Автоматическое создание гистограммы с линиями Density, Normal:

histDenNorm <- function (x, main = "") {
  hist(x, prob = TRUE, main = main) # Histogram
  lines(density(x), col = "blue", lwd = 2) # Density 
  x2 <- seq(min(x), max(x), length = 40)
  f <- dnorm(x2, mean(x), sd(x))
  lines(x2, f, col = "red", lwd = 2) # Normal
  legend("topright", c("Histogram", "Density", "Normal"), box.lty = 0,
         lty = 1, col = c("black", "blue", "red"), lwd = c(1, 2, 2))
}

set.seed(454)

# Normal data
x <- rnorm(n = 5000, mean = 110, sd = 5)

# Exponential data
y <- rexp(n = 3000, rate = 1)

par(mfcol = c(2, 1))

histDenNorm(x, main = "Histogram of X")
histDenNorm(y, main = "Histogram of Y")

par(mfcol = c(1, 1))