Category Archives: Human Evolution

Cosmic Bombardment of the Earth ca 2.2 Million Years Ago?

There are bacteria that use Iron (and other elements) to make tiny magnets that they carry around so they don’t get lost. (I anthropomorphize slightly.) There are isotopes of Iron that are not of the Earth, but are found only elsewhere in the universe.

Suppose an event happened elsewhere and spewed some of that cosmic Iron isotope, say Fe-60, onto the earth, and the bacteria who were busy making their tiny compasses at that time used some of it. Then the bacteria died and were trapped inlayers in seafloor sediment and later examined by scientists looking for … well, looking for evidence of cosmic events trapped in bacterial compasses!

Well, that happened.

A bit of sea floor was found to have Iron-60 in it a few years back. Iron-60 is radioactive and decays into Cobalt-60, with a known (but only recently known as it turns out) decay rate. That bit of rock was taken as possible evidence of an ancient supernova. The event was tied, conjecturally, to human evolution as all things must be whenever even remotely possible:

Cosmic fallout from an exploding star dusted the Earth about 2.8 million years ago, and may have triggered a change in climate that affected the course of human evolution. The evidence comes from an unusual form of iron that was blasted through space by a supernova before eventually settling into the rocky crust beneath the Pacific Ocean.

The team has now analysed a … piece of ocean crust, where the supernova detritus is concentrated into a clear band of rock that can be accurately dated. The researchers found small but significant amounts of an isotope called iron-60 in the rock, which could only have come from a supernova.

“We’ve looked at all the possibilities and we can’t find anything else that could produce such quantities,” Korschinek says.

The human evolution impact idea comes from a possible cooling effect the exploding star would have had on the earth. Back in 2004 it was estimated that the earth would have been bathed in extra cosmic rays for about 100,000 years which would have, it was said, created condensation in the atmosphere which would have cooled the earth. There was a cooling event around that time (but quite possibly well after this date, so don’t hang any hats on this) so I suppose this could be. But, I’m not going to assume that the cooling effects of cosmic rays are a thing at this point. I do know that people have gotten the effects of upper level vapor wrong a few times so I’m going to avoid making any assumptions about that here.

Anyway, last April, a paper was given at the American Physical Society conference giving preliminary findings related to some follow up research. Shawn Bishop and his team obtained a core from the Pacific dating to between 1.7 and 3. 3 million years ago. They sampled it at 100K intervals and extracted and separated out Iron in a way that would show Iron-60 if there was any. And …

“It looks like there’s something there,” Bishop told reporters at the Denver meeting. The levels of iron-60 are minuscule, but the only place they seem to appear is in layers dated to around 2.2 million years ago.

And, the iron was concentrated in the target layers by the action of compass-using bacteria.

Notice the change in date from 2.8 to 2.2. This is, I think, because the half life of Iron-60 was refigured based on some intervening research. Now, the date is probably too late for a significant cooling event. But really, there were a whole bunch of cooling events from somewhere over 5 million years ago to about 2 point something million years ago, and there is a long list of candidates for what caused them, including numerous big volcanoes, continental movements, and now, a supernova.

I don’t think anyone is claiming to know what star exploded.


Photo Credit for picture of fancy science machine: Gottfried not Bouillon via Compfight cc

Common misconceptions and unproven assumptions about the aquatic ape theory

Common misconceptions and unproven assumptions about the aquatic ape theory

A Guest Post by Marc Verhaegen
*2013 m_verhaegen@skynet.be

It is often assumed that Alister Hardy’s and Elaine Morgan’s aquatic ape theory (AAT) suggests that more than 5 Ma (million years ago) there was a semi-aquatic phase in our past (explaining e.g. human fur loss, fatness and upright bipedalism), which was followed by a savanna phase on the African plains. In 2011, AAT proponents published an eBook, Was Man more aquatic in the past?, which showed a rather different picture of AAT. Here I very briefly describe my view of ape and human evolution (for details and references, see my publications at the end of this article).

