Thursday, June 6, 2013
PHYLOGENY AND MEDICAL RESEARCH
EVOLUTION, PHYLOGENY, AND MEDICAL RESEARCH
Evolution refers to the gradual changes giving rise to new forms over many generations. Phylogeny is the description of the relationships of species sharing a common ancestor. The less ancient the common ancestor, the more alike its descendants are expected to be.
Errors in research studies of evolution and phylogeny can waste your money and your health when inaccuracies creep in as described in my previous post (Science Screw-up #1). The direct cost of the research is minor and somewhat compensated for by educational opportunities provided graduate students.
How accurate studies of evolution and phylogeny can help you
Basic biomedical research can use organisms other than humans and other primates. Even bacteria, especially E. coli (Escherichia coli), have revealed basic information about gene functioning and basic biochemistry common to all animals. Simple animals can provide some additional information of value, especially when they are in the ancestral line leading to us.
A phylogenetic “tree” representing the ancestral branching pattern along which the existing animals evolved can be helpful if it is accurate. If system and organ features of animals are compared and two are found to be alike, all others on the tree that branch after the common origin of the two are better prospects for research into that common function. Even better are the ones that are not on side branches. The ultimate sample to study may be your own cells if the genetics of a disease has been determined.
The preceding approach, using a close phylogenetic relationship, may be more fruitful in solving more finely targeted problems. Some instances of remarkable progress have been made using organisms more distantly related that have other valuable features. Two examples are provided by the fruit fly and the squid.
The fruit fly
The fruit fly (Drosophila melanogaster) was especially useful in early studies of chromosomal inheritance. Their short life cycle, completed in a few weeks, and their small size and ability to go through the cycle in a small bottle, growing on some inexpensive nutrient, enabled students to repeat findings about heredity. The salivary glands of the larvae have giant chromosomes due to multiple strands of DNA. That is more of a curiosity, but a more distantly related insect had chromosomes that showed puffing due to developmental hormones in specific locations that led to further studies about how genes are controlled.
Squids have relatively enormous nerve fibers extending from two major nerve cell clusters to enervate mantle muscles forming their tubular body. The largest fibers go the greatest distance, but transmit the nerve impulse faster. The graded speeds make the impulse reach all parts of the tube simultaneously so the contraction is most powerful for expelling water used for their “jet propulsion”.
The fibers (axons) are so large they were the first nerve fibers for which the molecular events (depolarization waves consisting of ion release and transport back across the axon membrane) of a nerve impulse were discovered. The fundamentals of the process seem to be much the same for us and other animals.
The power of phylogeny
An accurate view of phylogeny gives us the power to multiply the value of biomedical research to speed the treatment of disease. Dollars are spent more wisely if the phylogeny upon which research is designed is accurate. Phylogeny should not be the major determinant if other considerations are known to be important. For example, mice may be better a better choice than monkeys because of small size, short life cycles, and mice are not on the endangered species list.
Joseph G. Engemann June 6, 2013