Twelve Days of Evolution: #1: What’s evolution?

I’ve just noticed that this is post #12,002 since we began nearly six years ago. That’s a lot of posts!

“It’s okay to be smart” and PBS are producing a series of short videos, “Twelve days of evolution.” I’ll put up one a day, which should ultimately take us close to the end of Coynezaa.

This first one explains what evolution is. There are a few problems, though: it conflates evolution with natural selection (you can have common ancestry without natural selection), it equates natural selection with differential survival (actually, the differential reproduction of genes, whose vehicles are organisms, is the key), it doesn’t define “allele”, and there’s a long blurb for Dropbox at the end.

To me, the modern theory of evolution is as follows, and this is what I’d prefer to have seen in the video:

  • Evolution occurs, and by that we mean genetic change in populations.
  • That change is usually gradual, i.e., substantial change requires lots of time: more than just a generation or two. What evolves are populations of organisms, not an individual itself.
  • A lineage can not only change, but split, producing new species and new lineages.
  • (Flip side of the previous): If you take any two species or individuals, you can go back in time to find their common ancestor. The more recently in time that that ancestor existed, the more closely related the species. All living species descend from a single form of life that lived between three and four billion years ago.
  • The only process that can produce the appearance of design that so amazes and delights us is natural selection: the differential ability of genes to get themselves copied into the next generation. But there are also processes beyond natural selection that cause evolution, including genetic drift. Those processes, however, don’t cause adaptation.

Well, check out the video and tell me if you find it enlightening:

h/t: Alan


  1. Posted December 17, 2015 at 2:23 pm | Permalink

    Ignoring the posts that would occur on one leap year day and the 13 days left in 2015, a very slight underestimate:

    12002/2190=5.5 posts per day, on average

  2. Merilee
    Posted December 17, 2015 at 2:26 pm | Permalink


  3. Jean Hess
    Posted December 17, 2015 at 2:51 pm | Permalink

    So are beagles a result of evolution? I thought they were created through humans selectively breeding to get the traits they wanted.

    • Mark Sturtevant
      Posted December 17, 2015 at 3:47 pm | Permalink

      Yes. Evolution of domestic varieties is by ‘artificial selection’.
      I like to use the term ‘selective breeder’ rather broadly to convey the different ways that evolution by selection occurs. Of course humans are selective breeders of their domesticated plants and animals. But in natural populations selection is ‘natural selection, and here nature is the ‘selective breeder’. In the special case of natural selection called sexual selection it is usually the females that are selective breeders of males.

    • Posted December 17, 2015 at 4:33 pm | Permalink

      Indeed, but the base Canis familiaris (or Canis lupus familiaris) was the result of natural selection.

      Beagles, bassetts, borzois, bloodhounds, &c. are all the same species, and within logistic limits can interbreed to create fertile offspring.


  4. Posted December 17, 2015 at 3:11 pm | Permalink

    Nerd that I am, I transcribed the video:

    “A smart person once said: “Nothing in biology makes sense except in light of evolution” (Theodosius Dobzhansky). Evolution is what lets us understand the history of life. We’re used to seeing things change over time, but biological evolution is about something more. Centuries of observing nature has shown us that all life is related. And just like the physics here on Earth is the same physics that rules the Andromeda galaxy, the same basic biological rules apply to all creatures great and small. If life has a point, it’s making more life. The instructions parents give to the next generation come with a few random changes. Every new generation ends up slightly different than the generation before it. But nature doesn’t always make survival easy. So any creature that lives long enough to make more life, passes on its traits more often. This is what Darwin and Wallace figured out, the beautiful theory of natural selection we still study today: that all life is descended from a common ancestor (common descent), that new generations show variation (descent with modification), and that more often a trait survives, the more common it will become (change in allele frequency). It might not tell us how life began, but it tells us how all living things came to be the way they are. Bacteria, bugs, or Beagles. Stay curious.”

    “all creatures great and small” hints of Christian undertones, but “if life has a point, it’s making more life” seems to combat this. The metaphor of genes as parental instructions implies point of life is procreation. Ending with “It might not tell us how life began, but it tells us how all living things came to be the way they are” argues that genetic history explains diversity but ends with a Christian undertone.

    Maybe unconscious on the part of the video makers, but it might leave a K-12 audience open to accomodationism.

