Lamarckism revisited - Epigenetics

[john5746]

http://www.bbc.co.uk/sn/tvradio/programmes/horizon/ghostgenes.shtml

 

I have always thought there was more influence from the environment and our response to it on our genes. I admit this is mostly from ignorance and the inability to conceive such a huge passage in time, but if this is true, it might fill in some gaps.

 

What say you?

[lucaspa]

John, it doesn't "fill in gaps" nor shorten the time. The time-line of life on the planet is established independent of evolution. Recent studies have shown that natural selection can act up to 10,000 times faster than seen in the fossil record. So there is not an issue of not having enough time for evolution, but rather the question has become: why was evolution in the fossil record so SLOW?

 

You need to read this article and the work VERY carefully. The headline hints at a revolution. It's not that. It's a minor adjustment.

 

"Epigenetics adds a whole new layer to genes beyond the DNA. It proposes a control system of 'switches' that turn genes on or off – and suggests that things people experience, like nutrition and stress, can control these switches and cause heritable effects in humans."

 

What they mean by "heritable effects" is how the embryo develops. It has long been known that, if you change the chemical environment of the embryo, you can change development. For instance, increase retinoic acid in a chick embryo and you can get duplicate limbs. The timing when the RA is introduced determines where the duplicate limbs start. On day 2 and you get two complete limbs from the hip. Wait until day 5 and the humerus is set, but you get 2 lower limbs and feet/hands. Wait until day 6 and you only get two hands/feet.

 

So, change the stress and you change the amount of cortisol the mother produces. Cortisol is a steroid, and steroids bind to transcription factors and can turn the expression of genes on or off. If the mother has more cortisol, this could affect the baby. In THAT sense the change is "heritable". BUT in the Darwinian sense it is not -- because the base sequence of the DNA is not changing.

[john5746]

Well, if there is no change to the DNA in subsequent generations, then it isn't much to think about in terms of evolution.

 

Thanks,

[lucaspa]

Well, if there is no change to the DNA in subsequent generations, then it isn't much to think about in terms of evolution.

 

Thanks,

 

No, it isn't. And the research focuses on diseases, not evolution. IOW, the health of the mother can influence the health of the child. That is something to worry about if you are a doctor (or member of the family). It's not something that is going to be a major player in evolution.

 

Only if the mother has a heritable variation to put her (or the embryo) in better health is it going to be useful for evolution. For instance, say the mother has a variation that produces an enzyme only in the placenta to deactivate cortisol. That is going to shield the embryo from the effects of stress on the mother. Thus, the baby is going to be healthier.

 

So, women with that variation are going to have relative reproductive success compared to women without it -- because they produce healthier babies.

[MedGen]

I might possibly add that genomic imprinting is an evolved epigenetic mechanism, as a way of preventing overexpression from duplicate genes. E.g. the differential imprinting of Igf2 and H19 in many mammals, including humans and mice.