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.A while ago, I had another post along these lines and I will probably return to the subject in the future.
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.
1. 1. Örstan, A. 1990. How to define life: a hierarchical approach. Perspectives in Biology and Medicine, 33:391-401.