2017-10-04 14:12:59

Prelude

Prelude

Today's Topics

  • The evolution of the nervous system

Public acceptance of evolution

Types of evidence

  • Fossil
    • Fossil dating
  • Geological
    • Where fossils are found relative to one another
    • How long it takes to form layers
  • Genetic
    • Rates of mutation
  • Anatomical

Dobzhansky

  • "Nothing in Biology Makes Sense Except in the Light of Evolution"

(Dobzhansky 1973)

Dobzhansky

"Seen in the light of evolution, biology is, perhaps, intellectually the most satisfying and inspiring science. Without that light, it becomes a pile of sundry facts some of them interesting or curious, but making no meaningful picture as a whole."

(Dobzhansky 1973)

Why Gilmore thinks it's controversial (in the U.S.)

  • Contradicts verbatim/non-metaphorical reading of some religious texts
  • Makes humans seem less special
  • Time scales involved beyond human experience
  • Scientific method vs. other ways of knowing
  • Found in nature ≠ good for human society

Why Gilmore thinks it's controversial (in the U.S.)

  • Few negative consequences of 'disbelief'
  • U.S. culture individualistic, skeptical, anti-elitist
  • Lower levels of religious belief among U.S. scientists
  • Politics

Ontogenesis and phylogenesis

  • Ontogenesis
    • Development within lifetimes, history of individuals
  • Phylogenesis
    • Change across lifestimes, history of species

Ontogeny does not recapitulate phylogeny (Haeckel), but…

Complex multicellular life emerged "recently"

Time scales

Nervous system architectures

An animal with a nerve "net"

How nervous systems differ

  • Body symmetry
    • radial
    • bilateral
  • Segmentation
  • Cephalization (concentration of sensory & neural structures in anterior portion of body)
  • Encasement in bone (vertebrates)
  • Centralized vs. distributed function

Cephalopods have "intelligent arms"

Biological imperatives

  • Ingestion
  • Defense
  • Reproduction

Information processing schematic

Information processing universals

  • Sense/detect
    • Sensors
  • Analyze, evaluate, decide
  • Act
    • Effectors
    • e.g., approach/avoid, manipulate, ingest, signal

Sensors

  • Specialize by information source/type
  • Specialize by target location
    • Interoceptive
    • Exteroceptive

Analysis, evaluation, decision

  • Current state
    • World
    • Organism
  • Current goals
  • Past state(s)

Effectors

  • Move body
  • Send signals
  • Change physiological state

From nerve net to nerve ring, nerve cord and brain — evolution of the nervous system (Arendt, Tosches, and Marlow 2016)

(Arendt, Tosches, and Marlow 2016)

(Arendt, Tosches, and Marlow 2016)

Take homes

  • Neurons and nervous systems 520-570 M years old
  • Similarities at molecular level in how diverse nervous systems develop

Similarities in overall vertebrate CNS organization

Variation in overall brain mass/body mass

Evolutionary trends in cortical size

Evolutionary trends in cortical size

Evolutionary trends in cortical size

Evolutionary trends in primate brain size

Take homes

  • Brain sizes scale with body size
  • Brain sizes scale with animal class (more or less)

Old story

  • Within mammals, human brains bigger than expected
    • Higher encephalization quotient
  • Humans have larger cerebral cortical gray + white matter than comparable mammals

New story

  • Does brain size/mass matter (that much)?
  • "Size matters" (brain mass) presumes similarity among brains at micro-level
  • Big (large mass) brains arise in multiple animal lineages

New story

  • # of cortical neurons more important difference than brain mass
  • The primate advantage -> more cortical neurons, but not larger neurons
  • Human brain just scaled up (non-ape) primate brain

# of cortical (or in birds, pallidum) neurons predicts "cognition"?

The Human Advantage (Herculano-Houzel 2016)

  • More neurons in cerebral cortex than other animals, but not disproportionately so
  • Less time spent foraging
    • Higher quality/more energetically dense food
    • Higher food availability
    • Cultural factors (agriculture + cooking)
    • See also (Wrangham 2009)

A further human advantage

Next time…

  • How ontogeny reflects phylogeny
  • Brain development

References

Arendt, Detlev, Maria Antonietta Tosches, and Heather Marlow. 2016. “From Nerve Net to Nerve Ring, Nerve Cord and Brain — Evolution of the Nervous System.” Nature Reviews Neuroscience 17 (1): 61–72. doi:10.1038/nrn.2015.15.

Dobzhansky, Theodosius. 1973. “Nothing in Biology Makes Sense Except in the Light of Evolution.” The American Biology Teacher 35 (3). University of California Press on behalf of the National Association of Biology Teachers: pp. 125–29. http://www.jstor.org/stable/4444260.

Herculano-Houzel, Suzana. 2016. The Human Advantage: A New Understanding of How Our Brain Became Remarkable. MIT Press. https://market.android.com/details?id=book-DMqpCwAAQBAJ.

———. 2017. “Numbers of Neurons as Biological Correlates of Cognitive Capability.” Current Opinion in Behavioral Sciences 16 (Supplement C): 1–7. doi:10.1016/j.cobeha.2017.02.004.

Hofman, Michel A. 2014. “Evolution of the Human Brain: When Bigger Is Better.” Frontiers in Neuroanatomy 8 (March). doi:10.3389/fnana.2014.00015.

Miller, Jon D, Eugenie C Scott, and Shinji Okamoto. 2006. “Public Acceptance of Evolution.” SCIENCE-NEW YORK THEN WASHINGTON- 313 (5788). American Association for the Advancement of Science: 765. doi:10.1126/science.1126746.

Northcutt, R Glenn. 2002. “Understanding Vertebrate Brain Evolution.” Integr. Comp. Biol. 42 (4): 743–56. doi:10.1093/icb/42.4.743.

Rakic, Pasko. 2009. “Evolution of the Neocortex: A Perspective from Developmental Biology.” Nature Reviews Neuroscience 10 (10). Nature Publishing Group: 724–35.

Wrangham, Richard. 2009. Catching Fire: How Cooking Made Us Human. Basic Books. https://market.android.com/details?id=book-ebEOupKz-rMC.