• Question: why, do i not have a tail if i used to be an egg with a sperm, which acording to pictures does have a tail?

    Asked by turtlecalledpat to Davie, Gemma, James P, James V, Nuala on 25 Jun 2012.
    • Photo: James Pope

      James Pope answered on 25 Jun 2012:

      Heya turtlecalledpat,

      Have you ever landed hard on your bottom when falling over and felt a pain in a bony bit? This is the remains of the tail we used to have but have evolved out of having as we moved away from monkeys and apes and became our species (over several million years). Biologists call this a vestigial organ and I think the appendix is another of these.

      As for the tail on a sperm, that is essentially like it’s engine. When a sperm fertilises an egg everyting of it dies and is lost apart from it’s nucleus, which contains all the genetic information from your father to make you. That genetic information doesn’t contain anything about growing tails, beyond the little bony stump we still have, so despite the sperm having one, we don’t have one.

    • Photo: James Verdon

      James Verdon answered on 26 Jun 2012:

      Hi turtlecalledpat,
      The majority of the sperm never goes on to form part of you. When the sperm meets the egg inside your mother, the sperm injects it’s DNA into the egg. The sperm DNA (from your father) combines with the DNA in the egg (from you mother) to create a new set of DNA which makes up your DNA (a combination of your father and mother). This is called fertilisation.

      Once the egg is fertilised, the sperm dies away. The fertilised egg starts dividing, creating the cells that go on to become you. Initially, you are a little sphere of cells. Gradually, over the 9 months in your mother’s womb, our bones, organs and limbs start developing. But we don’t grow tails, and the reason why is because of evolution.

      Because we evolved from primates, we have a remnant tail (your ‘bum-bone’). However, a tail wasn’t useful to our ancestors. This means that you had a better chance of survival and having children if you had a shorter tail, because you didn’t have to waste all that energy growing and pumping blood to a heavy but useless tail. So the animals with smaller tails had more children, who would have inherited the same smaller tails.

      Gradually, the whole population would have had smaller and smaller tails, until eventually we have no tails at all. This process, where certain advantageous traits, in this case smaller tails, are are passed down because they give you a better chance of survival, is called natural selection. Natural selection is a key part of evolution.

Comments