Study Detects Recent Instance of Human Evolution

New York Times ^ | 10 December 2006 | Nicholas Wade

[Alter Kaker]

A surprisingly recent instance of human evolution has been detected among the peoples of East Africa. It is the ability to digest milk in adulthood, conferred by genetic changes that occurred as recently as 3,000 years ago, a team of geneticists has found.

The finding is a striking example of a cultural practice — the raising of dairy cattle — feeding back into the human genome. It also seems to be one of the first instances of convergent human evolution to be documented at the genetic level. Convergent evolution refers to two or more populations acquiring the same trait independently.

Throughout most of human history, the ability to digest lactose, the principal sugar of milk, has been switched off after weaning because there is no further need for the lactase enzyme that breaks the sugar apart. But when cattle were first domesticated 9,000 years ago and people later started to consume their milk as well as their meat, natural selection would have favored anyone with a mutation that kept the lactase gene switched on.

Such a mutation is known to have arisen among an early cattle-raising people, the Funnel Beaker culture, which flourished some 5,000 to 6,000 years ago in north-central Europe. People with a persistently active lactase gene have no problem digesting milk and are said to be lactose tolerant.

[Alter Kaker]

Yep, it's my own inability to accept the impossible that makes me so stubborn.

I don't think you have any idea how long 3.5 billion years is. I can get creationists to accept that incremental changes do occur to genotypes, but you people are inevitably lost on the cumulative effect of those changes over many generations. That stems entirely from a poverty of vision -- the numbers just get too big and you just throw up your hands and say "Prokaryote! Human! It's just too complicated for me to imagine!"

t couldn't be that evolution can never answer the big questions, like how did life form from inanimate matter?

Evolution also doesn't explain why the earth is round, why peanut butter sticks to the roof of your mouth, or why beer tastes better out of a tap than it does in a can. It simply explains a change in allelle frequencies over time, and that's not a failure on its part.

You get all your PhD's together, gather up all the water, oxygen, nutrients, and anything else you want, all of it inanimate, and make a single-celled form of life, then give me a call.

In any event, wouldn't that be Intelligent Design?

[muawiyah]

Wild cattle were being caught, corraled and milked long before it occurred to anyone to domesticate them.

[RobRoy]

This is a sample of the kind of evolution very few will argue with. Although I don't know that the word "mutation" would be accurate. All people are slightly different in some ways. If something happened in our environment that favored people less than 5 feet tall, the population would shrink in height in a few generations. If something happened to suddenly favor those over 6' in height, the general population would increase again in height in a few generations.

It is not evolution of the individual members of the populateion that is happening. It is simply a change in the numbers of a particular subgroup that was always there - and still is. It just became the dominant group.

Same thing here. If something happened to our environment that suddenly made it deadly to adults that could digest milk, in a few generations, the general population would again be unable to digest milk.

This isn't the type of evolution that stirs the fun debates here. ;)

[Alter Kaker]

I'm not an expert in cattle domestication (it's just a little bit outside my field :-) ), but my point is simply that I think we can imagine plenty of ways for humans to have exploited cattle before this mutation.

[muawiyah]

Since folks were drinking the milk of wild mammals thousands of years prior to the domestication of those same mammals, it's interesting that it took so long to come up with a genetic variation that allowed for this into adulthood.

I'm guessing cheese was invented far earlier than these researchers imagine.

[Alter Kaker]

Although I don't know that the word "mutation" would be accurate.

Why not? A genetic mutation clearly took place, in a specific individual 3000 or so years ago. Before that point, no adult in East Africa had the gene that would allow digestion of lactose. That gene resulted from a genetic mutation. Whether you believe that the mutation was natural or that God for whatever reason decided to intervene (in accordance with Intelligent Design) the mutation clearly took place.

[Alter Kaker]

Fermented milk may be older than cheese (I don't know that to be true, I'm just speculating of course).

Remember also that human children could digest animal milk all along (to at least some degree). Maybe animals were exploited in order to provide an extra food source for unweaned infants. Since infants were the most likely members of society to die, even a slight increase in infant nutrition would probably confer huge evolutionary advantages.

[muawiyah]

Alter, baby, the culture didn't need to have domesticated animals ~ just have "useful" animals around ~ like pregnant cows ~ and this would cover a wide array of animals anyway ranging from goats, to sheep, to reindeer, to aurox, etc.

Even American Indians regularly milked wild bison.

Interestingly enough, no comprable gene change happened in the Americas.

What I think is going on here is a much more recent finding that vitamin D may be a natural antibiotic. If you don't get enough vitamin D you get sick and die. If you get enough, you thrive and live.

