Archive for the ‘Evolutionary Biology’ Category

Jon Kaas (2006) discusses some of the research on the evolution of the neocortex throughout mammals. He notes some interesting facets of this process, such as the “late makes great” rule, where brain regions that form late developmentally are especially large in bigger brains. The inference that humans and other large-brained mammals must have an especially large neocortex follows trivially.

He describes early primates as small, nocturnal creatures that spent most of their time feeding in tree branches. This lends credence to the hypothesis that primate brain size increased initiallly due to an opportunity for animals with improved visual and sensorimotor abilities to thrive. Based on the fossil record of extinct and extant primates, the temporal cortex in particular was expanded, which was probably devoted to vision.

Finally, he speculates that the reason for the especially cognitive success of humans is due to excessive modulation of brain regions that chopped them up into more and more areas. These areas were then forced to become more automonous in order to cut down on the need for anatomically long processing.

Semendeferi et al showed that the volume of the frontal lobes had not changed throughout primate evolution. Perhaps this increased specialization hypothesis could explain how executive functions changed so dramatically without altering the volume of the region.


Kaas JH. 2006 Evolution of the neocortex. Current Biology 16:910-914. Link to PubMed.

Semendeferi K, Damasio H, Frank R, Van Hoesen GW. 1997 The evolution of the frontal lobes: a volumetric analysis based on three-dimensional reconstructions of magnetic resonance scans of human and ape brains. Journal of Human Evolution 32:375-88.


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Zalc et al published a paper earlier this year in Current Biology hypothesizing that vertebrate myelination developed in the now extinct class placoderms. It is a horrificly concise paper (that is a good thing), and their evidence is simple. As compared to ostreostaci, a class that preceded them, placoderm fossils suggest oculomotor nerves that are 10 times longer, despite having oculomotor foramina of similar diameter.

In living animals, a higher ratio of nerve length to diameter is found whenever the nerves are myelinated. This makes sense, because myelin allows action potentials to propagate down nerves faster and with less energy because the potentials can “hop” from one node to the next. Without myelin, another strategy to make nerves longer is to increase axon diameter, which also increases impulse speed, although it comes at the cost of higher energy and space constraints. Therefore, if placoderms are shown to have had a high ratio of nerve length to diameter compared to unmyelinated species, it means that their nerves were most likely myelinated.

Myelin evolution is interesting in particular because some species have the ability to regenerate their myelin when it is damaged (for example, in goldfish), but at some point this ability was lost. If we could figure out the exact mechanism by which myelin sheathing evolved, we could perhaps develop a drug that allowed for myelin regeneration in humans as well.


Zalc B, Gouget D, Colman D. 2008 The origin of the myelination program in vertebrates. Current Biology (18): 511-512.

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The Stuff of Thought book notes

Steven Pinker’s The Stuff of Thought starts off a little bit verbose, but by the end of the book he has really hit his groove, and he uses the architecture that he has built up to make a number of fairly profound points. Here are my notes:

  • Linguistics is often studied based on simple intuitions. “Designating a sentence as ‘ungrammatical’ simply means that native speakers tend to avoid the sentence, cringe when they hear it, and judge it as sounding odd.”
  • “Language acquisition is an example of the problem of induction — making valid generalizations about the future from limited data available in the present, whether they involve language acquisition by a child, learning by a computer, or theorizing by the scientist.”
  • We naturally think about objects geometrically: “when the mind conceptualizes an entity in a location or in motion, it tends to ignore the internal geometry of the object and treat it as a dimensionless point or a featureless blob.”
  • Objects are conceptualized as having a certain amount of dimensions; we literally have maps of objects in our brains. He illustrates this fact brilliantly using linguistics.
  • On humans trying to do statistics: “It’s as if people heard the statistic that women outlive men on average and concluded that every woman outlives every man. The image of one orb floating above another seems to come more naturally to the mind than an image of two overlapping bell curves.”
  • How language works. “We gather our ideas to put them into words, and if our verbiage is not empty or hollow, we might get these ideas across to a listener, who can unpack our words to extract their content.”
  • There are two natural systems for keeping track of quantities. “One is an analogue estimation system, in which quantities are gauged in an approximate manner by relating them to some continuous magnitude in the head, such as a vague sense of ‘amount of stuff,’ or the extent of an imaginary line. The second system keeps track of exact quantities, but only up to a small limit, around three or four.” Neither of our innate systems can do complex math, for which you need a number system and language. There is some evidence that the first continuous magnitude one may be on a logarithmic scale–see this post from Columbia’s Statistics blog.
  • People report that they “think in” their native language, “but these echoes are not the main event in thinking; most information processing in the brain is unconscious.”
  • Enst Poppel believed that “We take life three seconds at a time. That interval, more or less, is the duration of an intentional movement like a handshake; of the immediate planning of a precise movement, like hitting a golf ball….” This is a pretty ambitious theory, but it is interesting. Perhaps the time frame varies a little bit from person to person? Regardless, this should be testable.
  • Politeness is about pretending to give the listener options. For example, “would you pass the salt?” is more polite than simply “pass the salt.”
  • Evolutionary psychologists believe that aside from language, humans stand out because of their propensity for tools and a talent for cooperation. The former is a manipulation of the physical world, the latter is a manipulation of the social world.
  • Evolutionary psychological mechanism for abstract thinking: “Now imagine an evolutionary step that allowed the neural programs that carry out such reasoning to cut themselves loose from actual hunks of matter and work on symbols for just about anything. The cognitive machinery that computes relations among things, places, and causes would then be co-opted for abstract ideas. The ancestry of abstract thinking would be visible in concrete metaphors, a kind of cognitive vestige.”
  • Bribing maitre d’s works nearly every time. If you remember one thing from these notes, it is to bribe maitre d’s, you will skip lines in restaraunts nearly every time.
  • He deconstructs our courtship patterns brilliantly. Essentially our current practices our built to ensure plausibility deniability for all parties involved. Tactless pick-up attempts are too bold, which is awkward. It’s not about whether the person knows that you’re interested in them, it’s whether they know that you know that they’re interested in you, and whether you know that they know that you know that they’re intersted in you. Seriously.

