Questions about Evolution
(re: rates and complexity)
contents of this page:
6D. Questions about Evolution
Fossils and Gradualism (neo-Darwinism
and Punctuated Equilibrium)
Questions from Supporters (of
evolutionary theory)
Questions from Critics (re:
Rates of Change, Irreducible Complexity)
plus an APPENDIX with ideas from Section 6F:
Questionable Criticisms of Evolution
Thermodynamics and Evolution
For two years, this was Section 6D in my Overview of Origins Questions. In 2002, Section 6D was streamlined and merged into other pages. Here is the original long version of 6D, with minor revisions:
6D.
Questions about Evolution
In an effort to achieve conceptual clarity, a previous
section (6B, which has been condensed and revised to form a new 6B-page, The
Process of Logically Evaluating Evolution and Creation) examined
some ways in which theories of creation agree and disagree with each other
and with a generic
theory of evolution (E). The
process of clarification continues in this section, with a recognition that
there is not a single theory of evolution,
but a range
of theories. All of these E-theories accept neo-Darwinian fundamentals,
such as those outlined in Section 6A-and-6B, but disagree about important details.
Fossils and Gradualism
Theories of old-earth
creation (oeC) agree with basic fossil-E,
but challenge a "total fossil-E" claim
that the fossil record provides strong support for Total Macro-E [which is
defined in the new 6B-page, which is linked-to above]. But
in the near future, perhaps the fossils won't provide conclusive support for
either
oeC or E. Why?
In principle, if a species that was quickly
created (by oeCi or oeCm) has a changed body structure, this historical discontinuity
in natural process might be observable in the fossil record.
In reality, however, finding strong observational
support for an oeC conclusion might be difficult because:
1) Some theories of E, such as punctuated
equilibrium E — which proposes that new species usually form relatively
quickly (on a geological time scale) in small populations — are consistent
with a "geologically sudden" appearance of new species in the fossil
record. Therefore, it could be difficult to distinguish between a fossil
record produced by natural-appearing punctuated equilibrium
evolution and
by miraculous-appearing old-earth creation by genetic
modification — i.e., creation by extensive modification
(by changing, adding, or deleting) of the genetic material for some members
(or
all members)
of
an
existing
species.
2) The fossil record is incomplete due
to the rarity of fossilization — which occurs only under special conditions,
with most animals and plants simply decaying after they die — so even if "links
between radically different species" were produced naturally and gradually,
these transitional forms might not be fossilized and observed. This
could make it difficult to distinguish between
a fossil record produced by gradual
evolution and by punctuated equilibrium evolution or old-earth
creation by genetic modification.
Therefore, it is difficult to distinguish
between an apparent gap (due to fossil data being incomplete) and a real gap
(due to an absence of the transitional intermediates proposed by neo-Darwinism).
But there seem to be good reasons, based on fossil evidence, to question a theory
of "evolutionary gradualism" proposing that most macro-E changes are
caused by a gradual accumulation of micro-E changes. These gradualist
theories have been challenged by some evolutionists, especially since 1972,
beginning with Niles Eldredge and Stephen J. Gould.
According to Gould, "The
extreme rarity of transitional forms in the fossil record persists as the trade
secret of paleontology [of those who study fossils]. The evolutionary
trees that adorn our textbooks have data only at the tips and nodes of their
branches; the rest is inference, however reasonable, not the evidence of fossils.
... The history of most fossil species includes two features particularly
inconsistent with gradualism: 1) Stasis. Most species exhibit
no directional change during their tenure on earth. They appear in the
fossil record looking much the same as when they disappear; morphological change
is usually limited and directionless. 2) Sudden appearance.
In any local area, a species does not arise gradually by the steady transformation
of its ancestors; it appears all at once and 'fully formed.' " (The
Panda's Thumb, 1980, pages 181-182)
In this statement, Gould is not challenging
Total Macro-E. He is questioning the plausibility of gradualist theories that claim Total Macro-E is mainly the result of slowly accumulating
micro-E changes. Instead, Gould proposes a theory of punctuated equilibrium
in which the fossilization of intermediates is expected to be rare because
a new species forms quickly in a small population. For example:
Imagine that a small subpopulation becomes
isolated from the large main population of a species. If the subpopulation
is a small "bottleneck" it probably won't be a statistically representative
sample, so its gene pool may differ significantly from the gene pool of the
main population. And if it is on the fringe of the area inhabited by the
species, it may have a different environment and different selection pressures.
Due to these two factors, soon (perhaps in a thousand generations, spanning
5000 years) the subpopulation can undergo changes, including the development
of reproductive barriers that prevent interbreeding with the main population,
and a new species has formed. If the number of individuals in this new
species then increases, stabilizing influences (which operate more effectively
in a large population) may minimize further changes.
If the new species survives for 5 million
years, most fossilization will occur during the long period of "equilibrium"
stasis, not in the 5000 years when "punctuated" change was occurring.
The fossil record will show a changed new species that appears suddenly (since
transitional fossils probably won't form during the short transition period
of 5000 years) but does not continue to change. During the 5 million year
lifetime of the species, other suddenly appearing species can "branch off"
to produce more evolutionary diversification.
