Posted on 02/08/2005 3:50:43 AM PST by PatrickHenry
A group of four-footed mammals that flourished worldwide for 40 million years and then died out in the ice ages is the missing link between the whale and its not-so-obvious nearest relative, the hippopotamus.
The conclusion by University of California, Berkeley, post-doctoral fellow Jean-Renaud Boisserie and his French colleagues finally puts to rest the long-standing notion that the hippo is actually related to the pig or to its close relative, the South American peccary. In doing so, the finding reconciles the fossil record with the 20-year-old claim that molecular evidence points to the whale as the closest relative of the hippo.
"The problem with hippos is, if you look at the general shape of the animal it could be related to horses, as the ancient Greeks thought, or pigs, as modern scientists thought, while molecular phylogeny shows a close relationship with whales," said Boisserie. "But cetaceans – whales, porpoises and dolphins – don't look anything like hippos. There is a 40-million-year gap between fossils of early cetaceans and early hippos."
In a paper appearing this week in the Online Early Edition of the Proceedings of the National Academy of Sciences, Boisserie and colleagues Michel Brunet and Fabrice Lihoreau fill in this gap by proposing that whales and hippos had a common water-loving ancestor 50 to 60 million years ago that evolved and split into two groups: the early cetaceans, which eventually spurned land altogether and became totally aquatic; and a large and diverse group of four-legged beasts called anthracotheres. The pig-like anthracotheres, which blossomed over a 40-million-year period into at least 37 distinct genera on all continents except Oceania and South America, died out less than 2 and a half million years ago, leaving only one descendent: the hippopotamus.
This proposal places whales squarely within the large group of cloven-hoofed mammals (even-toed ungulates) known collectively as the Artiodactyla – the group that includes cows, pigs, sheep, antelopes, camels, giraffes and most of the large land animals. Rather than separating whales from the rest of the mammals, the new study supports a 1997 proposal to place the legless whales and dolphins together with the cloven-hoofed mammals in a group named Cetartiodactyla.
"Our study shows that these groups are not as unrelated as thought by morphologists," Boisserie said, referring to scientists who classify organisms based on their physical characteristics or morphology. "Cetaceans are artiodactyls, but very derived artiodactyls."
The origin of hippos has been debated vociferously for nearly 200 years, ever since the animals were rediscovered by pioneering French paleontologist Georges Cuvier and others. Their conclusion that hippos are closely related to pigs and peccaries was based primarily on their interpretation of the ridges on the molars of these species, Boisserie said.
"In this particular case, you can't really rely on the dentition, however," Boisserie said. "Teeth are the best preserved and most numerous fossils, and analysis of teeth is very important in paleontology, but they are subject to lots of environmental processes and can quickly adapt to the outside world. So, most characteristics are not dependable indications of relationships between major groups of mammals. Teeth are not as reliable as people thought."
As scientists found more fossils of early hippos and anthracotheres, a competing hypothesis roiled the waters: that hippos are descendents of the anthracotheres.
All this was thrown into disarray in 1985 when UC Berkeley's Vincent Sarich, a pioneer of the field of molecular evolution and now a professor emeritus of anthropology, analyzed blood proteins and saw a close relationship between hippos and whales. A subsequent analysis of mitochondrial, nuclear and ribosomal DNA only solidified this relationship.
Though most biologists now agree that whales and hippos are first cousins, they continue to clash over how whales and hippos are related, and where they belong within the even-toed ungulates, the artiodactyls. A major roadblock to linking whales with hippos was the lack of any fossils that appeared intermediate between the two. In fact, it was a bit embarrassing for paleontologists because the claimed link between the two would mean that one of the major radiations of mammals – the one that led to cetaceans, which represent the most successful re-adaptation to life in water – had an origin deeply nested within the artiodactyls, and that morphologists had failed to recognize it.
This new analysis finally brings the fossil evidence into accord with the molecular data, showing that whales and hippos indeed are one another's closest relatives.
"This work provides another important step for the reconciliation between molecular- and morphology-based phylogenies, and indicates new tracks for research on emergence of cetaceans," Boisserie said.
Boisserie became a hippo specialist while digging with Brunet for early human ancestors in the African republic of Chad. Most hominid fossils earlier than about 2 million years ago are found in association with hippo fossils, implying that they lived in the same biotopes and that hippos later became a source of food for our distant ancestors. Hippos first developed in Africa 16 million years ago and exploded in number around 8 million years ago, Boisserie said.
