Posts Tagged Human

Unnatural Selection

As a veterinarian, atheist and scientist I have championed the cause of natural selection all my life. It is a magnificent device that has driven evolution for eons, constantly upgrading and improving species to better allow them to adapt to their environments. Through natural selection we have moved from unicellular animals to multicellular ones to the incredibly complex array of species we have today, species that run, fly and swim, enabling them to find homes in every possible niche on the planet.

There is, however, one species that appears to stand above natural selection, and that species is our own. I have been short sighted and wearing glasses since I was seven years old. If natural selection had had its way with me I would surely have missed seeing that truck, bear or crevasse and perished long ago. I certainly would not have lived long enough to produce my own pair of myopic humans. Now I have a dicky heart and sleep apnoea. However, our ability to overrule natural selection once again affords me the opportunity to live on.

Every day we try our best to cancel out the effects of natural selection. From vaccinating ourselves to prevent diseases that might otherwise kill us, to treating ourselves with antibiotics when we are sick. From artificial insemination and embryo transfer when we can’t conceive naturally, to Caesarean sections when we can’t deliver the fruits of those conceptions. And it is not just ourselves that reap these benefits. We make sure that our friends do too. Many are the cows that I saved from almost certain death (at least long enough to make it to the dinner table) by assisting in the delivery of their calves. Ease of delivery (at least in humans and domestic animals) has been virtually removed from the selection process.

Will the fact that large numbers of short sighted, infirm, sub-fertile humans that can’t give birth, are passing their genetic material on for generations come back to bite us? We must surely be weakening our species as a whole, but who would refuse the artificial fixes that are available to us? Certainly not I. It does seem a tad hypocritical, however, to laud the marvels of natural selection while studiously stepping around it ourselves wherever possible.

Dr. F. Bunny

 

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Cooking With Gas

Recently I watched a TED talk by Suzana Herculano-Houzel (http://www.suzanaherculanohouzel.com/lab) entitled, “What is so special about the human brain?” (http://www.ted.com/talks/suzana_herculano_houzel_what_is_so_special_about_the_human_brain.html). In this presentation she makes the intriguing assertion that our brain is as large as it is, at least in part, because we cook our food.

Size, as in brain size, is not as important as neuron number when it comes to intelligence. Although the elephant brain is three times as large as the human brain it contains 23 billion neurons, compared with 86 billion in the human brain (http://en.wikipedia.org/wiki/List_of_animals_by_number_of_neurons).

Unfortunately the human brain is incredibly expensive to run, 25% of the energy consumed daily goes to fuel the brain. It costs around 6 kCal to run one billion neurons per day. Despite great apes being physically larger than us, their brains are smaller. Herculano-Houzel proposes that this is because they cannot consume enough calories on a daily basis to run a bigger brain. They do have a fairly low energy diet consisting predominantly of high fibre plant material with a few fruits and, in the chimpanzee’s case, some meat. This may be why the chimpanzee can afford to run 5.5 to 6.2 billion cerebral cortical neurons compared with the gorilla’s 4.3 billion.

However, humans maintain between 19 and 23 billion cerebral cortical neurons. Herculano-Houzel believes we can feed this number because of cooking, which effectively predigests our food releasing more energy and allowing us to more completely absorb our food. She depicts a graph, which correlates the increase in brain size of our ancestors with the invention of cooking.

Paradoxically we are now moving away from cooking and processing back to a more unprocessed diet because we appear to have overdone it, consuming too many calories and becoming extremely obese in the process. If we could only divert all those extra calories to our brains instead of our bodies imagine how incredibly intelligent we could become.

Dr. F. Bunny

 

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