Here’s the entry that I submitted to our Medical School photo contest. It actually won for the best photo overall (in a four-way tie)!

This little fellow is a mayfly (Order Ephemeroptera). He was my friend for his entire adult life. Mayflies can live underwater in a juvenile stage for a year before they erupt out of the water into their adult, winged, beautiful, forms. Their adult bodies lack mouths, however, and so they can only survive for a single day. Their sole purpose at this point is to reproduce before they die. Personally, I believe mayflies to be the most elegant of insects on earth.

I must admit, that my heart made a fond little leap this morning when I discovered genetics on our timetable for the first time! Not only that, but our lecturer made a foray into the one area of genetics that I find most intriguing: genetic geography. Here’s something new that I learned:

Over the course of human history, it appears that women have migrated more, and over greater distances, than men. You may ask, how could we possibly know that? And that’s where a couple convenient features of genetics come into play.

Mitochondrial DNA is passed from mother to offspring. Paternal mitochondria are never normally inherited. Thus, if you are a female reading this, then you can be quite certain that your mitonchondrial DNA came from your mother, which came from your grandmother, and so on up your maternal line of descent.

There is a similar set of DNA for male descent: the Y chromosome. Genotypically normal females lack the Y chromosome, and so males will have inherited their Y chromosome from their father, which came from their grandfather, and so on.

Once a set of DNA can be distinguished for male descent versus female descent, then it becomes possible to compare genetic variation between the two sets. The results of this comparison show that mitochondrial DNA is far more uniform geographically than Y-chomosomal DNA. It can be inferred then, that women were historically more travelled than men because their variation has been distributed more evenly geographically.

A possible anthropological explanation for this finding is that when women were married, it may have been the tradition in most human societies for the wife to move to the husband’s home. I have lingering doubts about this hypothesis, however, because the opposite is what normally happens with our closest ape relatives.

I find human ancestry fascinating. How are we all related? What did my ancestors look like, and where did they live? What are the stories of our forbearers as they struggled for survival, made discoveries, and lived together?

Adam and Eve were African. That’s not a new discovery, but many people have never heard it. The immediate consequence is that you yourself, regardless of where you come from or where you live now, have African ancestors. The reason that we can be sure of that comes from population genetics.

Here’s a TED Talk that took place in my home-country, Tanzania, that explains in simple terms how you can be sure that you have an African heritage. The speaker is Spencer Wells, who is the director of the Genographic Project. They analyze DNA from indigenous people around the world, building a family tree for the human races. If you want to purchase the kit, you can actually participate in the project yourself by sending in your own DNA for analysis.

Here’s what I found interesting about this talk:

Adam and Eve never met each other. That’s because, by ‘Adam’, I mean the most recent common ancestor of all the men that are alive today (according to the biblical account, ‘Noah’ would have been a better name since all men are said to descend from him more recently than Adam). Correspondingly ‘Eve’ refers to the most recent common ancestor of all the women that are alive today (Noah’s wife).

Now men generally have more disproportionate reproductive success. That is, some men father many children while others father none. For example, Ghengis Khan had so many concubines that it is believed he is an ancestor to more than half the men on the planet (does that explain a lot to you ?). Women, on the other hand, are generally more evenly reproductively successful. The consequence of this difference between men and women, is that ‘Adam’ appears in our history far more recently than ‘Eve’. So much so, that they lived in completely different time periods and could never have met.

Another interesting realization about Adam and Eve, is that they weren’t the first “humans”. Far from it. The origin of our species dates much earlier, but we defined Adam and Eve as the most recent common ancestors. To find the actual first “humans” is an impossible task, given that evolution works along gradients making only gradual changes. It would be like trying to find the first moment that a child is “grown-up”.

Finally, Adam and Eve lived side-by-side with other non-human bipedal apes. Actually it’s been that way throughout our history. There has almost always been other walking, thinking hominids living with us. It’s a fair question to ask why there’s just our species left now. Did we kill-off, or out-compete the others?

Well, if you find ancestry like this interesting, I highly recommend Richard Dawkin’s book “The Ancestor’s Tale”. It takes you on a journey back to the most recent common ancestors of humans, apes, mammals, vertebrates, and eventually all of life.  It’s a beautiful book.

The story of Earth’s origin captures my imagination. It is the grandest of epics, a comprehensive myth (in the sense of ‘myths’ being stories that define who we are), the most dramatic story ever told.

I strongly believe we need to tell this story more often! It surprises me how few people know its major scenes or actors – even among those who study the life sciences. Origins are more than history, they are more than biology – they define who we are. In our unavoidably secular, globalized society, here’s a myth that embraces us all. Children should grow up learning this tale, and re-tell it to their own children with all of the modifications added by modern science.

This particular telling is orchestrated by Frans Lanting, a photographer for National Geographic. Although humans are his heroes/heroines (he ends with a focus on mammals and primates), he draws satisfying attention to plants, insects, invertebrates, and algae – the players of any real consequence in this drama (humans appeared too late to matter much). I was a little disappointed that he gives air-time to the KT extinction (non-avian dinosaurs), but not to the much larger end-Permian extinction.

This rant is dedicated to Diana, who knows better, but who still takes pleasure in provoking me.
Also note that I cannot take credit for any of the photos in this post.

As an insect lover, jellyfish groupie, and worm advocate, the term ‘lower organism’ sends a shiver down my spine. What a condescending, unkind, prejudicial label! Thankfully my invertebrate friends are spared the offense, as they have no appreciation for terminology, nor indeed any spines that shivers might be sent down. As such, they also cannot defend themselves, so I will try my best on their behalf.

There is no zoological basis for classifying invertebrates as ‘lower’. What does such a term even mean? If you think it indicates lower biological complexity, I point to the cephalopods (octopi and squid) who independently evolved sophisticated nervous systems including eyes that are more practically arranged than our own. As another counter-example, there is more anatomical variety among the animals we collectively refer to as ‘worms’ than in all vertebrates taken together.

If you think ‘lower’ refers to social complexity, I refer you to E. O. Wilson’s ‘The Ants‘, which documents the castes, hierarchies, and rich community life of this insect group. There is no feature, whether anatomical, or social, that has not first been explored by invertebrate animals long before the vertebrates even existed.

If ‘lower’ referred to evolutionary success, I’m afraid we would find ourselves with the lowest of the low. In geological time we are relative newcomers, and we seem poised to drive ourselves to extinction after a lightening-quick appearance of just a few million years. Contrast that to the insects, who have been on our planet almost 300 million years and have dominated every ecological niche available through vast swathes of natural history.

I suspect that most readers believe invertebrates to be ‘lower’ because “they do not have a brain.” In technical terms, the collection of nervous tissue towards one end of the body is called cephalization, and it is a hallmark in the development of vertebrates. But that’s an entirely arbitrary criterion on which to base a hierarchy of life!

In ‘The Ancestor’s Tale‘, Richard Dawkins points out that we use cephalization as a benchmark for evolutionary “progress” mostly because it puts our own species on top. He amusingly speculates that if elephants were to generate a similar hierarchy, perhaps they would base it on proboscity (length of nose), thus raising elephant seals and elephant shrews to newfound glory.

Our ego-boosting bullying of invertebrates because of their brainless-ness is just as ridiculous. So let’s put away our anthropocentric bias, and stop referring to the vastly more diverse, more numerous, and more successful animals of our planet with derogatory terms.