Why Evolution is True is a blog written by Jerry Coyne, centered on evolution and biology but also dealing with diverse topics like politics, culture, and cats.
When I was a psychology student, I was taught about Maslow’s hierarchy of needs, which suggested (as I recall) that we had to be nourished and sheltered and have all sorts of basic needs satisfied before we could pay attention to higher needs such as being creative. I remember being a smartass in a tutorial and saying: ‘But what about the starving artist?’.
Whatever the validity of Maslow’s hierarchy of needs, this portrayal of the hierarchy of *internet* needs is most definitely correct. You can’t do anything on the internet without first satisfying that most basic of human needs: kittehs.
I have taken this from here, but I’m not sure who actually made it…
One of the most amazing things about social insects – bees, wasps, ants and termites (hornets are just big wasps) – is the way they have a division of labour. At its simplest, this division of labour is morphological and involves having a reproductive individual or group of individuals who is the queen. She is genetically identical to all the other females in the colony/hive, but she is specialised for producing loads of eggs. We know there’s nothing genetic about being a queen – there’s no special ‘queen gene’. It’s simply a matter of how much food she is given when she’s a larva. The same seems to apply to those ant species that have specialised workers – ‘soldiers’ – that carry out defensive or aggressive tasks. There’s no gene involved in being a soldier, it is environmentally determined.
This raises a fascinating question: how does the genome of a single species code such a wide variety of forms? In other words, how are the different developmental pathways turned on and off?
Things get even odder when you realise that although many ant or termite species have ‘soldiers’, there are no known cases of bees or wasps having morphological worker casts. There are no ‘soldier bees’ or ‘soldier wasps’. Why not?
Two recent papers – one in Science on ants, the other on bees in Proceedings of the National Academy of Sciences (USA) (PNAS as it is generally known) – have addressed these issues, giving some insight into how the ability to have soldiers may have evolved, and revealing that in one species of bee at least, there ARE soldiers!
The PNAS article, from researchers in Sussex (UK) and Sao Paulo (Brazil), studied the neotropical stingless bee Tetragonisca angustula. This species has two kinds of guards that protect the nest: standing bees near the entrance, and ‘hovering bees’ that do pretty much that. Together, only about 1% of T. angustula workers in a nest are guards.
The guards are much bigger (both in size and weight) than their sisters who go out foraging, or those who take the trash out, suggesting that they are actually determined to perform this function (no, bees don’t have free will, either). Furthermore, they are not simply scaled up versions of their smaller sisters, bits of them are proportionately bigger, suggesting that they are specialised in certain functions.
T. angustula forager (left) and guard (right). Grüter et al (2012), PNAS.
Having shown that this species of bee does have ‘soldiers’ – a morphological worker subcaste – the next question was ‘why’? These stingless bees can’t defend themselves by stinging (the clue is in the name), and yet they are regularly attacked by much larger robber bees (the clue’s in the name there, too).
In a final step the scientists carried out a classic experiment: they set up a bug fight. T. angustula guards were paired off with their deadly foes, Lestrimelitta limao robber bees. The larger the guard, the longer the fight lasted.
L. limao bee (right) with the head of a T. angustula guard clamped onto it. The robber bee has decapitated its foe, but has not been able to shake off the head, and cannot fly. Grüter et al (2012), PNAS.
The increased size, and perhaps the altered shape, of the guards, may be involved in their defensive ability. As the authors say in a nice closing sentence: their discovery ‘serves as a reminder that stingless does not mean defenceless’.
In the best scientific tradition, this finding merely raises more questions: if T. angustula has morphological soldiers, why don’t other bee species, or wasp species, for that matter? Is there something different about the ecology of ants and termites (you’ll have noticed they are both terrestrial) compared to that of bees and wasps that means that the evolution of soldiers is more likely?
In some closely related ant species can vary for the presence of soldiers. For example, in the genus Pheidole, although all species have two worker subcastes (minor workers and soldiers) as well as the queen, eight species also have ‘supersoldiers’ – much larger individuals, with significantly wider heads and with tiny vestigial wings. It is thought that juvenile hormone (JH) levels – largely influenced by the amount of food the insect has received as a larva – are responsible for these switches. The presence of apparently useless vestigial wings in supersoldiers is probably due to some developmental link between extra-high JH levels and wing development, which is required for queen development. Don’t forget, all these kinds of ants have the same genes, they are just being activated in different ways at different times in different tissues, due to the amount of JH, which in turn is affected by food.
