Saturday, 25 July 2015

The meaning of heredity

I generally use the term "heredity" to refer to the transmission of traits from one generation to the next.

However, I notice that some sources differ - confining the idea of "heredity" further. The Encyclopedia Britannica is explicitly DNA-gene centric:here:

heredity: the sum of all biological processes by which particular characteristics are transmitted from parents to their offspring. The concept of heredity encompasses two seemingly paradoxical observations about organisms: the constancy of a species from generation to generation and the variation among individuals within a species. Constancy and variation are actually two sides of the same coin, as becomes clear in the study of genetics. Both aspects of heredity can be explained by genes, the functional units of heritable material that are found within all living cells. confines the idea of heredity even more - to organisms that experience meiosis - with this:

heredity:the transmission of genetic characters from parents to offspring: it is dependent upon the segregation and recombination of genes during meiosis and fertilization and results in the genesis of a new individual similar to others of its kind but exhibiting certain variations resulting from the particular mix of genes and their interactions with the environment.

These sources are simply wrong. However, their mistake is widespread and leads to confusion about cultural evolution. For example, Larry Moran defines evolution using the term 'heredity' - saying: "Evolution is a process that results in heritable changes in a population spread over many generations." - and then goes on to argue that:

I've already alluded to one of the classic questions that a proper definition can answer — the increased height of Europeans over the past five centuries. Armed with a good definition of biological evolution we can focus on one of the key requirements; namely, heritable change. It turns out that the increase in height is due to a better diet and not to genetic changes. Therefore, this is not evolution according to the scientific definition.

This is a serious conceptual mistake. European diet has improved (largely) through memetic evolution. Memes are passed from one generation to the next in cultural evolution - and rather obviously this should meet any sensible scientific definition of evolution - as is attested to by the now-massive literature on cultural evolution. Yet Moran dismisses it - apparently due to his conception of the definition of the term 'heredity'. This seems like a spectacular mess to me.

Larry is not alone in this evolutionary denialism. Here's Mark Ridley on why cultural evolution doesn't qualify as being "evolution":

Changes that take place in human politics, economics, history, technology and even scientific theories are sometimes loosely described as evolutionary. In this sense "evolutionary" means mainly that there has been change over time - and perhaps not in a preordained direction. [...] human ideas and institutions can sometimes spit during their history - but their history does not have such a clear-cut branching tree-like structure as does the history of life. Change and splitting provide two of the main themes in evolutionary theory.

His complaint appears to be that cultural evolution is too reticulated - one of the most dopy objections to cultural evolution ever - once you consider how reticulated bacterial evolution is.

Anyway, these days, almost everyone agrees that cultural evolution is a type of evolution. The remaining debate in the area is mostly over whether cultural evolution is Darwinian. However we obviously have a mopping-up operation to do - as some folk don't even regard cultural evolution as being a type of evolution! That position seems indefensible to me.

1 comment:

  1. I'm extremely disappointed that there has been little interest from the wider population on your blog. It's certainly one of the finer ones on memetics that I now know of.

    Came here by way of your critique on Constructal Theory, since I had never heard of it before a comment posted by Bejan himself in a now insanely popular blog here (forgive me, I do not know the shortcuts for hyperlinks in comments:

    Not as "adult" as yourself, but eh, that's just the price of popularity I'm afraid. Still marvelously interesting and pretty funny. I guess I found my new fixation, as Tim blogs insanely slowly these days--which i'm sure you understand why if you see it.

    Getting back to the matter at hand, you would be very happy that indeed some scientists would not make this mistake put forth by biologists: Harrington at UC Davis for example, developmental psychologist. He had a great lecture wherein he basically describes exactly what you mean: that the cultural features and idiosyncratic nuances of any given thought could potentially spread like an epidemic to anyone on earth, greatly affecting portions of people's lives.

    Given the rather poor understanding of what makes memories "stick", Memetics is indeed a very valuable interdisciplinary field to flesh out the basis of thoughts as they co-habitate. Also, the scope of the feild may not be as parochial as human-based memes, either: it all depends on how generalized a definition of "meme" we use.

    P.S. You wouldn't happen to know German would you? I have a wonderful tome on the Mneme: "Die Mnemischen Empfindungen" (1909). Googling it again, indeed it is exactly the same book by Richard Semon, translated, as this one:

    I'm sure that you've run across the translated one, which until just now I was unaware of. Yet another book to add to the stack to read, I'm afraid