Recent Problems in Evolution - 1996
- Dates calculated from "molecular evolution" do not match those in the fossil record
- Invariant genetic sites in chlorophyll and bacteriochlorophyll cast doubts on proposed evolutionary schemes
- Hox genes controlling limb development are similar in primitive fish and mammals
- Lucy kicked out of the human family tree?
- Evolutionary Pulse Theory Challenged by new data
Fossil evidence indicates that ancient bacteria, Archea (Archaebacteria) have existed on the earth for at least 3.5 billion years (1). A study published in January, 1996 examined the origin of life through molecular evolution of " 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 clocks" (2). A total of 531 The order of nucleotides in a DNA or RNA molecule, or the order of amino acids in a protein molecule.sequences of the genes of 57 metabolic enzymes from 15 phylogenetic groups were plotted based upon the known divergence dates in the fossil record. The seven divergence points of these phyla were plotted verses the time of divergence, resulting in a straight line (r = 0.94, where r = 1.0 is a perfect fit). The line indicated the origin of life occurred ~1.5 billion years ago, even though there is definitive evidence for life at 3.5 billion years ago. Drs. Mooers and Redfield attempted to explain the discrepancy with various alternatives (3). They suggested that the molecular evidence may be misleading. However, to reconcile the data, much of molecular biology would have to be discarded. They also suggested that the fossils chosen for use in the Doolittle et al. study may have been misdated. They discounted this possibility, since the fossil record of these creatures has been confirmed by numerous investigators in numerous studies. They suggested that there might have been a slower rate 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 Replacement of one nucleotide in a DNA sequence by another nucleotide or replacement of one amino acid in a protein by another amino acid.substitution in early life forms. However, these creatures, being bacteria, have generation times of minutes, compared to later creatures, which have generation times of days to years. They concluded, "This idea has no basis in theory." Mooers and Redfield then suggested that the results might be explained by multiple Replacement of one nucleotide in a DNA sequence by another nucleotide or replacement of one amino acid in a protein by another amino acid.substitutions at the same site, thus underestimating divergence times. However, Doolittle et al. tested departure from the standard model and found that this had little effect upon divergence times. The model, in fact, predicts a divergence between the plants and the animals/fungi at one billion years ago, which many scientists would think was too long ago. The only conclusion Mooers and Redfield could come up with was that present day Archea are examples of convergent evolution and are not directly descended from the ancient Archea. They propose the original Archea arose, diversified, died and arose again two billion years later. The alternative theory, that God, the Creator, does not necessarily work through a 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 clock, was not discussed.
- Schopf, J.W. 1993. Science 260: 640-646.
- Doolittle, R.F., D.-F. Feng, S. Tsang, G. Cho, and E. Little. 1996. Determining divergence times of the major kingdoms of living organisms with a 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 clock. Science 271: 470-477.
- Mooers, A.O. and R.J. Redfield. 1996. Digging up the roots of life. Science 379: 587-588.
Current evolutionary schemes hypothesize that photosynthesis arose first in prokaryotes (using the photosynthetic pigment bacteriochlorophyll). Other widely accepted theories rest on this hypothesis (i.e., the theory that eukaryotic chloroplasts arose from endosymbionts of these early prokaryotes). However, recent genetic evidence analyzing 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 of bacteriochlorophyll and chlorophyll suggests that eukaryotic chlorophyll could have appeared prior to bacteriochlorophyll (Lockhart, P.J., A.W.D. Larkum, M.A. Steel, P.J. Waddell, and D. Penny. 1996. Evolution of chlorophyll and bacteriochlorophyll: the problem of invariant sites in The order of nucleotides in a DNA or RNA molecule, or the order of amino acids in a protein molecule.sequence analysis. Proc. Natl. Acad. Sci. USA 93: 1930-1934.
Studies using Drosophila (fruit flies) have demonstrated a series of homeobox (Hox) genes, which control limb development during embriogenesis. Variants of these same genes are found in other animals that develop limbs. In tetrapods, the developing limb skews from the main axis of the limb, runs from the ulna through the ulnare triquetrum and then bends anteriorly through the distal carpals However, in primitive fish (teleosts) the developing limb does not bend anteriorly, and is truncated. This development is a paradox, since the mammalian Hox genes contain the same number of clusters, containing the same set of genes (Muragaki, Y., S. Mundlos, J. Upton, and B.R. Olsen. 1996. Altered growth and branching patterns in the synpolydactyly caused by Permanent structural alterations in DNA, consisting of either substitutions, insertions or deletions of nucleotide bases.mutations in HOXD13. Science 272: 548-551)
The recent discovery of one of the most complete skeletons of an australopithecine since "Lucy" has cast serious doubts on the current theories of human origins. The 2.6 million year old fossil of Australopithecus africanus is indisputably arboreal, although its 3.2 million year old ancestor, "Lucy" (Australopithecus afarensis), was bipedal. In addition, James Shreeve states, "the only two known partial skeletons of Homo Habilis, the earliest member of our genus, also have more apelike body proportions." In the April 1996 annual meeting of the American Association of Physical Anthropologists, Dr. Lee Berger stated, "One might say we are kicking Lucy out of the family tree." (Shreeve, J. 1996. New skeleton gives path from trees to ground an odd turn. Science 272: 654).
(Kerr, R.A. 1996. New mammal data challenge evolutionary pulse theory. Science 273: 431-432).
Last updated January 2, 1998