The Homo-Pan last common ancestor (LCA)

My 1994 paper concluded:
Continue reading Common misconceptions and unproven assumptions about the aquatic ape theory

Fighting Over Hobbit

The Hobbit is a book by JRR Tolkien, a just released blockbuster movie, and a hominid from Indonesia. Here, we are speaking about the hominid from Indonesia.

A while back I wrote a review of a book by Dean Falk, for American Scientist. You can find that review here, and you can find a different review of the same book here on my blog.

Falk’s book is about endocasts and brains her area of specialty and she goes into the study of two specific hominids in particular, Taung, and LB1. Taung (pronunced “Tah oong,” roughly) is the type specimen of Australopithecus africanus, the first described Australopith and probably the first early hominid recovered in Africa, which by the way was in 1924. LB1 is one of the diminutive Homo found on the island of Flores, Indonesia, sometimes called “Hobbit” that shook things up a bit a few years back. Assuming this is what most experts say it is, this is a new species in the human family, Homo floresiensis. Go and read the reviews cites above to find more, or better yet, read the book. A cool feature of Dean’s book is that she is a scientist writing about the research she knows about, but it is NOT a general “here’s what happened in human evolution” book, but rather, focuses much more on a smaller subset of issues.

My old friend Maciej Henneberg and Robert Eckhardt have a very different opinion of this fossil than Dean Falk does, and as far as I know, different from the broader consensus. Henneberg and Eckhardt (and some others) view Homo floresiensis as a previously existing species (ie., Homo sapiens) but pathological. They may be right, but they probably aren’t. And, the whole story of who has done what with these fossils, and to each other, is one of the more rollicking adventures in paleoanthropology. If this drama was playing out in the 18th century, there would have been a few duals by now.

Anyway, I just found out that Maciej and Robert wrote an extensive comment on my book review, and sent it to American Scientist who did not want to publish it because it was too long. Subsequently, the’ve published their original review on a blog and sent American Scientist a shorter version, which has been placed on the American Scientist web site. The blog post is: Response to American Scientist Review – Longer Version and the American Scientist version is A letter regarding Greg Laden’s review of The Fossil Chronicles. I invite you to read them both, but I’d start with the American Scientist version because the longer one is very long.

Stories from the field: Jon Kalb’s Newest Book

People who do a lot of field work end up with interesting stories to tell, especially if the fieldwork is diverse and the conditions are adverse. Often, the sort of thing people want to know about is very different from the repertoire of available stories, but as long as the expectations of the audience is not too rigid, experienced fieldworkers in the various sciences that do field work make the best cocktail party extras.

I never met Jon Kalb, but we have a lot of colleagues in common. I first heard of him as one of the scientists on the same expedition that found the famous fossil “Lucy” (and her various friends and families). The whole Ethiopian foray was interesting as stories go. Research in the Afar region as well as down in the Omo basis was linked to numerous interesting stories worthy of a great deal of lecture time in any reasonable course on human evolution, or several pages of descriptive prose in any book on human evolution. And this is entirely aside from the actual discovery of any actual fossils.

I recalled that Kalb was the guy who was accused of being a CIA agent and thus tossed out of the country (Ethiopia) after doing quite a bit of work there. The person who told me that also assured me that it was not true; he was not a CIA agent. But that particular story goes with a lesson: don’t ever let anyone think you are a CIA agent because they’ll toss you out of the damn country.

The reason I’m telling you all this is because Joh Kalb has written a book, perhaps I can fairly call it a memoir if that term has not been broken into a million little pieces by some other author, of his time in the field. The Ethiopian bit is part of the story, but only a small part, as Jon had done quite a bit of work both before and after. Much of the attraction of books on human evolution and other field sciences is the fieldwork stories, and that’s what Jon’s book is all about. There are stories from North America, South America, Africa, from the driest regions of the world to under the sea. The research is all over the map as Jon was himself, with human origins work being only part of it. (Jon is a geologist so he is not bounded by taxon!)