In parts of the world where normal human processes could provide sufficient Vitamin D, no variation in the lactose processing gene(s) would convey any particular advantage on anyone. On the other hand, where normal human processes could not provide sufficient Vitamin D, e.g. at high latitudes, inland, such a gene would definitely convey an advantage.

However, the "advantage" is not in terms of having a "superior process" that others don't, it's in having an "additional process" that confers equality of condition when it comes to living long enough to successfully reproduce.

There are about 600 such gene changes that have been found in European populations. Almost all of them seem to have something to do with "getting lighter and/or more transluscent", and that's gotta' be related directly to the business of producing enough Vitamin D to survive into adulthood.

[Doc Savage]

That would be MICROGenetic alterations. Evolution doesn't exist, happen or be reality.

[Alter Kaker]

That would be MICROGenetic alterations. Evolution doesn't exist, happen or be reality.

So evolution takes place for a while, until God smacks a giant red OFF button? Is that how you see it?

[Alter Kaker]

The genetic mutation described in the article occured among cattle raising populations in East Africa. I'm not sure I see access to Vitamin D being a problem in East Africa, as opposed to general nutrition.

[RobRoy]

>>Why not? A genetic mutation clearly took place, in a specific individual 3000 or so years ago. Before that point, no adult in East Africa had the gene that would allow digestion of lactose.<<

Out of curiosity, do we really KNOW that, or is it educated guess or speculation. I am talking about the mention that NO ADULT had the gene. That is a pretty powerful statement and, in the absence of clinics to verify this at the time in question, I am understandably skeptical.

[RobRoy]

Actually, it's green.

[muawiyah]

The mutation probably doesn't demonstrate anything more than that we have a gene subject to frequent mutation. Those guys got one. You got another. I've got the original one.

Three species already!

[bert]

.......Very low threshold for this fairy tale of a theory.....

Mythical certainty is a far easier to swallow than natural selection.

[EternalVigilance]

Gosh. At this rate, in a gazillion years or so, we're all probably gonna be milk cows!

Hey! Does that mean it turns out that the Hindus were right?!

/s (added for the benefit of those lacking a sarcasm detector...)

[Alter Kaker]

Out of curiosity, do we really KNOW that, or is it educated guess or speculation. I am talking about the mention that NO ADULT had the gene. That is a pretty powerful statement and, in the absence of clinics to verify this at the time in question, I am understandably skeptical.

Correct. That's the purpose of this study -- it traced back the existence of this one genetic mutation to a specific individual 3000 years ago. Now that doesn't mean that other individuals hadn't had analogous mutations at earlier points (remember that a similar mutation occured in Northern Europe 3000 years earlier), but if they did in East Africa, then their genes have not survived to the present day.

[Alter Kaker]

Actually, it's green.

Ok, but do you have a substantive response? If evolution takes place on the small scale, then clearly something (again I'm picturing God with a big OFF button of the color of your choice) actively intervenes to stop it after a certain point. Otherwise you'd soon have large scale evolution.

That's a somewhat strange image, which is why I have trouble entertaining creationism as a serious explanation for much of anything.

[AndrewC]

Before that point, no adult in East Africa had the gene that would allow digestion of lactose. That gene resulted from a genetic mutation.

Wrong. You seem to misunderstand what has happened. People have the innate ability to digest lactose. It is turned off. When it is needed it is turned on.

Fron the article.

The mutations Dr. Tishkoff detected are not in the lactase gene itself but a nearby region of the DNA that controls the activation of the gene. The finding that different ethnic groups in East Africa have different mutations is one instance of their varied evolutionary history and their exposure to many different selective pressures, Dr. Tishkoff said.

This is from Dr Shapiro showing how cells compute and it involves the same sugar. http://shapiro.bsd.uchicago.edu/21st_Cent_View_Evol.html

CELLULAR COMPUTATION AND GENOME SYSTEM ARCHITECTURE

        There are many ways to visualize the systemic nature of genomic coding. One that is discussed in other parts of these PROCEEDINGS is the organization of protein molecules as systems of discrete structural and functional domains encoded in evolutionarily mobile DNA modules (14; these PROCEEDINGS, Symposia B6 and B7). Here we will examine the basic principles of gene expression and transcriptional regulation and the evolution of our one-dimensional concept of the gene into the more complex notion of a genetic locus.

