mailbag

Re: "How widespread is Denisovan ancestry today?" and "Potato sack race":

Question about Denisovan DNA. Once introduced into a population, beginning many millenia ago, what keeps it from being in the DNA of everybody in the area? I exclude new arrivals, but what kept the Denisovan DNA from being spread to the homeland of the new arrivals what with the traveling salesmen, the refugees from tribal pushing and shoving, armies marching, cross marching and countermarching? It isn't as if Denisovan genes cause assortative mating by making the possessor either a hell of a catch or a last-man-on-earth scenario. Is it? Selective survival against diseases that come and go, while not so good in between, a la sickle cell? Is the blender model of human reproduction faulty somehow.

As to potatoes, I'd heard that one advantage is that armies, used to pasturing their horses in the grain of the enemy's peasants' fields, had to move on more quickly when the supply officers gave up trying to get their foraging parties to dig potatoes.

If, as Keegan hypothesizes, the ration was one pound of meat and two of bread (requiring two pounds of firewood) per man per day, an army of 30,000 ate out a location pretty quickly. If spuds were the local staple, they'd have to move. You just can't feed 30,000 guests who arrived unannounced by digging potatos. Not fast enough. Do horses like potatos? So, the army moves on--win--and the peasants get out the potato forks and do okay, more or less. Win.

Re: potatoes -- I think you've pointed to an important factor -- also, they can't be burned when the army retreats. The sheer productivity of tubers really does outweigh the available grain crops in Northern Europe.

Re: Denisovan DNA -- The genes should have diffused into other populations, all things being equal. That they did not do so is a pretty strong indication that SE Asia today shares little genetically with SE Asia 30,000 years ago. There must have been a massive influx of people who lacked Denisovan ancestry, well after the initial mixture with Denisovans happened and Denisovans themselves left the scene.

From a reader:

Hello Dr Hawks I am a reader of your blog and respect your expertese so I thought you would be the right person to ask this question to. I was debating a creationist about human genetic history the creationist is a literal believer in Noah's ark andi was saying to the creationst that one of the reasons we know the story of the global flood is nor true is because if it were all species including humans would have a bottleneck of two individuals dating to the exact same time. The creationist then cited this article as proof that humans could have been bottlnecked to 2 or six individuals

"However, the global extent of ß[beta]-globin divergence has at first sight some startling demographic implications because the hunter-gatherers who migrated from Africa. Europe and Asia have rather similar haplotype frequencies. Hence, the emigrants must have undergone the major change in haplotype frequency in the interval between leaving Africa and dispersing throughout the rest of the world. Assuming--and this is little more than an informed guess--that this interval was 20,000 years, population-genetics theory tells us that the mean effective size of the ancestral population for all non-Africans throughout this period must have been 600 individuals; or alternatively ;that ;the bottleneck was 6 individuals for 200 years, or even a signle couple for 60 years. (The expected time for the loss of a neutral gene present in thepopulation at frequency p is E(T) = -4N plnp/1-p, where N is the population size. We assume a generation interval of 20 years and that the 4 common haplotypes were present at equal frequencies in the ancestral African population.) If this is the case, much of mankind was an endangered species during an imporant part of its evolution." ~ J.S. Jones and S. Rouhani, "How Small was the Bottleneck?" Nature, 319, Feb. 6, 1986, p. 450

What is this article actually saying? Is it saying that it really is possible for every human alive today to have sprung from only 2 or 6 people? Because that contradicts everything Ive read that says genetics shows that our population could neevr have been bottlnecked below at least a few thousand individuals. Can you explain it to me. kind regards

A single gene can never provide evidence showing such a bottleneck, it requires every gene in the genome to show a consistent pattern. In this case, the most obvious genes to examine are those with the *most* variation. For example, the human HLA genes have hundreds of allelic variants in human populations that have existed for thousands of years. Each of these genes (including HLA*A, HLA*B, HLA*C, DRB1, DRB2, DQB) has old variations, the oldest alleles have been retained from our common ancestors with chimpanzees and gorillas. These could never have been retained for so long if we had undergone a bottleneck to two or a few individuals.

