Lecture IV: Major Points. 10/11. - University of Arizona IV Summary.pdf · Lecture IV: Major Points. 10/11. 1. 1st reviews of The Origin emphasized the deficiencies one might expect

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Lecture IV: Major Points.

10/11.

1. 1st reviews of The Origin emphasized the deficiencies one

might expect.

a. Limited variability in modern species.

b. No examples of species in process of being created.

c. No transitional forms1

d. Cambrian “explosion.”

e. Structures that only work when fully formed.2

f. Consistency ≠ proof – e.g., homology, development.

g. Conflict with religion.

1 Archaeopteryx first described by Owen (1863a; b), who declared it unequiv-ocally to be a bird. See Wellnhofer, P. (2010. Pp. 237-250, In, Moody, R. et al. (eds) Dinosaurs and Other Extinct Saurians. Geol. Soc. London. Spec. Publ. 343) for description of all known specimens and interpretations. 2 “Irreducible complexity” in contemporary parlance.


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2. Noteworthy Reactions:

a. Owen (1860)

i. Origin one of many at-

tempts to grapple with

the species problem.

ii. A few new facts; the rest

speculation.

b. Sedgwick (Letter to CD)

“a machinery as wild … as

Bishop Wilkin’s locomotive that

was to sail with us to the Moon.”

c. Herschel:

i. “law of higgledy-pigglety.”

ii. ”with some demur as to the

genesis of man”

d. Carpenter: “new ideas which have served for the colligation of

facts.”

First page of Richard Owen’s (1860. Edinburgh Rev. 3: 487-532) anonymous review of The Origin and other works.


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3. Science vs. Religion.

a. Bridgewater Treatises: Five of Eight authors divines; the

rest committed to natural theology to varying degrees.

b. Persistent clerical / Oxbridge[3] antipathy to DwM.

c. But this not the whole story.

i. Jenkin, Darwin’s most effective critic, an atheist.

ii. Some clerics endorsed creation by law: Kingsley,

Powell, Essays and Reviews

iii. E&R authors included Frederick Temple who later

became the Archbishop of Canterbury.

iv. Darwin himself buried in Westminster Abbey.

v. Apparent errors in The Origin allowed opponents to

criticize on scientific grounds.

d. The conventional telling of the Huxley-Wilberforce “de-

bate” may be history written by the victors.

3 The professors were mostly Anglican clerics.


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10/16.

1. Scylla and Charybdis.

a. Like Hutton and Lyell before

him, Darwin assumed pleni-

tudes of time and variation as

evidenced by his

i. Overly generous esti-

mate of the age of Creta-

ceous Weald strata

ii. 1857 Letter to Asa Gray

b. But by 1870, CD was having

to grapple with paucities of

both.

i. Antithetical to the gradual

transformation of species

by selection of variations

of small magnitude.

ii. Resulting doubts contrib-

uted to so-called “Eclipse of Darwinism”

Formation of the Weald by uplift and erosion. Bottom. In late Cre-taceous times. Top. Today. By Mole Valley Geological Society. (http://www.mvgs.org.uk/up-liftanderosion.html)

http://www.mvgs.org.uk/upliftanderosion.html

http://www.mvgs.org.uk/upliftanderosion.html


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The Weald. Chalk refers to upper Cretaceous strata overlying older de-posits. Reproduced from Burchfield (1974).


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South Downs Chalk meets the sea. Shown here are the so-called “Seven Sisters” cliffs near “Beachy Head” on the preceding page


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2. William Thomson (Lord Kelvin)

a. Co-discover of 2nd Law of Thermodynamics – absent con-

tinuing inputs of energy / materials, machines run down.

b. Calculated 28-100 m.y. for earth to cool from molten state.

c. Obtained comparable estimate for age of the sun assum-

ing its heat derived from gravitational collapse.

3. Kelvin was

a. Britain’s most famous scientist.

b. Religious – “strong proofs of intelligent and benevolent

design”, but

i. 1st writings on earth’s age antedate The Origin.

ii. Quarrel, at least initially, with uniformitarian geology.

iii. Imagined earth seeded by meteoric remnants from

“the ruins of another world”.

4. Kelvin’s estimates dominated age of earth discussions until

the discovery of radioactivity and radiometric dating.


