Meet your great-(~10 million times)-grandmother

In my blog The Tree of Life, published a few months ago, I wrote about the Last Common Ancestor (LCA) of all placental mammals, that it was a shrew-like animal, living about 65 million year ago. Terrestrial, with insects and fruits as food.

Our maternal ancestor

Yesterday Yale University has published an interesting update. Our ancestor most probably was not terrestrial, but lived in trees. More a squirrel than a shrew. This conclusion was drawn, based on a study of fossil ankle bones of Purgatorius as our LCA was named.


The Tree of Life

The Evolution Theory of Darwin is now generally accepted, although an astonishing 42% of the American population still thinks that the Christian God created humans more or less in their present form, about 10.000 year ago, according to a Gallup poll, held in May this year!



In 1860, after Darwin had published his book “On the Origin of Species, a debate was organised in Oxford between proponents and opponents of this new theory. Supposedly in this debate Bishop Wilberforce asked proponent Huxley  whether it was through his grandfather or his grandmother that he claimed his descent from a monkey

Huxley is said to have replied that he would not be ashamed to have a monkey for his ancestor, but he would be ashamed to be connected with a man who used his great gifts to obscure the truth.

Actually both were wrong in assuming that humans descend from monkeys. Humans and monkeys have a common ancestor which may have resembled neither a human nor a monkey. Our closest relatives are the chimpanzees and the bonobos and our Last Common Ancestor (LCA) is estimated to have lived about 6 million years ago. For the LCA with the gorilla we have to go back ~ 7 million year, for the orang utan ~ 14 million year and for the gibbon ~ 18 million year.

Here is our extended family, in a diagram and as a collection of (baby) photos.

Our family

Homo: Humans                         Pan: Chimpanzees & Bonobos Gorilla: Gorillas                Pongo : Orang Utan                 Hylobates: Gibbons


our family

Of course the story does not end here. Our extended family belongs to the class of the “placental” mammals, together with mice, elephants, whales and bats and more than 5000 other species. The LCA of this (sub)class has lived around the time that an asteroid impact in Mexico may have caused the extinction of the dinosaurs, about 65 million year ago.

Last year an interesting article was published in Livescience: Meet Your Mama: First Ancestor of All Placental Mammals Revealed . It is an attempt, using advanced techniques, to determine the age of our Last Common Ancestor. In this article even an artist expression is given of our LCA (by palaeoartist Carl Buell )

Our maternal ancestor

Now, look at this picture carefully. This could be the (maternal) ~ 10 million-greats-grandmother of every living mammal, including you and me! Think about that for a while. You came from the womb of your mother, as she did from the womb of your grandmother. Repeat that ~ 10 million times and you end op with this shrew-like critter.

The Mammals are a class in the (sub)phylum of the Vertebrata, which contains six more classes (birds, reptiles, amphibians and three classes of fishes). Also here there has been a Last Common Ancestor, living somewhere around 500 million year ago. May have looked like a kind of segmented worm, with a gut, a mouth and an anus…:-)

Look at this interesting way to show the development of the seven vertebrate classes. To the left you see the geological eras Cambrium, Perm, Trias etc. The thickness of the various classes indicates the number of families in the class.


Notice the sudden change in thickness at certain times. They mark mass extinctions.. During the Perm-Trias extinction ( ~ 250 million year ago) numerous families and species became extinct.  The other extinction shown is the one caused by the asteroid impact, 65 million year ago. Note the reduction of the reptile class (dinosaurs!)

The Vertebrata phylum belongs to the kingdom of the Animalia, together with eight other phyla. The most important of them are the Arthropods (insects, spiders, lobsters, centipedes)  Sponges, sea urchins, jellyfish, earthworms are all animals and have their own phylum.

Confused by all these concepts like  family, class, phylum, kingdom? This part of biology is called taxonomy Here is a diagram of our human lineage.

human taxonomy

To keep it simple, I have skipped the category Order (we are Primates), taken the sub-class Placental Mammals and the sub-phylum Vertebrata, because the term is more familiar than Chordates.

So we humans are a member of the kingdom Animalia. Together with how many other species? Present count is ~1.5 million (mostly insects…haha) Estimated total animal species count between 2 and 20 million…


The kingdom of animals. Are there more kingdoms? Yes, there is also the kingdom of plants and the kingdom of fungi. All three contain multi-cellular organisms. And there are other kingdoms of unicellular organisms, like the paramecium, almost always present in stagnant water, and visible under the microscope                                                                                                                                                                                                                     Paramecium

Keep in mind that there has been a Last Common Ancestor of you and this amoeba-like critter! 

