Posts Tagged ‘senses’

Hearing came before ears existed (as sight must have come before eyes)

February 12, 2015

Of course all our senses lie in the brain and not in the sensors receiving the input from our surroundings. So while our ears, eyes, skin and taste-buds detect certain physical characteristics and convert them into electrical signals, it is our brains which interpret the electrical signals they receive as being sound or colour or taste or heat. Our sense organs are merely transducers, converting some physical characteristic into an electrical signal. So how did the brain evolve and develop the interpretation “software” for these signals before the sensors had even been developed?

Two new papers show that Lungfish and salamanders can hear, despite not having an outer ear or tympanic middle ear. 

  1. C. B. Christensen, H. Lauridsen, J. Christensen-Dalsgaard, M. Pedersen, P. T. Madsen. Better than fish on land? Hearing across metamorphosis in salamanders. Proceedings of the Royal Society B: Biological Sciences, 2015; 282 (1802): 20141943 DOI: 10.1098/rspb.2014.1943
  2. K. Knight. Lungfish hear air-borne sound. Journal of Experimental Biology, 2015; 218 (3): 329 DOI: 10.1242/%u200Bjeb.119487

Aarhus University Press Release:

Lungfish and salamander ears are good models for different stages of ear development in these early terrestrial vertebrates. Two new studies published in the renowned journals Proceedings of the Royal Society B and The Journal of Experimental Biology show that lungfish and salamanders can hear, despite not having an outer ear or tympanic middle ear. The study therefore indicates that the early terrestrial vertebrates were also able to hear prior to developing the tympanic middle ear. …….

……. However, available palaeontological data indicate that the tympanic middle ear most likely evolved in the Triassic period, approximately 100 million years after the transition of the vertebrates from an aquatic to a terrestrial habitat during the Early Carboniferous. The vertebrates could therefore have been deaf for the first 100 million years on land. ….. 

…… They studied the hearing of lungfish and salamanders by measuring auditory nerve signals and neural signals in the brainstem as a function of sound stimulation at different frequencies and at different levels. Surprisingly, the measurements showed that not only the terrestrial adult salamanders, but also the fully aquatic juvenile salamanders – and even the lungfish, which are completely maladapted to aerial hearing – were able to detect airborne sound despite not having a tympanic middle ear. By studying the animals’ sense of vibration, the researchers were able to demonstrate that both lungfish and salamanders detect sound by sensing the vibrations induced by sound waves. …..

My experience in the engineering world suggests that there must be a connection  – a feedback loop – between the “software” interpreting the signals in a brain and the development of the transducers generating the signals. For example, rotating equipment (turbines, compressors or pumps) are routinely plastered with pressure and temperature and stress (really just pressure) sensors. But the 4 – 20 mA signals they generate have to be interpreted by software in a brain. Over the last 40 years I have observed that simple interpretation software has led to improved (more focused and more accurate) sensors which has in turn given even more sophisticated software.

And so it must have also been with our senses. Primitive brains must have interpreted some “sound waves” picked up incidentally as “sound”. Some feedback loop must have then provided the impetus for the evolution of a “sound detector”. The improved sensor would then have increased the sophistication of the interpretation in the brain and given rise to further development of the sensors. Today our ears detect pressure waves of frequency between 20 and 20,000 Hz and convert them into electrical nerve signals interpreted by the brain as sound. Evolution is really not about pro-active selection of advantageous characteristics but of deselection of those not fit enough to aid survival. Evolution has nothing to do with the selection of the “best” or even of the “fittest” characteristics but is all about deselection of those having an insufficient fit. Of course in a competitive environment between individuals, those with “advantageous characteristics” would surely have helped in the culling – directly or indirectly – of the less fit. But that begs the question as to why we cannot hear ultrasound? Was the ability to hear ultrasound of no survival benefit? Was it too much for the “software”? Or was the audible range just a compromise between range on the one hand and intricacy of the sensor on the other?

There must have been a similar start to the development of sight. The incidental or accidental detection of certain frequencies of electromagnetic radiation must have led to a feedback loop between the interpretation software in the brain and the development of suitable sensors. And now our eyes detect electromagnetic radiation of frequency between 430 and 790 terraherz (TH) and convert them into electric signals which are sent to the brain for interpretation. We find benefit in cameras which can “see” uv and infrared light. But it is not an ability that has evolved in our eyes.

