My last post concerned the loss of genetic diversity in fallow deer over a period of 140,000 years, shown by comparing the genomes of modern fallow deer with DNA recovered from 140,000-year-old fossils from Germany. Creationism, of course, has no explanation for the age of fossils from some 130,000 years before the mythical 'Creation Week', nor for how evolution can result in a loss of diversity, since creationist dogma insists that any loss of 'genetic information' must necessarily be deleterious.
Now we have an even more difficult paper for creationists, recently published in the Royal Society journal Biology Letters by Assistant Professor Victoria McCoy, of the University of Wisconsin-Milwaukee, and researchers from the Field Museum of Natural History, the Lauer Foundation for Paleontology, Science and Education, the David and Sandra Douglass Collection, and the University of Ottawa. The paper explains how the hagfish eye has evolved to become less complex, having lost its pigment and lens, and is now covered by soft tissue.
To add insult to injury for creationists, the authors also show that the 308-million-year-old hagfish fossils they examined, recovered from the Mazon Creek site in northeastern Illinois, were already showing evidence of reduced complexity. Their eyes were intermediate between the normal vertebrate eye and those of modern hagfish, confirming the hypothesis that hagfish eyes evolved from more typical vertebrate eyes by a stepwise process of complexity reduction. Creationists continue to insist that there are no intermediate forms in the fossil record, despite the regular discovery of exactly such forms, as this hagfish example neatly illustrates.
Today, hagfish inhabit the abyssal plain, where there is little or no light. They are scavengers, feeding on the bodies of dead animals, and are among the creatures that help strip the soft tissues from large carcasses, including whale falls, on the ocean floor. Yet these are the descendants of hagfish that lived in a shallow, near-shore, well-lit environment, such as that preserved at what is now Mazon Creek. The conclusion is that the loss of eye complexity was not simply an adaptation to a dark, deep-sea environment, but was driven by some other environmental factor or factors. This reduction in visual ability then appears to have enabled hagfish to extend into and exploit their present environment, eventually disappearing as coastal species.
And this refutes yet another creationist assertion: that scientists only ever publish findings that conform to scientific orthodoxy. This paper challenges the long-held assumption that deep-sea conditions drove the loss of eye complexity in hagfish. It is now clear that the process preceded the move onto the deep-ocean floor.
Background^ Hagfish. Hagfish are among the strangest living vertebrates. They are jawless, eel-like marine animals, although they are not true eels, and are placed with the lampreys among the living agnathans — the jawless vertebrates. Their bodies are long, soft, scaleless and supported by cartilage rather than bone. They lack paired fins and jaws, and feed with horny tooth-like structures that allow them to rasp flesh from carrion or from dead and dying animals.The paper in Biology Letters was accompanied by a news release from the University of Wisconsin-Milwaukee:
Modern hagfish are mostly animals of cold marine waters, often living on or in soft seabed sediments, where they may lie partly buried with only the head exposed. They feed largely as scavengers, but this should not be taken to mean that they are merely passive cleaners of the deep sea. Observations have shown that hagfish can also prey on other animals and may play a more varied ecological role than was once assumed.
Their most famous feature is their slime. When attacked, hagfish eject a mixture of mucus and fine protein threads from rows of slime glands along the body. In seawater this expands rapidly into a gelatinous mass that can clog the mouth and gills of a predatory fish, forcing it to release the hagfish. The hagfish can then tie itself into a knot and pass the knot along its body, scraping away excess slime and helping it escape or feed.
Hagfish are also important in evolutionary biology because they occupy a key position close to the base of the vertebrate family tree. They show that evolution is not a simple march from “simple” to “complex”. Modern hagfish are not primitive failures or unfinished animals; they are highly specialised survivors, well adapted to a particular way of life.
Their eyes are especially significant. In living hagfish the eyes are extremely reduced, lacking the lens and pigmentation typical of more familiar vertebrate eyes, and are covered by soft tissue. For that reason, hagfish were once tempting candidates for the idea that their eyes represented an early, primitive stage in the evolution of the vertebrate eye. Fossil evidence now shows something more interesting: hagfish eyes are not primitively simple, but secondarily simplified. In other words, their ancestors had more complex eyes, and the modern condition evolved through loss and reduction.
