Download Darwinlecture_files/Darwin slides copy

Darwin and the biological determinant of behaviour
Aristotle’s Natural State Model
The difference between a dachshund and a
greyhound, for Aristotle, lay only in deviations
from a true type that both kinds of dog were
unable to fully express because of interfering
forces.
Variation is a kind of noise that has to be seen
through to arrive at the ideal type underlying the
differences between members of a species.
For Darwin, variation between individuals was
the key to evolution of species.
…any variation, however slight and from
whatever cause proceeding…will generally be
inherited by its offspring ... I have called this
principle, by which each slight variation, if useful,
is preserved, by the term of Natural Selection.
Darwin was influenced by Locke
Names of biological objects were invented by
human beings for the purpose of communication;
they should not be taken to refer to genuine
essences that exist in the natural world.
Erasmus Darwin argued that what has been
referred to as instinct in animals could be
understood as arising from experience and
learning.
The Origin of Instincts
(Instinct)...is...acquired like all other animal actions, that are
attended with consciousness, by the repeated efforts of our
own muscles under the conduct of our sensations or
desires’.
Learning can take place in the fetal environment prior to
birth.
The ability of a newly hatched chicken to walk could
also be accounted for by assuming that the fetus
engaged in repeated swimming and kicking movements,
so that the chicks’ have considerable practice before
their birth in their ‘manner of walking....and hence
accomplish it afterwards with very few efforts’.
Lamarck’s Theory of Evolution
There are two reasons for paying special attention to
Lamarck. First, he emphasized the importance of behaviour
itself as the agent of evolutionary change.
Lamarck informed his students that he
‘could prove that it is neither the form of the body nor
of its parts that gives rise to the way of life of animals,
but that to the contrary, it is the habits, the way of life,
and all the influencing circumstances that have over
time constituted the form of the body and of the parts
of animals’.
It is biological need, according to Lamarck, rather than will or
volition that leads to behavioural and ultimately physical
changes.
Animals have sensations generated by physical needs that lead
to actions. The outcome of this behaviour may be either
beneficial or harmful to the creature.
Habits were acquired in the repeated fulfillment of basic
biological needs like eating, catching prey, avoiding predators,
mating and so on.
As environments changed over time, animals acquired new
habits in response to their biological needs.
These learned behaviours resulted in animals using some
organs more and some less than they previously did.
The acquired behaviour patterns produced small physical
and cognitive changes that were passed on to the next
generation. As time progresses. these changes
accumulated over generations to result in new species.
One may perceive that the bird of the shore, which
does not at all like to swim, and which however needs
to draw near to the water to find its prey, will be
exposed to continual sinking in the mud. Wishing to
avoid immersing its body in the liquid, it acquires the
habit of stretching and elongating its legs. The result of
this for the generation of birds that continue to live in
this manner is that the individuals will find themselves
elevated as on stilts, on long naked legs.
Lamarck’s idea of
evolution by ‘willing’ is
absurd.
This description of Lamarckian theorizing is incorrect,
however. It is biological need, according to Lamarck, rather
than will or volition that leads to behavioral and ultimately
physical changes.
‘In every frequently repeated action, especially those that become habitual,
the subtle fluids producing it carve out and progressively enlarge, by the
repetition of particular displacements that they undergo, the routes that
they have to pass through, and render them more and more easy’.
cells that fire together wire together.
However, renewed interest in Lamarck is that
some of his thinking is consistent with recent
developments in our understanding of the effect
of behaviour on species change.
Darwin’s theory of how instincts develop was based
on the notion that any learned action will become
habitual with enough practice. By some unknown
mechanism (and this is the weak part of his
argument, as well as Lamarck’s), habits ‘...whether
congenital or acquired by practice often become
inherited’.
How might a learned behaviour
eventually become an instinct?
From “Evolution in four dimensions”
by Eva Jablonka and marion j. lamb
But could instincts evolve by natural selection?
In other words, could learned behaviour (acquired during the
lifetime of an individual) somehow be transferred by natural
selection to the individual’s children?
The earliest attempt to develop such
an explanation was published by a Scottish biologist, Douglas
Spalding in 1873.
Here is the scenario creatively imagined by Spalding.
