Creative Destruction

January 23, 2008

Human Evolution

Filed under: Media Analysis,Science — Brutus @ 3:31 pm

The BBC News has an article reporting that scientists have found evidence to suggest that human evolution is “speeding up.” Scare quotes are used for speeding up in the title of the article for good reason: it’s a reckless remark that can’t be proffered with a straight face. The study on which the article is based

looked specifically at genetic variations called “single nucleotide polymorphisms,” or SNPs. These are single-point mutations, or changes, in the genetic sequence of DNA on chromosomes.

If the mutation is advantageous then it will spread rapidly in the population, along with DNA on either side of the mutation.

It’s unclear to me whether it’s fair to conclude that evidence of a few changes in genetic sequence is tantamount to evolutionary change on the order of species change, which the article never states. Is there a term that describes minor genetic changes without meaningful change in the species? Put another way, isn’t a wide range of genetic variation within the species pretty normal without being evolutionary?

Researchers found evidence of recent selection in 7% of all human genes, including lighter skin and blue eyes in northern Europe and partial resistance to diseases, such as malaria, among some African populations.

This makes me wonder if the usual four mechanisms influencing evolution – natural selection, mutation, random genetic drift, and gene flow — shouldn’t be amended to include cultural election in the case of culturally preferred attributes such as skin type and eye color. (Nope, no suggestion of cultural bias or racial preference there. Move along.)

Also, if I’m not mistaken, when human evolution is discussed by regular folks without specialized training in genetics, the usual context is science fiction and the mode of evolution is either cultural (evolved minds) or biological (evolved bodies) or both. These are wildly divergent from a more narrowly defined science of genetic evolution, which apparently considers even modest change or variation evolutionary.

Without providing suitable context for the science and disclaiming the obvious associations with science fiction, the article invites credulous readers to infer that we’re pointed toward an a evolutionary breakthrough of some sort. What else could “speed up” suggest? The article muddies the waters further with these poorly framed quotes by Steve Jones, a genetics professor at of University College London:

“The general picture that evolution has speeded up in the last 10,000 years as we change from, to put it bluntly, being animals to being humans is clearly true,” he explained. “To suggest it is happening at this instant, I would suggest, is probably wrong.”

“At the moment we are in an evolutionary interval. We are in between two storms. One storm has more or less blown itself out, the storm of farming.”

I won’t bother to comment on the idiotic suggestion that humans aren’t animals. The more immediate problem is timescale. In evolutionary time, 10,000 years is almost nothing. Whether you believe in gradualism or punctuated equilibrium or some blend of both, it typically takes tens of thousands of years to observe changes to the genotype that aren’t merely chromosomal variations. Evolution is happening now, this instant; it’s always happening. But it isn’t instantaneous. Neither is a sunrise. Disclaiming such a thing is absurd to even a novice.

Perhaps it’s worthwhile to remind gentle readers not to get science news from the popular press. Whereas the study may have uncovered something meaningful to a geneticist, it holds almost no value to the general public the way it is reported and veers dangerously toward suggesting things from the realm of science fiction. Science is very good a discovering how things work. It’s not so good at predicting things or even extrapolating trends more than one step beyond the evidence. Take the “suggestion” of human evolution “speeding up” with a sizable grain of salt.

About these ads

8 Comments »

  1. Is there a term that describes minor genetic changes without meaningful change in the species? Put another way, isn’t a wide range of genetic variation within the species pretty normal without being evolutionary?

    No. Everything is evolutionary. Evolution works on tiny things and large things too. “Meaningful” is code for “that I notice”. Us not noticing it doesn’t make it not evolutionary.

    A wide range of genetic variation is normal. That range is the raw material of natural selection.

    Things like preference for skin color or what have you fall under sexual selection. It doesn’t have to be adaptive or rational to be selected for.

    If you think it’s idiotic to think that there’s an evolutionary divide between humans and animals, I’m not sure what to tell you. You could go discuss it with the chimpanzees, except for the part about them not having evolved linguistic abilities and abstract thought. Whoops, there’s that divide again. Pardon my idiocy for thinking it meaningful. ;)

    Comment by Robert — January 23, 2008 @ 5:08 pm | Reply

  2. Robert: “You could go discuss it with the chimpanzees, except for the part about them not having evolved linguistic abilities and abstract thought.”
    ********************************************************************

    Excuse me, Robert, how do you know that chimpanzees have no linguistic abilities or abstract thought? Have you spoken with Jane Goodall? What if chimpanzees had their own language that you, mere human, cannot understand? How should chimpanzees manifest abstract thought? By writing books on literary criticism?

    Comment by obie1993 — January 23, 2008 @ 5:35 pm | Reply

  3. In the Linnaean system of classification of living things, biological science defines (four or) five kingdoms:

    monera: bacteria, blue-green algae, and spirochetes
    protista: protozoans and algae of various types
    fungi: funguses, molds, mushrooms, yeasts, mildews, and smuts
    plantae: (plants) mosses, ferns, and woody and nonwoody flowering plants
    animalia: (animals) sponges, worms, insects, fish, amphibians, reptiles, birds, and mammals

    Modern-day humans are classified as

    Kingdom: Animalia
    Phylum: Chordata
    Class: Mammalia
    Order: Primates
    Family: Hominidae
    Genus: Homo
    Species: H. sapiens
    Subspecies: H. s. sapiens

    Humans fall within the animal kingdom. If you want to argue that we are not in fact animals, that is your prerogative. I think we are animals. But of course, we are different from other animals in some fundamental ways, just as a particular species of bird is different from a particular species of snake.

