How did humans become such unique animals?

After conducting experiments on the preferences of "semi-free-ranging" chimpanzees when presented with cooked food, Felix Warneken and Alexandra G. Rosati [1] suggested that: "The transition to a diet of cooked foods – involving the use of heat in food preparation – was a fundamental change for our species." This point was taken up in an article by Pallab Ghosh, the BBC Science Correspondent [2]:

According to Dr Warneken [and Dr Rosati], his experiments show that most of the mental skills needed to cook were there in human ancestors between 5 to 7 million years ago and so all it took for the first emergence of the culinary arts was the controlled use of fire and the ability to trust other people not to pinch our food while our back was turned..

..The motivation for the study was to investigate a controversial theory that cooking was necessary for human brains to become larger. The idea by the primatologist Prof Richard Wrangham.. ..is that cooking enabled our ancestors to eat more protein, which helped our ancestors develop their brains.

The BBC article went on to include extracts from an interview with Professor Fred Spoor of UCL:

Cooking did not happen until 300,000 to 400,000 years ago. That is late in 7 million years of human evolution, so to put it bluntly, who cares that early humans may have liked the idea of cooked food?..

..Substantially larger brains initially emerge around 1.5 million years ago and a major leap was around 500,000 years ago.

The series of quotes led me to think about how humans developed their unique position in the Animal Kingdom, with the power to manipulate the environment to an extent quite unlike that of any other organism. I dismiss the Creationist argument that humans resulted from the invention of a supernatural force and accept that our extraordinary capacities evolved from the nucleus of possibility in our ape-like ancestors. It was the phrase "the ability to trust other people not to pinch our food while our back was turned" that had me wondering about an explanation.

Let's assume our distant ancestors lived in family groups and that they foraged for food, gathering vegetable material and hunting animals, all of which were eaten without cooking, as this method of food preparation had yet to be discovered. Families are closely related genetically and the survivorship of individuals, and thus their "selfish genes", will have been enhanced if the hunters were successful in providing plentiful food to ensure the survival of all individuals. Let's assume further that hunters from several families joined together to make hunting more efficient and make the capture of larger prey possible. Interactions between members of this larger group would have required signals – vocalisations, movements of limbs, and facial expressions – that had evolved to give clearly understood information.

After years of successful co-operative hunting, what if one group of individuals gave the signal to co-operate, but then took the catch for themselves, maybe killing some individuals in other families to ensure plenty for their own family at a low cost? The signals no longer have their original meaning and the offer to form joint hunting groups, of advantage to all participants, now carries the risk of a different, less advantageous, outcome. There was thus a need to interpret meaning in communication, with the most successful manipulators, and the best readers of false signals, having the highest chance of survival.

If there was also selection of the optimal neural pathways needed to aid interpretation, these would be fixed in the population and the process of analysing hunting signals, and signals of many other kinds, would become more and more refined. This new consciousness would extend to humans asking questions about the environment around them, forming a complex language structure to explain meaning, and, with further development of the brain, a need to ask abstract questions like: "Why are we here?”; “Is there a supernatural force?”; and “What is good and evil?”.

Or perhaps it was not like that at all?

[1] Felix Warneken and Alexandra G. Rosati (2015) Cognitive capacities for cooking in chimpanzees. Proceedings of The Royal Society B 282: 20150229. http://dx.doi.org/10.1098/rspb.2015.0229

[2] http://www.bbc.co.uk/news/science-environment-32976352

Being fooled by Bee Flies

There have been a lot of Bee Flies in our garden in the past few weeks. Their forward-pointing proboscis and hovering skills make them easy to recognise, although I admit that I used to think that they were a rather unusual type of Bumble Bee. The confusion comes from their body shape and covering of hairs, both of which make them resemble Bumble Bees, although they are in the Order Diptera (true flies) not Order Hymenoptera (ants, bees and wasps). 

Bee Flies in the genus Bombylius have a world-wide distribution [1], with 278 species being recognised, all with similar life histories and feeding habits [2]. Their larvae are parasitoids (parasites that kill their hosts) of the immature stages of Bumble Bees, and other solitary bees and wasps, that all produce a brood in a nest hole in the ground. Eggs are laid, or flicked into, the hole by the Bee Fly females and hatching larvae migrate to find the larvae of the host and continue development. After pupation, adult Bee Flies emerge to complete the cycle.

Both male and female Bombylius adults feed on nectar, for which their forward-pointing proboscis is well-adapted, and females also feed on pollen, which is required for the development of eggs [2]. In this foraging activity, they are effective pollinators of plants and the only cost to the plant is the production of nectar and the excess pollen that is utilised as food. Interestingly, Boesi et al. [2] write: "Foraging activities of host and parasitoid populations are seasonally (and often daily) synchronized". The resemblance between Bee Flies and their hosts thus extends to their behaviour as well as their appearance.

