Dining out on the intriguing topic of evolutionary genetics

OK, so this column might be confusing, but bear with me: evolution is a fun, if sometimes challenging, topic. The topic for this column came about after a dinner conversation with my brother, a human geneticist. Put a few geneticists together, add wine and this is the result.

Let’s get into it then. Genomic imprinting refers to a pattern of gene expression in which a specific parent’s allele is either underexpressed or completely silenced. If you are familiar with bog standard Mendelian inheritance, genomic imprinting has a different set of rules. Here’s an analogy: it’s your birthday and your parents each give you a lovely present. Each of them gives you a set of building blocks which look a tiny bit different but do pretty much the same thing. Yet for some reason, you just can’t open the set of blocks your dad gave to you, so the only set of blocks you will ever use is your mum’s set of blocks. In biological terms, something in your mum’s egg silenced an allele in your dad’s sperm and his allele is never expressed.

Here’s where it gets interesting. Genomic imprinting is thought to maximise a female’s investment into the current male’s offspring at a cost to her and her investment in future offspring. Females in these types of mating systems are less likely to reproduce again with the same male. From this, you would expect species that are highly polygamous to have a high degree of genomic imprinting, and this generally stands to be true when levels of imprinting have been studied across species. Counter to that, low levels of imprinting should and do correlate with species that have a high degree of monogamy.

So of course, this begs the question: where do humans sit on the genomic imprinting spectrum?

Well, according to my brother — who quite delightedly told me in front of his wife — humans are about the middle, indicating we are naturally neither highly polygamous or monogamous. That goes for both genders, I might add (check out ‘‘Sexual Conflict in Primates’’, Stumpf et al. 2011, Evolutionary Anthropology, for more information on this).

We’re on a roll now. I never thought I would write a column about polygamy, so why not push the boat out and address another sensitive topic — human menopause.

Menopause is pretty much unavoidable for women of a certain age, yet it has long been an evolutionary puzzle. Humans are one of very few species who go through menopause — apparently killer whales do too.

As an evolutionary tactic, it doesn’t really make sense: why would a species limit their maternal ability to have babies? Well, a study has shown that when a motherinlaw has a baby at about the same time as her daughterinlaw, their offspring are less likely to survive (by up to 66%). The same effect is not seen if a mother has a baby at the same time as her daughter — it is a real motherinlaw phenomenon! Therefore, grandmothers, under evolutionary theory, have been selected to stop reproducing beyond 51 years, hence the prevalence of menopause in today’s society (check out ‘‘Severe intergenerational reproductive conflict and the evolution of menopause’’, Lahdenpera et al. 2012, Ecology Letters).

And just to show human geneticists don’t have all the fun. Remember the stinking Corpse plant in the Dunedin Botanic Garden earlier this year? The stinking flower has evolved to attract a certain type of pollinator, the types of insects that like to feed on dead animals — dung beetles, flesh flies and other carnivorous insects. The smell of the

Corpse flower tricks the insect into thinking the flower might be food; they fly inside, wander around looking for food and fly off with pollen on their wee legs — ingenious.

Do let my brother or me know if you have a child or relative who is even moderately interested in genetics. We will be sure to encourage their careers in the very best way we can.

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