You need to add backticks for the column names:
A small hint to remember this: if the column names are coloured in the same text as ordinary text it is interpreted as text and not as a variable. (in my RStudio setting it's red, but this isn't the default)
library(tidyverse)
# generating fake data with long column names
cars = mpg %>%
rename("mpg in the city" = cty,
"mpg on the highway" = hwy)
# this doesn't work as the columns are interpreted as text
ggplot(cars, aes(x = 'mpg in the city',
y = 'mpg on the highway')) +
geom_jitter()
# this is working
ggplot(cars, aes(x = `mpg in the city`,
y = `mpg on the highway`)) +
geom_jitter()
PS: for the ethnicity you don't need any ticks at all.