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Does Keeping the Less Fit Alive Help or Hurt Us?

KT's picture

Does Keeping the “Less Fit” Alive Help or Hurt Us?
An Exploration of Natural Selection and Diversity.

Some people look at medical technology, or even kind acts, in their role in keeping people alive as a negative thing given that it interferes with the natural process of selection and thus our ongoing evolution and survival as a species. [1] I’m curious to examine if this is the case. Is this interference sacrificing future survival of a species in order to keep the “less fit” alive? To explore this query, I’d like to take a closer look at one of its elements: the role of natural selection on diversity and diversity’s effect on the survival of a species. I will attempt to show that the net result of natural selection acting on its own is a reduction in variety and that reduction is detrimental to future survival.

An overriding theme in the theory of natural selection is the differential reproductive success of varieties of species in passing their genes on to a subsequent generation of viable and reproductively successful offspring. The inevitable consequence of this imbalance pulls diversity in opposite directions, simultaneously increasing and decreasing it as a result of the expansion of dominant forms and extinction of others. The effect of these opposite forces, however, is not equal. 

Let’s first look at the role of extinction in reducing diversity. As the population of a species grows, varieties with features advantageous to survival will produce more offspring, thus increasing in number, while those that are less well suited to the environment are slowly reduced in numbers as a precursor to finally becoming extinct. [2] There is an undefined amount of diversity that is lost through extinction and you can never add variety to organisms that have been eliminated, that lineage is lost forever.

Counteracting this effect, however, is the diversity that’s created as a result of natural selection. A particular variety of species that is better suited to its environment will grow in numbers. As Darwin discusses, the Hive-Bee has evolved to make its honeycomb in such a way as to preserve the limited resource of nectar (which it uses to make wax). As a particular variety of Hive-Bee, by chance, was able to conserve wax, it gained an edge on those that were not as efficient. This effect in nature allows the number of offspring with the favorable characteristic to grow larger and produce more varieties which, in turn, allows it to become even more dominant and create even more diversity in future generations. [1] Consistent with this theory, we can observe that there has been a huge increase in the diversity of life over millions of years. Organisms have progressed from single-celled prokaryotes through various intermediates to complex multicellular organisms. The number of species that exist is so great that the exact number is unknown but could be as high as 100 million. [3]

Given that extinction and expansion are both in play with natural selection, why should one outweigh the other in terms of the effect on overall diversity and future survival?

The deciding factor is that future conditions are unknown and the lost traits may be the key to survival in the new environment.   As put forth by Douglas Futuyama, author and professor of evolutionary biology at the State University of New York at Stony Brook, “… there’s no way that it [natural selection] can look forward to the future or guard against the possibility of extinction. What individuals have right now that gives them superior adaptation may lead to disaster tomorrow.” [4] With the future being unpredictable, species with a wider diversity of traits would have more “tools” available to be able to survive when selective pressures change. Dr. Grobstein, Eleanor A. Bliss Professor of Biology and applied neurobiologist at Bryn Mawr College, puts forth that, “…the biological process aims to produce variants. This is the only way to be prepared for unknown challenges, times when the environment, the reality which selection reflects, changes in unpredictable ways.  It is the variants which provide the basis for dealing with such challenges. The odds against the survival of a completely homogeneous species are exceedingly grim.” [5] If a species has naturally selected itself away from diversity of form, and future conditions favor an extinct form, the survivors will not be able to continue producing new varieties because they too will be extinct.  

So if natural selection is at work and it eliminates variety, why has diversity increased over time?

There are two factors to consider:
Firstly, the theory I present places more significance on the diversity that is lost through extinction versus the amount of variety that’s created by a dominant form. Although I would argue that it’s better to keep variations around, this is a topic that would need further exploration.

Secondly, although living organisms demonstrate an abundance of genotypic diversity despite being subject to the principle of natural selection, differential reproductive success is not the only force acting on adaptive evolution. In order to prevent natural selection from eliminating all of the unfavorable genotypes that are not as suitable to the present environment, other mechanisms are at work. For example, within diploid organisms, recessive alleles are hidden in a genome and not subject to selective pressures; random mutations within DNA increase variety; random mating, sexual reproduction and meiotic crossover produce new combinations of genes and gene flow into and out of new environments alter allelic frequency. [6,7] So while we have seen an overall increase in diversity over many millions of years, it’s been affected by the balancing of many evolutionary devices.

I have attempted to show within this limited inquiry that if not for the compensating forces that work alongside natural selection, we would see a decrease in diversity and, therefore, a reduction in future survival rates due to the unpredictability of selective pressures and the total loss of possibly useful extinct traits. Applying this result to the issue of science, technology and kindness in keeping the “less fit” alive, these methods are just additional forces that serve to counterbalance natural selection.  While more exploration is necessary to look at the sum total of all of these interactions and the diversity before and after extinction, these findings are in favor of human interference with evolution: you never know if the individuals (and their genes) that are being preserved to reproduce will unlock the key to future survival in an unknown world.


Bibliography and Works Cited

[1] amirbey (username), Natural Selection Among Humans, Serendip 2/12/09 /exchange/node/3799 (Accessed February, 2011)

[2] Darwin, Charles, On the Origin of Species Ed. Joseph Carroll. Canada: Broadview Texts, 2003.

[3] Thompson, Andrea, How Many Species Exist on Earth? August 3, 2007.

(Accessed February, 2011)

[4] Futuyama, Douglas, How Evolution Works. December 2004. (Accessed February, 2011)

[5] Grobstein, Paul. Diversity and Deviance: A Biological Perspective. Bryn Mawr Alumnae Bulletin, Spring 1989. /gen_beh/diversity.html

[6] Campbell, Neil A. et al. Biology, Eighth Edition. Pearson Education Inc, 2008.

[7] Sadava, David et al. LIFE: The Science of Biology, Ninth Edition. Sinauer Associates Inc, 2011.





Paul Grobstein's picture

The role of human intention in biological evolution

 "you never know if the individuals (and their genes) that are being preserved to reproduce will unlock the key to future survival in an unknown world"

Point well made, and important.  "in favor of human interference with evolution"?  Depends a bit on what the objective/method of the interference is, no?  "Conservation" in a literal sense may not be a desirable (or even possible) "interference."  Promoting or at least sustaining diversity might be?