Friday 9 February 2024
The concept of the chronospecies is becoming a palaeospecies?
Fossil Friday: Chronospecies, a Sinking Ship
In my public presentations and articles on the problems for neo-Darwinism raised by the ubiquitous discontinuities of the fossil record, I usually do not just present a series of abrupt appearances of new body plans in the history of life. Rather, I also describe how gradualism fails to be supported even on lower taxonomic levels. One example is my Evolution News article from September 2019, where I showed how all the three major textbook examples for alleged gradual species-to-species transitions have been debunked by more modern mainstream research (Bechly 2019).
The Concept of Chronospecies
A potential response by Darwinists could be to refer to the concept of chronospecies in paleontology (sometimes called paleospecies or morphospecies), which was introduced by George (1956) for the naming of successive species in a single evolving lineage. Putative examples are known from marine protozoans (e.g., foraminiferans, see Wei 1987), marine invertebrates (e.g., ammonites, see Dzik 1990), and a few cases in vertebrates, such as fossil water rats (see Escudé et al. 2008) and the extinct endemic bovid Myotragus from the Mediterranean Balearic islands of Mallorca and Menorca (Moya Sola & Moya 1982, Köhler & Moya-Sola 2004, Bover & Alcover 2005, Moya Sola et al 2007, Bover et al. 2010).
Of course, such chronospecies are not at all uncontroversial. Some experts deny that these represent macroevolutionary speciation, but instead simply represent microevolutionary changes within a single species (e.g., Willmann 1985, Allmon 2016), and thus are completely arbitrary delimitations (Cain 1954, Thomas 1956, Simpson 1961: 165, Mayr 1963: 24, Mayr & Ashlock 1991: 106) of chunks of a genealogical nexus (Kitts & Kitts 1979, Kitts 1983, Lyman & O’Brien 2002). But in all fairness, such fuzzy chunks arguably are what we should expect to find if there were indeed gradual species-to-species transitions, especially in cases of anagenetic change within a single evolving species lineage.
A Common Pattern
But, even in the few known cases, it has become a common pattern that new research tends to challenge and refute the status of chronospecies. One example are the marine sloths of the extinct genus Thalassocnus, which lived with five successive species in the Late Miocene and Pliocene along the Pacific coast in South America. “They were regarded by McDonald and Muizon (2002) as segments of a single lineage representing the initial and progressively more aquatic adaptations” (Muizon et al. 2003). Nevertheless, the study by Muizon et al. (2003) concluded that:
Parsimony analysis does not resolve the relative positions of T. antiquus and T. natans, and, therefore, does not fully confirm the possibility of a single Thalassocnus lineage, which spans over 4 Ma. However, Thalassocnus is an endemic genus and the stratigraphic distribution of its four species is well known. Furthermore, some characters indicate a continuous evolution from the oldest (T. antiquus) to the youngest species (T. carolomartini). Therefore, we prefer the hypothesis of a single Thalassocnus lineage, although a more complex evolutionary scenario is not discarded.
The authors elaborated that:
The new parsimony analysis presented here indicates that the four species of Thalassocnus may not represent a single evolving lineage. … Although parsimony analysis indicates that the absence and existence of a single time-successive lineage including all four species of Thalassocnus are equally parsimonious, we are reluctant to accept the first interpretation. … To conclude, a definitive decision is not easy to establish because reversals could explain the morphology … In spite of the result of the parsimony analysis, we believe that the exclusion of T. natans from a ‘‘Thalassocnus lineage’’ would be a surprising coincidence and that only a single Thalassocnus lineage is likely to have existed in the southeastern Pacific. … However, we do not discard the possibility of a more complex evolutionary scenario for Thalassocnus.