    Comment by Brutus — January 23, 2008 @ 6:56 pm | Reply

  4. Oh for heaven’s sake. The man was speaking poetically.

    Comment by Robert — January 24, 2008 @ 2:41 am | Reply

  5. you should mess with brutus, robert. he likes to be taken seriously.

    Comment by obie1993 — January 24, 2008 @ 3:31 pm | Reply

  6. i meant, “you should NOT mess with brutus…” see what happens when you don’t proofread or edit…

    Comment by obie1993 — January 24, 2008 @ 3:31 pm | Reply

  7. A few points.

    1. Non-scientist critics of evolution try to make a distinction between what they call “micro-evolution” and what they call “macro-evolution” that does not exist. The key to understanding why this distinction doesn’t have to exist is to understand in a big picture cruder than back of napkin numbers idea of what is in a genome.

    Your genome is 90%+ biochemistry (e.g. codes for the kinds of tissues that exist in the bodies, for the kinds of hormones and neurotransmitters that are produced, for the structure of individual cells) and 10% or less morphology (how many stomachs, how many arms of what length, how many eyes and where, etc.). An extra arm is a single gene mutation. The genome has huge chunks devoted to making muscle tissues, tendon tissues, bone and bone marrow, blood vessel tissue, etc., and then a moderate sized chunk devoted to the arrangement of tissues that goes into a making an arm, and then a tiny itty bit of code saying put an arm here and here. Ditto extra eyes.

    Also, there is a lot more fine texturing to lower level brain function which has the equivalent of built in operating system and ROM data — like how to breath, when to secrete growth hormones, and “be afraid of spiders”, while the much more massive cortex associated with higher primates, and homonids in particular, is more like a blank RAM card with a far simpler less detailed genetic pre-coding. Each item in the menagerie of things we are instictually afraid of used by horror movie writers everywhere, probably takes up as much genetic code as the part of the genome that allows humans to do calculus while chimps can’t.

    2. Natural selection doesn’t just mean people with loser traits die before reproducing, while people with winner traits live long and prosper. Reproduction rates and timing are also important. If one trait produces three kids and another two kids, that trait has a huge impact on the gene pool over a modest number of generations even if no one dies. Also, the difference between a human having kids as a teen v. having teens at age 30, is roughly equivalent to the difference between have three kids v. two kids, even if both people have precisely two children. The age difference allows the quick reproducer to fit in three generations of reproduction for two generations of reproduction in the slow reproducer.

    One interesting modern human example is related to child birth. Until very recently, C-Sections were extremely rare and any trait that would cause complications in pregnancy was very strongly selected against as it would usually kill both mother and child, both of whom have very high mortality rates. Now, almost ever pregnancy carried to term produces a live mother and a live child, which has allowed all sorts of traits (such as large infant head size and late term pregnancy) which were selected against despite also having benefits to flourish.

    Another case of modern obsolescence is the appendix. They now know what it does. It is a reservoir of gut bacteria that reboots your digestive system after you kill it off by starving yourself or using a toxic substance to kill off parasites in your GI system But, since better sanitation means fewere instances where you need to reboot your GI system, it is largely useless and people born with a mutation eliminating it are no longer selected against.

    What is driving human evolution is to a large extent a dramatic change in the things that are and are not important for survival. Mutation is a pretty slow force of evolution, but shifting proportions in the gene pool based upon selective effects is much, much faster. In 10,000 years we have had 400 generations, and that is a lot of iterations of the selection game whose most dramaticly selected effects can move a trait from high frequency to low or visa versa in just a handful of generations.

    3. Some really interesting evolutionary paths are omitted in this list.

    One is the germ line virus that changes your genetic code when you are infected with it in a way that impacts the genetic makeup of your children (some have been observed in South America).

    A second is hybridization where two separate species mate to produce young who belong to a third and separate species which is itself fertile (lots of examples of this in Alpine butterflies exist, and there are even more in plants).

    A third is symbosis that culminates in the symbionts becoming a single new organism (a process that explains some of the bigger steps in early protist evolution, for example — one possible human level example is the hypothesis that your immune system may have once been a separate symbiotic organism) and the converse of that which is colonial species like ants and bees which have separate organisms that act like organs of a single being and have a common genetic code.

    Comment by ohwilleke — January 24, 2008 @ 4:44 pm | Reply

  8. “A wide range of genetic variation is normal. That range is the raw material of natural selection.”

    FWIW, there is more genetic difference between two silverback gorillas than there are between almost any two human beings. We aren’t a genetic monotype, but we are surprisingly close.

    The estimated bottleneck size for all modern humans is on the order of 10,000.

    Close to one-half of Ashkenazi Jews, estimated at 8,000,000 people, can be traced back to only 4 women carrying distinct mtDNAs that are virtually absent in other populations, with the important exception of low frequencies among non-Ashkenazi Jews.

    Similarly low numbers have been established for the ancestors of pre-Colombian Americans.

    Comment by ohwilleke — January 24, 2008 @ 5:00 pm | Reply


RSS feed for comments on this post. TrackBack URI

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s

The Rubric Theme. Blog at WordPress.com.

Follow

Get every new post delivered to your Inbox.

%d bloggers like this: