 Just for a moment, I want you to think about an attractive man. Did you? Was he an young or an old man? Well, you don't have to tell me. But the choice you just made, female in nature make the same choice all the time. A female may prefer to meet with a young or an old man. Why, you ask? Studies have shown that male age can affect female reproduction. For example, young milk may have better sperm, while older milk can provide other resources, like more food or better parental care. So, whom shall the female choose? Let's find out, shall we? You see, males in the wild start mating as soon as they mature and they keep on mating until they are very old. So an older milk naturally gains way more sexual experience than a young male. This is confusing. Because if a female chooses an old milk, is it because of its age, or all the sexual experience he has gained as he grew older? And how can we test it if age and experience are often correlated in nature? This question, although very important, is quite hard to test in the field. But in the laboratory, we can do this. Here, I have a male and female gambusia that I have collected from the Sullivan's Creek. Using these little fishes in the lab, I experimentally separated the effect of male age and their sexual experience so that I can work out who each male performed better at pursuing female and making more babies. So in my PhD, I raised young and old male who were either virgin or had a lot of sexual experience almost for a month. That's like five years in human timeline. I wanted to know who each male performed better in reproduction. My results show that older male makes significantly more babies than young male. Why? Because they make twice as much sperm as young males. Old males that has been virgin for a long time spend significantly more time chasing a female and making more mating approaches. Now that's all well and good, but whom did the female choose? Drum roll, please. Chairs out, female do not care about male age. They just like to hang out with bigger males repeatedly. Gambusia females went for the looks. I get that. All this result from my thesis takes us one step closer in understanding how male age affects reproduction and the importance of studying female maturese. You see, in nature, female may not always get to marry the male she likes. In my case, although Gambusia female like to hang out with bigger males, she might end up having more babies from older males. But that's alright. Luckily, there's plenty of features in the creek. Both for my females and for me.