Slowly Sinking
In short: There is by no means unequivocal evidence for gradual anagenetic speciation in the case of the aquatic sloth Thalassocnus. Given the other refuted examples (see Bechly 2019), this raises further doubts about the validity of the few remaining cases of alleged gradual species-to-species transitions. Stanley (1978) found in his seminal analysis of chronospecies that “most net evolutionary change must have been associated with saltational speciation.” Also the metastudy of Hunt (2010), who looked at 150 years of research on the fossil evidence for speciation since the time of Darwin, found no evidence for the directional change predicted by anagenetic (or even cladogenetic) speciation (see Bechly 2019). The “ship” of chronospecies seems to be slowly sinking, which suggests that non-gradual processes dominated the history of life even on the lower taxonomic levels. That is consistent with intelligent design theory but inconsistent with neo-Darwinian evolution.
The Ovum vs. Darwin.
The Exquisite Design of Egg Cells
In two previous articles (here and here), I discussed the irreducible complexity of sperm cells and the seminal fluid for successful fertilization. Now, I will review the exquisite design features of a female egg cell (also called an ovum, plural ova). Here is an animation of the incredible process of reproduction, from ejaculation to birth.
Oogenesis
Oogenesis (the process of egg cell formation) begins during embryonic development when the primordial germ cells are specified. These cells migrate to the genital ridges, which later develop into the female ovaries. Prior to birth, the primordial germ cells undergo mitotic divisions to form oogonia, the precursor cells for eggs. These oogonia transform into primary oocytes, which are diploid cells arrested in prophase I of meiosis. This arrest typically occurs before or shortly following birth.
Primary oocytes are surrounded by somatic cells to form primordial follicles, which go through a process called folliculogenesis, where they develop into primary, secondary and eventually tertiary follicles. As a female reaches sexual maturity, some primary oocytes are activated each menstrual cycle. The activated primary oocyte completes meiotic division I, resulting in the formation of a secondary oocyte and a smaller cell called a polar body (the primary purpose of the polar body is to discard the extra genetic material that is produced during meiosis). However, the secondary oocyte is arrested in metaphase II.
The mature follicle ruptures during ovulation, releasing the secondary oocyte into the fallopian tube. If fertilized by a sperm cell, the secondary oocyte completes meiotic division II, resulting in a mature egg (ovum) and another polar body. If fertilization does not occur, meiosis II is not completed. After ovulation, the remaining follicle transforms into the corpus luteum, which secretes hormones like progesterone to prepare the uterus for a potential pregnancy. If fertilization doesn’t happen, the corpus luteum degenerates, resulting in a drop in hormone levels. This triggers menstruation, and the cycle resets.
Fertilization
As I discussed previously, sperm cells swim through the female reproductive tract, directed by the cilia, in addition to chemical signals. Chemicals called chemoattractants are released by the egg cell, and these serve as signaling molecules that generate a concentration gradient. The sperm cell is capable of chemotaxis, a process that results in the sperm cell moving up the concentration gradient, towards higher chemoattractant concentrations. Changes in chemoattractant concentration are detected by specialized receptors on the surface of sperm cells. When an increase in concentration is detected, a signaling cascade is triggered within the cell, which influences the flagellum’s beating pattern. Thus, the sperm moves progressively in the direction of the egg — that is, the source of the chemoattractants. As the sperm swims towards the egg, the concentration of chemoattractants is continuously being measured, which allows it to adjust its course in order to fine-tune its movements. Once the sperm gets within close proximity of the egg, it encounters other signaling molecules that further guide the sperm cells and direct it towards the egg’s plasma membrane, the site of fertilization.
Upon reaching the egg, the sperm cell encounters the zona pellucida, a glycoprotein rich matrix that surrounds the egg. Sperm-egg recognition begins with the interaction between glycoproteins on both the sperm surface and zona pellucida, thereby guiding the sperm cell towards the egg cell’s surface.
In a previous article, I wrote about the acrosome, a specialized structure possessed by sperm cells, that contains enzymes that aid in penetrating the egg’s protective barriers. Contact between the sperm and the zona pellucida results in the acrosome undergoing exocytosis, releasing these enzymes. These enzymes help to create a pathway for the sperm to arrive at the plasma membrane of the egg. Once through, fusion occurs between the egg and the sperm’s plasma membrane, thereby allowing the sperm’s genetic material to come into proximity with the egg’s cytoplasm.