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5. Kelvin and the Geologists

a. Having struck his estimate from 3rd edition of The Origin,

Darwin now sought to “speed things up”. Meanwhile,

b. Kelvin and his mathematical allies successively reduced

the original maximum grant of 100 m.y. to 10 m. y.

c. Geologists began producing their own estimates based

on geological processes – with results more or less con-

sistent with Kelvin’s maximum grant.

d. Huxley

i. Questioned Kelvin’s assumption that earth initially mol-

ten (“What you get out depends upon what you put in”)

ii. “Biology takes her time from geology”

6. Ironically, there was considerable geological resistance to

radiometric extension of geological time scale:

a. Impossibly long.

b. Inconsistent with geological estimates.


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7. Reconciliation of cooling calculations & deep time proposed

by Perry (1895). Kelvin’s model wrong on 3 counts:

a. Conductivity of rocks increases with temperature.

b. Increasing density with depth => more iron => better heat

conduction from core to periphery.

c. Most important: If earth’s in-

terior even partially fluid, con-

vection will greatly increase

rate of heat transfer

8. Jenkin

a. Engineer, business associate (cable laying) of Kelvin’s

and essayist.

b. An atheist most of his life, but took communion at the end.

c. His 1867 review of The Origin caused Darwin considera-

ble grief both by virtue of

i. Jenkin’s own arguments

ii. Public promotion of Kelvin’s calculations.


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9. Among Jenkin’s arguments:

a. Loss of variability consequent to blending inheritance and

exhaustion by selection.

b. DwM works if sports (Darwin’s “single differences”) breed

true, but Darwin’s theory not one of saltation.

c. Patterns of similarity do not necessitate successive deri-

vation – e.g., chemical elements, human inventions.

d. Correlation of parts (Cuvier); adaptive “fairy tales”.

e. Justified his right to an opinion regarding “pure reason” as

opposed to factual claims, the validity of which could only

be assessed by specialists.

10. Additions to the final edition (1872) of The Origin.

a. Single variations rarely perpetuated.

b. Individual variations induced en masse by environment.

c. Inbreeding.

d. Faster rate of evolution way back when.


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11. Darwin also placed increased reliance on use and disuse.

12. Pangenesis.

a. “Gemmules” produced by all tissues – hence the “pan”

and circulate through the body.

b. Modified by organism’s activity and environment.

c. Return to the reproductive organs, incorporated into the

sex cells and determine offspring development.

13. Darwin believed that pangenesis could account for

a. Variability

b. Blending inheritance.

c. Inheritance of acquired characters

d. Atavisms.

e. Concordant variation en masse which he now required.

14. Historical note: Pangenesis antedates Jenkin’s review.

Traces 1840-41 according to Hodge (1985).


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10/18.

1. The 20th century would restore variation and time: the for-

mer by particulate inheritance; the latter by radiometric

dating.

2. Meanwhile, the case for DwM strengthened by advances in

a. Anatomy.

b. Embryology.

c. Paleontology especially – e.g., the “dawn bird”, Archae-

opteryx.

3. While The Origin pretty much settled matters RE DwM, ac-

ceptance of the selection theory lagged.

4. Huxley a good example.

a. NS might be a vera causa, but was it sufficient? Probably

not. No examples of species having been created

thereby.

b. Likewise, his opinion of gradualism.


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c. His own research equally if not more heavily influenced

by German idealism, especially as manifested in the work

of Ernst Haeckel. Emphasized

i. Neo-platonic archetypes

ii. Inheritance and modification of body parts.

iii. Recapitulation – i.e., phylogeny reflects development.

d. Huxley nonetheless contributed greatly to the case for

DwM:

i. Equivalence of ape – hu-

man anatomy.

ii. Dino-bird connection: Ar-

chaeopteryx, Compsogna-

thus.

iii. Darwinian takeover of Brit-

ish science.

Compsognathus a carnivorous dinosaur believed close to the origin of birds by THH.


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5. Owen likewise attached to archetypes.4

a. Accepted but did not emphasize, DwM / creation by law.

b. Rejected the selection theory. Regarding the Aye-aye’s

specializations opined (1863c) that “Darwin seems to be as far

from giving a satisfactory explanation … as Lamarck.”

6. Huxley-Owen antagonism rooted in animus. Thus an unan-

swered request for recommendation provoked the following:

“I was going to walk past, but he stopped me, and in the blandest and

most gracious manner said, ‘I have received your note. I shall grant it.’

The phrase and the implied condescension were quite ‘touching,’ so

much that if I stopped for a moment longer I must knock him into the

gutter. I therefore bowed and walked off.” [Gross, 1993, 406]

7. Neo-Darwinism.

a. Emphasized selection to exclusion of other mechanisms,

IAC in particular.

b. Rejection of IAC; compatible with August Weismann’s

germ plasm theory – sequestration of germ.