I begin to think that in considering evolution we must distinguish between external forces which direct the death of unfit species (environmental changes mainly) and the internal forces within the individuals of a species which leads to “deficient” individuals being “deselected”. And the feedback loop between the brain and our sensory organs – which is no doubt still operating – is probably one such internal force.

To put it crudely, our ears and our eyes are as good as they are because those individuals who had worse ears or eyes could not survive to reproduction. And our ears and eyes are not any better than they are because being any better does not contribute to any increased survival and reproduction.

Sensory and evolutionary deficiencies

August 18, 2014

What shapes our bodies? We can only sense what our shapes permit but are our shapes a result of the survival advantages of what we can sense? Certainly there is much of the physical world that we cannot sense directly – but which we can sense by the instruments we have crafted.There may be many things we don’t even know about which are outside the range of our senses and our instruments (lumped together as extra-sensory things and the source of much speculation and much fraud). Our view of the world and of physical reality is totally dependent upon our senses and what we can perceive directly or through our instruments. Even what we can imagine is limited (a la Rumsfeld) to areas that we know we don’t know. But we cannot even conceive of – let alone imagine – what we don’t know we don’t know.

But why are the ranges of what can be detected by our senses limited to what they are? As hunter-gatherers surely it would have been of survival advantage to see in the dark at least as well as the big cats that were our predators. We must – before agriculture – have had the ability to track our prey. Did humans have a more acute sense of smell then, in the distant past? Did we once use smell as a communication tool as some animals apparently do? Has our sense of smell deteriorated as we have developed as an agrarian society. We can feel minute changes of heat flow on our skins but we cannot “see” thermal images with our eyes. Is there no survival advantage in seeing further into the ultra-violet or the infra-red? Why is our ability to hear high frequency sounds so much inferior even to animals we have domesticated?

There is also a fundamental difference between our ability to perceive some sensory inputs and our ability to generate such sensory signals. We can make as well as detect sounds. We can see certain wave-lengths of reflected radiation but we are not luminescent. Our olfactory sense can detect some trace chemicals but we cannot generate smells at will. Taste buds taste but cannot generate tastes.

It is now thought that humans have many more than just the five traditional “Aristotelian” senses of sight, hearing, touch, taste and smell. Nowadays some recognise pressure, itch, balance, thermoception, proprioception, pain, magnetoception and perhaps even chronoception (the ability to discern passage of time) as being human senses. We can even perhaps sense the force of gravity. If our inherent senses were powerful enough and varied enough, we would not need any instruments. What we cannot detect because our senses are limited could well be called sensory deficiencies, but whether these are evolutionary deficiencies or not depends upon whether the lack of capability could have provided some survival advantage.We can measure brain waves in a fashion with our instruments but we don’t always know what they mean. The existence of an instrument to measure something is itself evidence of a sensory deficiency. But what an instrument can measure we can also imagine some organ may be able to sense.

There are some who point to the evolution of the eye as some kind of proof of Intelligent Design. But it is actually the reverse. Human eyes actually see a very small part of the spectrum available to be discerned. Compared to what it could be, vision is a key area of sensory deficiency. Electromagnetic radiation exists in the range from gamma rays having a wavelength of 0.1 Angstrom (10−11 m  corresponding to a wavelength of 1019 Hz) all the way up to long wave radiation with a wave length of about 1,000 m and a frequency of 100,000 Hz. Within this range we find radio waves (wavelength 50 cm – 10 m), microwaves and radar (between 1cm – 10 cm wavelengths), infra-red (between 1 μm and 1 mm), “visible light” (between 360 nm to 720 nm), ultra-violet (20 nm to 100 nm) and X-rays (0.2 nm to 1 nm). The gases in the Earth’s atmosphere prevents much of the electromagnetic radiation from reaching the surface. But the atmosphere is virtually transparent in 3 main bands

