Evolution can happen faster than you think

I'm contributing to Voice, a new group column on environmental science at Ensia. My first piece is about those swallows in Nebraska that seem to have adapted to highway traffic and what they can teach us about the speed of evolution and the way invasive species adapt to new homelands.


  1. Honest question: is it really correct to say that the swallow population “evolved” in 20-30 years, or is this really just the first piece of evolution: differential survival rates?

    I don’t know whether anyone has studies the swallow DNA, but I would guess that all of the genes that are in the swallow population now were already in that population 30 years ago, just at different frequencies. I would guess that there hasn’t been any significant mutation or new recombination to create new genes.

    This may be semantics, but if we killed all of the people that were taller than five foot, and then saw that in a single generation the average size of the human race was much shorter than today, is that evolution? Or is that simply the near-elimination of all the tall genes from the existing pool?

    Evolution usually requires (1) differential survival, (2) parents passing traits to their offspring, (3) new genetic variation of offspring. It seems that only 1 and 2 are being observed in the swallows case.

    Naturally, given enough time offspring will be born with new variations on the wingspan genes, and these variations will be differentially selected for based on the highways. At that point I think we can all agree that it’s unambiguously evolution. But can we definitely do so before then?

    1. Differential survival rates isn’t “the first piece of evolution,” it’s the whole thing.

      1. Not true. Asteroids exhibit differential survival rates, but that’s not evolution. Killing all the females in a population would be differential survival as well, but certainly not conducive to evolution.

        Full disclosure: I’ve written evolution curriculum for middle schoolers, so I’m not speaking from complete ignorance.

    2. “but I would guess that all of the genes that are in the swallow population now were already in that population 30 years ago, just at different frequencies”

      That is evolution.

    3. The example of killing all people taller than 5 foot would be artificial selection and not natural selection.

      However, something like that is being seen with cane toads in Australia, where the snakes are adapting and becoming smaller simply because the smaller snakes couldn’t eat the cane toads and die. Big snakes are selected against. The genes for smaller snakes were probably always in the population, and would have been neutral, or perhaps mildly deleterious. The cause of the smaller snakes could easily be some recurrent mutation.

      The same with the wingspan of swallows, you have a change in the environment which selects for alleles, which become more frequent within the population. Random mutation and natural selection are the engines of evolution.

  2. What is the difference here between “evolution” and “learned behavior”?  If a swallow teaches the next generation to change their flight patterns because of traffic, isn’t that a learned behavior and not an actual physical evolutionary change?  I am just curious…

    1. Because the original paper says that the average wingspan of the birds has decreased. That’s not something that can be learned.

  3. There’s a strong strain of pop evolutionary psychology that assumes that human beings are adapted to the environment that prevailed 50 or 100 thousand years ago and that interprets human behavior through that filter. But if evolution can happen faster (much faster) than that, such ideas may need to be reconsidered. Lactose tolerance in adults evolved after humans started domesticating animals, and perhaps other large changes involved brain mutations that don’t show up in fossils.

    1. I think a lot of the problem with ev psych is that they, much like creationists, fixate toom much on human uniqueness, and look TOO recently in our evolutionary history for the selective pressures that might have shaped us (not every trait comes from selective pressure, some are just associated with traits that are selected for.)  Monkeys are a lot more like us than a lot of people give them credit for, and ev psych people have been know to look for the sources of  things that obviously go back way further than our divergence from monkeys in our recent history on the savannah.

      1. Monkeys are a lot more like us than a lot of people give them credit for…

        Or perhaps, we’re more like monkeys than we’re willing to admit.

        1. You say tomato, I say tomato. (I’m perfectly willing to admit it. I see a bald monkey in the mirror every morning.)

  4. Let’s not forget the Dandelions that used to have long stems and now grow close to the ground so they don’t get cut by lawn mowers. 

  5. I’ve had this argument regarding urban bird species before. Whilst some migratory bird species continue to smack into the side of glass in large numbers, species that dwell in cities tend to hit them a lot less. I’ve always put it down to the fact that they’ve had exposure to the buildings for longer, and probably did hit them in large numbers, killing a lot of them when they first went up. Other species that simply migrate through only get this exposure for small parts of their lives, and thus will take a lot longer to adapt to be able to judge the open sky, and the reflection of the open sky.

    There’s good discussion on the topic here, although from an urban planning perspective:

Comments are closed.