Hunting Tapir During the Great Flood and Other Tales of Exploration and High Adventure is a rollicking adventure very much worth the read.

Kalb is also the author of Adventures in the Bone Trade: The Race to Discover Human Ancestors in Ethiopia’s Afar Depression.


More on Human Evolution

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Aquatic Ape Theory: Another nail in the coffin

I just want to say that Huxley is pretty bad at swimming.

I quickly add, for a 3 year old human, he’s pretty darn good at it. Amanda’s family is very aquatic, as tends to happen when everyone spends several weeks per year (or longer) on the edge of a lake. They can all ski really well, they can all swim really well, etc. etc. So, very soon after Huxley was born, his grandfather started to bring him to age-appropriate swimming lessons. He is now 37 months old and has been to a swimming lesson almost every week. In addition to to that, Amanda brings him to the pool pretty close to once a week, often more. In addition to that, during the summer, he has spent several days at the lake and gone in once or twice almost every day the conditions allowed. In short, he should be about as good a swimmer as any 3 year old.

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And he is. In fact, better. He is far beyond his age to the extent that he’s skipped grades, and the people at the swimming school have to keep making adjustments in order to ensure he is always getting the next level of training rather than being held back by the other kids who are not as good as he is.

But still, this means he can drag himself underwater for several bananas (the unit of time used by swimming instructors, apparently), and he can thrash around moving his body across the surface several inches in a predetermined direction. He can get himself to the bottom of a pool as deep as he is tall and easily pick up a ring or some other object, and he can float around in various positions comfortably.

So he swims better than a new born through 1 month old hippo (they can’t swim at all, really) but he’s nowhere near as good as dolphin. But the thing is, this is after three years. Had Amanda and I been aquatic apes, Huxley would not have survived to this ripe old age. The diving reflex, proffered as evidence for an aquatic stage, during which we spent considerable time in (not near, in) water, happens in mammals generally and alone is not enough to count as a retained adaptation suggesting an earlier evolutionary stage. If human ancestors subsequent to the split with chimpanzees went through a significant aquatic phase (not just living near water, which is one of the backpedaled versions of the AAT) then our children would probably … not necessarily but probably … be much better at swimming than they are.

This does not disprove the Aquatic Ape Theory. Nor does a single nail secure a coffin. But it certainly does not inspire confidence in the idea.

Huxley tells me that he plans, someday, to teach me to swim.

Palaeowomaen: Barbara Isaac, Women in The Field, and The Throwing Hypothesis

Following on discussion arising from this post, here is a revised discussion of throwing in human evolution.

The question of diversity in science, and more specifically, success for women, is often discussed in relation to bench or lab oriented fields. If you read the blogs that cover this sort of topic, they are very often written by bench scientists, for bench scientists, and about bench scientists. Which makes sense because most scientists probably are bench scientists.

Here I want to do two separate but related things. I want to discuss certain aspects of the nature of fieldwork in my area in the 20th century that have had a strong effect on the way women have pursued their careers (or not). Although I characterize this as the situation of the 20th century, this does not mean that the situation has or has not changed substantially since then. Simply put, I’m not discussing the current career related situaton for women in field paleoanthropology here in this post.

The second thing I want to do is to talk about a successful female social scientist with a strong connection to fieldwork in palaeoanthropology, as well as theoretical and administrative contributions. This person is also someone who straddles the boundary between classic mid- to late-Twentieth Century patterns of professional activity (in these field sciences) and more recent patterns. I’m speaking here of Barbara Isaac.

The link between these two topics is a bit tenuous but it is also meaningful. There is nothing stereotypical about Barbara Isaac’s career, and there is nothing short of admirable about her as a person and a scholar. My intention here is to not make strong links between these two parallel topics.
Continue reading Palaeowomaen: Barbara Isaac, Women in The Field, and The Throwing Hypothesis

A Book about Taung and "the Hobbit"

The Fossil Chronicles: How Two Controversial Discoveries Changed Our View of Human Evolution is by a scientist Dean Falk, who has contributed significantly to the study of evolution of the human brain, and who has been directly involved in some of the more interesting controversies in human evolution.