So, why do Bee Flies look, and behave, like Bumble Bees? Their behaviour brings them into contact with potential hosts and increases the chance of locating their nest holes, while their appearance may prevent attack during egg-laying (although this is speculation). The appearance of Bee Flies might also be explained by Batesian mimicry, deterring predators such as insectivorous birds by resembling other insects with a powerful sting. Although we don't know the explanation, their appearance, and behaviour, evolved by selection of advantageous genetic mutations long before humans first appeared, although that would be disputed by Creationists.

Whatever our views on the origins of living organisms, all humans have a tendency to view Nature from a human perspective. However, we need to be cautious of our anthropocentricity, as our perceptions may be quite different to those of other animals. Perhaps the appearance of Bee Flies is just a result of coincidence rather than the unconscious mimicry of the appearance and behaviour of Bumble Bees? That does seem unlikely, but how are we to know?

[1] http://www.nhm.ac.uk/nature-online/species-of-the-day/biodiversity/loss-of-habitat/bombylius-major/

[2] Roberto Boesi, Carlo Polidori and Francesco Andrietti (2009) Searching for the right target: oviposition and feeding behavior in Bombylius Bee Flies (Diptera: Bombylidae). Zoological Studies 48: 141-150.

“When believing in Creation can seem like an easy option”

I used the title of this post as a heading when discussing the extraordinary adaptations shown by some organisms [1]. The examples I chose to illustrate this point were female bolas spiders and the larvae of black flies. Female bolas spiders use a sticky blob of silk on the end of a line that they use to drop on moths attracted to the smell that they produce, mimicking a pheromone produced by female moths. Silk is also used by blackly larvae, both for attachment and for building a cocoon in which pupation occurs. However, their remarkable feature is their head fans that are wonderful examples of precision engineering and which fold to allow the larva to remove tiny particles that have been trapped from currents of water.

These were just two examples from a huge number in Natural History where one’s sense of wonder forces the question “How did that evolve?”. Recently, a further example of extraordinary adaptations was reported. The Cinereous Mourner (Laniocera hypopyrra) is a grey bird that is relatively common in the northern Amazon rain forest (see below centre). The chick is quite different in appearance and has orange-red, spiky plumage, with white tips to each spike, that causes it to resemble poisonous caterpillars of similar size (of the genera Megalopyge or Podalia [2] - a Podalia larva is shown below left; a Laniocera chick, below right). 

Not only does the bird look like a caterpillar; it also moves like one:

In their paper, to be published in The American Naturalist in January 2015 [2], Gustavo A. Londoño, Duván A. García and Manuel A. Sánchez Martínez suggest that, as the young chicks of this species are highly vulnerable to predation, mimicry of a poisonous caterpillar reduces the risk of attack. Chicks are slow-growing and do not beg for food like other nestlings, so their behavioural responses, as well as their appearance, are under genetic control. After about 16 days, the behaviour of the chicks changes, as they become more mobile and can avoid attackers. At this time the downy feathers begin to drop and the adult, grey plumage begins to emerge. The authors write:

The close match in size, morphology, and behavior between the nestling and the caterpillar supports the hypothesis of Batesian mimicry being used by the nestling, possibly to reduce nest predation. Therefore, nestling morphological and behavioral characteristics could have evolved as a result of the combination between the slow life-history nesting strategy observed in L. hypopyrra (e.g., long nestling period) and the high nest-predation pressures observed at the study site.

I agree, but how did this evolve and over what time period? Were there chance mutations that caused the changes of appearance and behaviour that coincidentally mimicked poisonous caterpillars of similar size? It must be so, although it is very difficult to see what the steps in the process might have been. Were there dramatic mutations, or a sequence of much smaller ones? If the latter, how were they selected if they conveyed only a tiny advantage at each step, or no advantage at all? There are so many questions, but no answers - only much speculation. Do you see what I mean when I say that believing in Creation can seem like an easy option?

[1] Roger S. Wotton (2012) Walking with Gosse: Natural History Creation and Religious Conflicts. Southampton, Clio Publishing.

[2] Gustavo A. Londoño, Duván A. García and Manuel A. Sánchez Martínez (2015) Morphological and Behavioral Evidence of Batesian Mimicry in Nestlings of a Lowland Amazonian Bird. The American Naturalist 185 [in press]

I would like to thank Bob Carling for alerting me to this remarkable story.