TED Conversations

Pabitra Mukhopadhyay


This conversation is closed.

Goodbye Mr. Darwin and the selfish gene?

Jaroslav Flegr, a self-described “sloppy dresser,” the 53-year-old Czech scientist has the contemplative air of someone habitually lost in thought, and his still-youthful, square-jawed face is framed by frizzy red hair that encircles his head like a ring of fire. He is trying to change the way we think about Darwinian Evolution.

He suspected that Toxoplasma Gondii, an obligate, intracellular, parasitic protozoan that causes the disease toxoplasmosis, and with which he is infected is changing his behavior subtly so that his ‘selfish’ genes are more or less now slave to those of the genes of the parasite. If what he thinks is true, Jaroslav is under more the selective pressure of the parasite than his own genes.

For fact, parasites inducing behavioral changes in hosts have been reported by many scientists. Toxoplasmosis is one of the most prevalent infection among humans. If you have affinity for cats, you are likely infected.

Jaroslav has come up with the idea of frozen evolution, which suggests that new adaptations by accumulation of random mutations happen only when their members are genetically uniform, i.e., only after a portion of the population of the original species has split off, balanced on the edge of extinction for several generations, and then undergone rapid expansion. After a short period of time,polymorphism accumulates in the gene pool due to frequency-dependent selection; and thus, in each generation, new mutations occur in the presence of different alleles and therefore change their selection coefficients from generation to generation. The species ceases to behave in an evolutionarily plastic manner and exists in this state until such changes accumulate in the environment that the species becomes extinct.

When you are a host, it is unknown in which direction your evolutionary future lies – survival or extinction.

So is it goodbye to Mr. Darwin or his celebrity proponent Dr. Richard Dawkins?


Showing single comment thread. View the full conversation.

  • thumb
    Dec 19 2013: Very good discussion going on....
    My thoughts are , what Jaroslav is saying is rather stregthening Darwin's proposition about "VARIATION".
    Well the differences are in how "VARIATION" happens , if I have understood the discussion here well.
    What Gerald is considering is that Parasites are part of environment from which actually the selective pressure for mutation coming in, but I feel Pabitra that is where differences of opinion are coming from.
    Like Gerald in my thoughts also , I consider parasites to be part of environment.

    Whether something is disease or not as pointed out by Herald, can be another subject for long debate. This something like what is NORMAL mental condition and what is not which sometime back I came across while studying depressive conditions or Schizophrenia. Hallucination or delusion someone with specific mental condition goes through are REAL experiences to them , which is unreal to all other who are wit so called stable Mental Condition.

    Molecular genetics was not that developed at the time of Darwin, moreover Genetics & Theory of Evolution didn't converge together that well during Darwins time. Darwin rather drew a very much "Helicopter View" on the process of changes happening in nature.

    So my understanding is that with the evidences of parasitic influence on mutation is rather strengthening Darwins proposition of VARIATION , STRUGGLE For Existence " Survival of the Fittest" as well as Natural Selection.

    Thanks Pabitra for bringing a thought provocative discussion.
    • thumb
      Dec 19 2013: I cede to Gerald and you in accepting that yes parasites are also part of the environment of the host, because unless that is not the case the parasite host relationship will not develop at the first place. Well may be I should call it habitat or favorable environment?
      This is exactly the heart of the debate. Whose genetic expressions we are in the end? Our own or the parasite that infests us?
      Allorecognition and rejection of non-self part play an important role in maintaining genetic homogeneity throughout the life of an individual organism by preventing invasion of genetically different foreign entities that might parasitize the organism. What baffles me is that how come the parasites evolve to get past allorecognition of the host in as much as fooling its immune system whereas the hosts always lag in evolutionary terms not be clever enough to save themselves. They both are in the same environment, aren't they?
      • thumb
        Dec 19 2013: Pabitrada , I am not sure from where Gerald came in, the point from where I am coming is....... here I was considering the cell itself where the gene is lying as it's macro environment. The parasite influencing the gene is also living in the same macro environment of the cell. From that sense it's part of environment of that gene. But for the host as a whole that becomes part of it physiological of biochemical environment.

        Other than the parasite host relationship , in the biological kingdom there are also other relations which you are aware of i.e. symbiotic relationship or commensalic relationship and those also I feel part of the micro environment.....something like a tiger is part of the environment for a deer in the macro environment of a forest. In food chain Deer & Tiger has a predator prey relationship which is analogous to host and parasitic / symbiotic / commensalic realtion.
        • thumb
          Dec 19 2013: Interesting point made Salim, thank you. I was mentioning environment as more macro term than the cellular environment of the host body. In fact I recognize parasites as independent genetic entities from the hosts which by nature require a host's body to live and complete its life cycle.
          Moreover, symbiosis or commensalism is fundamentally different in terms of biological goals of organism from parasitism as parasites benefit at cost of host's harm. Allowing harm of an organism without developing a evolutionary antidote seems to be a weak argument for evolution itself. Flegr's hypothesis attempts to explain this as frozen plasticity of evolution as far as the host is concerned.
      • thumb
        Dec 19 2013: Welcome Pabitrada and you are right that parasites are independent genetic entities from the host as it is for Tiger Vs Deer. In the totality of ecosystem of forest they again becomes part of environment.

        You definitely are aware that there are some viruses which displays basic features of life when those are in host body , if outside those are like non living things. Those viruses are considered to be the junction between living and non living world.

        Grasping concept of evolution seems to be easier when one goes into micro level look into the simpler form of life. More complex the species becomes more difficult it is to grasp evolutionary process at least to me.

        If I bring more analogy from physical world and focus on radio active matters the process of change from one matter to another becomes easier to understand. Same applies to biological world.

        I need to read about Frozen Plasticity and Flegrs hypothesis to understand this new concept. Thanks for your reference.
        Have a good day

Showing single comment thread. View the full conversation.