Deep Ancestry: Our Story

Anyone who is interested in family history, or anyone who has ever gone to a library or archive to undertake genealogical research knows that while the subject is an exciting one, the work can be tedious and the resulting picture often fuzzy.

This is where we stand with regards to family research writ large, that of modern humanity. To be sure, we have come a long way since we humans even became aware of the fact that we had a very long history, or a deep ancestry. Consider the day, now more than 180 years ago, when people went into a cave in Belgium and encountered remains later identified as belonging to a Neanderthal individual. Compare that against our current understanding of human evolution. How we got here is an interesting story and it is an interesting tale to relate,. Where we go from here is equally intriguing.

Here is part one: how did we get here?

Traditionally, we rely on three main sources of information when studying human origins, our origins. These sources are: the material remains of that past (including both fossil remains and man-made tools), genetics and comparative primatology. The latter refers to observation of current non-human primates and possible correlations between their habitat and behavior with the environment in which our ancestors once lived and their behavior. If there is one constant in the picture generated by these sources is that it is always being refined and updated. Such is the nature of scientific endeavor: it never stands still. Thankfully, our thirst for greater understanding is never slaked either. There is always more to investigate.

Material remains have been the backbone of paleoanthropological studies. After all, what could be a better illustration of human evolution than a fossil of an ancient ancestor, or a tool made by a distant relative of ours? By carefully plotting where these remains have been found, we can reconstruct a picture of human evolution, we can start to see where our earliest ancestors once arose, evolved and eventually migrated from. By studying their tools, we can see human inventiveness at work. At first this is a tediously slow process, but eventually we see it picking up pace to the point we are today: new gadgets developed on a daily basis.

For a while, as people were studying fossil human remains, others were investigating genetics. However, initially the practitioners of these two pursuits did not know of each other’s work, or, did not realize how their work could benefit from the other person’s insights. And so we see how Mendel and Darwin were contemporaries, but their respective scientific insights and breakthroughs did not cross over and inspire the other.

DNA rendering
Creative Commons License photo credit: ynse

Our genetic makeup is the result of millions of years of evolution.

Since the Human Genome Project was completed in 2003, we have learned a lot about our genetic makeup. Since then, the chimp genome, gorilla genome, and the orangutan genome have been finished; by the way, the latter was sequenced in our own backyard here in Houston. This provides a nice platform to start comparing our genetic makeup with that of our close primate relatives, and find out where we differ, and, more interestingly, how similar we are below the surface. It turns out we are quite similar.

The difference 1% makes.

Differences, no matter how ostensibly small, remain important. One can be in awe about the fact that we share around 99% of genes with chimps. One could also turn that around and say “See how much difference 1% makes?” That difference, in turn, may help us figure out when in time we started to go our own way, after the split from a common ancestor. This is where the notion of a molecular clock comes in. This concept has been used to “to investigate several important issues, including the origin of modern humans, the date of the human/chimpanzee divergence, and the date of the Cambrian explosion.”

Thus we see in the literature that orangutans, with whom we share around 97 % of our DNA, split from the family tree around 16 to 15 million years ago. Humans and chimps became their own branches on the family tree around 6 to 5 million years ago.

As one researcher recently put it: “There remain signals of the distant past in DNA, and our approach is to use such signals to study the genetics of our ancestors.”

The concept of the molecular clock continues to be refined as our understanding of its potential and limitations has grown. For better or worse, however, it provides us with a tool to help situate major branching events on the family tree. This brings us to our own immediate past, our place in history, when modern humans appeared on the scene.

Modern Humans

Discoveries made in East Africa date the emergence of modern human beings to about 200,000 years ago. Two skulls, found in 1967 in Ethiopia were recently identified as the earliest known modern humans. While that makes all of us Africans, it data from mitochondrial DNA have suggested that our ancestors did not make it out of Africa until 60,000 years ago. The archaeological record seems to disagree, however. Man-made tools twice that age have recently been found in the Arabian Peninsula.

