Happy Belated Darwin Day
My graduate school project dealt with issues of menopause, hormone replacement, and cognition. Specifically I wanted to know how long-term loss of ovarian hormones, or long-term hormone replacement, impacted performance on tests of learning, memory, and attention. I also wanted to study the neurotransmitter systems affected by chronic hormone loss/replacement. Now obviously this sort of work is difficult to do in women, and for a variety of reasons I won't go into now. Suffice to say that an appropriate animal model needs to be employed if these sorts of experiments are to have appropriate controls.
So who do we turn to? Click below to see.
Our obvious first choice would be our closest cousins the Great Apes. However, apes are not feasible to work with in large numbers; they live almost as long as humans, are expensive to care for, and freakishly strong. Restrictions also prevent invasive research from being conducted on them. So where else can we look?
We start by looking at phylogeny; which extant animals are phylogenically close to us? Barring the apes, the next closest group would be the Old World monkeys. Monkey lineages split from ours more recently than any other group of primate species, but there are two to choose from. It turns out the New World monkeys aren't such a good choice, as these monkeys evolved after South America split from Africa. New World monkeys remained arboreal while Old World monkeys spend at least some of their time on the ground. Recently, Old World monkeys shared the habitats and to some extent the diets of their ape cousins.
It turns out that certain macaque species share numerous features with humans. Macaques have 28 day menstrual cycles that are virtually identical to those of a human female. They also undergo an eerily similar menopause. Their cardiovascular and skeletal systems respond to hormone loss and replacement in ways similar to humans. So from an endocrine standpoint, macaques are a good choice for the sort of research I want to do.
What about the brain? After all, I'm a neuroscientist, so I kinda care about that aspect. It so happens that macaques share a number of similarities in this department as well. They can be taught to perform tests of memory and attention that are directly adapted from tests used in clinical settings. Furthermore, their brains are arranged quite similarly to ours; each cytoarchitectonic subdivision identified in the macaque has a homologous area in the human. These areas have connection patterns that resemble those of humans, and the major neurotransmitters distribute themselves throughout the brains of monkeys in patterns similar to humans.
Ok, I've spent enough time on this for one day. In closing I would like to say thank you, Chuck, for the theory. Common descent helps me to understand why my chosen model works, and is much more satisfying than the untestable, unfalsifiable "they had a common designer, so they look similiar".