Egg Activation
Upon fusion of the plasma membranes of the sperm and egg, various changes are triggered in the egg, collectively referred to as “egg activation.” First, the egg’s membrane becomes less permeable to other sperm, in order to prevent a single egg from being fertilized by more than one sperm cell. The fast block to polyspermy involves a change in the electrical properties of the egg’s plasma membrane. When the sperm’s outer layers are successfully penetrated by the sperm cell, it triggers the release of calcium ions (Ca2+) from intracellular stores in the egg.
The influx of calcium ions serves as a signal to initiate changes in the egg’s membrane potential. Ion channels on the egg’s membrane are opened, and facilitate the entry of sodium ions (Na+). The consequence is that the egg’s plasma membrane depolarizes. Normally, the egg’s membrane is maintained at a negative resting potential. However, the influx of positive sodium ions neutralizes this negative potential, making the membrane potential less negative. The altered membrane potential makes it more difficult for other sperm to initiate the fusion process, and thereby creates a temporary electrical barrier that inhibits additional sperm from fusing with the egg. The depolarization is a temporary phenomenon. After a brief period, the egg membrane potential is restored to its normal resting state (often referred to as “resetting” the egg).
A secondary defense against polyspermy is known as the slow block, or the “cortical reaction.” As calcium ions are released upon fertilization, this triggers the exocytosis of cortical granules, located just beneath the egg’s plasma membrane, containing enzymes. The glycoproteins in the zona pellucida are cross-linked by these enzymes, and this results in the hardening of the zona pellucida, reducing its permeability. The modified zona pellucida forms a structure called the “fertilization envelope,” which surrounds the egg, forming a barrier that physically blocks additional sperm from gaining access to the egg’s surface.
Changes also take place in the egg cell that promote the completion of meiosis and initiate early embryonic development. The genetic material of the sperm and egg, consisting of a single set of chromosomes each (23 chromosomes in humans), combine to form a diploid cell called the zygote, which contains the full set of chromosomes needed to develop a new individual. This instantly determines gender, eye and hair color, and many other traits.
After fertilization has occurred, the zygote begins to undergo a series of rapid cell divisions through a process called cleavage. This results in the development of a multicellular embryo, which travels through the fallopian tube towards the uterus. Eventually, it arrives at the uterus and attaches to the uterine lining in a process called implantation.
An Exquisite Design
As one can see from the foregoing discussion, the development of an egg cell and its activation in response to encountering a sperm cell exhibit exquisite design, being contingent upon multiple mutually dependent processes, all of which are needed for successful reproduction. When considered in conjunction with the incredible engineering features of the sperm cell and the seminal fluid (discussed in a previous articles), it would seem to put the thesis of design almost beyond question
Survival of the most reproductive?
A Darwinian Dilemma: The Paradox of Reproduction
Fundamental to the understanding of life is the study of physiology. Physiology is that branch of biology which describes the functions of the various organs and tissues that make life possible. All the separate organ systems perform different functions that are required for life to exist, e.g., respiration, circulation, digestion, detoxification, excretion, metabolism, etc.
Without all of the systems working constantly, consistently, efficiently, and effectively, life would cease. Together, they are necessary and sufficient to sustain the life of the individual. Because life is all about survival, correct? According to Charles Darwin, organisms are here solely on the basis of their ability to survive, with natural selection eliminating those unable to prevail against their more fit competitors.
A Unique Organ System
And yet… Astonishingly, there is one unique organ system that actually detracts from the chances of survival of even the fittest individuals. One organ system that makes survival less likely, even to the point of seriously endangering the life of the individual. Writing here this morning, biologist Jonathan McLatchie detailed one part of it.
That system is the reproductive system. In order to survive in the wild, an organism has to acquire food, conserve energy, find a safe niche, and avoid predation, injury, or mishap. However, reproduction requires that an organism give up food, expend energy, and dispense with safety by engaging in risky behaviors. All these activities actually decrease the odds of individual survival.