The lac operon: A simple but illustrative example

        Our example is the lac operon encoding the capacity for lactose utilization in the bacterium E. coli. Like virtually all classical genes, lac began existence as a point on a genetic map in the late 1940s, soon after the discovery of genetic exchange in bacteria (Fig. 1; see 15, 16, for detailed references to lac operon history).



Fig. 1. The lac gene, site of mutations affecting lactose utilization by E. coli (1947).

In the following years, Jacques Monod studied lac genetics because he had discovered that E. coli could discriminate between glucose and lactose; when given a mixture of the two sugars, the bacteria would invariably consume all the glucose before starting to consume the lactose. In 1961, Monod and his colleagues proposed the operon model. In the operon, lac had evolved into a system of "structural genes" encoding the proteins of lactose transport and metabolism (lacZYA), a "regulator gene" encoding a repressor (lacI), and a completely novel type of genetic element, the "operator" (lacO) (Fig. 2).



Fig. 2. The lac operon (1961)

It is important to recognize that lacO was not a "gene" encoding a product. Instead, it was a site on the DNA where the repressor bound to block the initial step of lacZYA expression from the adjacent DNA. This conceptual development was revolutionary in its impact on our understanding of genome function. Such cis-acting binding sites for proteins are now recognized as key components of the genome, essential for processes such as replication, transcription and genome distribution to daughter cells.

After the operon model, other scientists discovered additional binding sites in lac, including the site of RNA polymerase binding or "promoter" (lacP),  a site for binding the Crp transcription factor that mediates glucose control of lacZYA transcription (CRP), and two additional operator sites that permit cooperative binding of the repressor (lacO2, lacO3). Thus, by the mid 1980s, molecular genetic analysis had decomposed the dimensionless lac gene into a structured system of protein-coding and cis-acting regulatory sites (Fig. 3).



Fig. 3. The lac operon (1990)

The importance of the organization of the various lac regulatory sites is that they permit the molecular computations that allow E. coli to discriminate glucose from lactose ? that is, to control expression of the lactose metabolic proteins so that they are only synthesized once glucose is no longer available. The basic biochemical reactions and molecular interactions involved in this computation can be stated as logical propositions that can then be combined into partial computations (Table III). These partial computations illustrate the molecular logic allowing the cell to execute the following overall computation: "IF lactose present AND glucose not present AND cell can synthesize active LacZ and LacY, THEN transcribe lacZYA from lacP."

Table III. Computational operations in lac operon regulation

Operations involving lac operon products
? LacY + lactose(external) ==> lactose(internal) (1)
? LacZ + lactose ==> allolactose (minor product) (2)
? LacI + lacO ==> LacI-lacO (repressor bound, lacP inaccessible) (3)
? LacI + allolactose ==> LacI-allolactose (repressor unbound,lacP accessible) (4)

Operations involving glucose transport components and adenylate cyclase
? IIA^Glc-P + glucose(external) ==> IIA^Glc + glucose-6-P(internal) (5)
? IIA^Glc-P + adenylate cyclase(inactive) ==> adenylate cylase(active) (6)
? Adenylate cyclase(active) + ATP ==> cAMP + P~P (7)

Operations involving transcription factors
? Crp + cAMP ==> Crp-cAMP (8)
? Crp-cAMP + CRP ==> Crp-cAMP-CRP (9)
? RNA Pol + lacP ==> unstable complex (10)
? RNA Pol + lacP + Crp-cAMP-CRP ==> stable transcription complex (11)

Partial computations
? No lactose ==> lacP inaccessible (3)
? Lactose + LacZ(basal) + LacY(basal) ==>lacP accessible (1, 2, 4)
? Glucose ==> low IIA^Glc-P ==> low cAMP ==> unstable transcription complex (5, 6, 7, 10)
? No glucose ==> high IIA^Glc-P ==> high cAMP ==> stable transcription complex (5, 6, 7, 8, 9, 11)
 

        Two aspects of this particular genomic computation deserve special mention. The first aspect is that the computation involves many molecules and compartments of the cell, not just DNA and DNA binding proteins. For example, the membrane transport proteins LacY and IIA^Glc are essential. The second noteworthy aspect is that the computation involves the use of chemical symbolism as information is transmitted. Thus, the presence of allolactose inducer represents the availability of lactose and the ability of the cell to synthesize functional LacY and LacZ. Similarly, the concentrations of IIA^Glc-P and cAMP represent the availability of glucose to the cell. Both whole cell involvement and transient chemical symbols are typical of cellular computation and signal transduction in general.

[Alter Kaker]

This isn't a speciation event as individuals with and without the mutation can obviously interbreed succesfully. Don't be fatuous.