Three for the price of one: juvenile hormone levels alter morphology in Pheidole ants (adapted from Rajakumar et al (2012) Science
A study in Science by an international group of researchers looked at the evolution of supersoldiers, and how they might develop. The starting point was a chance observation on a field trip, where they found some odd soldiers in a nest of Pheidole morrisi, which does not have supersoldiers.
These odd ants were larger than their sisters (see below), and looked a bit like supersoldiers – right down to the vestigial wings – suggesting that this species might also possess the developmental pathway to produce these extra-large soldiers, even though they are not normally found in nature.
Wild-caught P. morrisi soldier (SD) and anomalous supersoldier (aXSD). Rajakumar et al (2012)Science
By looking at a number of Pheidole species, the authors concluded that naturally-occurring supersoldiers had probably evolved separately, even though similar developmental mechanisms seem to be involved.
To investigate what those mechanisms might be, the researchers put methoprene (an analog of insect juvenile hormone – JH) onto larvae of P. morrisi and produced extra-large ants a bit like the ones they had seen in the wild. They then tried a similar experiment in other species that do not have supersoldiers and found similar results. It seems that all Pheidole ants they studied share the ability to produce supersoldiers, if the right environmental conditions apply.
Evolutionary history of ancestral developmental potential and phenotypic expression of supersoldiers (XSDs). MYA, million years ago. Purple represents the expression pattern of the sal gene in the larval tissues ('wing discs') that will give rise to wings; asterisks indicate the absence of vestigial wing discs and sal expression. Green arrows and boxes represent the induction of XSD potential. From Rajakumar et al (2012) Science
To confirm that JH levels are involved in the production of supersoldiers, they studied a species that has this caste, and put JH on larvae that had yet to ‘decide’ whether they were going to be ordinary soldiers or supersoldiers. The treated larvae produced a higher proportion of supersoldiers, suggesting that JH is indeed involved in determining whether a supersoldier is produced.
This neat study doesn’t resolve the issue of why only some Pheidole species have this extra caste, but it seems very likely to be related to their ecology – some of the species with supersoldiers have to fight off attacks of army ants.
Whatever the case, JH levels, driven by food supply, appear to be responsible for morphological variation in these ants – and, I would bet, in the stingless bee soldiers too. The question of why such variability occurs remains unclear, and probably does not even have a single answer.
References (links to abstracts; pay wall for full articles)
While Jerry’s away hiking, here’s an excellent 60 min lecture by the marvellous Richard Fortey, speaking about my second favourite extinct organisms: trilobites.
As I head into the wilds of southern Costa Rica for three days of hiking and botanizing, I leave you with this:
Pia is an old, toothless tabby owned by Malgorzata Koraszewska and her husband Andrzej Koraszewski, friends of mine who run the Polish rationalist website Rasjonalista. When they translate my articles into Polish for their site, I always ask for two photos of Pia as payment.
Now, on his Facebook page, Andrzej is having dialogues with his cat; brief interchanges in which Pia shows her wisdom and often pwns her owner. Here’s a good one (I originally explained to Malgorzata about the concept of “nom” as both verb and noun for cat eating and cat food, respectively), showing Andrzej and Pia:
The Pia Dialogues are in Polish, but you can see a translation on Andrzej’s site. Here’s what Malgorzata explained:
Andrzej gave an explanation to Polish readers: “NOM” or “nom nom” is an English cats’ equivalent to Polish “mniam mniam”. NOMA (non-overlapping magisteria) is an amusing attempt to say that there is no conflict between science and religion”.
I have landed in Costa Rica to find this email from a reader awaiting me:
Professor Coyne:
Free will aside, your biological determinism means that it’s not Shakespeare who wrote Hamlet but Shakespeare’s brain. That’s an absurdity; isn’t it?
Might there be a place in this world and in literature for common sense even if there is a place too for science?
Of course it was Shakespeare’s brain, and his neurons and his molecules!
