The Reproductive Imperative 1
For most biologists, it seems that life is defined by reproduction. If it reproduces, it's alive. Life = reproduction. Death = non-reproduction.
But this idea of life doesn't square with a more general view that a creature (an animal, a human) has died when it stops breathing, or its heart stops beating, or it ceases moving and turns blue. No-one asks whether it has stopped reproducing. Not even the paramedics who show up at the scene of death.
The result is a mismatch between what biologists regard as alive, and what more or less everyone else regards as alive. And when biologists insist that the essential characteristic of living creatures is that they reproduce, everyone else has to shrug and accept. After all, they should know. They're biologists. They study life.
But there may be a simple explanation of why this mismatch has arisen. And it grows from the way that biologists (or rather microbiologists) determine whether bacteria are alive. Discussing how to determine what proportion of a bacterial population is alive, the microbiologist John Postgate wrote:
To discover how many cells in a bacterial population are dead (if any) the microbiologist has to take a sample of that population, count the cells in it, place it on the surface of a medium in which all living cells can divide, incubate it for a few hours - usually overnight in a Petri dish - and see how many cells have taken advantage of the situation and multiplied to form colonies. Those which have not done so are presumed to be dead.
What's interesting about this is the last sentence: bacteria which have not reproduced to form colonies are presumed to be dead. Given the right environment and nutrients, living bacteria reproduce every half hour or so, which is why, over a 12 hour night, a single bacteria which divides and then divides again every half hour will generate a population of 224 bacteria. That's about 17,000,000 bacteria, and even though individual bacteria are invisible to the naked eye, that number of them produces a visible growth on the surface of the Petri dish.
It's very convenient for microbiologists that bacteria reproduce so rapidly. If bacteria reproduced once a day, it would take 24 days to get the same population. If bacteria reproduced once a year, then it would take 24 years. In that circumstance, microbiologists would have to find some quicker way of determining whether bacteria were alive or not. They can't wait 24 years to find out whether something is alive or not. They'd quite likely be dead themselves by the time the results were produced.
Using bacterial reproduction rates is a convenient way of determining whether bacteria are alive, because they reproduce so rapidly. It is probably the case that it is not possible to tell, even looking through a microscope, whether a single bacterium is 'alive' in the sense of showing some sign of activity. So instead microbiologists use one of the characteristics of life - reproduction - to test whether any members of a bacterial population are alive, because this is the most convenient way to determine the fact. And yet there are pitfalls in using this method , as Postgate points out:
Would they have survived and divided if the microbiologist had chosen a different culture medium?
Maybe not. In which case the microbiologist would state that they were all dead because they were not reproducing.
But, it seems, once having become accustomed to determining life status this way, biologists slip into the habit of thinking that the only way of telling whether something is alive - rather than one way - is to see whether it reproduces or not. If it reproduces, it's alive. If it doesn't, it's dead. And the insistence by biologists that the essential characteristic of life is that it reproduces simply reflects standard laboratory practice.
But it gets worse. Once biologists have begun to equate life with reproduction, they then go on to start thinking that the primary purpose of life is reproduction, that the creatures exist simply so as to produce more creatures, to make as many copies of themselves as they possibly can. And the next thing you know they're on TV saying:
Everyone in a sense knew that what animals work for is not their own survival but their own reproduction.
'Everyone' here refers to the closed biological community. And 'in a sense knew' refers to the habitual way biologists think about life.
A habit of thought, which arose from using just one of the characteristics of life to test for life, has been elaborated into the fully-fledged sociobiological dogma, with living creatures vying to reproduce and pass on their genes to subsequent generations, and absolutely everything they do is explained as assisting, in one way or other, this imperative.
The individual organism is only the vehicle (of genes), part of an elaborate device to preserve and spread them with the least possible biochemical perturbation.. The organism is only DNA's way of making more DNA."
If the explanation offered here of the equation of life with reproduction - that it is a habit of thought peculiar to microbiologists - has any validity, it is unlikely that the mentality will ever pass into general use, simply because most non-biologists have never acquired this habit of thought, and are never likely to. Most people will probably continue to think that their pet cat has died when it stops breathing and turns cold, not when it stops having kittens.
But since (if Richard Dawkins is right) the entire biological community is now infected with the idea that life is reproduction, it now requires non-biologists to muster arguments that re-emphasize the other characteristics of living creatures, of which reproduction is just one. Niles Eldredge, a palaeontologist, is one who has stepped into the argument.
Fitness to Darwin meant something like overall vigor. Those individuals best suited to cope with life's exigencies were the more 'fit'. The more 'fit' were more likely to to be the ones to produce more offspring, thus leaving more copies of their genes to the next generation. But following the lead of Ronald Fisher and other early population geneticists, the definition of fitness became elided - now simply meaning 'reproductive success'.
Although it is unfashionable these days to think of organisms as machines, to me, [a] fox is a matter-energy transfer machine that needs to catch and devour [a] rabbit merely to continue to exist. Williams thinks that the fox eats the rabbit on order to pass on its genes. I see ... reproduction as a physiological luxury rather than an imperative that is necessary for that fox to go on living. In my view, if and only if that fox's economic life is going well can it afford to reproduce.
A re-assertion that living creatures actively induct and expend energy (metabolize) is needed, that they eat and breathe and grow and move.
They hate to admit it, but the life scientists, whether the natural historians of the 19th century or the biologists of the 20th, cannot explain what life is in scientific terms. They all know what it is, as we have done since childhood; but in my view no one has yet succeeded in defining life.
Lovelock outlines 3 scientific approaches to life:
Thermodynamics is Lovelock's choice, but "so far it has made the least progress".
Author: Chris Davis
Last edited: 9 April 1998