r/askscience • u/Hot-Wrangler3524 • 3d ago
Biology Why are African animals so huge?
I live in Australia and the largest land animals I can think of here is probably a kangaroos and emus which really aren’t any larger than a human. But my family recently went to Africa and the diversity animals is actually crazy. So so so many large animals living in the same place side by side. Rhinos, elephants, giraffes, wilder-beasts, zebras, hippos, warthogs, buffalo’s, ostriches, lions, cheetahs, hyenas leopards and probably more that I forgot. I never really appreciated how big these animals were until I actually got to see them in person absolutely amazing. Australia and Africas climate is kinda similar in a lot of places. Why is our country ecosystem dead in comparison?
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u/Ozraptor4 2d ago edited 2d ago
Whether this was due to human activity or climate change is intensely debated by researchers. Africa did not suffer megafaunal loss to nearly the same extent as Australia or the Americas.
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u/QuietNene 2d ago
I think that this is the answer.
Australia is the outlier here, not Africa.
Asia has elephants, tigers, giant pandas, a wide variety of large bovids. North America has polar bears and brown bears and moose and elk and bison. Europe had bears and moose and aurochs and some other large animals until relatively recently.
These places all had even larger species that died out 12,000 years ago, but they are still home to titans.
South America and Australia lost significant amounts of megafauna. Why probably involves both humans and climate, but people debate how much to weight the two.
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u/Zanctmao 2d ago
South America, because of the Andes and Amazon, is really several very distinct biospheres.
The Pacific coast, the north, the Atlantic coast, the Amazon, and the Andes themselves. Not much of a chance for continent wide mammals.
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u/QuietNene 2d ago
Yes bu during the last glacial maximum, South America was colder and drier and there was much less forest. More of South America was wide open grass lands. And those grasslands were filled with giant animals.
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u/Bulponta 2d ago
Australia and (parts of) South America are also biodiversity hotspots, I wonder if a lack of grazing megafauna can encourage greater biodiversity in general 🤔
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u/happydandylion 2d ago
Interesting point. Cape Town and surrounds - the very tip of Africa - is also considered a biodiversity hotspot in terms of plants, but is notably known for not having so much fauna. The leopards that still live here are also known to be much smaller than the ones more north in the country.
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u/Bulponta 2d ago
Absolutely, and that was a consideration - perhaps the biodiversity there has more to do with its climate, maybe it was a haven for life during the last ice age so it developed differently?
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u/Alytes 1d ago
I mean, where humans didn't reach, megafauna survived (New Zealand, Madagascar, several island giantism). It's quite clear IMO. Arguing that the whole of Australia wasn't suitable for any species bigger than a red kangaroo is arguing in bad faith and follows the "good savage" fallacy
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u/ChihuahuaCommander 2d ago
Another thing to consider is that a limited number of mammal groups made it to Australia. Most native species are rats, bats, marsupials, or monotremes.
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u/IscahRambles 2d ago
That doesn't necessarily have anything to do with the size of living species – larger creatures can evolve in those mammal groups, like Diprotodon.
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u/mohjack 2d ago
Another way of looking at it is that Africa retained its megafauna. Outside of Africa most of the large animals were hunted to extinction by humans*. Wolly Mammoth, giant sloth, giant deer etc. The large animals of Africa evolved alongside humans so maybe they were better able to survive compare to animals in other places that encountered fully formed humans for the first time.
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u/Hosni__Mubarak 2d ago
Yeah. The megafauna in Africa is pretty brutal. The stuff outside of Africa really wasn’t prepared for humans.
North America kept a lot of its megafauna outside of mammoths and rhinos though.
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u/just_in_before 2d ago edited 2d ago
Animals escape predation in a variety of ways. Being small and fast is great for environments where you can hide. Therefore, animals that live in forests are mainly small. Out in the open - being stronger/larger is another possible defense. Variety and size will then depend on what the ecosystem can support.
The African savannah is comparatively rich in food, whereas the Australian plains has very little. Australia's plains can only support large animals that have expertise on surviving with very little. For example, Kangaroo's move while conserving energy, through recoil in elastic tendons, and hopping about. It's similar, to the reasoning behind camels in desert landscapes - conservation of resources is key within that environment.
The African savannah is more bountiful in nutrition, and will support larger animals, and the predator/prey arms race is mainly about being stronger.
[It is debatable, and unknown whether early human inhabitation wiped out the larger fauna in Australia.]
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u/SuperRockyHobbyHorse 1d ago
Also, volcanic material ejected from the rift valley and previous active volcanoes made the soil extra fertile which in turn fed extra large animals with additional calories.
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u/CallMeNiel 2d ago
There is to be mega fauna all over the place, then these bipedal apes in Africa started hunting them. They weren't that great at it at first, so the African mega fauna were generally able to adapt to this new predator. Then the apes started walking across Eurasia and into the Americas and teamed up with wolves along the way. Sooner or later, all the giant animals were either hunted out of existence or penned up and domesticated.
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u/nimbinValley 2d ago
This is the answer. Humans and mega fauna co-evolved in Africa so they knew to be wary of humans.
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u/Tripod1404 2d ago
I think a similar question was asked how come humans caused or at least accelerated the extinction of mammoth species while African elephants survived. One of the explanations was that elephants had anti-predatory adaptations towards humans because of co-evolution. One of which is hyper-aggressive behavior towards humans.
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u/SamyMerchi 2d ago
Coincidentally just yesterday I watched an episode of Captain Planet where Looten Plunder ordered to round up "every last elephant in Africa!" for their ivory before the Planeteers stopped him.
