Ultrasound imaging technology is coming along so fast that you can now get a near-real time, moderate resolution image of a living fetus. Unfortunately, this new technology is also having an unfortunate consequence.
Sophisticated ultrasound scans that show foetuses as early as 12 weeks appearing to “walk” in the womb have had a dangerous impact on the public debate over abortion, leading doctors and scientists said yesterday.
The emotive photographs, taken with new fourdimensional imaging technology, have created a misleading impression that foetuses become viable and potentially self-aware at a much earlier stage than is actually the case, according to experts on foetal development.
Of course some people are interpreting generic activity as some sign of special human attributes in fetuses. Kevin Beck has found one prime example of a right-wing blog trying to imply that this is “dangerous” information, because it undercuts abortion arguments.
Nonsense. Fetal tissue moves. One of the things we know from developmental neurobiology is that embryos don’t form inert blobs of muscle first, and then at some later date start plugging the neural wiring into it—it’s all concurrent. As the first relatively undifferentiated scaffold of muscle and connective tissue is assembling in a region, the first threads of nerves reach out to contact it. Among other reasons, it means the major pathways can get laid out at a time when distances are short and the number of alternative choices small. Embryos are busy places, where cells are shuttling around everywhere and whole masses are shifting, and sure, in many species fetal growth is accompanied by twitches and shrugs and all kinds of superficially impressive activity. If you were trying to wire your house by stringing live cable to all of your outlets and appliances, wouldn’t you expect sparks and flashes and all kinds of odd activity?*
Here, for instance, is a zebrafish embryo at 24 hours post-fertilization.
That’s what they do: they twitch, repeatedly. Initially, it’s uncoordinated and slow, and they gradually get better at it, and send these rolling waves of muscle contractions down the length of their bodies to generate these rhythmic thrashing motions. You can’t read too much into it, though. The number of neurons involved in the circuit can be counted on the fingers of two hands in each hemisegment. It’s a handful of cells in a poorly understood circuit, repeated over and over again for each myotome. There isn’t even any central control—at this age, neurons of the hindbrain reticular formation are sending axons into the spinal cord, but they’re creeping along at a rate of about 100 µm/hour. They aren’t even there yet!
It’s even neater to watch (but much, much harder to photograph) the embryos at 18 hours post fertilization. The muscles are just beginning to differentiate—you can see some striations starting to emerge—and the first motor growth cones creep out of the spinal cord and head towards their targets. Even before they get there, random activity in the neurons is releasing transmitter, causing the fibers to twitch feebly. All you need is two cells interacting to get spontaneous motion. Sometimes just one is enough.
It’s a sign of the lack of awareness of the general public, and their willingness to be sucked into emotional visuals, that they think the movement of embryos somehow implies the onset of humanity. Movement and growth is what embryos do. Awareness and thinking, eh, not so much.
*One curious thing is that invertebrate embryos seem less prone to the kind of spastic activity I’m used to seeing in vertebrates. Grasshopper embryos were always a little eerie, I thought; they were completely still (except for a set of specific purposeful movements like katatrepsis, that position the embryo within the egg) while all these axons were precisely and silently wending their way through the tissues. Speaking of emotional interpretations, I find the impression of planning and intent more apparent in embryos that are sitting utterly still, rather than the ones that wobble and twitch. Malign, sneaky little buggers, hiding their busy, busy little plots…but naturally, they aren’t really doing anything consciously, either. They have even fewer neurons than my fish.