>>Questions about ancestry testing frequently come up in my classes. The idea of ancestry
testing is to use genetic data and evolutionary concepts to determine your genetic heritage.
For example, how much of your genetic material is Irish? Or are you related to a famous person?
Things like that. Does ancestry testing have a practical importance? It might seem like
it has a practical importance because it impacts people's perceptions of their identity, but
we're stretching the term "practical" here. There are some approaches to medicine where
knowing a patient's recent geographic ancestry could be important. For example, if much of
your recent ancestry was from central Africa, you may want to check to see if you're a carrier
for the genetic trait that causes sickle-cell anemia. So ancestry testing could be useful,
but it's also often misguided and very frequently its significance is exaggerated.
We noted in this class that all life as we know it is consistent with a single common
ancestor. This means every person you've met, every skeleton in every coffin, every historical
person who has ever lived—from Julius Caesar, Cleopatra, Genghis Khan, the Aztec emperor
Montezuma—everyone is at a minimum, your cousin. This extends further to nonhumans.
All life as we know it is a minimum a cousin, from the duck-billed platypuses to the Venus
flytrap to the flies in the Venus flytrap, to all the creepy-crawlies around the Venus
flytrap, even down to the bacteria—all of it are your cousins, very distant cousins,
but your cousins. So when you hear in the news that an actor was found to be related
to a kind or emperor, you should not be surprised because you're also related to that king or
emperor. That said, it's exciting to hear when you have a famous direct ancestor. In
other words, not a cousin, but a grandparent or great-grandparent, et cetera.
We are all guaranteed to have some interesting grandparents, but unfortunately a lack of
historical information prevents us from telling their stories. But here's one that applies
to probably everyone watching this. Around 200 to 160,000 years ago is the approximate
time in which everyone in the world today converges to a common ancestor. But from 200
to 20,000 years ago, there was more than one type of human walking around in the world.
Most of our ancestors at that time were what we call today anatomically modern humans,
otherwise known as homo sapien sapien. This is the same species and subspecies as you
and me, everyone. But to be fair, even though we call ourselves homo sapien sapien, the
vast majority of us, most likely all of us, also have ancestry to non-anatomically modern
people, otherwise known as archaic humans, such as the Neanderthals. It's quite obvious
that these admixture events with Neanderthals were happening even 35 to 40,000 years ago.
Thus, in all likelihood, one of your prehistoric grandparents was an archaic human. What we
find is that some areas of the human genome have diversity much greater than you would
expect from a common ancestor 200 to 160,000 years ago. And as a result, this implicates
an event in which archaic humans contributed to our gene pool.
Interestingly, some areas of the genome that have been implicated by this admixture are
also involved in our autoimmune system. It's hard to imagine that this is coincidental.
A current hypothesis is that this contribution to our autoimmune system was adaptive and
allowed otherwise anatomically modern humans to resist disease as they began peopling the
world. Remember humans today have very little diversity over all. Ways to obtain diversity,
such as interbreeding with archaics, could have certainly been adaptive. Maintaining
diversity in our autoimmune system is clearly important for fighting off diseases. Species
that are very inbred are highly susceptible to infections. Most of us see this today.
A specialized interbreeding of dogs and horses and many domesticated plants lead this domesticates
to be very vulnerable to infections.
This connects back to our earlier discussion of trying to breed super humans. Maybe we
could breed a human thoroughbred population for a specific task, but the next avian flu
might just wipe them all out. So thousands of years ago anatomically modern humans who
interbred with archaics could have had a distinct reproductive advantage over those anatomically
modern humans who didn't, and these admixed individuals appear to be our direct ancestors.
Thus, it appears that everyone today has an archaic grandparent. There's still a chance
that there are people today that are an exception, maybe in parts of Africa, but I wouldn't bet
on it.
Understanding the aspect of the human genome that has archaic contributions can provide
information about natural selection. There may be archaic alleles out there today that
provide valuable contributions to disease resistance.