On multicellularity and slime molds

Maximum Likelihood Phylogenetic Tree of Metazo...
Phylogenetic Tree of Metazoan Relationships (Photo credit: Wikipedia)

Human beings are great big conglomerates of millions upon millions of cells. In this respect, we are very similar to other animals, as well as land plants, algae and filamentous fungi — we are multicellular.

Multicellularity is thought to have evolved independently several times throughout history. Traditional thinking was that the ancestors of land plants evolved multicellularity separately to the ancestors of animals, who evolved multicellularity separately to the brown algae forebears. It was thought to have evolved multiple times in fungi, red algae and slime molds. Even some bacteria — the blue-green cyanobacteria — figured out the secret to multicellularity somewhere along the line

Phylogenetic trees illustrates how different organisms on the tree of life relate to each other. The example on the left is best imagined as a tree lying on its side with the trunk at the far left and smaller, more recently formed branches toward the right. As you can see, the metazoans (animals) branched away from fungi and the amoebazoa (which includes slime molds) fairly close to the trunk of the tree. All of the branches within the metazoan block — separating worms and crustaceans and jellyfish — are more recent evolutionary divergences. Continue reading “On multicellularity and slime molds”

Reproductive quirks (part 2): Why did menstruation evolve?

As I’ve noted previously, humans are strange beasts and our reproductive biology illustrates this well. Menstruation and menopause are both rare in the animal kingdom. Of all mammals, only us, our primate relatives and elephant shrews menstruate. Menopause is even harder to come by — killer whales are our only sisters in hot-flushes, apparently.

This begs the question: why? How did each of these reproductive quirks evolve in humans?

I’ve written two pieces for The Conversation about the evolutionary theories that try to explain where menopause and menstruation come from. The first, about menopause, can be found here. The second, on why women menstruate, has also now been published. 

Reproductive quirks (part 1): Why did menopause evolve?

my grandmother
Women go through menopause when they still have a third of their life ahead of them (Photo credit: paul goyette)

Humans are oddballs in the animal kingdom for many reasons, but one of the quirkiest things is how we reproduce. Or, more to the point, how our bodies behave when we aren’t reproducing. Menstruation and menopause are both very rare. Of all mammals, only us, our primate relatives and elephant shrews menstruate. Menopause is even harder to come by — killer whales are our only sisters in hot-flushes, apparently.

I’ve written two pieces for The Conversation about the evolutionary theories that try to explain where menopause and menstruation come from. The first, about menopause, is out today. Check it out!

The prisoner’s dilemma — how cooperation leads to “survival of the fastest”

English: A CISV educational activity - coopera...
Cooperation is ubiquitous in nature, but how did it evolve? (Photo credit: Wikipedia)

You’ve committed a crime. You and your co-conspirator have been nabbed, but fortunately, there’s not enough evidence to put you both away for the time you deserve. You’ll be sentenced to just one year in prison. Unless, that is, you turn on your criminal associate, who will take the fall for a three-year sentence, while you walk free. The one catch: the prosecution have offered your partner the same Faustian bargain. If you both keep your mouths closed, you’ll each serve a year. But if you both spill the beans trying to profit at the expense of your partner, you both get two-year sentences. No conferring — you’re both in separate cells. What do you decide?

This is the Prisoner’s Dilemma, first framed in 1950 by mathematicians Merrill Flood and Melvin Dresher, and later given its evocative name by Albert Tucker. In its original form, the best option for both parties would be to each adopt a ‘no-squeal’ policy — in other words, cooperate with each other for mutual benefit. But if you think your partner is a bit of a soft touch who’s likely to cooperate, then as an individual, the option of betraying them (or defecting) becomes almost too tempting to pass up. Except, of course, that your partner could be thinking along exactly the same lines, which would lead to both of you getting a longer sentence than if you just cooperated. But do you cooperate, knowing that your compatriot might end up taking you for the sucker? Continue reading “The prisoner’s dilemma — how cooperation leads to “survival of the fastest””