Pinker’s other work is more famous, but I’d recommend this book wholeheartedly. Just remember to power through those first 100 pages–you’ll be thanking me later.

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Given that evolutionary psychology and molecular neuroscience are both relatively recent fields and that both study what is going on in our head, there seems to be fairly little interplay between the two subjects. In their review article, Pankseep et al. attempt to rectify this dearth of collaboration.

The authors concede two crucial points that evolutionary psychology has given to the scientific community: the idea there is a some core human psyche that is a product of our sociobiological evolution, and the correct predictions that it has made in understanding our current mental processes. However, some evolutionary psychologists may go too far in presupposing that our reward system itself is unique, as it was probably co-opted from a shared ancestor of mammals in evolution and adapted to fire to general symbols instead of specific signs. I’m not sure if this is a straw man argument that they are presenting, but if it is not, it deserves serious attention.

Furthermore, many of the social processes regulated by the hypothalamic-pituitary-adrenal axis are seen in other animals as well. For example, consider the “resident-intruder” paradigm common in studies of rats. In these studies, the intruder is almost always the “loser” of the social interaction and very commonly exhibits physiological changes following this defeat. These include loss of weight, testicular regression, and increased fearfulness. The changes are especially evident when the “loser” rat is not placed back in a social housing condition but is instead housed in isolation. It is quite evident that humans are not the only intensely social animals, so why should we limit our study to them?

With this groundwork in play, the authors present what they term the “seven deadly sins of evolutionary psychology”:

1) The assumption that the neocortex is the primary region for human differentiation from other animals may be foolhardy since the system is maintained between mammalian species. Perhaps some of the differentiation emerged epigenitically because of cultural changes?

2) An overemphasis on one species, when others have useful insights to yield as well.

3) They may focus too much on the specifics and miss the general point. What are the general processes that could have evolved that could account our current psychological state?

4) Since the idea of “brain centers” was cast aside a few decades ago, evolutionary psychologists must explain how their ideas fit within an integrated brain.

5) Too often conflating emotions–the will to do something–with reasoning-based decisions. Although they are closely related, there may be a way to distinguish between the two and note where evolutionary adaptations have developed as emotions, and where they have developed as decision making skills.

6) There is no need to ignore the brain, since molecular neuroscience is providing a solid base upon which others can build. They generalize this criticism to all social scientists.

7) Declaring a mental process to be an “algorithm” is silly, because more and more research suggests that the brain does not work with this sort of distinct processes. Although they can be useful as models, ultimately the best models will discuss an integration with the rest of the brain processes. Again, this criticism could be reasonably applied to just about anyone, and probably has more to do with the current system of science than any one researcher’s desire to specialize.

The authors then go on to discuss how some of these “sins” can be resolved through a study of molecular genetics and neuroscience. These demands on evolutionary psychologists are challenging, but if they meet half of the demands of their toughest critics, it will probably be enough for the rest of the scientific community.


Panksepp J, Moskal JR, Panksepp JB, Kroes RA 2002 Comparative approaches in evolutionary psychology: molecular neuroscience meets the mind. Neuroendocrinology Letters 23: 105-115. pii:NEL231002R11.

