Evolution Didn’t Rob Snakes of Their Limbs – Other Animals Gained Them

Jan 22, 2015

Image credit: H. Krisp/Wikimedia CommonsCC BY-NC-ND 3.0

By Rebecca Boyle

Snakes don’t have necks, shoulders, arms, hips, legs or any other familiar vertebrate body parts — but that doesn’t mean they are simple animals. They might have evolved in a completely different way than scientists thought, a new study says.

Scientists have long thought that snakes developed their slender, limbless form because of disrupted Hox genes, a set of genetic blueprints that help establish the body plans of vertebrates. Changes in Hox expression are thought to be a main mechanism driving the evolution of new body forms. In mice and men, Hox genes establish where our necks, trunks, lumbar, sacrum and tail regions go, along a head-to-tail axis. Since snakes don’t have most of these distinct areas, it was thought that Hox genes were disrupted in a snake ancestor, resulting in their simplified form as compared to their four-legged lizard ancestors. Scientists from the University of Nebraska-Lincoln and Indiana University turned this theory upside down in a new paper published this month in Nature.

If a loss of Hox genes caused snakes to evolve in their slim, limbless form, then scientists would expect to see fewer differences in the shapes of snake vertebrae compared with other animals, as one of the study’s authors, Jason Head of UNL, explains in a statement. They compared snakes and limbed lizards, and found the exact opposite: “Snakes have the same number of regions and in the same places in the vertebral column as limbed lizards,” Head says.

Then the researchers compared snake vertebrae with Hox gene expression, and found the two matched. This suggests that Hox genes are still at work in the serpentine body — it’s just that, instead of forming body regions like the neck and lumbar spine, they control the organization of subtle curves in snakes. So snakes didn’t lose bodily regions after all. It would be more accurate to say that mammals and birds gained them, by somehow augmenting Hox expression. This turns the evolutionary sequence of events on its head, notes coauthor P. David Polly of IU.

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12 comments on “Evolution Didn’t Rob Snakes of Their Limbs – Other Animals Gained Them

  • [ ] vestigial legs

    An owner friend of a male red-tail boa showed and explained spurs as vestigial legs, too. For a while, I helped with the care – an educational and fun experience. They are lightening fast snatching prey!

    what’s the deal

    As stated in the abstract > Nature.

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  • vestigial legs

    A male boa’s spurs were shown/explained to me as vestigial legs, too – used for copulation stimulation.

    what’s the deal

    Nature abstract explains better.

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  • Is the article reporting the study very badly written -that is: way, way too sensationalistic- or is there some major problem with the fossil record here?
    I mean: Lizards appeared ~199 Mya, while snakes “begin” at ~112 Mya… I’d find very hard to believe that lizards evolved from snakes, or any scenario that is in conflict with the current dating. Except if someone can come around and show that the dating is very wrong, or if it turned out that snakes slithered out of the sea -which I believe it’s the “mosasaur hypothesis”.

    By reading the abstract (of yet another inaccessible article) it seems that the conclusion drawn is that snakes didn’t lose the body segmentation typical of vertebrates after all and Hox genes seems to be still there.
    And, in a way, it would be very surprising if it was otherwise: what natural selection acts upon is not genes directly -there’s nothing and nobody scanning through the genome and sayin,ìg “oh, let’s keep that”- but phenotypes. If a gene manages to sink “under the radar”, it’s not selected and it just survives.

    Of course it would be interesting to read the full article, because the claim is not very clear -and as presented by the journalist rings not very believable…

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  • There can also be confusion between legless lizards, which have lost their legs during evolution, and snakes, which have a different reptilian ancestry.


    The females give birth to live young (ovoviviparous birth). In the days leading up to birth, the female can often be seen basking in the sun on a warm road.

    Although these lizards are often mistaken for snakes, a number of features differentiate them from snakes.
    The most important one is that they have small eyes with eyelids that blink like lizards’; this feature is not found in snakes.
    They may also have visible ears as do lizards, which snakes do not have.
    They shed their skin in patches like other lizards, rather than the whole skin as most snakes do.
    Slow worms also shed tails (autotomy) by breaking one of their tail vertebrae in half, as a defence mechanism, as lizards do.
    Also, the pattern of their ventral scales is totally different from that of snakes.

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  • Roedy Jan 23, 2015 at 9:58 pm

    Could you please translate the relevant section of the abstract.

    These specialist papers are seriously heavy reading, with a depth of study needed even to understand the concepts behind the terminology. –

    Which makes it even more comical, when some scientifically illiterate YEC who cannot even grasp the basics of Gregor Mendel, claims to have read them and refuted them!!!

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  • I agree with Lorenzo that this is too sensationalist. The simple explanation is that snakes and lizards use basically the same trans-acting regulatory system for establishing positional information, but cis-acting components respond differently to that information. I published on this (in a Drosophila system) more than 20 years ago (“Conservation of Molecular Prepatterns During the Evolution of Cuticle Morphology in Drosophila Larvae”: Evolution 476, 1993, pp. 1396-1406.)

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