November 2: Mammalian Heritage Day

Finally a fake holiday I can get behind. We humans in our evolution find ourselves benefitting fully from our mammalian heritage. Mammals appeared on the scene around 500 million years ago and have diversified into many different forms since. Consider their (our) primary characteristics. Being warm blooded confers a crucial independence from ambient conditions, an independence humans have taken to an ultimate degree. It is not just that mammals have adapted to many different environments around Gaia, including returning to the ocean, but we have further enhanced our independence by controlling and changing these ambient conditions, perhaps to own detriment but then no species continues forever.

Consider another characteristic: live births. This is especially important for three reasons. First, infants born viably but immaturely permit an incredible amount of post-partum growth. The benefits of this are astounding: increased brain growth and size and critical periods of maturation where experience affects brain development in deep ways. Second, parenting becomes a lot more than regurgitating food into infant mouths and then kicking them out of the nest. Oxytocin, a most important hormone for parenting energy and prosocial behaviors, has been around, according to some estimates, for over 530 million years. Over the course of evolution mammalian brains developed the capacity to respond more powerfully to this hormone—parenting and family life became more prominent in any adaptive success, and that leads us to the third reason: If you want to raise more intelligent children and pass on to them the benefits of prior generations’ experience, birth them live and immature, maintain a nurturing family structure, and extend their juvenile period so that they do not begin to reproduce until they are a decade or so old. The discovery of controlling fire was not really that big of a deal; the passing on of this technique, however, was; just ask Prometheus.

Our immediate (relatively speaking) ancestors who showed the culmination of these characteristics are the primates who appeared around 53 million years ago. That means mammals evolved for 450 million years before our large brained, visually oriented, socially engaged, and quick intelligence kinfolk appeared and then simians appeared a few million years after that. Our line split off from the great apes around 8 million years ago and our partners, the dogs, appeared around 3 million years ago. Fire was important because it furthered this trend. Cooking food releases more calories, making digestion more efficient, and more energy from food powers increased brain capacity. Fire warms us and draws the family group to the hearth. Civilization began at the hearth (and it looks like it will die in committee).

So this November 2 take a moment to reflect on our genetic heritage and thank a mammal, any mammal, all mammals for continuing this genetic stream and tend to your hearth.

bonobo1

We sing a song of mammals today . . .

Many ancestors and they were busy

Several stories from recent Science News issues paint a picture of human ancestors 2.8 million years ago shaping stone tools as their brains grew in size, and then around 40,000 years ago, Homo sapiens crowded out Neanderthals with the help of dogs (says one author).  The 3/21/15 issues has a story about finding a human gene that promotes larger brains which wrinkle it up to squeeze it all in.  A chimpanzee has a similar gene but it does not promote as much growth.  They found this out by injecting the genes into mouse embryos (remember the movie, Secret of NIMH?).  Further research on our variant indicates that it appeared in our lineage about 5 million years ago around when our stock split off from the chimpanzees.  One researcher points out our brains did not really begin to increase in size until 2 million years ago so this gene was not fully functional, maybe, for 3 million years.

skulls of different hominds

skulls of different hominds

Two articles in the 4/4/15 issue speak to the 3 million year mark.  One is about the controversy on how to classify a newly found fossil from 2.8 million years ago.  Is it part of Homo, which was just emerging from the gene pool, or an ancestor like the Lucy fossil, Australopithecus afarensis, or some transitional species in between?  In that same issue is a story about research into tools, presumably from some hominid line.  Though stone tool industry increased noticeably in the archeological record around 40,000 years ago, some shaped stone tools have been dated back to 2.6 million years ago.  Wow, I had not realized tool making was that old an art.  The story tells of the controversy between those who classify the tools by time/location and those who say that is not very informative and instead classify by the techniques used to form the tool.  Several of this latter group are expert stone ‘knappers’ themselves and that seems a good study.

Tool use in modern humans is supported by the left parietal lobe, the center for praxis.  If I remember my brain evolution correctly, our brain’s early enlargement came in the parietal lobe and then the temporal lobe, then later on frontal areas expanded.

parietal in yellow, temporal in green

parietal in yellow, temporal in green

Where these two lobes meet is where language abstraction is centered in Wernicke’s area.  So we have a gene which promotes brain growth in the embryo beginning to come on strong around 3 million years ago and shortly thereafter tool making appears.  We do not know how such creatures organized socially nor how they communicated.  We can be sure that empathic connectedness had emerged and that tool making techniques continued to develop over this time suggests cultural transmission and change.  Quite a history a long ways back.

Also in the 4/4/15 issue is a review of a book by anthropologist Pat Shipman who traces the domestication of dogs to 40,000 years ago when Homo sapiens left Africa and migrated into Europe.  Shipman finds linkages between modern humans and dogs and the eventual disappearance of Neanderthals, Denisovans, and large mammals like mammoths and cave bears.  Thus, the “Fido hypothesis” offers some explanation as to Homo sapiens ascendance during that time.  Oh, and other articles in those two issues speak about dogs’ abilities to read our emotions.  Yes, early humans traveled far and wide and met many friends along the way.  Travel on.

Basic conversation

Conversing is one of the most human things we do and we do it a great deal.  Our brains have evolved with special channels in and out for language.  Most people know of the posterior Wernicke’s area important to language comprehension and of the anterior Broca’s area important to language production.  These are basic to conversation of course.

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The speech signal is an unbroken stream of sound produced by air blowing through the vocal folds and then modulated by the speech tract (pharynx, nasal cavities, tongue, teeth, lips) to mark phonemes (vowels and consonants).  The auditory system processes this signal and somehow recovers the linguistic units to find words, sentences, etc.  Our brains do this rapidly and all at once, which makes it possible to interrupt someone to say what we want rather than listen to them. More on manners later.  Here is a graph of the speech signal for a sentence that took 1.5 seconds to utter (must have been a slow drawl at that).

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No breaks are between words, the stress or accent on different syllables is indicated by the amplitude of the graph, and the phonemes are there somewhere.  That is not the whole story, however, because while the left side of the brain is encoding/decoding the syntactic units, the right side is doing the same for the paralinguistic aspects of the signal, the intonation patterns carrying the sentence modality (statement, question, exclamation, etc.), the emotional cues therein, even the basics of the speaker’s identity, sex, age, geographic origin, etc.  This is done all the while as the right side also monitors the non-verbal cues for the listener’s interest and attitude along with the rest of the immediate concrete situation.  Again the left side’s language may be about information immediately available in the current situation but more probably is about information displaced in time and space, real or unreal.

The term ‘voice’ is used in many ways, a speaker’s basic necessity, a singer’s instrument, a poet’s distinctive mode of expression, etc. Biologically voice is the special sound to which our brains are attuned; a good part of our brains is dedicated to receiving and producing this figure so distinctive from the ground of ambient noises.  And not just humans.  The latest issue of Science News reports a study in which dogs were trained to lie very, very still in an MRI while sounds were played.  The results indicated that dogs also pay special attention to voice though not to the same degree as humans, which only makes sense given how well they engage with us and us with them in a special sort of conversation in which they are the better listeners and speak with their eyes, tongue and tail.

Coming soon: conversation and music