    • Karin Lindhagen
      Posted December 17, 2015 at 5:42 pm | Permalink

      I rather liked the slight, obviously intended irony of using the phrase “all creatures great and small” in a video so clearly giving a non-religious explanation of evolution and life.

      But then, I live in a secular country, where evolution is taken for granted in school biology, and where atheism is not an encumbrance for a politician.

      • Mark Joseph
        Posted December 17, 2015 at 10:23 pm | Permalink

        Can I go live there? Please?

  5. eric
    Posted December 17, 2015 at 4:06 pm | Permalink

    I like your bullet list, but I would probably change two things about it. First, I would separate bullet #2 into two separate points. The idea the populations evolve is important enough that it deserves its own bullet, and I think its also a difficult enough concept for laypeople that it deserves the emphasis of being its own main point. Second change: I might consider changing “natural selection” to “selection,” just to avoid the quibbling about whether sexual selection and artificial selection count as types of natural selection or are different from it. The way you’re using the term in the last bullet, they count as part of what you’re including. But that may not be clear to everyone, and some people might quibble over the terms either out of ignorance or to be persnickety (see, for example, Jean Hess’ #3 post. Offered in good faith I’m sure, but still evidence that some readers are not clear what counts when you say ‘natural selection.’)

    • Charlie
      Posted December 17, 2015 at 6:42 pm | Permalink

      I was wondering why sexual selection was not included as something that produces amazing traits. They don’t necessarily look like ‘design’, unless you want to believe that the bright colors of birds seem to be designed to delight the eye.

      • eric
        Posted December 17, 2015 at 11:20 pm | Permalink

        The “natural” in natural selection can be used in a broad sense or a narrow sense. Today, I think scientists tend to use it in the broad sense of something like “doesn’t break the laws of physics.” In that sense, sexual and artificial selection are both forms of natural selection; they operate within nature’s laws. People are part of nature, after all.

        But that’s not how Darwin used the term. He used a much more narrow sense of it and actually contrasted natural selection with artificial (i.e. human-controlled) breeding. I suspect a lot of laypeople still think of the term in the narrow sense, as being a different thing from dog breeding or the mechanism that gave rise to the peacock’s tail.

        Neither is ‘more right’ because words like ‘natural’ in English have multiple meanings; it’s just a confusion we have to live with and hopefully overcome by being specific and clear when we talk about such subjects.

  6. David McCrindle
    Posted December 17, 2015 at 4:24 pm | Permalink

    Question from a non biologist. Apparently migrating birds (and other animals) use the earth’s magnetic field to navigate by. How does this work when the magnetic field reverses? This reversal is fast compared with evolution.

    Is it because they travel in flocks – so a young bird ‘feels’ the magnetic field when it first travels with its elders and then follows that the next year?

    • eric
      Posted December 18, 2015 at 7:26 am | Permalink

      If it screwed badly with their navigation then I would guess there would be a bunch of bird deaths, but some would survive and their kids would reap the benefits of being the one of the few that did. Or maybe none would survive and the more magnetoreceptive species go extinct. There is no rule saying homing pigeons must survive such an event, though in my mind its still completely speculative to assert that they wouldn’t.

      There are loads of local magnetic anomalies in the environment which they already adaptively deal with, and a pole reversal still allows an animal with this sense to detect the correct north-south axis (i.e., if you have a compass, the needle still points in the same two directions, it’s just that the red and black ends switch places). So I would hesitate before claiming it would be a major problem for them. I’m not saying it wouldn’t, I’m saying its not clear one way or the other.

  7. Curt Nelson
    Posted December 17, 2015 at 5:26 pm | Permalink

    I have a question, too. When we say that all living things are evolved from a single organism, how do we know that life didn’t emerge more than once the same way, that there was more than one original organism?

    Maybe the Earth’s route to life is heavily favored somehow (because the elements C, O, S, N, P etc. are common and versatile). Since life arose right after the Earth cooled the necessary reactions may not be uncommon.

    What are the chances that life on other Earth-like planets is based on the same biochemistry as ours?

    • Posted December 17, 2015 at 6:20 pm | Permalink

      Someone more knowledgeable than I should answer this, but here goes. The existence of a universal common ancestor (UCA) is inferred from the fact that all life shares the same DNA, consisting of the same amino acids and nucleotide coding. Also the same energy currency (ATP)and TCA cycle. Read Nick Lane’s book The Vital Question if you want details.