Now a post-doctoral fellow in the Human Evolution Research Center run by integrative biology professor Tim White at UC Berkeley, Boisserie decided to attempt a resolution of the conflict between the molecular data and the fossil record. New whale fossils discovered in Pakistan in 2001, some of which have limb characteristics similar to artiodactyls, drew a more certain link between whales and artiodactyls. Boisserie and his colleagues conducted a phylogenetic analysis of new and previous hippo, whale and anthracothere fossils and were able to argue persuasively that anthracotheres are the missing link between hippos and cetaceans.
While the common ancestor of cetaceans and anthracotheres probably wasn't fully aquatic, it likely lived around water, he said. And while many anthracotheres appear to have been adapted to life in water, all of the youngest fossils of anthracotheres, hippos and cetaceans are aquatic or semi-aquatic.
"Our study is the most complete to date, including lots of different taxa and a lot of new characteristics," Boisserie said. "Our results are very robust and a good alternative to our findings is still to be formulated."
Brunet is associated with the Laboratoire de Géobiologie, Biochronologie et Paléontologie Humaine at the Université de Poitiers and with the Collège de France in Paris. Lihoreau is a post-doctoral fellow in the Département de Paléontologie of the Université de N'Djaména in Chad.
The work was supported in part by the Mission Paléoanthropologique Franco-Tchadienne, which is co-directed by Brunet and Patrick Vignaud of the Université de Poitiers, and in part by funds to Boisserie from the Fondation Fyssen, the French Ministère des Affaires Etrangères and the National Science Foundation's Revealing Hominid Origins Initiative, which is co-directed by Tim White and Clark Howell of UC Berkeley.
You are perhaps thinking of how your #1 website guru says that Genesis is correct because the flood really happened ergo evolution is false ...
Demvolution.
I would suggest that there is no really good definition of species. (At least, I heard that over 50 years ago; it's gotten worse.) "Species" is not a property of an individual (or even a group); I suggested calling assuming so, the Cladistic Fallacy. It is a result of our classification methods.
Of course, to make things worse, the real world doesn't give clear boundaries among what we might like to call species. Things are even more complicated with plants and bacteria.
Entire books have been written debunking that creationist pap. There's no need to do it again simply because you demand it.
I'm sure you will respond now with some kind of accusation that somehow I am incapable of responding to your brilliant post. Sorry to disappoint, but I'm really just too lazy to waste my time arguing with a fencepost.
Why would God design an imperfect "reproductive system" for humans in which there is a high probability of an aborted fertilized egg each time unprotected sex occurs?
ok, I'll bite:
one of the principal tests of the utility/viability of a theory (an explanation of available data) is its accuracy as a predictive model for data not available when the theory is coined.
Evolutionary theory has been confirmed as a useful predictor thousands of times by the biological and other physical sciences.
Creation "theory" cannot claim even ONE such confirmation.
Given the history of this (and many other CREVO threads), I sincerely doubt this data set shall make any change in your stance. So be it.
It would be useful to me, and the others here, if you would deign to clearly define what you would consider sufficient proof of evolutionary theory's utility/viability/scientific accuracy. After years of battling leftists in political debate, I have no love to spare for anyone's propensity to use mobile goalposts in a debate of science, so answer the question definitively and finally. After all, you know where WE stand - where do you?
I sadly recognize these facts... it just galls the precision machinist in me.
Since the bibul has no real meaning at all, literal or otherwise, it is a waste of time to print it, as it belongs in the dark corner of a museum. What needs to be said is that it is an almost complete waste of time to use your eyesight to read it at all. It is just a tool used to lay a guilt trip on people and to force morality on people.
"Don't take the bibul literally" is a very dumb statement, it should be replaced by "don't waste your time in the bibul at all"
Read Asimov or Huxley instead.
Alleles are alternative characteristics at a particular loci (place) on the chromosome. Mendel's pea experiments illustrate alleles. You might have white flowers or yellow flowers. One might be dominate and the other recessive. This gives rise to hybrids.
A mutation might occur that makes a red flower. Then there is a third allele. An individual can only have a pair of alleles. Populations have the total allele alternatives for a given loci. Each gene loci might have a number of different alleles (short or tall, big leaf or little leaf etc)
There may be tens or hundreds of different alleles for the same loci. As the total percentage of each allele changes or by the addition of new alleles through mutation or other mechanisms, evolution in the population occurs. As natural selection operates on these alternatives, the optimum mixture for survival in the enviroment of the population begins to emerge.
