"Because" versus "so that".

I want to make a quick point about how evolution works and how it does not. The reason is that two stories about non-coding DNA posted today include a major misconception about evolution. Unfortunately, this is a misconception attributed in the articles to biologists, so I can only imagine what the state of comprehension is among non-scientists.

The distinction is between “because” and “so that”. In evolution, things evolve “because,” meaning that there are causes and effects that can be identified. Why are some strains of bacteria resistant to antibiotics? Because a mutation that occurred that happened to be beneficial under the conditions of antibiotic treatment became common in the population over the course of several generations. By contrast, things do not evolve “so that”. Bacteria do not experience mutations so that they will become resistant to antibiotic agents.

Why is there so much non-coding DNA? Because transposable elements spread, or because there are accidental duplications that are not eliminated by selection, or because of the interaction of some other mutational processes and their consequences (or lack thereof). So much non-coding DNA did not evolve so that it might someday be useful, or so that it could be coopted when needed, or so that evolution would have more potential in the form of genetic raw materials.

So why, then, do we see quotes like these?

Wired One Scientist’s Junk Is a Creationist’s Treasure:

“I’ve stopped using the term [‘junk’],” Collins said. “Think about it the way you think about stuff you keep in your basement. Stuff you might need some time. Go down, rummage around, pull it out if you might need it.”

Reuters Human instruction book not so simple: studies:

“It is not the sort of clutter that you get rid of without consequences because you might need it. Evolution may need it,” [Collins] said.

That little extra padding might be just what an animal needs to adapt to some unforeseen circumstance, the researchers said. “They may become useful in the future,” Birney said.

The latter quote by Ewan Birney illustrates the problem that can arise when a detailed, nuanced discussion is summarized into a short soundbite. I know this from experience, and I suspect that this is what has happened here, given how his very reasonable interpretation is paraphrased in New Scientist ‘Junk’ DNA makes compulsive reading:

Birney says that the additional switches may be mutations that appear by accident and then generate new slugs of RNA, but because they are produced randomly, most are evolutionarily neutral ‘passengers’ in the genome. There might be rare occasions, however, when a new RNA does confer an advantage.

Collins, on the other hand, seems to have said his bit to two different reporters, so I strain to give him the benefit of the doubt on this one. When I began this blog, I did not think I would be pointing out obvious misconceptions about evolution, genomes, and DNA as propagated by the likes of Collins or Nature. But here we are.

7 thoughts on “"Because" versus "so that".

  1. In a paper “in press” at Theory & Psychology, I make a similar point: there is an important distinction to be made between “progress from” and “progress toward.”

    In this case, “because” implies “progress from” (and is therefore evolutionary or developmental), while “so that” implies “progress toward” (and is therefore vitalist or teleological).

    I like the way you put it….

  2. I would not use the term “progress” (from or towards) in discussing evolutionary processes, but I agree with the general correspondence between the concepts you noted.

  3. Collins is pretty bad when it comes to evolution. It’s become quite apparent that he doesn’t understand how evolution works.

  4. While that’s certainly the base condition, I would point out that the accumulation of traits and surroundings (for example, specialized niches) can actually “create” purpose.

    For example, once an ur-gazelle type committs to “running away” as their primary response to predators, any change that makes them better runners (other things being equal) is more likely to stabilize, while anything that interferes with running, must offer a drastic advantage to be retained.

    At that point, I’d say it’s fair to say, e.g., “they evolved longer legs in order to run faster”. Their prior evolution has bequeathed them a mandate that constrains future developments, to the degree that “being a good ur-gazelle” now implies “running fast”. Rephrasing that in turns of “purpose” may not be strictly equivalent, but it’s good enough for casual discussions.

    (I’m ignoring questions of “good enough”, because in the long term that tends to be a moving target.)

  5. Whoops, that was a compositional blip. The later “good enough” was supposed to refer to the point that in practice, the ur-gazelles mostly need to be faster than their ur-tigers. After that, getting even faster yields diminishing returns.

  6. At that point, I’d say it’s fair to say, e.g., “they evolved longer legs in order to run faster”.

    I realize that you use this only as shorthand, but it is indistinguishable from a hybrid between the teleology of Lamarckism and the inevitability of orthogenesis. Given that Lamarckian (mis)understanding of evolution is very common among students and non-experts, I would stay far away from anything that will only exacerbate confusion.

    What really happens is still what I described. Why did gazelles evolve longer legs? Because undirected (“random”) mutations that produced longer legs were preserved in the population while mutations causing shorter legs were eliminated as a result of a selection pressure imposed by fast-running predators.

    More specifically, the genetic composition and associated phenotypic characters of the population changed because longer legs, which resulted from a mutation(s), allowed those mutant alleles to be passed on more often than the alleles associated with shorter-legged, slower-running phenotypes.

    Gazelles evolved longer legs “because”, not “so that”.

  7. The difference between “because” and “so that” is also key to the misunderstanding of probability behind the “tornado in a junkyard” fallacy.

    The chance of random variation acted on by selection achieving a particular goal identified in advance is minuscule. The chance that the same mechanisms will achieve some lasting changes that we can look back on and call “evolution” is a near-certainty. (It’s the distinction between the chance of me winning the lottery – unfortunately, minuscule – and *someone* winning the lottery, which nearly always occurs, week by week.)

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