  1. an “optical window” including the visible spectrum along with the near uv and near ir regions,
  2. a partial infra-red window, and
  3. a radio wave window
emr windows - based on wikimedia

emr windows – based on wikimedia

There is some reason therefore for life on earth to develop senses which take advantage of these windows to detect the electromagnetic radiation that passes through the atmosphere and bombards the earth. Yet no animal can detect all radiation just in the “optical window”. Some of the infra-red radiation can be detected as warmth on the skin. Bats can both see and emit along the radar bands but not at longer radio wave-lengths. Humans are virtually blind in the top two windows.

daffodil in visible and UV light image Dr. Mccarthy

daffodil in visible and UV light image Dr. Mccarthy

Even within the optical window, the range of wave-lengths that are “visible” to humans is much narrower than the range visible to all animal-life. Pollinating creatures (bees and butterflies), for example, see well into the ultra-violet. The colours and patterns on flowers look quite different in ultra-violet light. They appear like landing lights to guide the pollinator “home”.While the picture on the right above is exclusively in uv light, an extended range of human visibility would lead to “seeing” some combination of the two pictures above. And so it would be if we could see further into the infra-red as well. We would need non-existent – but imaginable organs, to sense radiation within the other two windows.

Whether or not an extended range of vision could have helped humans better to survive, it is apparent that human vision is – compared to what is possible in the animal world – deficient. Compared to what is there to be “seen”, we see only a tiny fraction. It is highly unlikely that having an extended range of vision would have been a disadvantage in the survival stakes. It may not have provided a critical advantage but it still remains a sensory and an evolutionary deficiency!

Humans also lack the organs which allow bats to be radar receivers and emitters. A deficiency. We lack the organs that allow sharks to detect electric currents or birds to detect and navigate along magnetic lines of force. Our olfactory senses are far inferior to that of most animals. Dogs may be able to smell cancer cells but we can’t. Our hearing of high frequency sounds is also much inferior to that of most animals. All deficiencies. Humans do very well with low frequency sounds and perhaps only elephants and the largest of whales can generate and hear lower pitched sounds than humans can. We do not have the senses to even discern what some of our instruments measure.

For every human sense, and comparing only with the range exhibited by other life on Earth, our range of detection is deficient. There is no instance where the range of a human sense represents the entire range available within the animal world. Clearly, with a greater sensory range, humans could be much more capable – inherently – of discerning the world around them than they actually are.

Evolution of course is not about excellence. It is not even about the survival of the fittest. It is just the result of the demise of the unfit and therefore represents the minimum required to survive. Evolution is not about being “best” but only about being “good enough”. Evolution therefore sorts out individuals with sensory deficiencies when they are debilitating and prevent survival but evolution does not – except by accident – lead to an increase in a sensory range.

Natural de-selection which has dominated evolution so far is essentially without direction and is not a “selection for excellence”. Now as artificial selection comes into play, it becomes possible for humans – for the first time ever – to consider the direction to be taken for the development of future humans. This is the stuff of Frankenstein and Dr. Moreau and other evil genetic manipulators. Nevertheless I wonder which senses I would want/desire to be improved or enhanced or even created. (Though I would prefer that the deterioration of senses with age be addressed first).

Vision: I would quite like to have a much better night vision sensitivity together with some further range into the infra-red (but perhaps not much further into the uv range). I exclude Superman like X-ray vision as being too far removed from the optical window. To be able to “light-up” whatever I was looking at – say within 1 m – would require some new organ of luminescence which may be asking for too much.

Sound: A slightly larger range of hearing into the high frequency bands is, I think, to be desired. At least so I can hear what a dog hears. This would change human music and musical instruments quite drastically. I don’t think I want a more acute hearing sense (we are surrounded by enough noise as it is) but I would like to be able to hear a greater range of sounds than I can produce.

Magnetoception: It would have been a boon for explorers 500 years ago if they had had an innate sense of magnetic north. As we go out away from earth, humans will be exploring again and being able to discern lines of magnetic force without relying on instruments could well come in useful.

I have no great desire for enhancing the sense of touch or of smell. They are fine as they are and I see no clear benefits in their enhancement. But a new organ of extra-sensory perception (esp) to pick up the brain waves of others could be very handy. In its simplest form it would just detect when somebody was lying or some kind of “empathy” level being broadcast. But in its most evolved form it could be what is so beloved of science fiction writers. An organ that allowed mind-to-mind contact would lead to a profound paradigm shift in communication between humans which would rival the introduction of speech and language.

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