07
Jan
10

Orcas Diverging?


Evolution in Action

The idea of species as fixed groupings of individual living beings is a slippery one, and species are not easily defined nor delineated.  This is one reason the creationists claim that they accept micro- but not macro-evolution in defense of their holding on to their belief in separate creations for all kinds, or baraminology.  Wilkins, the Modern, explains briefly how the concept of species itself evolves:

Some years ago, I published an idea that I think might be the resolution to this (2003) in which I argued that species is like any other property of organisms, something that has evolved in its own way. The reason there is no universal notion of species for the same reason there is no universal notion of leg: species, like legs, are the outcome of evolution. In other words, these kinds themselves evolve. This applies also to other apparently universal aspects of biology: genes, or rather replicators, cells, individuals, and so on. It is not the case that, as Dupré thinks, that anything goes, but that there are evolved modalities, as I called them – ways of being whatever it is that we are trying to understand. This applies not only to the organisms and their traits, but to the kinds of organisms, and even to the kinds of kinds. Taxa, units, ranks, entities, systems – all these are evolved, and so to understand what it means to be, say, a bird species or a eukaryote gene, you need to understand the evolutionary relations of that group.

It may seem like a “moving of the goalposts” when defining evolution, but the important thing to know is that there is no definite barrier between species that can be demonstrated to delineate one grouping of creatures/plants/algae from each other to say when a species has diverged.  But in the example of ring species, the greenish warbler of Asia and Europe have had several minor divergences and enough so that two species of them are identifiably distinct.

And we may be seeing the emergence of a divergence of Orca orcinus among the North Atlantic pods, near to Great Britain.  This is based on observations of living pods of orcas, their feeding habits and differences in sizes among males and the examinations of the bones and jaws of beached orcas over the last 200 years.  Here’s the article in the Beeb’s News Service:

Dolphin is healthier for teeth than mackerel

Dolphin is healthier for teeth than mackerel

“We found that one form, which we call ‘type 1’ had severely worn teeth in all adult specimens,” explains Dr Foote.

“The other form, ‘type 2’, had virtually no tooth wear even in the largest adults.”

In the wild, killer whales that “suck up” herring and mackerel display this tooth wear.

Knowing this, the researchers suspected a difference in diet and ecological niche between the two groups

So, they did genetic analyses and found key differences to postulate that there is a divergence in process. Now, the reason that I find that interesting is that I have always been curious about mammals in the sea and especially whales. There are two main things that I find fascinating about how they adapt to from a land-based form with legs and hips and hooves, to fully marine animals over the course of millions of years. Whales got no legs, but they have vestiges of hips in their skeletons. The other question that intrigues me is the question of the evolution of baleen whales. These are whales who don’t bit, but strain water to get their food through a web of fibers that they use instead of teeth. They don’t bite down, but they have remnants of teeth in their jaws which indicates that they once did.

Brian Switek of Laelaps has found an article which proposes a solution to the question of the development of baleen over millions of years:

But how does Mammalodon relate to other whales? This is where the discussion has to get a little more technical. The group containing the earliest whales, or everything from Pakicetus to Basilosaurus, is called the Archaeoceti. So many new species and genera have been found so quickly that the relationships of the archaeocetes to each other are a bit fuzzy, but the Archaeoceti undoubtedly contains the ancestors of the other major group of whales, the Neoceti. The Neoceti can be split into two subgroups, the odontocetes (toothed whales, such as orcas and porpoises) and the mysticetes (baleen whales), with Mammalodon sitting fairly close to the base of the early baleen whales. This means that it might provide some clue as to what the common ancestor of the odontocetes and mysticetes was like, which in turn might contain some hint as to what subgroup of archaeocetes the first members of the Neoceti evolved from.

Evolution involves minor divergences, and at fits and starts.  The idea behind natural selection is the differential reproduction helps determine which species thrive and which die out.  Population dynamics and scarcity of resources leads to competition for food among groups, or it also leads to a divergence of diet.  If these two groups of North Atlantic are able to survive and thrive in the same seas because they are developing different diets from each other then perhaps in thousands of years they will be distinct enough to easily separate and to be able to say, “Yep, evolution happened here.”

Baleen whales and toothed whales evolved out of the same common ancestors, exactly what steps happened along those divergent pathways have as yet to be discovered.  Brian points to one possibility, but also reminds his readers that there has yet to be more evidence to be found and until then it is a “just so” story.  The value of just so stories is that they suggest further research, but they remain suggestions and evidence builds on evidence to find answers.

There is no clear distinction between very similar taxa of life and at no point can one take a look at similar species and say “Now they have diverged and are separate.”  We can only tell after they have diverged enough to avoid confusion that they have diverged.  This has been going on for billions of years, and illustrates how evolution works.  They will select each other sexually, for whatever traits they find desirable in each other.  They will eat and fight and find new spaces for the foods that they prefer.  They will wander in an out of each others’ territory.

The orcas may be diverging, and evolution is laid before our eyes yet again.

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