The Ecology Book

88

B

y the early 20th century, it

was accepted that multiple

species could evolve from a

common ancestor. However, it was

not clear how this evolution process

actually occurred. In fact, there was

some debate about precisely what a

“species” was. In 1942, evolutionary

biologist Ernst Mayr proposed a

new definition of species: groups

of interbreeding natural populations

that are “reproductively isolated

from other such groups.”

What this means is that two

populations of the same species

living in the same area may at

IN CONTEXT

KEY FIGURE

Ernst Mayr (1904 –2005)

BEFORE

1686 Naturalist John Ray

defines individual plant and

animal species as those that

derive from the same seed.

1859 Charles Darwin’s On the

Origin of Species introduces

the idea that species evolve

through natural selection.

AFTER

1976 The Selfish Gene by

Richard Dawkins popularizes

gene-centered evolution: natural

selection at a genetic level.

1995 The Beak of the Finch

by Jonathan Weiner follows

the work of biologists Peter

and Rosemary Grant on the

Galapagos Islands.

2007 Massimo Pigliucci and

Gerd B. Müller use the term

“eco-evo-devo” to suggest how

ecology is among the factors

affecting evolution.

“REPRODUCTIVELY

ISOLATED” ARE THE

KEY WORDS

BIOLOGICAL SPECIES CONCEPT

some point become separated by

geography, mate choice, feeding

strategies, or other means, and then

begin to change through natural

selection or genetic drift. Over time,

as a result of this initial separation,

two distinct species evolve, which

cannot interbreed. This type

of speciation commonly occurs

in small populations of creatures

on remote islands.

Key differences

The biological species concept is

primarily focused on the breeding

potential between organisms. Two

The capacity to

interbreed is key

to the definition

of a species.

“Species” can be

defined as population

groups that are able

to reproduce.

When two groups

of the same species

become reproductively

isolated they

evolve separately.

Eventually, they

become separate

species that cannot

mate with each other.

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