Back when I was a graduate student I was assigned by my advisor a set of literature to absorb and comment on. The mix of published and soon to be published papers included a series of papers written by Ralph Holloway and Dean Falk. These represented a fight over the interpretation of early hominid brains as studied through endocasts. Endocasts are fossilized casts of the inside of an animal’s brain case or the artificially produced version made of casting material poured into a skull. Either way, you get a roundish blob that resembles the exterior of the original brain. Endocasts are of limited value, as layers of tissue in a living mammal separate the brain from the skull, attenuating detail. As Falk point out in her book, endocasts are a rather “surficial” view of a brain, but are not without their uses.

Fossil endocasts are compared to endocasts made from the skulls of “living” primates and humans, which in turn are understood via Continue reading A Book about Taung and "the Hobbit"

Evolution for Conservative Christians

Lewis Black has a formula for addressing creationists. You carry around a fossil. Then, when someone starts talking about creationism, you pull it out and hold it up in plain view and say “Fossil!” Then, if they keep arguing, you throw it over their head. That makes me laugh.

Despite the fact that I am a raging secularist and activist atheist, not all of my friends are. And, I have a friend for whom I have nothing but love and respect who happens to be a fundamentalist evangelical Christian. Personally, I’m sure that down inside she is also an atheist, and I know she knows I think that of her, and it is sometimes a matter of discussion. Here’s the thing: She’s very very smart, knows a lot of stuff, and is on my personal top ten list of Most Thoughtful People. (Thoughtfulness is actually a characteristic of the regular non-Troll readers of this blog, so you know what I mean.) Anyway, she totally gets science even though she is not a scientist nor does she have a lot of training or education in science. (Rather, she can read numerous dead languages and has all sorts of other smarts.) She understand that science is real, it is a process of thinking and discovery, that it is important, and that it should shape much of our policy as a society. And all that is by way of introduction for the following video, which she has recommended. I’d like to know what you think of it:

So, if you don’t want to carry around a fossil, you can just carry around this video.

What is Dunbar's Number?

The term “Dunbar’s Number” refers to a particular hypothesis by primatologist Robin Dunbar. It is a very simple idea with rather complex implications, and it is one of those simple ideas that gets more complicated than ideal as we look into it more and more. Eventually, the idea is required by many who contemplate it to do more work than was ever intended, and in this way seems to fail, though it really doesn’t. I personally think Dunbar’s number is useful if it is properly understood, so I want you to give it a chance, and to help you do that I’d like to use an analogy.

I’m thinking of a number called Carrier’s Number. Carrier, in this case, refers to the company that installs air conditioners and heaters. Carrier’s number is the temperature in degrees F at which you, sitting there in your chair, notice it is too warm so you get up and go turn on the air conditioner. It is best measured as a post hoc number…we watch and wait, flies on the wall, as the room heats up, and when a person gets up and flips on the air conditioner, the temperature at that point was carrier’s number for that person at that time.

One might argue that a post hoc measure like this isn’t much use in science because in science we like to predict things. But just because carrier’s number is best measured pot hoc does not mean that it only exists post hoc. It existed before the test subject got up, we just didn’t know what it was. For a large number of test subjects, we should be able to estimate carrier’s number (it is probably in the upper 70’s F). However, this will vary across cultures, across seasons, humidity, as clothing styles change (in the days of Polyester Leisure Suits, it is said that Carrier’s Number went down by about four degrees) and so on. The fact that it varies does not make it a bad number. In fact, its variation and reasons for it can make it an extra good number depending on what one is trying to do with it.

