Download Human Nature

F. Ayala Human Nature
• U.C. Irvine biologist
• Past President of AAAS
• Genetics, evolution, philosophy of science
In God’s Image
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We are like other apes
We are unlike other apes
Cultural as well as genetic inheritance
Cultural evolution much faster
Genes make us able to be ethical
Culture (inc. religion) provides the code,
norms
Hominid Species
• "Hominid" refers to members of the family
Hominidae, which consists of all species on
our side of the last common ancestor of
humans and living apes.
• Hominids are included in the superfamily of
all apes, the Hominoidea, the members of
which are called hominoids.
Human phylogeny
• Diverged from chimp line 5-7 Mya
• By 1.8 Mya, Homo erectus
• Other, older hominids too: not all on lineage to
Homo sapiens
• H. erectus spread outside Africa
• H. sapiens (archaic) ca. 400,000 years ago
– no clear dividing line between late erectus and archaic
sapiens
• H. sapeins neanderthalensis 200,000 years ago
until 30-40,000 years ago - coexisted with H.
sapiens. Mostly lived in cold climates. Buried
Homo sapiens sapiens (modern)
• First appear about 120,000 years ago.
• About 40,000 years ago, with Cro-Magnon
culture, tool kits more sophisticated. Art, music.
• Within the last 100,000 years, trends towards
smaller molars and decreased robustness
continuing.
– The face, jaw and teeth of Mesolithic humans (about
10,000 years ago) are about 10% more robust than
ours.
– Upper Paleolithic humans (about 30,000 years ago)
are about 20 to 30% more robust than us.
How did H. sapiens arise?
• Multiregional hypothesis: occurred in
various places
• Others think only happened once, in Africa
– Ayala favors this view
• “Mitochondrial Eve” a gene geneology
• How small a bottleneck ? - at least several
thousand individuals, not just two or a few
How are humans unique today?
• Anatomy
– Erect posture, bipedal gait (came first)
– Large brain (came later)
– Brain organization also different (large cortex)
How are humans unique today?
• Behavior
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Abstract thinking
Subtle expression of emotions
Symbolic (creative) language
Awareness of self, death
Science, humanities, ethics, religion
Cultural inheritance and
evolution
• Different than biological evolution
– More rapid
– Can be directed
• Transmission of experience to next
generation
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Fire
Clothing
Tools
Transportation
What about ethics? Like
language ...
• Capacity, proclivity, is biological
• Moral norms, codes, however, are cultural
What does he mean by ethical
capacity?
• Can anticipate consequences
• Can make value judgements
• Can choose between alternatives
Ayala rejects sociobiologists
thesis
• Grants a correspondence, isomorphism, in
consequences of moral behavior.
• Rejects thesis that the causes of human
moral behavior are products of natural
selection.
V. Elving Anderson
• Clinical, medical, human geneticist
• Past President of Sigma Xi
• Gene mapping research
From puppet to Prometheus
• Old genetic fatalism replaced by . . .
• New fears of “playing God”
What’s special about human
genes?
• No one “human” gene or genes
• 98.4% genetic identity with chimps
• Allelelic variation and expression of some
genes may be different from that in nonhuman primates
Development of human behavior
• Most is plastic, not stereotyped or
instinctive
• Inherit a range of reaction, behavior, based
on genes
• Environment and experience determine
actual behavior within that range
Twin studies show correlations
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Highest for physical traits
Mental ability next
Personality next
Interests least correlated
Some basics of gene expression
• Genes act together in networks
• Genes interact with environment,
experience
• Gene action on behavior is indirect
What about IQ ?
• 0.15 attributable to non-shared experiences
• Shared experience component declines with
age
– 0.30 from 4-20 years of age
– zero among adult twins
• Genetic component rises in replacement
– 0.51 from 4-20 years of age
– 0.80 among adult twins