Parasitic Limbs and the Four-Legged Duck

i-c2c3e03fbe96e866f2690963fc1472b8-Stumpy019_417763_full.jpg Earlier PZ Myers disputed the claim that the recently-notorious 4-legged duck was the product of "genetic changes" as reported by the media. Taking a look at the morphology of the poor bird's extra legs, it much more likely that the duck suffers from a phenomenon known as "parasitic limb" or "parasitic twin" in humans. For example, this child was born in Detroit with an extra leg, which was actually the remnant of a twin who never properly separated during development (below).

i-ac70d0b47066cbae7b00da8d1d2f471f-baby 3 leg.jpg

A parasitic twin results from the same general process which results in normal identical (monozygotic) twins: the division of the egg following fertilization. However, the process goes awry for some reason and the division was quite incomplete (nearly complete division would result in conjoined twins). This process usually occurs (in people) at about 13-14 days after fertilization. One of the "twins" becomes vestigial to the other, healthy and developed twin---called "parasitic" due to its complete reliance on the physical support of the healthy twin. When this occurs in people, the extra limbs, etc, are normally removed if it does not impinge on the health of the normal twin.

More like this

Variation is common, and often lingers in places where it is unexpected. The drawing to the left is from West-Eberhard's Developmental Plasticity and Evolution(amzn/b&n/abe/pwll), and illustrates six common variations in the branching pattern of the aortic arch in humans. These are…
tags: conjoined twins, siamese twins, ornithology, birds, avian, barn swallows, Hirundo rustica Conjoined twin Barn swallows, Hirundo rustica, found July 17, 2008 in Searcy, Arkansas after they fell from their nest. Image: Samuel Peebles (Daily Citizen, AP Photo). Last week, a homeowner…
This is interesting: Doctors began operating today on a 2-year-old girl born with four arms and four legs in an extensive surgery that they hope will leave the girl with a normal body, a hospital official said. Lakshmi is joined to a "parasitic twin" who stopped developing in the mother's womb. The…
What do you do when a child is born with ischiopagus? Sell her to the circus? Turn her into an object of religious veneration? Try surgery to correct the condition as much as possible? This little girl born with six legs and two arms had the option of all three; she's currently being…

I think you meant to say "disputed the claim that the recently-notorious 4-legged duck was the product of genetic changes." Too many negatives.

I love the blog that you have. I was wondering if you would link my blog to yours and in return I would do the same for your blog. If you want to, my site name is American Legends and the URL is:

If you want to do this just go to my blog and in one of the comments just write your blog name and the URL and I will add it to my site.