The Human Truth Foundation

What the Worst and Most Horrible Genetic Diseases?

By Vexen Crabtree 2016

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#disease #genetics #life

The Human species, just like other animal species, is afflicted with a wide range of genetic diseases - around 4,000 of them - which are mostly incurable1. Some are inherited and passed on from parents to children, others are the results of the failure of genes to reproduce properly. The cruellest ones are those that convey a "heterozygote advantage" if just one chromosome has it, but which have terrible effects if both chromosomes have it. This means that there is evolutionary pressure to promulgate the gene, but if two parents both have it, then their child suffers. One example is a gene that gives resistance to malaria - if both parents have this gene, their child gets sickle-cell anaemia. In 2007 we had found 1,250 disease-related gene mutations, all of which could potentially be fixed through genetic engineering2 - or avoided by screening at conception. This has theological implications: If us humble Human Beings are capable of fixing these errors, how could they be part of a 'design' that is maintained by an intelligent supernatural being? In other words, if these horrible diseases were part of God's plan, then, they wouldn't have such a reachable physical cause. They'd be no way to stop them. If, on the other hand, they are not part of God's plan, or, it is God's plan that we humans strive to reduce suffering by fixing these problems, then we have a clear mandate to do whatever we can to eliminate the horror caused by some of these diseases. Also, the existence of these types of diseases means that evolution is proven to be blind and meandering rather than intentionally directed.

1. Genetic Diseases3

#greece #india #italy

The following are some of the more horrific:

2. Genetic Diseases With Heterozygote Advantage

The way genetics works, some genes have terrible effects only when inherited from both parents. This means that the gene can be successful and get passed on from generation to generation, but, it occasionally wreaks havoc on a baby or child. It is very unfortunate that this type of gene exists, but, thankfully the march of evolution means that most dysfunctional genes are eventually removed from the gene pool because they reduce the average viability of offspring. It would be so much better if evolution could see what it was doing, because there is an unfortunate twist. Some of these terrible diseases, which only strike families occasionally, have an advantage when they're not showing their ugly side. This is known as "heterozygote advantage". Examples of this type of disease include sickle-cell anaemia. This disease is spread because in its hidden, harmless form it gives an advantage against malaria. Likewise, cystic fibrosis is believed to give protection against cholera, and the terrible neurodegenerative tay-sachs disease linked with protection against tuberculosis. Due to the advantage of having these genes in their heterozygote form they spread, but, this means that the terrible diseases caused by them occasionally afflict unborn babies and the very young.

Sickle cell [...] exhibits the phenomenon known as "heterozygote advantage." Heterozygotes have only one copy of a mutant gene. Since sickle cell is a recessive disorder, heterozygous people carry the sickle cell trait but do not usually get sick. It is now known that the mutation that causes sickle cell arose several thousand years ago in parts of Africa where the parasite that causes malaria had recently made its appearance. Over time, the mutation became widely disseminated in those populations, because, even though people who inherited two copies of the gene often died, those with just one copy, the heterozygotes, had significantly improved resistance to malaria.[...] Heterozygote advantage explains why some harmful mutations persist and proliferate.

"Babies by Design: The Ethics of Genetic Choice" by Ronald M. Green (2007)2

If I was an evil architect who wanted to create a species that would suffer needlessly, then, I would design evolution in such a way that terrible diseases were hidden by genes that conferred an advantage and therefore spread well in the population. If I was a good designer, I wouldn't create genetic diseases at all. Which way does the evidence point? The existence of genetic diseases with heterozygous advantage is evidence that, if there is a creator, or a designer of evolution, such a being is either malevolent or a very poor geneticist.

"God Must Be Evil (If It Exists): 2.5. Genetic Diseases" by Vexen Crabtree (2003)

3. Evolution: Unintelligent Design

Genetic diseases afflict not only mankind, but also all other animal species, and all other forms of life down to the simplest bacteria and harmless single-cell lifeforms floating in the oceans. In all these species and in plants there are seemingly endless cases of genetic flaws and problems. Perhaps the best indicator of how badly life is 'designed' is the stark reality that 99% of all species have gone extinct. The food chain requires that nearly every living being survives by killing other creatures to eat for food, and species naturally expand to use up all local resources, limiting the success of other species. Everywhere in nature, predator-and-prey chains are central to life. This isn't a design for life, but a design of strife and violence. The genetic defects of nature, and the violence and strife of the natural world, indicate that life was not designed by a good-natured creator god but maybe by an evil one. My favourite phrase to describe all of this waste and bad design is one I picked up from Paul Kurtz in the Skeptical Inquirer:

The existence of vestigial organs in many species, including the human species, is hardly evidence for design; for they have no discernable function. And the extinction of millions of species on the planet is perhaps evidence for unintelligent design.

Paul Kurtz (2006)7

See: Evolution and the Unintelligent Design of Life: Inherited Traits, Genetic Dysfunction and Artificial Life.

Current edition: 2016 Jul 038
Originally published 2007 Feb 25
Parent page: The Human Truth Foundation

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References: (What's this?)

Book Cover

The Economist. Published by The Economist Group, Ltd. A weekly newspaper in magazine format, famed for its accuracy, wide scope and intelligent content. See for some commentary on this source..

Barnes-Svarney, Patricia
(1995, Ed.) New York Public Library Science Desk Reference. Paperback book. Published by The Stonesong Press Inc. and The New York Public Library, New York, USA.

Green, Ronald M.
(2007) Babies by Design: The Ethics of Genetic Choice. Paperback book. Published by Yale University Press, USA.

Whatson, Terry
(2004) Exploring the Brain. Published by The Open University, Milton Keynes, UK. A neurology textbook.


  1. The Economist (2008 Nov 15) "Genetic disease and evolution: Bad old genes". Added to this page on 2011 May 19. Dr Domazet-Loso and Dr Tautz have published research on the ancient origins of harmful genetic mutations.^
  2. Green (2007) chapter Challenges and Risks.^^
  3. Added to this page on 2009 May 11.^
  4. Barnes-Svarney (1995) p190-1.^
  5. Green (2007) p66.^
  6. Whatson (2004) p75. Added to this page on 2011 May 19.^
  7. Paul Kurt in Skeptical Inquirer (2006 Sep/Oct, Vol 30:Issue 5).^
  8. 2016 Jul 03: The original text from 2007 was on my generic page on evolution. Now extracted to form a new webpage.^

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