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Patterns of Evolution 
Species evolution has resulted in enormous variation in form and function. When two species diverge 
from a common point of origin, it is called 
divergent evolution
. Divergent evolution can be seen in the forms 
of flowering plant reproductive organs, which share the same basic anatomies but can look very different due 
to selection in different physical environments and adaptation to different types of pollinators. (Figure 57). 
Figure 57.
Flowering plants shared a common ancestor. The appearances of the (a) dense blazing 
star and (b) purple coneflower differ, but they share a basic morphology
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. 
In other cases, distantly related species evolve similar phenotypes independently. For example, both 
bats and insects have evolved flight, and they both have structures known as wings that are adaptations to 
flight. However, the wings of bats and insects evolved from very different starting points. When similar 
structures arise through evolution independently in different species it is called 
convergent evolution
. The 
wings of bats and insects are called 
analogous structures
; they are similar in function and appearance, but do 
not share an origin in a common ancestor. Instead, they evolved independently in the two lineages. The wings 
of a hummingbird and an ostrich are 
homologous structures
, meaning they share similarities (despite their 
differences resulting from evolutionary divergence). The wings of hummingbirds and divergences did not 
evolve independently in the hummingbird lineage and the ostrich lineage—they descended from a common 
ancestor with wings. 
The Modern Synthesis 
At the time Darwin and Wallace developed their concept of natural selection, the mechanisms of 
inheritance, genetics, were unknown. This lack of understanding hampered understanding of many aspects of 
evolution. In fact, at the time, blending inheritance was the dominant (and incorrect) genetic theory, making it 
difficult to understand how natural selection might work. Darwin and Wallace were unaware of the genetics 
work of Austrian monk Gregor Mendel, which was published in 1866, not long after On the Origin of Species 
was published. Mendel's work was rediscovered in the early twentieth century, when geneticists were rapidly 
grasping the fundamentals of inheritance. 
Initially, biologists struggled to understand how gradual evolution could occur due to the newly 
discovered particulate nature of genes. But over the next few decades’ genetics and evolution were integrated 
in what became known as the