In my example above, the timings (for number
of generations, length of transition period, and lifetime of species) are within
the range of timings typically proposed by punctuationalists in their evolutionary
scenarios. I've chosen these timings for illustrative purposes, to show
that 5000 years can be a period of time which is biologically long (1000 generations)
but is geologically short (when we consider the long time periods recorded in
typical non-catastrophic geological formations), and that compared with the
life span of a species (5 million years) the time of rapid change (5000 years)
can be short, in this case only .1 % of the species lifetime.
A proposal of "geologically rapid"
speciation, as described above, is accepted by all evolutionists and oeCs, and
by some yeCs. The remainder of this section outlines some of the questions
asked by each group.
Questions
from Supporters:
According to a prominent college biology
textbook, in the modern evolutionary synthesis,
"The paradigm
is distinctly gradualist in its view that large-scale evolutionary changes are
the accumulations of many minute changes occurring over vast spans of time.
Microevolution, the changes in allele frequencies in populations, is extrapolated
to explain most macroevolution.
In the classical version of the modern
synthesis, natural selection is the major cause of evolution at all levels.
Populations adapt by natural selection, new species arise when isolated populations
diverge as different adaptations evolve, and continued divergence due to natural
selection differentiates the different taxa. The modern synthesis recognizes,
and in fact first described, how genetic drift can cause rapid, nonadaptive
evolution. But the major emphases of the synthesis are gradualism and
natural selection.
A number of evolutionary biologists dissent
from the view that the evolution recorded in the fossil record can be explained
by extrapolating the processes of microevolution. The debate is partly
about the pace of evolution. Many transitions in the fossil record are
punctuated, not gradual. Gradualists argue that... Punctuationalists
counter that... The debate is not just about the tempo of evolution, but
also about the degree to which microevolution compounded over time is sufficient
to explain macroevolution.
Some researchers favor a hierarchical theory,
with different mechanisms being most important at different levels of evolution.
In this view, natural selection is the key to adaptive evolution of a population
but is not usually the most important factor in speciation; it plays even less
of a role at the level of macroevolution." (Campbell, 1996, pages
477, 479)
Neo-Darwinian evolutionists discuss
a wide variety of controversial questions: Were most large-scale changes
(in Total Macro-E) produced by a gradual accumulation of small-scale changes
(in micro-E and minor macro-E) or was a major role played by radical changes
such as those resulting from mutations in regulatory genes that control embryonic
development; what were the relative evolutionary contributions of micro-E
and speciation, of adaptive natural selection and random genetic drift and
historical
contingency (due to nonbiological events like meteor impacts or continental
drift); what was the relative importance of competitive selection (caused
by differences in rates of survival and reproduction) for individuals, for
groups
within a species, and for different species; what was the tempo of change
in the Cambrian Explosion and what were the major causes of change; and
(to analyze the significance of a sudden appearance and subsequent stasis
of
fossils) in what ways and to what extent is there incompleteness in the fossil
record, and how much micro-E occurs in ways (such as changes in physiology
and
internal organs) that are not observable in the fossil record?
Questions
from Critics:
The questions above are debated among
evolutionists who accept the basics of neo-Darwinism, who claim to be arguing
only about details. But their questions — asking "how much diversity
and complexity can be produced, in what ways, and how quickly" — go far
beyond minor details, giving us reasons to think critically about essentials.
Until we have answers that are more satisfactory, creationists (both oeC and
yeC) think there are reasons for an open-minded scientist to question an extrapolation
of micro-E into Total Macro-E. Two of these reasons, rates of change and
irreducible complexity, are discussed below.
rates of change: We can gain
a deeper, more complete understanding of evolution by asking, "To produce
the changes we observe, what new types of biochemical systems would be required,
with how many proteins that are new or modified, and how much change in DNA?
How many mutations and selection (or drift,...) would be required, how long
would this take, and how probable is it?" {note: Rates of DNA change
are important even in cases where mutations in regulatory genes cause major
changes in body structure, because a new biochemical system cannot be produced
unless the genes for producing it already exist, so analysis of DNA change is
still relevant.}
irreducible complexity: In
Darwin's Black Box: The Biochemical Challenge to Evolution (1996), Michael
Behe claims that some biochemical systems are irreducibly
complex due to interdependencies between parts in the system, and therefore
could not have been produced in a step-by-step process of natural selection.
note: The rest of this section has been moved
(after expansion and revision) into a page about Principles
& Definitions of Irreducible Complexity.
Summary
According to oeC,
current evolutionary theories are adequate for explaining many observations,
but not
all. Yes,
micro-E can fine-tune populations of organisms that already have functioning
systems, thus helping them to compete more effectively and to adapt in changing
environments. And macro-E can produce new species that are minor variations
of existing species, to generate biodiversity. But could evolution
produce the changes we observe in the fossil record, in the time that was
available?
And does natural evolution have enough "creative power" to produce
irreducibly complex systems, and to produce other complex systems in the time
available?
Unfortunately for science, proponents
of
neo-Darwinian
evolution
usually
overestimate its scientific status
by
ignoring the basic Logical Principles
for Evaluating Evolution and Creation.
APPENDIX As explained above, we should NOT avoid logical criticisms of evolution. But we should avoid illogical criticisms, as explained below: 6F:
Questionable Criticisms of Evolution Thermodynamics
and Evolution |
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