4 With the acceptance of evolution, archetypes became ancestors.


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8. Biometrical School.

a. Statistical study of Darwin’s individual differences.

b. Reversion to the mean precludes indefinite departure

from an original type by the gradual accumulation of small

variations.

c. New types require saltation – Galton’s polygon.

d. Not surprising that biometry closely linked to eugenics.

i. Traits such intelligence, sobriety, etc., vary continu-

ously.

ii. Biometricians believed that such traits can and should

be selected for to benefit the human race.

e. Biometrics evolved into quantitative genetics where

genes exist but only “in back of the blackboard”.


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10/24.

1. Neo-Lamarckism.

a. Most widely accepted in North America – Cope, Marsh.

b. British neo-Lamarckians included Herbert Spencer who

promoted a law of universal progress similar to the Law of

Development enunciated in Vestiges.

c. Emphasized

i. Orthogenesis - inherent tendency to evolve in prede-

termined direction – often, but not always, progressive

– compatible with “directed” evolution, i.e., divine pur-

pose.

ii. IAC

Widely replaced by Mendelian genetics prior to WWII


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2. Summing Up.

a. Immediate responses to selection theory:

i. Discontinuities in the fossil record.

ii. Irreducible complexity.

iii. Law of higgledy-pigglety.

iv. Insufficient time.

v. Loss of variation due to blending.

b. Later responses.

i. Apparently non-adaptive characters – those that dis-

tinguish related species, in particular (Romanes).

ii. Orthogenetic trends – horses, brontotheres.

iii. Mal-adaptive evolution (presumed consequence of

“evolutionary momentum”); racial senescence – e.g.,

Gryphaea, Megaloceros) – in which regard concept of

allometry introduced.


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c. Rising intensity of opposition to Darwin as the century

neared its end may have been consequent to

i. Conversion of the scientific community to evolution

gave Darwin an initial leg up.

ii. Continuing theistic concerns.

iii. Emerging specialization reinforced rival opinions that

spoke to discipline-specific concerns.

iv. Emergence of biology as an experimental laboratory-

based science – the study of heredity, in particular.

3. More generally

a. Both immediate and delayed response to Darwinism in-

volved long standing disputes:

i. Nature of change: Continuing directional change vs.

steady state or recurrent cycles.

ii. Agents of change: External (IAC / selection) vs. inter-

nal (force vitale),

iii. Tempo: gradual vs. abrupt.


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b. In Kuhnian terms, collapse of pre-evolutionary paradigm

released scientists from the shackles of the prevailing par-

adigm that insisted on the compatibility of God’s two

Books.

4. 19th century ideas now discarded.

a. Orthogenesis.

b. Evolutionary momentum; racial senescence.

c. Neo-Lamarckism.

5. Ideas incorporated into the Modern Synthesis.

a. DwM.

b. Divergence; branching; tree of life.

c. Gradualism.

d. Isolation as speciation facilitator.


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6. Ideas initially de-emphasized / dismissed but subse-

quently resurrected / reconsidered.

a. Influence of the conditions of life (mutagenesis, reaction

norms, transgenerational effects, etc.)

b. Limits to variation (developmental constraints / toolkits,

baupläne, “spandrels,” etc.)

c. Saltations (pseudogene resurrection, punctuated equilib-

ria; mass extinctions).

d. Inherent tendency to progress – positive feedback be-

tween size and complexity.

7. From Darwin to Mendel and Back.

a. Mendel’s elementen rediscovered around 1900 initially in-

terpreted as basis for salutatory change.

b. Supported by de Vries’ Oenothera experiments in which

crossing over in a system with balanced lethals leads to

new chromosomes and the abrupt appearance of novel

forms.


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c. Exceptions to Mendel’s law of independent assortment –

consequence of crossing over – made possible the con-

struction of 1st genetic maps.

8. Demise of new saltation theories consequent followed

Fisher’s 1917 proposal that inheritance of quantitative

traits – Darwin’s individual differences – polygenic.

9. Made possible the Modern Synthesis.

a. Fundamental theorem of NS.

b. Adaptive topographies and Wright’s shifting balance

theory.

c. Synthesis equated evolution with changing gene fre-

quencies:

i. Mutation

ii. Selection

iii. Migration

iv. Drift


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d. Subsequently incorporated:

i. Systematics –theory of allopatric speciation (Mayr)

ii. Selection in nature (Ford, Dobzhansky).

iii. Paleontology (Simpson).

iv. Development (developmental toolkits)

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Lecture IV: Major Points. 10/11. - University of Arizona IV Summary.pdf · Lecture IV: Major Points. 10/11. 1. 1st reviews of The Origin emphasized the deficiencies one might expect