Notice two important features of this
story:
1) Mr. Crusoe selected for the best learners -- parrots that needed
to hear the utterance fewer times than their
ancestors to learn it.
So little learning was required after many generations that
behaviour was virtually inborn.
2) Another feature of the story is the emphasis on a second
Darwinian mechanism.
The second feature is sexual selection. Parrots had acquired
a taste for language utterances, and good speakers were
more likely to be chosen as mates. A parrot could enhance
its reproductive success by producing clear English.
Imagine a population of song birds in which the young have to
learn their song from adults.
Now imagine that a new type of predator emerges so that birds
are forced to sing less to avoid attracting the attention of the
predator.
The young will now hear the song less often and will have less
chance of learning it.
But assume that female birds continue to prefer good singers as
mates.
This will produce a strong preference in the population (due to
sexual selection) for birds that learn the song very quickly.
These birds will mate more successfully and produce more
offspring. some of these offspring may inherit their parent’s song
learning talent.
if both predation pressure and sexual selection persist over
generations, birds will occur many who need to hear very little
singing in order to learn their species-specific song.
The same argument applies to
the evolution of an instinctive fear response.
If young mammals have to learn from gradual experience how to
avoid a new predator, and learning exposes them to danger, the
fastest learners will be more likely to survive, and if this ability is
partly heritable, natural selection may eventually result in a fearavoidance response that requires so little learning as to be
“instinctive” .
Darwin on the evolution of morality
Our intellect, according to Darwin, was ‘a
modification of instinct -- an unfolding and
generalizing of the means by which an instinct is
transmitted’. Human intelligence arose when the
neural systems responsible for instinctive behavior
became more flexibly capable of dealing with
aspects of our world.
Are elements of human moral reasoning instinctive or
is this cognitive domain entirely determined by
experience and instruction?
Furthermore, are animals capable of moral
judgement? Darwin viewed our moral sense as
grounded in the kind of instincts that animals display
when (i) raising their offspring, (ii) seeking and
interacting with a mate or (iii) dealing with other
members of their group.
The development of conscience
‘Therefore I say, grant reason to any animal with social and
sexual instincts and yet with passion (..then...) he must have
conscience -- this is a capital view’
If conscience is based on instincts, our decisions may often
be determined by biological laws rather than free will.
‘Shake ten thousand grains of sand together and one will
be uppermost, so in thoughts, one will rise according to
law’, he wrote in one of his notebooks.
As Darwin wrote in frustration: ‘Neuters do
not breed! How is ...(this)... instinct acquired?’.
But after considering what can be done by artificial
selection, I concluded that natural selection might act
on parents, and continually preserve those which
produce more and more aberrant offspring, having
any structure or instinct advantageous to the
community.
It fortunately occurred to me to show several of the best plates,
without a word of explanation, to above twenty educated persons of
various ages and both sexes, asking them, in each case, ... what
emotion or feeling the ....(photograph depicted...); and I recorded their
answers in the words which they used….the most widely different
judgments were pronounced in regard to some of them.
. This exhibition was of use in another way, by convincing me how
easily we may be misguided by our imagination; for when I first looked
through Dr. Duchenne's photographs, reading at the same time the
text, and thus learning what was intended, I was struck with
admiration at the truthfulness of all, with only a few exceptions.
Nevertheless, if I had examined them without any explanation, no
doubt I should have been as much perplexed, in some cases, as other
persons have been.
Darwin assumed that emotional expressions have no
function and so confer no advantage to the survival of an
animal or its community.
The principle of associated habits.
Actions intentionally carried out, especially to stop an unpleasant sensation, may become routinely
associated with an emotional state. The action might then be automatically triggered when the emotion
is experienced.
The principle of antithesis
When certain actions were linked to a particular internal state, the contrasting mental state would tend
to evoke behavior that was also opposite.
Spilling over
The idea is that certain emotional expressions are the result of powerful nervous energy overflowing
into and thereby influencing the activity of other neural pathways. For example, trembling produced by
fear. According to Darwin, this kind of emotional response is ‘..of no service, often of much disservice,
and cannot have been at first acquired through the will, and then rendered habitual in association with
any emotion’.