> how do I explain evolution to a new learner as succinctly as possible?

As in biological evolution? When there's competition for resources in an environment the species that are best able (fit) to compete for those resources and raising offspring within the environment end up spreading their genes more than those that don't. Over a long period of time, this results in what we recognize as evolution.

> is there a current evolutionary trait that's been selected for in humans?

Even the fastest changes in species like humans takes many generations to show itself in a population and even longer to become dominant (Unless the selective pressure is extreme). Saying any certain trait (even obvious ones like lactose tolerance) is too speculative and subject to a rapidly changing environment in a biological context.