Dunbar’s number is the number of full blown social interactions you can manage. This number is lower or higher across species of social primates, as it tracks adaptive suites of sociality and the ability of brains to manage sociality. So, you can measure Dunbar’s number across primate groups by looking at how large effective primate groups get across species and figuring that the number is just about that maximum group size. Or, you could estimate Dunbar’s number (retrodict it, as it were) by looking at relative brain size, if we assume that brain size is linked to Dunbar’s number, all else being equal. In this way, Dunbar’s number is a way of linking primate sociality with brain evolution, which was the original idea.

In modern society, and in human historical contexts, we may see Dunbar’s number in a lot of places. This is the number at which, more or less, groups start to break down (in some societies) and villages split. Military units max out at about Dunbar’s number (companies are about 100 in size) and so on. This does not mean that Dunbar’s number and its associated dynamics explain everything. It might mean that the breakdown of social interactions can be more important than, say, resource limitations, on human group fission and fusion. That is exactly what many anthropologists have been suggesting for decades. Dunbar’s Number is simply this concept quantified somewhat and expanded to primates.

There are variations and adjustments. Some organisms have apparent smaller brain size because their diets cause a different body size, so that has to be adjusted for (leaf-eating monkeys may small relative brain size because their bodies are large, not because their brain is small, for example). What a fully blown social interaction is may vary. A group of primates may have a subgroup that hardly ever interacts with the others. Perhaps pre-adolescent monkeys don’t count for as much as sexually mature monkeys, so if there happens to be a baby boom a couple of years back, the group size if you count everyone is higher than Dunbar’s number. Or perhaps the group includes two or three social geniuses who temporarily facilitate an extra large group size, or temporarily force an extra small group size, for some reason.

It makes sense that there is a limit on effective sociality, and thus, on effective social group size. Dunbar’s number is nothing other than the number you end up with because when you are making the damn graph you need a damn number to put there on one of the axes. It has been over-interpreted or over-used as a number like many of those from Physics, like the freezing point or boiling point of water, which it is not.

Desiree Schell and I spoke about Dunbar’s Number on the Skeptically Speaking that just became ready for you to download. Check it out here.

This video includes, during the last third somewhere, a discussion by Dunbar of all this.

And, here’s a few items by Dunbar you might find interesting:

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  • How Many Friends Does One Person Need?: Dunbar’s Number and Other Evolutionary Quirks
  • Grooming, Gossip, and the Evolution of Language
  • Philip Tobias 1925-2012

    Philip Tobias passed away this morning, according to a mutual friend. I’ve not heard any details.

    Tobias is the most important hominid anatomist to have lived in the 20th and early 21st century, having taken the chair originally established by Raymond Dart at Wits University. He literally defined several of the hominids, being the anatomist to author the official diagnosis of several species. He was also a human rights champion, an excellent poet and decent singer and performer, an excellent teacher, a great friend, a strong and central personality in human evolution and unbelievably demure and humble for a man of such stature.

    Philip Tobias

    I remember the first time I met him. I was standing in the lobby of the Peabody Musuem, where we were hosting an LSB Leakey Foundation Event. I had just seen off Gordon Getty and his staff who were heading for lunch, ridden down the elevator with Yo-Yo Ma, I’m pretty sure the Presidents of two or three countries were milling around and some other stuff was going on when Mary Leakey and Philip Tobias walked up to me. I instantly dropped all the other names and gave them my full attention.

    “We heard you might be able to drive us to the bookstore,” one of them said. “Harvard Square is meant to have some good ones.”

    I thought for a moment and it occurred to me that I might not be a normal graduate student because I hadn’t soiled myself yet. Truth is, I wasn’t, having had a normal live before I started the project of Piling it Higher and Deeper.

    “I can,” I replied. “My pickup is out in front, but it has a miniature cab. One of you will have to ride bitch.”

    They walked to the bookstore.

    The last time I met Philip was in his lab at Wits. I’ve told part of that story before, so I won’t bother you with it now.

    RIP Philip. Thank you for everything.