An Evolutionary Tail

I was doing a little research on fetal development. By research, I don’t mean in a lab. If I don’t clarify that, the fundies will read that first sentence and think I’m some sort of monster.

Dr. Weird

Me, in my lab, researching fetal development.

What I mean is that I was reading stuff online about fetal development. Our ancient ancestors had tails. Our fetuses have tails at about the fourth week of development. It eventually gets absorbed into the body.

We used to be some sort of ancient primates with tails. Our environment changed, our lifestyles changed with it, the need for tails went away, so the the tails eventually evolved away.

There are three ways that I can think of that would allow the tails to disappear. The first is through a transcription error during DNA replication, and the tail gene is left out completely. This is unlikely. The error correction processes are pretty good, so it is hard for an entire gene to be left on the cutting-room floor.

The second way is through a mutation that just turns off the gene. One day out pops a baby without a tail. This is more probable than the first method, because it’s easier to turn a gene off than delete it completely.

The third way is for a gradual elimination. Through a mutation, a baby is born with a shorter-than-normal tail, which provides a survival advantage, etc. Through successive generations, the tail gradually shrinks and disappears. We still have tailbones, so obviously this is the route we travelled.

But here’s an interesting thing about genetics. Most traits are actually controlled by multiple genes. For example, one or several genes might control the length of the tail, others might control what types of muscles it contains, others might code for whether it is covered by hair, etc.

It appears that the gene that codes for the fleshy part of the human tail is still in our genetic code. The bone-genes made the tail shorter; those are still turned on. The flesh-genes were no longer needed, so they eventually got shut off.

Since there is a small error rate when copying DNA, every now and then one of those errors actually occurs in an important gene. Every great now and then, that error occurs in the tail-gene and turns it back on.

humans with tails

I got the above photographs from an interesting page by a guy named Mario Di Maggio. His page gives several stories of modern tail-people. One guy lives in West Bengal, and the locals think that he is the reincarnation of the Hindu monkey god Hanuman. Then there is the baby in India, who the locals think is — you guessed it — the reincarnation of the Hindu monkey god Hanuman. Religion. So predictable.

Di Maggio also has an excerpt about genetic throwbacks from Robert T. Bakker’s book, The Dinosaur Heresies. The article explains a bit about what is going on here. Here are a few choice excerpts:

[W]hen an organ has been “lost,” most of the time its blueprint is still there, in genetic storage. A wealth of evidence supports this theory of re-expression by genes that have been turned off for millions of years. Most of it occurs in throwbacks, the rare appearance of ancient organs in species that, as a whole, had lost the anatomical features millions of generations earlier.


Such throwbacks even occur in human infants. Hospitals occasionally register an entirely modern-looking baby characterized by all the expected organs, plus an unexpected tail, a long, caudal appendage protruding beyond the buttocks for two or three inches. Some of these tails are even bigger than the average caudal remnant displayed by our close kin, the chimps, gorillas, and orangutans.

So, there you have it. One more pebble in the mountain of evidence supporting evolution.

There was one more tasty nugget in that article:

Birds with teeth may have appeared ridiculous to creationists, but in point of fact modern birds do carry the ancestral genetic code for making teeth tucked away in their inactive file.

Well that explains a lot. I always wondered about this guy:


5 Responses to “An Evolutionary Tail”

  1. FreeThinker Says:

    Amazing. The term “getting some tail” aparently goes WAY back!

  2. kim Says:

    i believe all that you say except for the part about evolution…. i just cant bring myself to believe in darwin’s theory for the simple fact that apes don’t evolve anymore. how does science explain that?

  3. Ron Britton Says:

    Who said apes stopped evolving? They still are. All life continues to evolve.

  4. Sarah Says:


  5. mike Says:

    So Kim how many thousands of years have you lived to give us this information about “apes” not evolving? Also other animals other than apes exist, you know, right?