Practical Importance of Human Evolution – Phylogenetics: Model Organisms – Species & Adaptation

Practical Importance of Human Evolution – Phylogenetics: Model Organisms – Species & Adaptation


>>In the earlier lectures we showed how evolution
within species using population genetics really has a lot of practical importance. For example,
by its very definition these studies of natural selection are studies of reproductive health.
But what about the practical importance of evolutionary studies between species? As a
one-credit course, I wanted to keep this focused on humans, so we won’t go into the fact that
we use evolution to predict evolving pathogens like viruses and bacteria, but instead let’s
stay closer to human variation. Using evolutionary models to compare human genes to other species
has had a lot of practical applications. To understand this, we first need to discuss
homologous or orthologous genes. You see, much like the fact that all life as we know
it is descended from a common ancestor, all genes as we know them are descended from common
ancestral genes. But over the billions of years of evolution, genes have duplicated
and changed in a diversity of ways. Nevertheless, there are plenty of genes that have remained
relatively similar to each other, even over long periods of time. These conserved genes
often serve us very important functions, and as a result purifying selection prevents them
from diversifying much. Thus, there are genes that serve the same function and are found
among different species because the gene and the function was in place in the common ancestor
of those species. The gene has yet to change in a significant way. We call these genes
homologous, or more specifically orthologous genes. That is, orthologous genes are genes
that are similar between species because they remained mostly unchanged since the species’
shared ancestor. Evolutionary studies comparing orthologous genes between humans and other
species has had a lot of practical importance. For one, it provides a different approach
to discovering areas of the human genome that have undergone unique natural selection when
compared to other species. In other words, these studies provide an excellent approach
to find out what genes make us uniquely human. For example, we could align orthologous genes
between humans, and chimps, and gorillas to determine which of these orthologous genes
have experienced more changes in humans than any other ape. When you do this, one gene
that stands out is FOXP2. FOXP2 has known linkages to severe language and speech disorders,
and we know it is a fundamental gene involved in the evolution of language in humans. The
orthologous FOXP2 gene in songbirds has undergone a great deal of evolution and is associated
with song learning. And FOXP2 gene in bats is associated with echolocation, in other
words, bat sonar. By examining the evolution of FOXP2 in different species, we are gaining
not only a knowledge about what makes us uniquely human but also how the FOXP2 gene works biologically,
which serves as a foundation for interventions for FOXP2 associated deficiencies. Now ideally,
figuring out how genes work needs a setting where you can control the environmental variables.
But such experiments in humans would rarely be desirable. But because the common ancestry
of life retains orthologous genes, we don’t always need to look at humans to figure out
how human genes work. This is where the study of model organisms is so important. Instead
of controlled experiments on humans, we can do controlled experiments on fruit flies,
or worms, or plants, or even yeast, or any number of life forms that are easy to manage
and less ethically worrisome. Some of these experiments also take advantage of our knowledge
of evolution in unique ways, including imposing our own human-induced natural selection. One great example of this human-induced natural
selection is an experiment done with fruit flies and alcohol. I already like where this
one’s going. Fruit flies have been an incredible model organism for genetic research in general,
but in this study a population of fruit flies belonging to the genus Drosophila was placed
inside of an artificial chamber. Then the researchers gradually exposed this population
of fruit flies to alcohol vapor. Most fruit flies immediately exhibited changes to their
locomotor behavior. In essence, they were drunk. But other flies showed some resistance.
The resistant flies were then bred to create a new generation of fruit flies. The experiment
is repeated, increasing the levels of alcohol vapor. Over generations, a new population
of fruit flies is obtained that’s taken the genetic potential of the earlier parent population
and streamlined it to provide specific advantages to alcohol resistance. Much like natural selection,
we’ve created an artificial selective environment. In fact, arguably, this artificial selective
environment is natural selection, natural selection where humans are the selective pressure.
While not in a laboratory environment, the same process is what led to the domestication
of dogs from wolves, and cows from aurochs, and transformed the silky sweet domesticated
banana from a more seed-burden, tart, wild ancestor. As for our new population of alcohol-resistant
fruit flies, we can now examine their genomes in comparison to that of the parental population
to determine what areas of the genome were placed under selective pressure. Doing so
will reveal gene variants involved in alcohol resistance. When scientists found it, they
named the alcohol resistant allele “happy hour.” Now from my experience, scientists
studying insects tend to have a unique sense of humor. But the happy hour variant is a
serious finding. The associated gene has strong homology to a family of genes in mammals,
including humans, called Ste20. Happy hour was found to inhibit a growth factor in certain
body tissues, and this growth factor is involved in alcohol sensitivity. This fact led the
researchers to explore similar patterns in laboratory mice. The mouse models provided
further interesting patterns. In fact, when these growth factors were inhibited, mice
lost all interest in alcohol, likely because they no longer got the beneficial sedative
effects that alcohol typically brings. The researchers propose that this may be a pharmacological
path for interventions for alcoholism. If you no longer feel the effects of alcohol,
you probably lack the incentive to drink it. Seems pretty reasonable. So we’ve learned
that evolution-based statistical approaches to examining genetic variation within human
populations in between humans and other species have clear practical impact. Importantly,
these studies are not secluded. Remember in our foundations there was no clear line between
macro- and microevolution. All these studies are connected within the framework of evolutionary
theory. This is why evolutionary theory is called the cornerstone of biology. This is
why Theodosius Dozamsky said, “Nothing in biology makes sense except in the light of
evolution.” Evolutionary theory provides more than just a piecemeal application. Evolution
provides the foundation. It serves as the intellectual framework to build upon, to design
new tools, to resolve new problems, and to move our understanding forward.

One thought on “Practical Importance of Human Evolution – Phylogenetics: Model Organisms – Species & Adaptation

  1. I've always wondered the evolutionary effect of smoking and if we could develop a way to start voluntarily preparing for the worlds (or another world's) future status given global warming. 

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