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Cortical Expansion

26 Aug

So I stumbled across this abstract and picture a little while ago. Both come from similar patterns of cortical expansion during human development and evolution, a paper published at Yale earlier this year. The title basically sums up the idea, though I think some of the finer suggestions of why this happens are pretty neat.

Hill et al. notice that the newer portions of our brains (mainly, the giant cortex, which is responsible for our ‘higher’/more ‘human’ brain function, and is the most recent to be ‘tacked on’ as in Dr. Linden’s model) tend to develop considerably after birth, whereas the basic units responsible for survival–not so unique to humans–are already developed by the time we exit the womb. It’s interesting to think about how much is left to be shaped by our experience–and it seems that the equipment and allowance of extensive experience-based molding is a large chunk of what sets us apart.

Did you know…

24 Aug

… that 3.5 billion years ago, on an ancient version of Earth, a day was only about 15 hours long? Dr. Linden (again, The Accidental Mind) suggests that bacteria living during this period developed the same type of inner “circadian clock” that humans do today in our sleep/awake cycles.

This chart displays the continuing general trend towards a slowing rotational period over the last 50 years:

Why we keep men around… A.M Tidbit 3

24 Aug

Another bit from Linden’s The Accidental Mind

In the “Love and Sex” chapter, Dr. Linden points out that most female mammals “advertise” their ovulation – with different scents, changes in appearance, etc. Males and females won’t approach each other when the female has not begun ovulating. In human females, however, time of ovulation is completely concealed: our men have no way of knowing when we’re most fertile, and sex becomes more recreational. Why?

Here’s a direct quote from pg. 149:

“With concealed ovulation… the couple has to mate all through the woman’s cycle to have a reasonable chance of conceiving. Not only that, but if the male decides to stay and try his luck with another female, he cannot be sure that another male will not sneak in the back door and mate with the first female on her fertile days… Hence, with concealed ovulation, the best male strategy is to stick with one female and mate with her all the time.”

But what about the females? Does this type of mating system benefit us? He continues:

“Most other mammals are able to find their own food immediately after weaning, but human children do not achieve this level of independence for many more years. As a consequence, the reproductive success of a female human is much greater if she can establish a long-term pair bond with a male and he contributes in some form to child-rearing.”

So, we need concealed ovulation – so our big-brained offspring are properly taken care of by two adult parents. The bonding that comes as a result of more frequent, recreational sex stabilizes the whole situation… and even keeps us ‘doing it’ when conception isn’t in the picture (like after menopause or during pregnancy).

(These ideas are all from Linden, pgs. 147-150)

Pretty neat, eh?

Accidental Mind – Tidbit 2

19 Aug

Here’s a continuation of the memory discussion from Dr. Linden’s The Accidental Mind.

Throughout the course of the book, Dr. Linden stresses the fact that our brains were built by ‘tacking on’ new structures over the course of evolutionary history. As our brains became more and more complex, it was not due to a ‘wiping away’ of an old, less-complex brain and building a brand new one, but rather because new structures were simply lumped on top of the old ones and were forced to work together.

In addition, our emotionally-cued memories–which we retrieve actively, changing them every time we recall them–form the basis of the thought structure we use to perceive the world in the present.

So, Dr. Linden summed this up in a great snippet at the end of chapter five:

“Our memory, which is the substrate of our consciousness and individuality, is nothing more than the accidental product of a work-around solution to a set of early evolutionary constraints. Put another way, our very humanness is the product of accidental design, constrained by evolution.” (p. 144)