IB Bio SL vs. ESS SL as a sixth course?

My son transferred from a selective private high school into an IB Diploma school for 11th/12th grades. At his previous school he already took high school physics and Honors chemistry (their program had students take Bio in 11th grade) and got A’s with one B+ in chem (his only one in 9th-10th grade). In college he wants to study engineering and either econ/physics/business to be an “entrepreneur who invents something to help the world.” He is trying to prepare for application to HYPS-type schools.

His new school only allows three HL courses and does not offer ESS (Environmental Systems and Society) in HL, only in SL. Help us decide whether Bio SL is a better choice for his sixth course, or if he can make a compelling case for why he is taking ESS SL. In other words, how critical is Bio at HYPS-type schools if he is more interested in the environment? What about the fact that ESS may have the reputation of being an easier course?

Here are his courses:

Math HL
Econ HL
Physics HL
English SL
Chinese SL
Either Biology SL or Environmental Systems and Society SL
Theory of Knowledge, etc.

Thank you for any insight you could provide! He has a couple weeks to make changes to his schedule!

In the IB program at my school, ESS isn’t viewed as a “tough” science, and some universities see it as an easy way out for those who don’t like science. Biology, especially at SL, should be a good balance — but that’s just my opinion! Go to your son’s school and seek out the teachers in the respective subjects, talk to counselors, that sort of stuff.

Also remember that an IB courseload is already tough in itself, so taking either subject would not make or break your son’s application. Best of luck!

Bio will not make a positive difference and is more likely to make a negative difference. Sure Bio is harder than ESS, but the point here is balance and consistency of academic interests -not to mention total score.
For top 25 universities/LACs IB automatically has rigor, and the three HLs are extremely rigorous by all standards (physic and math HL are harder than what’s offered at the AP level). Chinese and English SL are also known as hard (your son could likely take the corresponding AP exams at the end of 11th grade in order to shore up credits, which SLs often don’t. Even at SL level these two will not be easy and your son will have to handle the equivalent of 5 core APs junior year, and the equivalent of three post APs and two APs senior year.) In short, even without Bio his course load is on the heavy side for all IB candidates. Taking Bio will NOT change that.
Having one easier SL will allow him to do better in the others. He should definitely aim for a 6 or 7 in ESS and shore up points this way. Getting a 7 in HL Math and HL physics is notoriously difficult (harder than in other subjects, and getting a 7 is way harder than getting a 6, which itself is harder than getting an AP5), so realistically don’t expect higher than 6.

Ivies will want a minimum of 38 predicted so having an easier 7/guaranteed 6 will make that goal more within reach ( think HL6 in math and physics plus HL7 in economics and SL7 ESS puts him within the ballpark right off the bat, how much higher than 38 depends on whether he gets 6 or 7 in his other SLs but even with 2 6s he’s OK. And everyone knows how good math and physics HL6 means compared to, say, calc BC 5. )
Cherry on the cake, finding ESS easier will actually leave him with a bit more time for the other five courses and thus greater likelihood he can do well without damaging his health thriugh stress or lack of sleep.
Finally, there’s academic consistency. Kids aiming for top 25 Universities/LACs who say they’re interested in a field need to show it (it’s easy to say you like something - at that level, if you want to work in solar energy or disaster prevention but have not taken a class that pertains to that wide field whereas your school offers one, they’ll wonder how serious you are and if you’re just repeating something that sounds cool, kind of like kids who wanted to be astronauts.) Having taken ESS and using some questions raised there as a potential problem you’d like to solve using STEM is much more solid and serious.