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The Moral Animal book notes

Robert Wright’s The Moral Animal is considered a “popular” introduction to evolutionary psychology. But contrary to expectations based on most “popular” literature, Wright’s foray is balanced, detailed, and funny. Here are some of my notes:

  • The naturalistic fallacy is when people attempt to derive basic moral values from natural selection, or any of nature’s workings. Indeed, just because it is “natural” does not mean that we should adopt it.
  • The watchmaker argument claims that since our current state is so complex, it must be the result of intelligent design. Darwin’s theory of natural selection offered a method by which evolution could function, thus providing a counterargument to intelligent design.
  • “Between us and the australopithecine, which walked upright but had an ape-sized brain, stand a few million years: 100,000 maybe 200,000 generations.” p 26. This means that we only have had a small amount of time to differentiate ourselves from our most recent ancestors.
  • The classic male/female experiment to demonstrate differences between the sexes: “In one experiment, three-fourths of the men approached by an unknown woman on a college campus agreed to have sex with her, whereas none of the women approached by an unknown man were willing.” p 43
  • Bonobos, a close relative of ours, can display homosexual behavior.
  • Women are generally attracted to high social status, men generally to beauty, and therefore youth, and therefore fertility.
  • Women do cheat on their mates: “Blood tests show that in some urban areas more than one fourth of the children may be sired by someone other than the father of record.” p 70
  • Frequency-dependent selection is when “the value of a trait declines as it becomes more common, so that natural selection places a ceiling on its predominance, thus leaving room for the alternative.” p 79
  • A polygynous society is better for women, whereas most men end up worse off. This is counter-intuitive and one of the strongest sections in the book.
  • Human beings are not “fitness maximizers,” they are “adaption executors.” Eliezer has posted upon this previously, it is a tough but crucial point to remember.
  • John Stuart Mill was a utilitarian, and believed in the most happiness for the most people, and happiness of the higher order (not just base pleasure).
  • Kin selection means that you want your shared genes to succeed in life too, not just yourself. It is used to explain a lot of altruistic behavior.
  • A gene for altruism will thrive if c < br, where…
    c = cost to agent organism
    b = benefit to target organism
    r = relatedness of agent and target
  • Poor families will invest in daughters, rich families in sons.
  • Group selectionism is a foolhardy temptation towards which you should not fall. Read about it on Wikipedia, or in the book, where it is given an excellent treatment. It doesn’t stand up empirically.
  • In a sweet iterated prisoner’s dilemma game with repeated trials, the program called “TIT FOR TAT” won, which was designed to essentially treat others how they treat you. This is another empirical explanation for why altruism could have developed.
  • Moulay Ismail the Bloodthirsty sired more children than anybody else according to Guinness world records, 888.
  • We may be biased into deceiving ourselves so as to be more proficient at deceiving others.

You will find many more nuggets if you read the whole book. Neuroscience is fascinating on the cellular and systems level, but in order to consider the brain on a macroscale level, evolutionary psychology must be a part of the equation.

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Saccadic eye motion evolved in early vertebrates as an adaptive mechanism to view more areas of a visual scene with the central fovea, and therefore increase overall resolution. Theoretically, it should come at the cost of making it more difficult to link a sequence of objects together, since these saccades would confuse you as to what exactly you are currently looking. However, our visual system compensates for upcoming saccades, resulting in three odd results:

1) Visual fields change their position in shape in real time in order to adjust to the saccade target. For example, in V4, receptive fields generally shift towards the upcoming saccade and modulate their size.

2) Very near to the time that the saccade moves (it’s onset), our perception is that briefly flashed stimuli are closer to the saccade target than they actually are. This is known as peri-saccadic compression, and there ought to be a wikipedia page for it.

3) In experiments that require subjects to both execute a target-directed saccade and discriminate an object (choose it from among a set, I presume), visual discrimation is naturally strongest when the stimuli is located near the target of the saccade.

Their model attempts to explain these distinct phenomena through oculomotor feedback, and show how the brain links the pre-saccadic visual field to the post-saccadic one. Mathematically their model is complex, and they do so not to yield an arbitrarily higher fit, but in order to make it more consistent with the anotomical constraints of visual receptors. Indeed, some of their parameters were so complex that they were forced to estimate their values because of a lack of independently found data to build upon. Nevertheless, their model is fascinating and their predictions robust. Check it out, it’s ungated.


Hamker FH, Zirnsak M, Calow D, Lappe M 2008 The Peri-Saccadic Perception of Objects and Space. PLoS Computational Biology 4(2): e31 doi:10.1371/journal.pcbi.0040031

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