that we can only use mineralized body parts (bones, shells, etc.)

Suppose (and it is entirely possible assuming sufficient morphological dissimilarity) that these two morphotypes were considered different species if found as fossils only. Then, were we to look back from the future at the fossil record of this change (assuming the short-legged lizards survive for some appreciable amount of time), we would see one morphotype of lizard then two separate morphotypes, with no evidence of the transition between them because it occurred far too rapidly.

Thus, identifiable and stable, discontinuous variation in morphology has been seen to occur very rapidly. Since variation in morphology is the standard method of identifying fossil species, this example tends to support the view that such morphological changes tend to occur far too rapidly to be adequately represented in the fossil record.

The literalist creationist would then ask "where is the transitional species with intermediate leg length?". The answer would be that it is in a short time window of only 20 years (in this case) and thus finding any would be an impossible task.

These findings support the view that transitionals would be very rare in the fossil record.

Look at it another way:

No. in original
Population
^
|
|
|
|        species A           species B           species C
|
|           * *                                     o o
|         *     *               @ @               o     o  x = fossils
|        *   x   *            @  x  @            o x     o
|       *  x x    *          @  x  x @          o  x   x  o
|      *       x   *        @   x x   @        o  x  x   x o
|     *    x x    x *      @ x      x  @      o  x  xxx     o
|   *   x  xx   x     *  @      x x      @  o      x     x    o
|*                    @  *      x x  x   o  @   x     xx  x      o
----------------------------------------------------------------------->
                              Morphology


Time
^
|
|                            |        |         |         |
|       |         |          |        |         |    C    |
|       |         |          |   B    |         |         |
|       |    A    |          |        |
|       |         |          |        |
|       |         |
|       |         |
-----------------------------------------------------------------------
             Morphological limits of species as found as fossils

Suppose species B evolved from A and C from B, in similar circumstances to those of the lizards. Then, looking back at the fossil record, we would see three distinct morphotypes which would be classed as different species. The total number of transitional individuals and the total length of time those transitional organisms existed is very small compared with the total numbers and length of time in existance of those organisms corresponding to the typical species morphology. Thus the morphological gaps between species A, B and C would be very hard to fill. The literalist creationist would point to the gaps and say "where are the transitionals? B cannot be transitional because it is a discrete species".

But supposing we were fortunate enough to find a small group of fossils intermediate between A and B, e,g:

|
|
|
|        species A      D     species B
|           * *         |
|         *     *       |       @ @              x = fossils
|        *   x   *      |     @  x  @
|       *  x x    *     |    @  x  x @
|      *       x   *   \|/  @   x x   @
|     *    x x    x *      @ x      x  @
|   *   x  xx   x     * x @      x x      @
|*                    @ x *      x x  x       @
----------------------------------------------------------------------->
                              Morphology


Time
^
|
|       |         |          |        |
|       |         |    D     |        |
|       |         |          |   B    |
|       |    A    |    ||    |        |
|       |         |    ||    |        |
|       |         |    ||
|       |         |
-----------------------------------------------------------------------
             Morphological limits of species as found as fossils

The cry would still go up "where is the intermediates between A and D and D and C?" This is the 'transitional fossil infinite regression'. But, as the lizard study tends to support, finding a complete series is next to impossible given the speed that discontinuous morphological variation between groups can occur.

My thanks to Jim Lippard for originally flagging the article.