That makes hagfish a particularly useful example of evolutionary change. They show that evolution can produce loss as well as gain, simplification as well as elaboration, and that reduced organs can be just as much the product of natural evolutionary history as complex ones.
UWM research sheds new light on the evolution of hagfish eyes
New research led by a University of Wisconsin-Milwaukee geoscientist provides insight into how one of the most primitive living vertebrates evolved its uniquely simple visual system. The study, published in Biology Letters on May 27, examines fossilized hagfish eyes to reconstruct how their modern, reduced structure came to be.
The study’s lead author, Victoria McCoy, assistant professor in UWM’s Department of Geoscience, collaborated with researchers from the Field Museum of Natural History, the Lauer Foundation for Paleontology, Science and Education, the David and Sandra Douglass Collection and the University of Ottawa.
Hagfish, often described as the most primitive living vertebrates, possess extremely simple eyes and are nearly blind. Scientists have long hypothesized that their eyes evolved from more complex vertebrate eyes through a gradual loss of structures, likely as hagfish adapted to the dark, deep-sea environments they inhabit today.
To test this idea, McCoy and her colleagues analyzed exceptionally well-preserved fossils of three extinct hagfish species from the approximately 308 million-year-old Mazon Creek site in northeastern Illinois. Unlike modern deep-sea habitats, this ancient environment was near shore and well lit.
The fossil evidence revealed that these early hagfish had eyes more developed than those of modern hagfish, yet still less complex than typical vertebrate eyes, representing an intermediate stage in eye reduction.
This study shows that the hagfish eye didn’t become simple all at once. Instead, it evolved through a gradual, stepwise loss of complexity over millions of years. Importantly, some of these changes appear to have happened before hagfish moved into the low-light environments where they live today.
Arjan Mann, co-author
Lauer Foundation for Paleontology, Science and Education
Wheaton, IL, USA.
These findings challenge the long-held assumption that deep-sea conditions alone drove the degeneration of hagfish vision, suggesting instead that aspects of this evolutionary process began earlier.
The research emphasized the importance of fossil evidence in understanding evolutionary transitions.
Fossils like those from Mazon Creek give us a rare window into evolutionary history. They allow us to see intermediate forms that bridge the gap between ancient organisms and their modern relatives, helping us understand how dramatic changes, like the reduction of a complex eye, actually unfold over time.
Assistant Professor Victoria E. McCoy, lead author
Department of Geosciences
University of Wisconsin-Milwaukee
Milwaukee, WI, USA.
The study highlights the importance of combining paleontological data with evolutionary biology to better understand how major anatomical transformations occur.
Publication:
Here again we have a fossil that should not exist if creationism were true: a 308-million-year-old hagfish from a world that existed hundreds of millions of years before the mythical creation week, preserving an intermediate stage in the evolutionary reduction of a vertebrate eye. It is not merely old; it is inconveniently old, inconveniently transitional, and inconveniently explanatory.
The significance of this discovery is not just that hagfish eyes became simpler, but that the fossil evidence shows how that simplification happened. Far from being an inexplicable loss of “information”, it is an example of evolution doing exactly what evolutionary theory says it can do: modifying existing structures according to changing circumstances, sometimes by elaboration, sometimes by reduction, and sometimes by removing what is no longer useful enough to justify its biological cost.
Nor is there any need to invoke magic, design, or supernatural tinkering. The history is written in the fossils and in the anatomy of living hagfish. Their reduced eyes are not evidence of failed design, nor of a primitive animal waiting to become something better; they are evidence of descent with modification, of ancestry, adaptation, and evolutionary change over deep time.
Creationism has no useful explanation for any of this. It cannot explain the age of the fossil, the intermediate condition of the eye, the stepwise reduction in complexity, or the way this evidence overturns an earlier scientific assumption without overturning evolution itself. All it can offer is denial, misrepresentation, or silence.
Science, meanwhile, does what it always does at its best: it follows the evidence, corrects itself when the evidence demands it, and improves our understanding of the natural world. The hagfish, blind or nearly so, has once again helped science see more clearly.
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