So, Darwin’s theory of natural selection really is not about survival of the fittest, but survival of those best at reproduction. He characterized this as “reproductive selection.” But he was not referring to the dangers of reproduction at all. He was referring rather to the ability of competing males to acquire breeding privilege.
But Therein Lies a Paradox
Why should an individual organism devote itself to something other than itself? If organisms are really just blindly generated collections of molecules, why would these “molecular aggregates” struggle for life, and even much more than that, risk their own life for the sake of offspring?
As always, the perennial answer to such questions comes back to purpose. As I have mentioned repeatedly in previous posts here on the science of purpose, life itself is nothing if not purpose-driven.
And this purposive intentionality, which extends all the way up from the DNA to the cell to the organ to total body physiology, culminates in the most purposeful action in all of life, renewal by reproduction. Because, in the words of St. Thomas Aquinas, “All things are ordered to their end.”
More on the humanity of ancient humans.
Human Origins and the Beginning of Art
Last week for Fossil Friday, paleontologist Günter Bechly noted here, “In my humble opinion, the evidence for symbolic thinking, language, and genetic admixture clearly suggests that Neanderthals belong to our very own species.” The reason such a statement might seem controversial in some quarters is that it was long held that Neanderthals did not think like modern humans do and could not have produced artwork. Put simply, they were not “like us.”
But there is now evidence of something like artwork among several ancient human types, not just Neanderthals. Thus, an academic controversy has arisen: “But is it really ‘art’?”
We are more accustomed to hearing that question debated fiercely in and around modern art galleries than paleontology departments. Thus, some seek to shift the discussion to something more general and basic. Take, for example, the Neanderthal etchings on a deer’s toe bone from the Unicorn Cave 51,000 years ago:
“The engraved bone from Einhornhöhle is at least 50,000 years old and thus ranges among the oldest known symbolic objects,” said Dirk Leder, an archaeologist with the Lower Saxony state government who has published research on the object. The meaning of the symbolism is lost to time, but it may have been “a device intended to communicate with other group members, outsiders, spirits or the like — we simply don’t know,” he said.
TOM METCALFE, “DID ART EXIST BEFORE MODERN HUMANS? NEW DISCOVERIES RAISE BIG QUESTIONS,” LIVE SCIENCE, FEBRUARY 2, 2024
Leder calls it “pre-art” but perhaps symbolic representation would be a useful term here. It seems to mean something but we are not sure what.
There are also the numerous stone “spheres” (spheroids) from 2 million years ago and onward.
What Are Cupules?
Science writer Tom Metcalfe also points to very ancient cupules, symmetric round holes made in rocks.
Were they all by-products of a routine activity? Or did they have a purpose of their own? Or was it perhaps a bit of both?
Archaeologist and psychologist Derek Hodgson told Metcalfe,
The ancient stone spheres, too, may be a sign that an interest in geometry was developing at that time, when early hominins experimented with symmetry to assess its merits, he said. But although this sense of symmetry is seen in early humans, it seems to be absent in some of our closest living relatives, Hodgson said. “Recent research on nonhuman primates, such as baboons, found that they were unable to identify symmetrical patterns… in contrast to modern humans, who found this task to be easy,” he said.
METCALFE, “NEW DISCOVERIES RAISE BIG QUESTIONS”
The fact that animals simply don’t do these things may be a sore point with some paleontologists. It would have been so satisfying to discover a long, slow, Darwinian progression of abstract ideas from the lemur through the chimpanzee to the human. Instead, we find humans of some type well over a million years ago apparently trying to shape a perfect sphere. As noted earlier, it is as if the human mind has no history.
The problem is, so much is lost that it is risky to draw conclusions. But what’s remarkable is how we humans have expressed ourselves with whatever is available.
And we keep learning new things about that. We learned last year that early humans hunted beavers in Europe 400,000 years ago. (The beavers’ bones show evidence of damage from tool use.) So little has really been explored that we can at least hope that new discoveries will shed light on the meanings of early human symbols.
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