Because of the early divergence from the therian mammals and the low numbers of extant monotreme species, the platypus is a frequent subject of research in evolutionary biology. In 2004, researchers at the Australian National University discovered the platypus has ten sex chromosomes, compared with two (XY) in most other mammals (for instance, a male platypus is always XYXYXYXYXY), although given the XY designation of mammals, the sex chromosomes of the platypus are more similar to the ZZ/ZW sex chromosomes found in birds.
The platypus genome also has both reptilian and mammalian genes associated with egg fertilisation. Since the platypus lacks the mammalian sex-determining gene SRY, the mechanism of sex determination remains unknown. A draft version of the platypus genome sequence was published in Nature on 8 May 2008, revealing both reptilian and mammalian elements, as well as two genes found previously only in birds, amphibians, and fish. More than 80% of the platypus' genes are common to the other mammals whose genomes have been sequenced.
Although I do not concur in Mann's assertion that pigs share more traits with humans than do chimpanzees, I do think pigs and humans share more than enough traits to suggest a relationship. For example, lightly pigmented eyes, in shades of blue, green, and tan, are never found in chimpanzees or orangutans.3 There is, apparently, only one known case of a gorilla with blue eyes.4 Light-colored eyes are also rare in other primates.5 Why, then, are they common in certain human populations? Where did this trait come from? One conceivable explanation is that it was inherited from blue-eyed pigs.
He argues that humans are probably the result of multiple generations of backcrossing to chimpanzees, which in nucleotide sequence data comparisons would effectively mask any contribution from pig.
A short list of differential features, for example, would include, multipyramidal kidney structure, presence of dermal melanocytes, melanoma, absence of a primate baculum (penis bone), surface lipid and carbohydrate composition of cell membranes, vocal cord structure, laryngeal sacs, diverticuli of the fetal stomach, intestinal "valves of Kerkring," heart chamber symmetry, skin and cranial vasculature and method of cooling, and tooth structure. Other features occasionally seen in humans, like bicornuate uteruses and supernumerary nipples, would also be difficult to incorporate into a purely primate tree.
During my years at the genetics department, I became increasingly dissatisfied with the standard explanation of evolution. The more I read about fossils, the more convinced I became that Darwin's account of the evolutionary process was fundamentally flawed. Moreover, in my study of hybrids I became aware that an alternative way of thinking about evolution, what I now call "stabilization theory," could do a better job of explaining the available data.
Over the years, in addition to the dry papers I published on such topics as new genetics software I had written, or surveys of the mouse and rice genomes, I wrote successive versions of a paper explaining the problems I saw with standard evolutionary theory and presented my alternative explanation. These manuscripts, once submitted, would promptly arrive in the hands of anonymous reviewers who would recommend rejection, because, they said, my claims contradicted accepted tenets of standard theory. Well, yes, of course they did — because I was trying to present an alternative evolutionary theory that, if correct, would imply that Darwinian theory is mistaken at an axiomatic level.
My evolving manuscript on evolution, repeatedly rejected, continued to grow and change as I revised it and passed it around to colleagues. Finally it became a book, which I submitted to Oxford University Press in the summer of 2007. After peer review, it was accepted for publication and we signed a contract. The working title for the manuscript was On the Origins of New Life Forms.
On the other hand, there were reviews that raised objections, all of the same ilk — that my claims were inconsistent with one tenet or another of accepted theory. For those who shy away from anything that rocks the establishment's boat, such objections can never be satisfactorily addressed. And yet, for someone like me, who is trying to critique and improve upon standard theory, they are not even valid. Obviously, a new theory that contradicts an existing theory will be inconsistent with the tenets of that theory!
The domestic pig is being increasingly exploited as a system for modeling human disease. It also has substantial economic importance for meat-based protein production. Physical clone maps have underpinned large-scale genomic sequencing and enabled focused cloning efforts for many genomes. Comparative genetic maps indicate that there is more structural similarity between pig and human than, for example, mouse and human, and we have used this close relationship between human and pig as a way of facilitating map construction.
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