Recent Problems in Evolution - 1994

Table of Contents

Discontinuous morphological changes in the hominid lineage

New data from paleontological discoveries and geochronology show that the pattern of morphological change in the hominid lineage was not linear, but mosaic. Adaptations essential to bipedalism appeared early, but some locomotor features changed much later. Relative to the highly derived postcrania of the earliest hominids, the craniodental complex was quite primitive (i.e., like the reconstructed last common ancestor with the African great apes). The pattern of craniodental change among successively younger species of Hominidae requires, according to evolutionary theories, extensive parallel evolution between at least two lineages in features related to mastication. Relative brain size increased slightly among successively younger species of Australopithecus, expanded significantly with the appearance of Homo, but within early Homo remained at about half the size of Homo sapiens for almost a million years. The fossil record indicates an accumulation of relatively rapid shifts in successive species, and certainly not any kind of progressive changes. (McHenry H.M. Proceedings of the National Academy of Sciences of the United States of America 91 (15): 6780-6, 1994.)

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DNA that does not carry the information necessary to make a protein.Non-coding regions of the chloroplast genome

The chloroplast genome (cpDNA) of plants has been a focus of research in plant molecular evolution and systematics. Despite a conservative rate of evolution and a relatively stable gene content, comparative molecular analyses reveal complex patterns which are difficult to explain on the basis of Relating to a permanent structural alteration in DNA, consisting of either a substitution, insertion or deletion of nucleotide bases.mutational changes. There are changes in DNA that does not carry the information necessary to make a protein.non-coding regions of cpDNA that are site dependent. Coding genes exhibit different patterns of A specific sequence of three adjacent nucleotides on a strand of DNA or RNA that specifies the genetic code information for encoding a specific amino acid into a polypeptide chain.codon bias that violate the equilibrium assumptions of evolutionary models. Rates of molecular change often vary among plant families and orders in a manner that violates the assumption of a molecular clock. Finally, An organic compound made of amino acids arranged in a linear chain, joined together by peptide bonds between the carboxyl and amino groups of the adjacent amino acid residues.protein-coding genes exhibit patterns of A group of 20 different kinds of small molecules that link together in long chains to form proteins. Often referred to as the "building blocks" of proteins.amino acid change that appear to depend on An organic compound made of amino acids arranged in a linear chain, joined together by peptide bonds between the carboxyl and amino groups of the adjacent amino acid residues.protein structure, which do not appear to be dependent upon structure/function relationships. (Clegg MT., Gaut BS., Learn G.H. Jr. and Morton BR. Proceedings of the National Academy of Sciences of the United States of America 91 (15): 6795-801, 1994.)

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Dorsal thalamus in vertebrates

"The evolution of the dorsal thalamus in various vertebrate lineages of jawed vertebrates has been an enigma." (Butler AB. Brain Research - Brain Research Reviews 19 (1): 29-65, 1994.)

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Rapid appearance of Cretacea (whales)

A recent fossil discovery (Pakicetus inachus) in Pakistan has demonstrated the appearance of nearly modern whales (Cretacea) over 50 million years ago. This species had no forearms and a very short femur (with no other hind limb bones). It has high dorsal neural spines and long ventral chevrons, necessary for swimming by dorsoventral oscillation with a heavily muscled caudal fluke. These characteristics necessitate the evolution of a fully aquatic, nearly modern whale from a non-aquatic ancestor in less than 10 million years, which is very unlikely. (Gingerich, PD., Raza, SM., Arif, M, Anwar, M, and Ahou, X. Nature 368: 844-847, 1994.)

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Recent appearance of Europeans

Of or referring to the mitochondria, the organelles that generate energy for the cell.Mitochondrial Deoxyribonucleic acid: the chemical inside the nucleus of a cell that carries the genetic instructions for making living organisms.DNA The order of nucleotides in a DNA or RNA molecule, or the order of amino acids in a protein molecule.sequences from 74 Swiss individuals were compared to The order of nucleotides in a DNA or RNA molecule, or the order of amino acids in a protein molecule.sequences from British and Finish populations. Researchers found that the One of the structural components, or building blocks, of DNA and RNA. A nucleotide consists of a base plus a molecule of sugar and one of phosphate.nucleotide The order of nucleotides in a DNA or RNA molecule, or the order of amino acids in a protein molecule.sequence differences between those populations are almost as low as those within the populations. However, larger differences between three African populations, suggest a recent origin of the European populations. Researchers suggested that the low diversity among European Genetic material found in mitochondria, the organelles that generate energy for the cell.mtDNA could coincide with the appearance of anatomically modern humans about 40,000-30,000 years ago or, alternatively, the spread of agriculturalists about 10,000-6,000 years ago. (Pult I, Sajantila A, Simanainen J, Georgiev O, Schaffner W, Paabo S. 1994. Of or referring to the mitochondria, the organelles that generate energy for the cell.Mitochondrial Deoxyribonucleic acid: the chemical inside the nucleus of a cell that carries the genetic instructions for making living organisms.DNA The order of nucleotides in a DNA or RNA molecule, or the order of amino acids in a protein molecule.sequences from Switzerland reveal striking homogeneity of European populations. Biol. Chem. Hoppe. Seyler 375: 837-840.)

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