# set up the plot
myplot <- qplot(data=tnffinal, log_100m, log_1500m, color=Female)
# add Least Squares fit lines (you can chose other methose like Loess)
myplot_fit <- myplot+geom_smoot(method=lm)
# output graph
myplot_fit

tnffinal = data.frame(
  log_100m = c(rnorm(10), rnorm(10,5)),
  log_1500m = c(rnorm(10), rnorm(10,5)),
  Female = factor(rep(0:1, each = 10))
)
library(ggplot2)
myplot <- qplot(data=tnffinal, log_100m, log_1500m, color=Female)
# add Least Squares fit lines (you can chose other methose like Loess)
myplot_fit <- myplot+geom_smooth(aes(group = Female),method=lm,)
# output graph
myplot_fit