It is true that human genetic variation is low relative to some other mammals, but it is not indicative of a bottleneck to a handful of individuals. When geneticists today refer to bottlenecks, they are estimating many hundreds of individuals at the least, and 10,000 individuals as a more likely value.

This past year and half I have read and studied pre-history including most of the books, dvd's, on evolution, human origins, and all related subjects. I have followed the 'time line' from Big Bang to the 21st century and returned to the 10 million year period addressing the study of man from our "beginning". To my surprise there was no clear beginning; after much study, I understand why now; after seven million years, the last hominid fossil "Toumai"then nothing but primate fossils from which
is presumed the first hominids came into being leading to the evolution of some 17-20 species thru four groups. It appears
that from 7 mya to 10 mya is the famous "missing link" or gap with no fossil evidence of the "split" or diversion therefrom is
the contentious question and debate.

It is very impressive what Paleoanthropology and related sciences have discovered of our origins and the progressive
patterns of human development that explains so much of our existence for some 10 million years and estimated 108
billion that have come and gone. Yet! the story of 'man' is incomplete without an explaination of how, within the science of
molecular evolution, the genetic codes and finally through sexual reproduction from our closest relatives..... the primates.

After all the reading and research I have done, I am convinced that you and the science of Paleoanthropology work daily
to find the answer to the first hominids, there is nothing you would desire more that answer this question. My question:
Is there sufficient knowledge acquired to date that a story or explanation can be published declaring a clear beginning
picture that will give us a new 21st century Genesis?? It appears to me that we now have enough molecular and fossil
evidence to achieve the task! Of course including related sciences, climate, ecology etc. What do you think?

Thank you so much for your kind words!

I am maybe less hopeful than you, because I see the great difficulty of the task. We understand much about the time when our ancestors first diverged from the apes but our fossil record from that time has really only just begun. We will more quickly have an idea of how our genes changed from that time, but genetics is a bit like driving on the road and taking a note of each town you pass, then tossing all the notes into a hat and drawing them randomly. We do not know which genetic changes were the first, and therefore we have difficulty seeing why the events happened at the beginning.

My lab is directing our attention to the origin of Homo, around two million years ago. Here, the fossil record also is starting to fill in, but we additionally have the ability to determine which genetic changes might have happened at around the same time. Ancient DNA evidence has totally transformed our ability to study this time period. When we can understand this kind of event from the perspectives you mention, then I think we will be ready to tackle the origin of the hominins!

Re: "The new look".

Dear Professor Hawks,

I am distraught you have trashed your own website. The internal links are gone. You provide no search routine. Your mail bag is gone. The Neanderthal data plots are gone. Your art is gone. Your Neanderthal child looks like every child in my family. For that I am pleased.

I have touted your website. After the remake I cannot forward the link with pride. I wish you the time to make redress. Pity those who contributed to your original website in vain.

Conversion from an internet PC format to a cell phone wireless format is reminiscent of the transformation from Neanderthal culture to Sapiens culture. The distinction in my mind is between high volume information processing and pablum.

I do apologize about search; this has proved to be a serious problem as my site has scaled up and all the viable solutions involve learning a new system. And I can no longer guarantee that the layout will look right on older (non-CSS compliant) browsers; if you are using an older version of Netscape or Internet Explorer, you may be seeing something very different from most people.

As for the rest -- everything is still where it was, including the mailbag:

http://johnhawks.net/weblog/mailbag

Believe me, the links within the site are so important that they're taking more time than any other aspect of the remodel. The links were actually very bad at directing people into the site and allowing them to discover things. So I'm revisiting them, counting clicks and programming a new linking system to direct people more intelligently.

Surely you don't imagine that I would undertake such a difficult course of action on a mere whim. I have to change these things, because in the next few months the site will be initiating four new projects, each of which will have its own distinct flavor.

Please let me share with you something I'll be introducing as a new area of the website next week:

[And here I sent something extremely interesting...]