Why are these kingdomscombined together? Because they share a very important property: their DNA is contained in a separate part of the cell, the nucleus. These kingdoms form the domain of the Eukaryota  Here is a visual representation of the kingdoms in this domain.


Again, keep in mind that there has been a LCA of all the organisms in this picture  Although we have to go back far in time…:-) About 2 billion years, there is still a lot of discussion going on about the timing. But it is clear that developing a nucleus containing the DNA and organising the various functions of the cell was a major breakthrough in the evolution of life.

Do cells exist nowadays that do not have a nucleus? Sure! There are two more domains where the cells have no nucleus. One of them will be familiar to everyone, the domain of the Bacteria.  The other one is the domain of the Archaea, also a kind of bacteria and only recognised as a separate domain during the last decade. Click here if you want to know more about the differences between the two (warning, very technical).

Bacteria are small organisms but there are many of them. The number of different species is unknown, estimates vary between 10 million and 1 billion…! They are everywhere! There are typically 40 million bacteria in a gram of soil and a million bacteria in a millilitre of fresh water. And don’t forget the bacteria in our own body. There are about ten times more bacteria in our body than there are body cells! On average about 2 kg in an adult human body, mainly in your gut. And important for your digestion, you would die without them.

Here is a picture of the most common bacteria in your gut, the E. Coli bacteria. I will write a separate post later about bacteria and the human body.


So, finally we have arrived at the beginning of life. About 3.5-3.8 billion years ago there lived the Last Universal Common Ancestor (LUCA) of every organism living now. We do not know much about it. It may have lived in the deep sea, near to a volcanic vent. Read Four Billion Year-Old Mystery of Last Universal Common Ancestor Solved for more information. Here is a diagram from this site, showing the first major evolutionary split, in Bacteria and Archaea .


And here is the tree of life, showing the split in the three domains. First the split in Bacteria and Archaea, with the Eukaryota branching off from the Archaea. Note that the Kingdoms of Eukaryota in the graph below have often different names from the names in the visual representation above. A clear sign how this field of evolutionary biology is still in development.

tree of life

A much more detailed tree of life, although looking less like a tree, you can see below. Click here for a larger version. In blue the domain of bacteria, in green the Archaea and in red the Eukaryota. Each domain showing some of its kingdoms in different shades. Try to find homo sapiens..:-) And notice how huge and complicated the domain of the Bacteria is.

The names in the outer circle of this diagram are representative species in their kingdom. You can spend hours checking details in Wikipedia…:-)  For example Anopheles Gambiae : Mosquito, Oryza Sativa: Rice, Takifugu rubripes : Pufferfish, etc.


That a single tree of life can be constructed for all the living organisms, suggests that life has only started once on earth.  If life arose repeatedly then all of the separate origins must have disappeared without trace.

All living organisms belong to one big family with a common past of ~3.5 billion years. Isn’t that a nice conclusion for this post…:-)?


Much of the information in this post comes from the monumental book The Ancestor’s Tale, written in 2004 by Richard Dawkins

My ancestors

As you probably know, our species, homo sapiens, evolved, 200.00-150.000 years ago in Africa. From there they migrated all over the world. All humans living now, have  common maternal  and paternal ancestors.

How do we know this? By studying mutations in our DNA!

The idea is simple. Every now and then mutations occur in our DNA. If a mutation occurs in the DNA of an individual, will this mutation also be present in the DNA of its offspring? In the reproductive process the genes of father and mother are mixed, so that is difficult to say. There are however two exceptions!

One is the Y-chromosome, which inherits exclusively from father to son.The other one is the DNA in the mitochondria, the power plants of a cell. They come from the egg, and therefore from the mother.

By studying the mutations in the Y-chromosome we can trace back our paternal lineage to the Y-Chromosomal Adam. And in the same way, studying the mutations in the Mitochondrial DNA, we  finally go back to Mitochondrial Eve

Here are the approximate migration patterns for the paternal lineage. When you click on the picture, you will get an enlargement, where you can see the numbers in the various branches, like M173, M175, etc. This are the markers for specific mutations in the Y-chromosome. In the table estimates are given when this mutation took place. People with the same mutation in their genes are said to belong to a haplogroup

Last year, surfing the Internet, I found the website of the Genographic Project, managed by National Geographic. For 99 USD you could order a DNA ancestry kit to determine either your paternal or your maternal lineage.