      Conceivably abiogenesis could have happened more the once but, if so, the others left no descendents. None that we’ve found anyway.

      • Torbjörn Larsson
        Posted December 18, 2015 at 3:24 pm | Permalink

        Yes. Theobald used the common descent of the genetic machinery to test one vs many emergences, and found the latter disfavored by > 10^2000[!]. [Nature, 2010]

        Koonin has used the extant viral genetic machinery (ss+RNA viruses, retroviruses, dsDNA viruses) to test his rather detailed theory of RNA strands over a RNA/DNA retrotranscription hybrid to today’s dsDNA evolution. I.e. major viral lineages too descend from a (RNA to DNA) universal common ancestry lineage.

  8. Diana MacPherson
    Posted December 17, 2015 at 6:17 pm | Permalink


    • Filippo
      Posted December 17, 2015 at 7:49 pm | Permalink


  9. John Switzer
    Posted December 17, 2015 at 9:35 pm | Permalink

    I saw you’re Youtube presentation on Free Will and tonite I found another discussion on the same.
    Here it is if you havn’t already perused.

  10. Shwell Thanksh
    Posted December 17, 2015 at 9:52 pm | Permalink

    To me this is what makes an ’emeritus’ — the ability to know and teach a particular subject so thoroughly that they can distill the essence of a beautiful and complex subject into 5 key thoughts, and then express each of them in a clear, easy to understand short paragraph, free of needless jargon.

    Thanks for writing the book, PCCE!

  11. Mark Joseph
    Posted December 17, 2015 at 10:27 pm | Permalink

    While I would not dream of disagreeing with the good Professor emeritus and his criticism of what did not appear in the video, my own take is that what did appear was very good (within the obvious limits of the minute and a half allotted to the question). Every little bit helps, and I think this type of presentation will stick in the minds of at least a few people who might watch it and would profit from it.

  12. Posted December 18, 2015 at 12:55 am | Permalink

    Birds can only fly forwards and fish can only swim forward. Is this evolution catering to a spherical world ?

    • Posted December 18, 2015 at 5:24 am | Permalink

      Hummingbirds can fly backwards. And I’m sure (some) fish can swim backwards.


  13. Torbjörn Larsson
    Posted December 18, 2015 at 3:38 pm | Permalink

    Thanks, very informative!

    Just to play Hitchen’s Devil’s Advocate, I note that the claim “a single form of life that lived between three and four billion years ago” isn’t future safe. Some results that put that claim in tension already today:

    – Valley’s 2015 review of Jack Hill zircon’s that show a habitable ( 4.3 Ga.

    – Timetree’s accummulated papers over the earliest dateable split, Bacteria/Archaea, witha median date > 4.2 Ga.

    – The recent fossil candidate of > 4.1 Ga age that conforms with the above two dates. (The C isotope ratio is exactly spot on a Calvin cycle (RuBisCO) metabolism, i.e. the two cellular remains were from a photosynthetic bacteria population after the B/A split. If it is a fossil, need both more finds and more work. Beware of Shopf’s futile pattern search of similar candidates, we need more data!*) [ ]

    * The consistent sizes and forms, as well as typical cell size and form, as well as the consistent isotope ratios and graphite structures, all make me tentatively optimistic. Does anyone else care to dig up and acid etch out another 10 000 zircons? Just 500 mt rock to work through…

    • Torbjörn Larsson
      Posted December 18, 2015 at 3:42 pm | Permalink

      The editor coughed over HTML look alike text. Let me try again:

      – Valley’s 2015 review of Jack Hill zircon’s that show a habitable (less than 100 degC) ocean > 4.3 Ga.

  14. Posted December 19, 2015 at 11:00 pm | Permalink

    Tinnitus (ringing in the ears) is a evolutionary symptom from the need for a prey to be ever vigilant of predators and now persists as a nuisance ( in some people) due to our changed environment.

  15. Wayne Tyson
    Posted December 22, 2015 at 4:17 pm | Permalink

    Culture involves changing the context of reproduction and survival. If I capture a pair of wild mallard ducks and protect their progeny from predation and some other “slings and arrows of outrageous fortune,” I will soon have a population that includes variants (e.g. white, poor-flying or non-flying Pekins) which, if turned loose in the wild, will eventually (and rapidly) “revert” to the original, adapted forms.

    The basic process of selection is the same–the context changes and the population responds accordingly.

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