In my near decade of higher education in Anthropology, I’ve developed one grand conclusion: life is awesome. I don’t mean my life (which like everyone’s is characterized by an endless series of stresses and satisfactions related to the pursuit of abstract goals of love and success; daily highs and lows that in retrospect even out to a satisfactory existence as a human). I’m talking about Life, as in living organisms and the ways in which they have evolved.
The focus of Anthropology is humans, but in order to understand human biology and culture, we study a lot of comparative species. All the time, I find myself jaw-dropping astounded over the diversity, complexity, and effectiveness of Life.
For example, ligers.
Ligers result from the cross between a male lion and female tiger. They are enormous—over 3 meters long and bigger than either parent species. The opposite cross—a female lion and a male tiger—produces a tigon, which is average sized. What’s going on? Why do male lions and female tigers produce monstrous offspring, while the reciprocal cross does not?
A compelling explanation is provided by the sexual conflict hypothesis, which attributes the pattern to the species’ respective mating behaviors and underlying genetics. Enormous offspring are observed across the animal kingdom when there is a cross between a male from a promiscuous species and a female from a closely related, monogamous species. In promiscuous species the animals have many sexual partners, which leads to a conflict of interests between males and females regarding reproductive strategies. Males invest very little in offspring (sperm, like 5 minutes of physical exertion) and try to have as many partners as possible. They want all of their progeny to be as big and strong as possible, to maximize survival rates with no additional cost to the fathers, who have already moved on to another mate.
Females, on the other hand, invest substantially in offspring (pregnancy, nursing, years of rearing). Big and strong offspring are extra burden. They deplete the females of resources that could be allocated towards themselves and future offspring. It benefits the females to have smaller, less costly offspring.
This is the conundrum and a genetic mechanism has evolved to balance male and female interests. IGF2 (insulin-like growth factor 2) is a gene involved in embryonic growth, and ultimately an offspring’s size. Animals receive one copy from mom and one copy from dad. In promiscuous species, the father’s copy is activated, which makes the embryo grow larger, but the mother’s copy is silenced and gives the embryo no additional growth signals. This balancing system is not present in monogamous species; rather, both parents contribute a copy of the gene functioning at a normal level because both parents are equally invested in raising that child and future children, together.
Lions are promiscuous and tigers are monogamous. What do you get when you cross a promiscuous male lion and a monogamous female tiger? Well, aside from tigress heartache symbolic of my own failed relationships, you get an overactive gene from lion dad, telling the embryo to grow as large as possible,and a normal gene from tiger mom, rather than a silenced one that would have neutralized the excess growth signals. Dad says, “Grow big.” Mom says, “Whatever.”
That is why ligers are huge and Life is awesome.
See ligers in action on YouTube: https://www.youtube.com/watch?v=8HgW86TwF_o
And my examples of why Life is awesome are to be continued…