As I was just reading the impressive masterpiece by Richard Dawkins, The Ancestor’s Tale, I became interested and ordered a kit. Here I am taking a swab to collect some DNA from my cheek.

The kit contains a code number that you can use to check the progress of the analysis.

After about two months I got the result. My haploproup was R1B. Nothing special actually, the majority of Europeans belong to this group…:-)


Here is the migration path of my (paternal) ancestors. About 50.000 years ago my paternal ancestor (M168) left Africa. His descendants traveled through the Arabian peninsula to Central Asia. They were hunter-gatherers, following the big game through the savannas, until they (M45) reached the big mountain ranges of Hindu Kush and Himalayas.

About 30.000 years ago, a branch split off with a new mutation (M207) and traveled to the West.  Keep in mind that they were not tourists, their movements were mainly determined by climate change and the availability of food!

In Europe this “Cro-Magnon” tribe met the Neanderthal people, which they outcompeted by their better skills and tools.

So that is my paternal lineage. Actually we ordered two sets, also one for Aric. His haplogroup turned out to be O, also nothing special, shared by the majority of Chinese in Southern China. It is interesting to see where our lineages split! In the image below I have combined our migration routes. The split occurred about 35.000 years ago in what is nowadays Tajikistan. In those days and in that region there has lived a man who is the (male) ancestor of both Aric and me. I find that fascinating.

So fascinating, that we ordered two more sets, this time to find out more about our maternal lineage.Here are the results combined in one picture.

Aric’s mtDNA haplogroup is D, mine is H Our common great……….great-grandmother migrated from Africa about 70.000 years ago. Still in Africa, about 65.000 years ago a split occurred, much earlier than in our paternal lineage. Aric’s maternal ancestor migrated far north to central Asia and Siberia. Members of haplogroup D eventually reached the Behring street and arrived in the Americas, about 15000 years ago

My maternal ancestors did not migrate as far east as my paternal ones, they remained in West-Asia and later migrated north across the Caucasus mountains into South-Russia and from there into Europe.

It is possible to make a more detailed (and more expensive) analysis of the mutations in the DNA, but for us this is enough. We know now, that we are family, LOL.

Mind you, our common maternal and paternal ancestors were NOT married, they did not even live in the same time! If you want know how that is possible, you should read Dawkin’s book.

The Great Debate: Are we alone? part 2

Two months ago I published The Great Debate: Are we alone? part 1

Here is finally part 2. My apologies for the long delay.

Quite a few of you gave their opinion about the question “Are we alone or not”.
Not surprisingly most ‘votes’ went to “We are not alone”, same as in the poll at the end of the Great Debate video.

My own opinion?
It will be wonderful and fascinating if (intelligent) life is found elsewhere in the universe, but personally I think we are alone.
Mind you, that is not arrogance, I would be more than happy if even primitive life is found elsewhere!

Let me explain why I have become (recently) more skeptical about life elsewhere in the universe.

In discussions about the probability of extraterrestrial life, you will often encounter the Drake equation.
In 1961 Frank Drake tried to make an educated guess about the number of intelligent civilisations in our own galaxy, the Milky Way.
He started with the (huge) number of stars in the Milky Way, then asked questions like: “how many stars will have planets”, “how many planets will be ‘habitable'”, “what is the chance that on such a planet (primitive) life will develop”, “what is the chance that intelligent life will evolve”, and several more of this kind of questions.
In his original estimate Drake comes to a number of about ten planets in our Galaxy at this moment, with intelligent, technologically advanced civilisations.

Many of the factors in the Drake equation are the result of guesswork.
For example, one of the points of discussion in the “Great Debate” is about the chance that intelligent life will evolve from primitive life. Drake’s estimate was 1 %. Marcy in the “Great Debate” thinks it might be close to zero. “Maybe we humans are just a freak evolutionary incident?

However, both Werthimer and Marcy agree: “primitive life will be teeming in the Universe.
Drake estimated the chance that life will develop on a habitable planet as 100%!
And Michio Kaku, an American ‘science communicator’, who always enjoys being in the limelight, goes even further: “The Laws of Probability Tell Us That the Universe Should Be Teeming With Intelligent Life Forms” Elsewhere he  writes (foolishly, IMHO) about a 100% probability!

Well, if they are right, why has until now no evidence of life been found on Mars?

