"People are no good. You can only trust animals and the bottle" - Delmao, half-elf thief.
Unlike the parents of mules, elves and humans are often attracted to each other, but just as often, they are the unwanted product of a casual encounter. Born from two worlds but not welcome in either, they find an attraction to the solitary wastes. In conjunction with a lack of unifying culture, most turn into lonesome, self-sufficient folk. Elves have no tolerance for them (the mother is expected to get rid of the child or be cast out) and most, though not all, humans believe their ears make them just another lazy thief and trickster. When everyone else sees you as the worst quality of your parent races, the half-elf turns away and has found kinship in the animal world unmatched by either of their parent races.
Half-elves are taller than most humans, standing 6 to 6 1/2 feet tall, are bulkier than elves and able to pass themselves off more as humans than full elves. The men can grow beards and they have a full range of skin tones and hair colors. Some enjoy proving themselves better than humans or elves at a task, and others simply turn to different cultures, such as thri-kreen or muls for friendship. They rarely maintain a friendship for long as it is their experience that everyone is going to let you down or betray you eventually, but at times it is necessary to ally or simply not be alone.
Half-elves don't form communities despite their numbers, and they can reproduce with either parent race. Most will never know their elven parent and they aren't welcome in elven tribes, seen as an embarrassment who can't keep up. Their affinity to beasts leads them to be valuable animal handlers. Some find acceptance in the ranks of templars, where service to the sorcerer-king or queen provides a welcome home. In adventuring parties, they tend to be aloof because it's likely to be a short-lived experience.
Half-elves are influenced by both parents, even if not accepted by either race.
Ability Score Increase: Your Wisdom score increases by 2 and two other ability scores of your choice increase by 1.
Age: Half-elves mature as humans, reaching adulthood around 20. Some live to 130 years.
Alignment: Lawful and neutral half-elves labor for acceptance from a parent race while chaotic ones have given up, rejecting a society that has rejected them.
Size: A typical half-elf stands close to 6 1/2 feet tall and weighs 140 pounds. Your size is Medium.
Speed: Your base walking speed is 30 feet.
Nomadic Life: You have proficiency in the Survival and Animal Handling skills.
Speak with Animals: You can communicate simple ideas with medium size or smaller beasts using sounds and gestures. This does not make the animal friendly to you or able to respond in kind.
Animal Affinity: At 3rd level, you can use an Action to attempt to charm a medium size or smaller beast with an Intelligence of 3 or lower. You must be able to touch and talk to the beast. It must pass a Wisdom save or be charmed for 24 hours. The saving throw is 8 + your proficiency bonus + your Wisdom modifier. If you or a companion damage the beast, the charm ends. You may use this once per long rest.
Languages: You can speak Common and Elvish, and if a city dweller, likely to adopt the distinct dialect of your home.
You don't consider yourself a separate race. You pride yourself on your self-reliance and refuse patronizing offers to help you. You'll do fine on your own, thank you very much. Take any chance to show humans you're just as talented as them or elves you're just as clever. If others view your attempts as irrational, well, they get to be wrapped up in the blankets of racial acceptance. You're left out in the cold. Praise should be viewed with suspicion because no one hands that out without an angle in mind. Other half-elves don't interest you by default. Just because they have the same ears doesn't mean you suddenly have anything in common. IN an adventuring group, you don't need charity and don't need someone else to cook your food or take your watch.
This does not mean you'll never form a lasting friendship. But it's hard to get over a lifetime of being on the outside and being constantly reminded of that. This is why you feel affinity with the beast. They're simple. They don't judge, and they don't act with malice.