You also need to understand the difference between phenotype and genotype.
And that is why the understanding of allele frequency change is crucial to understanding evolution. It is evolution.
OK nite nite
This is where you're mistaken. With computerized DNA sequencing technology, bacteria genomes can be assembled in a matter of weeks and compared with other previously assembled genomes within hours. Bacteria are relatively simple organisms, their DNA has been well-studied and their life cycles are well known. Cultures of bacteria are first sequenced and then exposed to a set of stressful environmental conditions. After the experiments are complete, DNA samples are taken from the surviving bacteria, run through the sequencing machines, and compared with that of their ancestors. From these experiments, the rate of change in bacteria DNA is objectively measured. From these experiments, predictions may be made and conclusions can be reached about if, or how far a certain trait might progress through several generations. The results are predictable and repeatable.
How can you honestly subject evolution to the scientific method and consider it anything more than a theory?
Consider that relativity and quantum mechanics are "nothing more than theories" too. A theory in scientific term does not mean exactly the same thing to the scientist that it does to the layman. When most people in these debates says theory, what they really mean to say is something more like "conjecture." To the scientist a theory is much more than conjecture, or even hypothesis.
Some of the people on this thread who are opposed to evolutionary theory clearly believe it is at best conjecture or at worst fraud. Often, evolution is dismissed as "only a theory." However, this is not only a misunderstanding of science, but it lessens other valuable scientific theories including the theories of relativity and quantum mechanics (upon which rests much of our technology of computers and electronics) and the theory of plate tectonics (upon which rests much of our sciences of geology and technology of oil exploration). Much of medical sciences rests directly on top of the theories of Charles Darwin and Gregor Medel. Without their contributions, it is unlikely that we would have the more recent contributions of scientists such as James Watson and Francis Crick.
Forget it. Your continuous ridiculing of God and His design have gotten too tiring. I suppose your contention is that God either doesn't exist, is a bad designer, or is not sovereign. This perverted worldview of yours affects how you interpret things, as demonstrated in this and many of your posts.
Pat yourself on the back. I'm quitting this discussion. You win.
Mean. I like it.
I have no idea where you stand. And I don't think "We" is an appropriate word to use when discussing communal beliefs of creationists.
Are you a "six day" creationist? Or an "old earth" creationist. Perhaps one of those that thinks there was "micro" evolution or one who thinks that there is no evolution at all.
Perhaps you're a creationist that goes to Mass, or one that thinks ill of papists. Perhaps you're a Moslem creationist, or Jewish creationist.
Just how many religious denominations are there anyway?
There is no "We" about what creationists believe, which is one reason why I put credence in science when the subject at hand is the history of the physical world. At least science pays attention to Gods creation, while creationists only concoct conflicting meanings from the same set of words and ignore the physical evidence.
hrmn...
do you consider the known and measured incidence of random mutation to gametogenic DNA due to radiation, chemical exposure, viral infection, and other causes to be "theoretical"?
do you consider the known fact that mutations can be recessive, non-lethal, beneficial, subliminal under some conditions but distinct in others (careful: I carry SEVERAL inherited mutations of this sort), as well as harmful, dominant, and lethal to be "theoretical"?
do you consider the observable fact that geographically separated individuals tend not to interbreed anywhere near as often as they do with readily accessable individuals to be "theoretical"?
do you consider the observable fact that these above givens lead to concentrations of genetic mutations unique to or at least quite distinctive of populations in one region but not in another to be "theoretical"?
do you consider the observable fact that these above givens lead to genetically distinct sub-populations to be "theoretical"?
do you believe that genetic sequencing pinpointing the time when a mutation or set of characteristics arrived in a particular population through genetic assay of the remains of ancestors to be "theoretical"?
forgive me if I err, but it truly does seem to me that you consider "theoretical" any evidence which counters your worldview.
When did whales stop breathing air? ;)
ah, sorry: I am not a creationist.
I accept the evidence pointing to the mechanisms of speciation.
I was directly answering Jaysun, but pinging the other "evolutionists" or "anti-creationists" (his words, his and those of his ilk) who have been active in this thread.
I was asking Jaysun to set the bar: what DOES rise to the level of "proof" in his dimension?
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