I’m a huge fan of literature, but am not sure what this reader is on about. Yes, the words of all those great plays came out of the pen held in the hand of the man (whoever he was) known as William Shakespeare. And he had no choice about what he wrote—most of my readers will agree that it was all determined when he sat down.
So what’s the absurdity? Can someone enlighten me?
Dr. Denis Alexander, head of the Templeton-funded Faraday Institute of Science and Religion at St. Edmunds College, Cambridge, is interviewed by the BBC on how he comports science with his evangelical Christianity. In the 30-minute interview, Alexander, a molecular biologist, explains his background, his transformation to Christianity, and his beliefs. They include his acceptance of the divinity and physical resurrection of Jesus Christ, and of the efficacy of prayer.
He also draws the usual distinction between science as answering the “how questions” and religion as answering “why questions.” But (at around 17:00) he draws a number of parallels between the scientific and religious searches for truth:
They’re both looking for coherence.
Scientific hypothesis are based on data, and so are religious beliefs, which, he says, are heavily reliant on evidence (e.g., the fine-tuning of the universe). At 17:40, he claims that if the stories in the Bible about Jesus aren’t true, and there’s no afterlife, then Christian faith collapses.
But he still sees the stories of Genesis as one of “figurative language,” not meant to be a “scientific textbook” (he refers to Augustine as holding this view, ignoring the many other church fathers who didn’t). Genesis, he claims, is meant to show us the “purpose of mankind”, which is:
The purpose of humankind is to know God, to worship Him, and to be good stewards of the planet that God has put into our charge, that we’ve made such a huge mess of.
AT 19:20, he explains to the interviewer, Joan Bakewell, why he considers the Bible to be “scientific evidence.” It’s bizarre: it’s because the Bible had the “amazing insight” that there was only one God and that he was a “god of love” (Alexander doesn’t explain how he knows these claims were true). Bakewell calls him out by asking why such a god would sacrifice his son. Alexander explain that Jesus was God’s “sacrificial lamb,” apparently to save us all.
As for the disparity in the different accounts of the Resurrection in the different gospels of the Bible (Bakewell asks him tough questions), Alexander replies, “The accounts we have of the Resurrection are exactly what you’d expect of eyewitness accounts. And I would myself be very suspicious if they were very coherent, and matched up, and so on. . ” And then he claims that these accounts are not contradictory. It’s a Biblical Rashomon!
At the end, he’s asked whether he thinks that Christianity is the one true faith, and after a bit of waffling about the Abrahamic faiths, he basically says yes, because they have Jebus, and there’s “honest disagreement” with faiths like Islam.
Make your own judgment; I find it remarkable that a trained scientist can find so much hard evidence in a book that by his own admission is largely metaphorical. As always, Genesis is a metaphor but the story of Jesus and his resurrection is non-negotiable truth.
I’m off today (Sunday) for Costa Rica, where the council of the Society for the Study of Evolution is having its midwinter meeting. Although that lasts only a couple of days, I can’t go to Central America—especially the country with the best system of biological reserves—without doing some biotourism. I’ll be tagging along with a colleague who’s doing botanical field work, and then travelling to La Selva, another reserve where, back in the Cambrian of my scientific life, I once spent several weeks.
The last time I was in Costa Rica was in 1973, when I took at two-month course in Tropical Ecology under the auspices of the Organization for Tropical Studies. It was a fantastic course, headed by Don Wilson and Dan Janzen. It will be great to revisit the place after all these years.
I’ll be back posting in a bit less than two weeks, and in the meantime stalwart pinch-bloggers Matthew Cobb and Greg Mayer will fill in. They’re both busy, so posting will be light at best. But I promise to take plenty of pictures to bore you with when I return.
Hasta la proxima!
TSA POSTSCRIPT: I have just gone through the Naked Scanning Machine at O’Hare and then was chosen to be patted down. As the TSA guy said, “I’m going to palpate your left forearm and then your upper left thigh.” (They’re using classier language now.)
My forearm, of course, had my watch on it. God knows what suspicious thing they saw on my thigh, but I didn’t like the grope. At least they didn’t “palpate” my buttocks as they did in Boston last January!