A few days after my first “Are we Alone” mail, I sent you a short email about the exciting discovery of a habitable planet, orbiting Gliese 581, a red dwarf star at a distance of 20 lightyear from the sun.
Here is the picture again. Planet g is causing the excitement. The blue band is the habitable zone.

The concept of a habitable zone is based on the assumption that you need liquid water for the development of life. The (surface) temperature of a planet should not be too low or too high.  For a (cool) red star like Gliese 581, this zone lies much closer to the star, than for a hotter star like our Sun.
Of course you can think about more exotic  forms of life, based on silicon, ammonia, etc. Click here for a detailed discussion.

Now, when you look at the picture above, you will notice that both Earth and Mars are orbiting in the habitable zone of the Sun.
The Viking and Phoenix missions to the Red Planet had as one of their main targets the search for life on Mars, and I am sure that many scientists were hoping, or even convinced that evidence of life would be found. So was I.
But “nothing” has been found yet. Of course more exploration is needed and quite a few new missions have been planned.
Still it is disappointing and personally I believe now that the chance that life will develop on a habitable planet, might be small, maybe even very small.
Sure, the Miller-Urey experiments have shown that it is “easy” to synthesize amino acids, the building blocks of life, when the conditions are right.
And organic compounds have been found even in interstellar clouds.

But the next step is huge. Life is characterised by two fundamental properties, replication and metabolism.
We know that this step has been made at least once, on Earth.
Even on Earth there is no evidence that this step has been made more than once! Click here for more information about what is called abiogenesis.

So, this is my position:
As soon as evidence of life will be found, on Mars or deep under the frozen oceans of Jupiter’s moon Europa , I will celebrate and be convinced that life indeed is teeming in the Universe.
Until then, I believe in the Rare Earth Hypothesis , that we might well be alone.

The Great Debate: Are we alone? part 1

On 26 April 1920, a debate took place at the Smithsonian Museum of Natural History (Washington DC), between two American astronomers, Shapley and Curtis, about the scale of the Universe. Point of contention was the distance of the “nebulae” like Andromeda.
Shapley argued that the Milky Way was the entirety of the Universe and the Andromeda nebula was inside the Milky Way.
Curtis contended that Andromeda and other nebulae were separate island galaxies.
The debate became known later as The Great Debate.
We know now that Curtis was right. The Universe is huge and our Milky Way is only one of ~ 100 billion galaxies. Each galaxy contains on average 100 billion stars.
Our Sun is one of these ~ (!) stars, and was formed relatively recently, about 4.6 billion years ago (The Universe is ~ 13.8 billion years old)
Eight planets orbit the Sun (sorry for Pluto, not a planet anymore…), and on (only?) one of them, our beautiful Earth, life developed, about 4 billion years ago.
Evolution took place. But it was only about 200.000(!) years ago that Homo Sapiens (yes, that’s us) evolved, most probably in Africa.

Was that a unique incident?

About half a year ago another astronomical debate took place, at Berkeley University, 30 April 2010, almost exactly 90 years later, and it was also called a Great Debate.
A bit preposterous, IMHO…:-)
This time the topic was: Are we alone in the Universe?
The recording of the debate can be viewed at . Be warned, it takes 1.5 hours…:-), but watching it is worthwhile…

Debaters were Dan Werthimer, the chief scientist of the SETI project, and Jeff Marcy, an astronomer who has discovered more extrasolar planets than anyone else.

The SETI project is Searching for Extra Terrestrial Intelligence, so Werthimer is, not surprisingly, convinced that there are many planets with highly developed technological civilizations around us. SETI is searching for about 40 years now ‘only’, it will just take more time to find evidence for intelligent life elsewhere in the Universe, according to him.

Marcy is a skeptic. Ok, many, if not most, stars will have planets orbiting around them. And he agrees with Werthimer that primitive life will be “teeming” in the Universe.
But intelligent life? Is that an evolutionary advantage? The dinosaurs ruled the world for 200 million years and never developed intelligence with their peanut brains! Why not?
Maybe speed or a thick skull will serve you better to survive. Maybe we humans are just a freak evolutionary incident?

He has other interesting arguments. For example the water content of a planet. Quite critical.
Assuming that water has been brought to the earth by asteroids, it should be about 0.03%. Not more, nor less.
Less, and the planet will be a desert. More, and it will be just oceans. Is a technological civilisation possible under those adverse conditions?

At the end of the debate, after a Q&A session, there is a poll for the audience. Are we alone or not?

I have an opinion myself, but will only tell you in the second part of this email…:-)