It is at times like these, when dates provided by genetics and archaeology diverge, that we hear voices criticizing the invalidity of this approach. What we will see happen, however, is that this apparent disjunction between two sets of data, will spur on researchers to find where the source of this disparity lies and resolve it. Were that to be impossible then we would have to go back to the drawing board and rethink our ideas about human evolution and the timing of critical events related to it.

Now for part two: where do we go from here?

As people become more mobile, we are now finding our mates much further away than we did just a few generations ago. This means that it will become more difficult to check that box on the census form asking for our ethnicity. It also means that we are slowly becoming more homogenized. Indigenous cultures are disappearing and language follow suit.

To get an idea of how exhilarating and mind-boggling this pursuit of science can be, I would like to invite the reader to attend an upcoming lecture.

On March 7, the Houston Museum of Natural Science will host Dr. Spencer Wells, lead scientist of the Genographic Project.

His lecture, entitled “Deep Ancestry: Inside the Genomic Project,” is brought to us by the Leakey Foundation. Dr. Wells is an Explorer-in-Residence at the National Geographic Society and Frank H. T. Rhodes Class of 1956 Professor at Cornell University. Dr. Wells will share with us how the Genographic Project, using data from hundreds of thousands of people, including members of the general public, the Genographic Project is deciphering the migratory routes followed by early humans as they populated the Earth.

I look forward to this lecture, and hope to see many of you at the museum that evening.

In the meantime, a pop quiz.

Q: What do the following individuals have in common?

Brazilian indian chiefs, Kaiapos tribe, during a collective interview.
Left to right: Raony (state of Mato Grosso), Kaye, Kadjor, Panara (Pará)
Creative Commons License photo credit: Valter Campanato, Agência Brasil (ABr). April 17, 2005
Ethiopian Orthodox Christian woman – Lalibela, Ethiopia
Creative Commons License photo credit: Dirk Van Tuerenhout
Lake Titicaca – Uros people
Creative Commons License photo credit: Dirk Van Tuerenhout

A: They are us. We are them. This is us.

The Great Cosmic Year

Our Milky Way Galaxy..
Creative Commons License photo credit: Sir Mervs

One of the biggest challenges in teaching astronomy to kids – or even to the general public – is that astronomy involves numbers so big as to be virtually meaningless. Consider the age of the universe, for example. Our best data indicate that the Big Bang, where space and time began, occurred about 13.7 billion years ago. As very few of us have seen 13.7 billion of anything before, how can we appreciate how long a time that is?

One way is to use a scale-model. Just as we use globes because the real Earth is too big to look at, we can ‘shrink’ the 13.7 billion year history of the universe into one year. Imagine a Great Cosmic Year, in which the Big Bang occurs at 12:00:00 am on January 1 and the present moment is 11:59:59.9999999 pm on December 31. On this time scale, each day represents (13.7 billion/365) years, or about 37.5 million years. Our best estimates for when the events listed below occurred are approximate; the dates listed may need to be adjusted slightly in the future.

Still, locating the events in the history of the universe, the Sun, and the Earth on this calendar can give us a better sense of how much time is involved.

January 1, midnight The Big Bang occurs.

January 13 The oldest known star in our galaxy (designated HE 1523-0901) forms.

‘HE’ here refers to the Hamburg/ESO (European Southern Observatory) survey, in which the star is catalogued. Being about 100 times too dim to be seen with the unaided eye, the star has no common name. It is in the constellation Libra.

Planet Earth (III)
Creative Commons License photo credit: Aaron Escobar

January 4-27 Re-ionization occurs.

We take for granted that the universe is transparent; that we can look through space and see galaxies, stars, and other planets. However, once hydrogen atoms formed in the early universe, this would have been impossible, as hydrogen atoms readily absorb photons (light particles). After the first billion years (corresponding to January 27 in the Great Cosmic Year), the hydrogen had been re-ionized. This happens when the electron in the hydrogen atom is too energetic too remain in orbit around the single proton which makes up the hydrogen nucleus. Newly formed stars and galaxies provided much of this energy.

