Welcome, my name is Dustin Rubenstein,
I'm a professor of ecology, evolution,
and environmental biology at Columbia University in the city of New York.
Today I'm going to introduce you to the topic of social evolution.
If you watch these birds
(these common or European starlings as they're known)
flying around, they're coming into roost in the evening.
If you're lucky enough to see this behavior in parts of the world,
you'll see this collective behavior,
this collective action of these birds.
By day, they are largely solitary or form small groups,
but by night they form these gregarious roosts, and as they come into roost
these groups form these complex displays as they land.
What you're seeing is a collective or complex form of social behavior,
and many species of animals exhibit social behavior at some point during their lives.
We begin by asking: what is social behavior?
We can define social behavior simply as
the positive and negative interactions between individuals of the same species,
and most animals are social at some point in their lives.
These frogs come together to form mating assemblages during the breeding season,
you can see multiple females and
multiple males coming to fertilize the eggs that you see here.
The process of reproduction is one form of social behavior that most species exhibit,
but some animals exhibit different forms
of social behavior at different times during their lives.
Many species form groups.
Those groups can be temporary
(like the breeding assemblages we talked about in the frogs,
or the groups we see in these walruses, or these penguins),
others (like these plains zebra) form more stable social groups called harems,
that sometimes form larger herds at
different times of the day or different times of the year,
and many insects form groups around food or around mating.