Sunday, November 16, 2008

Men Are From Mars Women Are.....

Maybe, but I like this description of sex differences too:

Some would deny there is a deep difference. Some would psychobabble about a nurturant sex and a competitive sex. Geneticists would point to the XX and XY chromosomes, economists to the relative parental investments in offspring, veterinary students (and others who go around peering between animal legs) to the shape of the creatures genitals. Freudians, fundamentalists and sexual politicians could add their own ideas.

But from the perspective of organelle conflict, all these criteria (in so far as they are valid) are superficial. They specify things that derive from the deepest of the sex differences. Sex chromosomes, genital shape, reproductive investment and perhaps even personality all arguably follow from the resolved conflict of the organelles. The deep nature of maleness is to eject organelles from reproductive cells; the deep nature of females is to keep them.

Great! Males throw stuff out, females like to collect things. Didn't we all know that! These days I am in a mood for reaching out for a book from my shelf and rereading a passage or two. This one is from Mark Ridley's The Cooperative Gene. I highly recommend the book. It makes you think about the deep general features that all multicellular life share.

One of these features is anisogamy which is sexual reproduction involving reproductive cells or gametes of unequal size. The evolution of the eukaryotic cell initiated through a merger of two bacterial cells over a billion years ago made complex life possible, but the merger came with its own baggage, literally. The merged cell had two independent genomes. This was a situation with a potential for conflict between the two genomes. One analogy that helps is to think of a corporate merger which creates two independent management teams. It won't work. They will start undermining each other. One team has to go or turn submissive.

Evolution changed the eukaryotic cell through such mechanisms. Over time one genome ceded control by transferring most of its genes over to the other genome. This cell with the smaller genome evolved into the organelles; mitochondria (and chloroplasts). Human mitochondria have 37 genes. Ancestral mitochondria probably had 2500 genes a figure typical of bacteria. So over 98 percent of mitochondrial genes have been transferred or lost during evolution. Transfer of genes was one solution to genomic conflict. But sexual reproduction created another problem. It brought together two sets of the remaining organelle genes in one cell after fertilization. So the problem of organelle genomic conflict remained.

The evolutionary solution was for one type of reproductive cell to eject its organelles before fusing with the other type. The ejector gamete became the smaller sized sperm and the gametes which kept its organelles became the eggs. Ridley argues that sex differences follow from this great fundamental divergence.

Evolution is a quirky process. The specific evolutionary pathway taken by lineages is contingent upon historical and developmental constraints. Evolution develops one on one solutions to changing ecological pressures. But early in the history of multicellularity, the biggest limiting factor was within.

Sexual reproduction, gender and meiosis were evolution's across the board general solutions that enabled life to cross a threshold of complexity. You can think of this as the evolution of evolvability. I like big themes like the one presented in the book. This is a very readable account of various types of genomic conflicts and the ingenious devices that evolved through natural selection that minimized conflict.

I mean who would have thought that the evolution of gender helped resolve a conflict :-)

Is there a lesson here for humanity? Sure, and here is my prescription for harmonious relations between men and women. Let women keep all the stuff they want. Men, don't to try to argue, cajole, plead, sulk or throw a tantrum. It won't help. Females are good at keeping things. They have had a lot of practice. They have been doing it for more than a billion years.


  1. I had to laugh when I read this, because in my family, and for most of the people I know *well*, it is the men who are the hoarders who have lots and lots of stuff, and the women who take a minimalistic approach to "things".

  2. i guess human behavior is quirkier than evolution! :-)