Specialties & Perspectives Intersect to Tell Us What We Know about Evolution
Our world is so complex and interconnected, it is no surprise that science
is too. This essay examines the multiple lines of evidence that align to provide our modern understanding of evolution and its mechanism.
Not surprisingly, Charles Darwin is often viewed as the primary
(or only) source of our knowledge of evolution. Open any biology text
and you will find a photo of the grand old man, something about the
voyage of the Beagle, and a definition of evolution. However, our modern understanding of evolution is now so much richer because of a
synthesis of evidence from intersecting specialties and perspectives.
Just consider the following.
Paleontology (Stories That Fossils Can Tell). Evidence in support
of evolution is often found within the layers of the Earth. From shells in
the Andes to hominin remains unearthed from caves, fossils suggest both
the appearance of and relationships between long-dead creatures. For
centuries, naturalists and field scientists used observation and detailed
field notes to provide us snapshots of living things long gone but preserved in the rocks.
Geology (Stories That Rocks Can Tell). Scientists have long used
geological superposition – the notion that new rock deposits form on
top of older rocks – to provide relative time comparisons of fossils. In
addition to suggesting relationships by relative position, technologies
such as radiometric dating provide a reliable timeline for the age of fossils
that are found, allowing more evidence of orders of succession of life past
Biogeography (Distribution in Space & Time). Building on fossil
discoveries, geographers can make comparisons between organisms
around the world based on their location. Biogeography specifically
looks at where we find similar fossils and maps ranges of organisms.
This mapping can be used to hypothesize timelines for migrations and
demonstrate that some landmasses were once connected and even suggests the order in which the landmasses may have joined and separated.
Comparative Anatomy (Homology, Analogy & Vestigial Structures). Fossils offer exemplars for comparison to known organisms.
Scientists have long used comparative anatomy to explore structures
in living and extinct forms. This idea of “descent with modification,”
that similarities among organisms can be explained by small changes
over generations, was described by Darwin, for which he is often
under-credited. Close examination of structures and functions allows
us to make hypotheses about relationships between organisms that
have evolved within the same line (homologs) or evolved in a similar
way in different lines (analogs). We can also observe remnants of traits
found in ancestral species that have slowly become less useful (vestigial
structures), like hind limbs in whales and the human appendix.
Comparative Embryology (Developmental Relationships). Build-
ing on our understanding of comparative anatomy, we have the ability
to examine structure and function on a more intimate scale through
comparative embryology. Examination of the earliest cellular states of liv-
ing things can provide evidence of evolutionary relationships and even the
degrees of separation of living things based on when specific traits appear
Genetics (Stories in the Genes). Darwin understood inheritance –
after all, he was a pigeon breeder – but he had no knowledge of genes.
The advent of genetics and related biochemistry allows us to understand
the details of descent with modification and the bigger picture of diversity.
Bones can suggest evolutionary history, but genetic material recovered
from those bones is useful in confirming hypotheses about speciation
and relationships. The ability to “look within” began with comparative
anatomy and fossils, but our present understanding is confirmed on the
genetic level. Evolutionary study of living organisms has demonstrated
the impact of gene flow and reproductive isolation on speciation, while
cladistics and “tree thinking” take us beyond comparison of homologous
and vestigial structures to DNA to verify proposed relationships, ances-
tries, and when speciation occurred.
Cultural Anthropology (The Story That Makes Us Human). As
Darwin stated in Origin of Species, “light will be thrown on the origin of
man and his history.” As much as we learn from bones and stones, the
evolutionary story of life, human and otherwise, now encompasses social
elements with the scientific. Diet, culture, art, beliefs, and other elements
of modern and historical human behavior greatly inform the narrative of
modern humans. While physical anthropology is focused on the stories
told by fossils, cultural anthropologists explore cognitive evolution by
exploring behaviors such as burial practices, shared belief systems, social
structures, and communication. This intersection of applied and social
sciences builds our understanding of who we are.
Observations in Real Time (Evolution in Action). A principal anti-
evolution argument is the notion that we can’t confirm the historical record
because we were not there to witness the events. While inference tells us
much, the argument that evolution cannot be witnessed is false. Evolution
as evidenced through descent and speciation are observable firsthand and
on very modest timescales. Some groundbreaking examples of this are
found in the work of Rosemary and Peter Grant with the Galápagos finches,
the work of David Reznick with Trinidadian guppies, and on a long-term
scale with the work of Richard Lenski on E.coli, just to name a few.
Synthesis: A Hallmark Trait of Science. Darwin was a man of
great vision and a quintessential scientist. He moved easily between
various fields of study in his quest for understanding. All who study
evolution are following the same method by synthesizing evidence,
data, and explanations from a wide range of fields and perspectives,
thereby demonstrating that evolution is the best possible explanation
for the unity and diversity of life.
THE AMERICAN BIOLOGY TEACHER GUEST COMMENTARY 69
Amanda L. Glaze