Recent Problems in Evolution - 2002
Table of Contents
- Review of inbreeding discredits "species sorting" of punctuated equilibrium
- Oceanic hydrothermal vents out as origin of life site
- Really quickly evolving dinos
- Rapid "evolution" of human brain
- Of mice and men - little genetic difference!
- Of chimps and men - more genetic difference!
Review of inbreeding discredits "species sorting" of punctuated equilibrium
Punctuated equilibrium claims that new species arise rapidly due to accumulated mutations that get expressed during "species sorting," when populations plummet due to natural disasters, climatic changes, etc. However, new data from wild populations and molecular and analytical tools for tracing patterns of relationship and inbreeding have determined that "inbreeding depression" (decreased fitness) occurs among diverse taxa. According to the recent review:
"This work reveals that levels of inbreeding depression vary across taxa, populations and environments, but are usually substantial enough to affect both individual and population performance. Data from bird and mammal populations suggest that inbreeding depression often significantly affects birth weight, survival, reproduction and resistance to disease, predation and environmental stress. Plant studies, based mostly on comparing populations that differ in size or levels of genetic variation, also reveal significant inbreeding effects on seed set, germination, survival and resistance to stress. Data from butterflies, birds and plants demonstrate that populations with reduced genetic diversity often experience reduced growth and increased extinction rates. Crosses between such populations often result in heterosis. Such a genetic rescue effect might reflect the masking of fixed deleterious mutations. Thus, it might be necessary to retain gene flow among increasingly fragmented habitat patches to sustain populations that are sensitive to inbreeding."
Although the authors did not relate their study to the theory of punctuated equilibrium, it has obvious implications. Species sorting, as a mechanism of producing new species, has never been shown to be anything other than a theoretical concept. This and previous studies suggest that the only "sorting" consistently resulting from decreases in population numbers is extinction. Although this may "make room" for new species, it certainly cannot be claimed to be a creative force in evolution.
Lukas F. Keller and Donald M. Waller. 2002. Inbreeding effects in wild populations. Trends in Ecology & Evolution 17: 230-241.
Oceanic hydrothermal vents out as origin of life site
The most common abiogenesis theories claim that life arose at hydrothermal vents in the ocean. However, recent studies show that polymerization of the molecules necessary for cell membrane assembly cannot occur in salt water (1). Other studies show that the early oceans were at least twice as salty as they are now (2). Therefore, the oceans could not be the site at which the first life was assembled. Although crude membranes can undergo assembly in fresh water, there would be a very limited source of organic molecules present in those waters - certainly not enough to form anything on the verge of living.
- Monnard, P.-A, C. L. Apel, A. Kanavarioti and D. W. Deamer. 2002. Influence of ionic solutes on self-assembly and polymerization processes related to early forms of life: Implications for a prebiotic aqueous medium. Astrobiology 2: 213-219.
- Knauth, L.P. 2000. Life on Land in the Precambrian and
the Marine vs. Non-Marine Setting of Early Evolution. First Astrobiology
Science Conference, April 3-5, 2000, NASA Ames Research Center, 403 (Abstract
353).
Knauth, L.P. 2002. Early Oceans: Cradles of Life or Death Traps? Astrobiology Science Conference 2002, April 7-11, NASA Ames Research Center. p. 9.
A recent study has demonstrated that reptiles disappeared and the giant
carnivorous dinosaurs replaced them within a period of less than
10,000 years of the Triassic-Jurassic boundary and only 30,000 years after the last Triassic taxa,
which were eliminated by a mass extinction event, probably due to an
asteroid collision. The rate of evolution of these dinosaurs is almost
beyond belief. Of course, it all fits into one or another of the current
evolutionary theories. Maybe we should try to short-circuit a near-earth
asteroid to repeat the experiment and see if evolution really works that
fast!
P. E. Olsen, et al. 2002. Ascent of Dinosaurs Linked to an Iridium Anomaly at the Triassic-Jurassic Boundary. Science 296: 1305-1307.
Rapid "evolution" of the human brain
Studies as early as1975 showed that the sets of proteins found in the brains of chimpanzees and humans were virtually identical. The question naturally arose as to why humans and chimpanzees are so different. A new study provides at least a partial answer to the question. Researchers collected brain, liver, and blood samples from humans, chimps, macaques, and orangutans, isolated RNA from each sample and calculated the amount of RNA produced for 12,000 genes. Little difference was found among the species for the liver and blood samples. However, big differences were detected in gene expression between humans and chimpanzees, although gene expression between chimpanzees' and the other primates' brains was about the same. The results show that regulation of gene expression is unique in the human brain compared to all other primates.
Pennisi, E. 2002. Gene Activity Clocks Brain's Fast Evolution. Science
296: 233-235.
Enard, W, et al. 2002. Intra- and Interspecific Variation in Primate Gene
Expression Patterns. Science
296: 340-343.
Of mice and men - little genetic difference!
Previous genetic studies have shown that chimpanzee and humans DNA differs by only 1.5%. This was said to be powerful evidence of common descent. Scientists are now sequencing the murine (mouse) genome and have come upon some rather startling data regarding a comparison of the murine and human genomes. So far, only chromosome 16 has been fully sequenced in both species. However, the results show that human and murine DNA differ from each other by only 2.5%. This is very surprising, since, according the evolutionary theory, the two species diverged 90 million years ago. The problem for the theory of evolution is that this small difference between mice and humans makes the difference between humans and chimpanzees look huge. Whereas it took 90 million years of evolution to produce 2.5% difference in DNA sequence, humans and chimpanzees diverge 1.5% in less than 10 million years. Why has evolution sped up so much during the evolution of primates? Maybe 1.5% is a really big difference?
Just 2.5% of DNA turns mice into men. New
Scientist, May
30, 2002.
R. J. Mural et al. 2002.A Comparison of Whole-Genome
Shotgun-Derived Mouse Chromosome 16 and the Human Genome. Science
296: 1661.
Of chimps and men - more genetic difference!
Previous genetic studies have shown that chimpanzee and humans DNA differs by about 1.5%. However, this difference was determined by examining the base pair sequence by another nucleotide or replacement of one amino acid in a protein by another amino acid.">substitutions within certain sequenced genes. Recently, the human genome was completely sequenced and sequencing of the chimpanzee genome is well on its way. Preliminary results confirm previous results regarding base pair substitutions (estimated at 1.4%). However, sequencing reveals that insertions and deletions result in another 3.4% difference between human and chimp DNA. Therefore, the overall difference between chimp and human DNA is nearly 5%, which represents an almost insurmountable amount of rapid evolution.
Britten, R.J. 2002. Divergence between samples of chimpanzee and human DNA sequences is 5%, counting indels. Proc. Natl. Acad. Sci. USA 99: 13633-13635.
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Last updated January 2, 2003