12 June 2006

Life inside a cocoon

Every week on the inside of its backcover, the British popular science magazine New Scientist publishes intriguing questions submitted by readers, followed by answers, also submitted by readers.

Several weeks ago, the following inquiry appeared.

When an insect is changing inside its cocoon, and has turned to slush, is it alive? And if so, in what way is it alive?
The questions of what life is and how it can be defined have long puzzled me. Many years ago, I even published a paper1 discussing some relevant points. So, after I read the above question, I e-mailed an answer, mostly extracted from my paper.

My answer and 2 others have now been published on the New Scientist’s web page (they should also be in the current print edition, which I haven’t received yet). Unfortunately, if you are not a subscriber you can read only the first sentence of my answer. But, here it is in its entirety.

An insect undergoing metamorphosis is alive regardless of what state its body may be in. For one thing, the individual cells are alive and are growing and dividing in a coordinated manner to form the organs of the new adult insect. An insect, or any other organism, could not be dead at one stage of its development and alive at a following stage, because the death of an organism is always irreversible.

However, the death of a multicellular organism such as an insect must be defined separately at different levels of organisation: the intact body; the organs and tissues; and finally, the individual cells. The body cannot survive without organs and cells, but the latter two groups can survive without a body. If you squash a cocoon the larva inside will be killed, but many of its cells will remain alive, at least for a while. Therefore, a multicellular organism can be killed by destroying its highest level of organisation, while leaving most of its organs and cells alive. If that were not the case, there would not be such possibilities as human organ transplantations or cell cultures.
A while ago, I had another post along these lines and I will probably return to the subject in the future.

1. 1. Örstan, A. 1990. How to define life: a hierarchical approach. Perspectives in Biology and Medicine, 33:391-401.


pascal said...

What really impresses me about cocoons is that the existing cells are broken down or rearranged and that new cells form in the right place.

It'd be cool to see a sequence of progression from breakdown of existing structures to the development and emergence of new ones.

Alun said...

I noticed the name as I went in to work on Thursday. Fame at last. Congratulations.


They also sent me a 512MB flash drive, which is more useful than 15 minutes of fame.

{{{Suzy Q}}} said...

HELLO Aydin,
I just wanted 2 let know thatI I loved ur answer it really was in depth!!! The whole reason that I was looking up info up on this was bcuz I found a BeAuTiFuL cacoon 2day & it looked like there was something still inside of it. So, I got a pair of tweezers & carefully pulled out the brown stuff inside!!! It very fragile & feels like dead skin! Most of it was paper thin!!! The whole idea that there was a living thing in that cacoon is just AwSuM!!! Luv ur answer & thank u so much!!!ツツツ