April 14 First Sun-like stars (population I) appear.

Hydrogen and helium are so abundant in the universe that astronomers lump all other elements into a catch-all category called ‘metals.’ Astronomers divide stars into three categories based on their ‘metallicity,’ or how much stuff other than H or He they contain. This is important because those ‘metals’ ultimately make up solid things such as planet Earth, or you or me. Our Sun is only about 2% ‘metal.’

Stars of comparable metallicity are the youngest and are placed in population I. Some older stars in the distant halo of our galaxy are much less ‘metallic’ than our Sun, in some cases by a factor of 1,000 or 10,000; these are population II stars. Since all elements heavier than helium are formed in stars, astronomers speculate that the very first stars had virtually no metals, but such ‘population III’ stars have yet to be discovered.

It took about four billion years to make the first population I stars, bringing us to April 14 in our Great Cosmic Year.

Andromeda, again.
Creative Commons License photo credit: makelessnoise

May 23 The Milky Way’s galactic thin disc forms. This part of our galaxy includes our Sun.

August 31 Our solar system forms from a spinning cloud of dust.

The first population I stars to formed back on ‘April 14′ did not include our Sun. Astronomers recently discovered decay products of 60Fe, an isotope of iron that results from supernovae (exploding stars), in some meteorites. This suggests that a nearby supernova ejected this material into the dust cloud that became our solar system, making our sun at least a second generation population I star.

September 2 Earth begins to form.

Bad Moon Rising
Creative Commons License photo credit: makelessnoise

September 3 The Moon forms when a Mars-sized object called ‘Theia’ strikes Earth.

September 21 Earth begins to solidify.

This corresponds to the end of the Late Heavy Bombardment, a period of frequent impacts on all bodies in the inner solar system. Up to this point, consistent bombardment kept the Earth molten, with magma seas. With the end of the bombardment, Earth began to cool, solid rocks appeared, and Earth’s geologic history began.

September 29 Life begins on Earth.

October 12 The first continent (called Ur) appears on Earth.

November 2 Oxygen (O2) builds up in Earth’s atmosphere.

November 14 Eukaryotes (with distinct nuclei in the cell) exist on Earth.

November 27 Multicellular organisms exist.

December 5 The supercontinent Rodinia forms.

December 17 Cambrian explosion: earliest forms of most types (phyla) of animals appear.

December 20 First life on land

triceratops
Of course, the real dinosaurs were bigger,
and not made of paper.
Creative Commons License
photo credit: kekremsi

December 25-29 Age of the dinosaurs

December 30 (morning) Chicxulub meteor impact helps cause extinction of about 3/4 of all life, including the dinosaurs.

The following events all occur on December 31:

9:17 am Drake passage completes the isolation of Antarctica; the continent freezes over.

7:30 pm Human ancestors diverge from chimpanzees.

9:57 pm Lucy lives in east Africa.

11:52 pm Homo sapiens sapiens exists.

11:59:14 pm Last Glacial Maximum (most recent Ice Age)

11:59:45pm Uruk, in Sumer, is one of the first cities on Earth.

Our existence as a species, compared to the whole universe, is about eight minutes out of a year. All of human civilization amounts to about 15 seconds. Once, I presented this calendar and was told that the smallness of our existence was an attack on religious faith. Perhaps, however, this need not be so. After all, an important virtue in most religious traditions is humility. This is not the denial of our talents and value, but the realization that we, with our goals, hopes, and dreams, are but one element of a much larger whole. As you reflect back on 2008 this holiday season, I invite you to reflect on the Great Cosmic Year. I find that the resulting wonderment and awe deepens my appreciation of the universe, and reminds me why I studied science in the first place.