Bred to die

Once every while, some creationist will come along who seems to believe that the fact that animals and humans die represents evidence against evolution. The “logic” is that natural selection should inevitably favour longevity/potential immortality since an infinite lifetime means infinite possibilities for reproduction. I’ve always considered this “proof” a proof of the person’s mathematical illiteracy and little else – after all, with any non-zero death rate, the chance to actually survive that long converges to zero with longish finite lifespans, and so does the benefit from potential immortality.

The last time this argument came up, I used the opportunity to practice my new programming skills, so here’s a little script that simulates mortals and “immortals” evolving within the same population. You can play with the parameters, such as extrinsic death rate and rate of reproduction, and decide whether there is a trade-off to (potentially) living longer in terms of slower maturation (there should be, because that’s what we observe in real animals), and whether there’s a bias in life-shortening vs. life-prolonging mutations (there should be, again). We’re pretending that (potential) immortality is actually physically possible for complex organisms, and in fact that once you’re able to survive 160 years, you might as well be immortal.

Here’s what you get when you run the model with biased mutation rates (.003 for life shortening mutations vs. .001 for life-prolonging ones), and no trade-off, and a rate of reproduction of 0.25 per adult per year. We see that there’s a lot of noise, but on the long run the type which lives up to 57 or so years carries the day. Beyond that age, being hypothetically able to live longer doesn’t carry enough of a benefit for selection to overcome the direction of drift when you aren’t going to live that long anyway:

conflated_youngsters

And here’s what you get when you include a very moderate trade-off: The most-short-lived individuals reach maturity at 4 (1 year before they’re bound to die), while the immortals reach it at six, and intermediate degrees of longevity have varying chances of joining the club when they’re in between. In effect, this represents about 10% later maturation per doubling of lifespan, which looks like a very fair deal, but alas this is enough to clearly favour the shorter lived variants over immortals:

percentages_tradeoffandbias

Code below fold. Don’t tell me it’s slow, but feel free to tell me how to make it faster: Continue reading

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Hierarchical structures, and linguistic wars

Via Norbert Hornstein’s blog, I came across a recent paper in Royal Society Proceedings B (Frank, Bod, and Christiansen, 2012). In this post, I will present my own two cents on the new “language wars”, focussing on Frank et al.’s arguments against overestimating the roles played by hierarchical structure in language use, and on Hornstein’s treatment or lack thereof as exemplifying the defensive reactions generative linguists often display towards any and all challenges from outside. Continue reading

Peripheral anatomy and cognitive traits in crows, with a word on humans

An new paper in Nature Communications (Troscianko et al, 2012; see also the discussion at Not Exactly Rocket Science) suggests that the extraordinory extent of tool use by the New Caledonian crow (NCC) is accompanied by a morphology that differentiates them from other corvids. Specifically, a straight bill and a ever so slightly different position of their eyes enlarging their binocular sector, i.e. the part of the visual field where they have increase depth perception, allows them to follow what they’re doing with their tools much better than other crows, even when operating in narrow openings.
Continue reading

Mice as vocal learners?

Short notice: There’s a new paper out in PLoS ONE (Arriaga et al., 2012) about signatures of vocal learning in mice. The main evidence is from neurological data – activation of the motor cortex during vocalisations, among others – and from behavioural experiments demonstrating sensitivity to feedback, both from others – mice modify their vocalisations when put into novel groups – and auditory feedback about their own vocalisations: the song of deafened mice deteriorates over time.

(Found through Brian Owens blogging at Nature.)

Arriaga, G., E. P. Zhou, and E. D. Jarvis (2012): Of Mice, Birds, and Men: The Mouse Ultrasonic Song System Has Some Features Similar to Humans and Song-Learning Birds. PLoS ONE 7:10: e46610. doi:10.1371/journal.pone.0046610

Adjective Order Restrictions and Perceptual Biases

A phenomenon that has been discussed much in the linguistic literature is the relative orders of stacked adjectives. In multiple unrelated languages, adjectives of different “semantic classes” display a tendency to show up in similar relative orders when jointly modifying a noun. For English, one formulation of the sequence, in abbreviated form, looks something like (1), modified after Scott (2002), but similar hierarchies can be found in other sources with sometimes very different analyses (e.g. Dixon, 1982), though some would describe them as trends rather than categorical (Bouchard, 2002; Truswell, 2009; among others).

(1) size > shape > texture > color > provenance > material > N

In other words, a stone that is both green and round would more naturally be described as

(2) a round green stone

than

(3) a green round stone

and similar effects are observed in many other languages (in languages with postnominal adjectives, the order is typically reversed, but what remains constant is that COLOR is closer to the noun than SHAPE in the unmarked case).

What I’m interested in is the cognitive basis for such ordering restrictions. Continue reading

pan faber – tool use and action, and the roots of language*

Language and labour

Along with language, extensive tool use is one of the defining characteristics of our species. Unlike compositional language, human tool use has clear homologues in our closest relatives. Nonetheless, there are qualitative differences between human and chimpanzee tool traditions. Only humans show cumulative evolution of (tool) culture, i.e. the innovations of one generation not only being transmitted to subsequent generations, but being built upon and refined over time in a way that allows a technological explosion.

Perhaps not surprisingly, philosophers and students of human evolution have long attempted to draw parallels and functional/causal links between the two faculties. Continue reading

Pragmatic prerequisites for human language

(This post is more a more or less verbatim replica of a post from April this year in a discussion board which I was intermittently spending way too much time on; if I were to write it now, I’d at least include a reference to Whiten (2011) (Whiten, A., Hinde, R. A., Stringer, C. B. & Laland, K. N. (2011). Culture Evolves. Phil. Trans. R. Soc. B 366, 938-948.), and maybe somewhat qualify that the dichotomy between cumulative human and non-cumulative chimpanzee culture may be based on relatively minor and gradual differences in underlying transmission mechanisms. This post was in response to another participant asking whether signing apes would “talk to researchers on their own” and what we could learn about their ways of thinking from them doing so.)

If by “talk to researchers on their own” you mean initiate a conversation untriggered by an immediate need, or by an object present in the immediate environment, the answer is no. This is in and of itself a very interesting result, though. It means that we have to be cautious when attributing differences in outcome between chimpanzees and humans to limitations on chimpanzees’ cognitive abilities – it may be that the most decisive difference underlying the presence of cumulative cultural evolution in humans (senso Tennie et al. 2009) and its absence in chimps isn’t in what chimps can’t do, but in what they won’t do. Continue reading