Family trees of species now help hunt for new drugs and solve court cases
A drug for severe pain, Prialt, comes from animal venom. To find more venoms worth testing, researchers consult evolutionary family trees: if one fish is venomous, its close relatives may be too. The same tree-building methods track how tumours evolve and weigh DNA evidence in criminal trials.
Phylogenetics reconstructs the evolutionary history of living things from inherited traits, whether body shape, protein sequences or DNA. Its product is a phylogenetic tree whose tips are species, genes or even fossils. A rooted tree marks a presumed common ancestor, while an unrooted one simply shows how closely the tips are linked without saying which way evolution ran. Ernst Haeckel coined the German word Phylogenie in 1866.
Before 1950 such histories were usually told as stories, with no clear way to judge between rival versions. Modern analyses use computers and explicit models of how traits change, through methods such as parsimony, maximum likelihood and Bayesian inference. Parsimony echoes an old preference, stated by Aristotle and later associated with William of Ockham, for the explanation that needs the fewest assumptions. An older approach, phenetics, grouped organisms by overall resemblance and is now largely obsolete, while cladistics recognizes only groups defined by shared new traits inherited from a common ancestor.
Choosing which species to include matters. Researchers usually study a sample of representative species, and poor choices can mislead; in long branch attraction, unrelated lineages get lumped together because they happen to share coincidental DNA changes. Comparisons using the same total amount of sequence suggest that reading more genes from fewer species tends to give more reliable trees than adding species.
The field also buried a famous idea. Haeckel's recapitulation theory, summed up as ontogeny recapitulates phylogeny, claimed that an embryo replays the adult forms of its ancestors as it develops. That has long been rejected, although embryos remain useful evidence, since closely related species share more embryonic features. In cancer research, tree methods follow how tumour cell lines split and change during treatment. In HIV cases, they can show two virus samples are related, but not which person infected the other, so they cannot prove transmission on their own.
Source: Phylogenetics