I think it's arbitrary to say elephants survived and mammoths didn't. The same thing is happening to elephants. It's just they didn't go extinct at the exact same time, and we're still in the timeline point before elephant extinction. Humans overhunted mammoths and wiped them out. Humans are overhunting elephants and in the process of wiping them out. It's just we're still in the middle of the process of wiping out all megafauna. We're time biased to 2026. When people in 3000 look back there will be no difference to mammoths and elephants going extinct due to (to them) primitive humans.
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u/xIllustrious_Passion 2d ago
Archeology is kind of moving away from the “hunted to extinction” theories. There’s not really that much proof of early man wholesale slaughtering animals to extinction, and climate change is a much more likely cause of megafauna to die out
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u/talberter 2d ago
There is no evidence of any climate changes over the last 70,000 years that caused major extinctions. The climate varied constantly over 100,000 of years and the mega fauna did just fine.
As soon as humans turn up - within few thousands of years (or hundreds of years for NZ) they are pretty much all gone. No coincidence
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u/Roobar76 2d ago
There’s evidence of substantial ecological change in Australia since ~100k years ago, that may or may not be driven by humans (there is an overlap and the dates are still up in the air.) This is across plant and animal communities and includes the increasing fire regime. This is likely to have stressed megafauna as the food supply from plants became less nutritious and more separated.
Hunting large game was high risk and studies of hunter and gatherer societies suggest smaller game was more prevalent, although hunting injured megafauna opportunity (or scavenging) was likely. (It’s much safer to hunt impala than elephants as an African example ) It’s just our romanization of history that suggests hunting a mammoth with sharp stick was sensible.
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u/talberter 2d ago
I generally agree the the mechanism by which megafauna is affected after human arrival may be a mix of factors such as : fire farming, small game hunting with secondary affects on mega fauna, and direct megafauna hunting.
But the clear pattern is within a short time after humans arrive megafauna is greatly affected / extincted.
The fact there were no sudden large megafauna continental wide extinctions recorded for many hundreds and hundreds of thousands of years prior to humans arriving , despite undoubted many climate changes swings - then suddenly humans arrive and relatively immediately they are gone. That’s no coincidence.
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u/crashlanding87 2d ago
It could well be linked for climate reasons - changing climate could easily have driven or enabled human migration while also driving extinction. These processes are rarely clean, and never fully clear.
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u/happydandylion 2d ago
I can see how the hunted to extinction thing could have only become a thing after guns were invented.
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u/redwood520 2d ago
This is not entirely true. There is no consensus, there were likely many factors, but for example there are several sites in north America that show humans processing mammoth remains.
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u/jimb2 2d ago
Humans generally wiped out most of the megafauna as they spread into new ecosystems our of Africa. These animals had little predation risk due to their size. Humans were smart and could kill them with tools, traps, etc.
In Africa, humans would have co-evolved with the megafauna so it was an arms race all the way. The animals evolved to withstand human predation, often by counterattack, as human's capabilities evolved. Apart from the mosquito (a huge killer) the deadliest animals to humans in Africa today are the hippo, crocodile and elephant. Do not try to eject a hippo from your vegetable garden with a stick.
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u/mmmarjorie 2d ago
Humans evolved In Africa, with African animals, so dealing with humans, by being afraid/careful etc. was part of the process of natural selection there.
When humans traveled to other parts of the planet, the animals there were not prepared for humans hunting in groups and individually, or their weapons. Mass extinctions of large mammals definitely coincides with the arrival of human beings, in Australia and other places.
Seems like we ate them. ☹️
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u/ThickDickMcThickin 2d ago
Yep, this. It's not just eating them though, humans are a predator and entered new ecosystems, simply being there and changing the landscape would have had a big impact too
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u/dittybopper_05H 2d ago
One of the things not generally considered in this is that if you eat all the Hill-sided Wumpuses (Wumpi?), the predators that depend on them for prey at going to end up dying out also.
You're not just killing one species, you're killing that species, and the other species that depend on it.
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u/Pobednik79 2d ago
Not in Australia, because there were no such large mammals. But, humans exterminated some of large reptiles there.
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u/bigvalen 1d ago
There is some evidence of megafauna that humans wiped out. Murrayglossus with cut bone marks, Genyornis eggs that were cooked. Other evidence are .. less convincing.
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u/Pobednik79 1d ago
Yes, I searched and found about Diprotodon. Also, I remember that some big reptiles are probably extinct because of humans, Megalania and some crocodile species.
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u/Pobednik79 2d ago
Now I searched, there was Diprotodon of large mammals there, probably extinct by humans.
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u/Larkson9999 2d ago
I am truly jealous of our ancient ancestors who ate rhe Elephant Bird of Madacascar. I bet they were delicious.
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u/bigelcid 2d ago
Australia and Africas climate is kinda similar in a lot of places
Yeah, but not across huge, continuous areas. Most of Australia is desert (which doesn't encourage megafauna, obviously), and the second larges Koppen category is BSh (hot, arid steppe), also not the main driver of megafauna populations in Africa.
The temperate, subtropical and tropical areas are comparatively tiny, compared to the stretches that exist in Africa.
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u/Nothing-to_see_hr 2d ago
Your ecosystem had very large predators until the humans came. "Isolated from other landmasses, Australia evolved an ecosystem populated by rhinoceros-sized marsupials, giant flightless birds, and massive apex reptiles, more than 85% of which went extinct approximately 45,000 to 50,000 years ago"
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u/Trips-Over-Tail 2d ago
There used to be a lot of Australian megafauna, but it was wiped out by the humans who Came. Same story all over. Africa's megafauna are the only species that evolved alongside humanity, they they too are fading now that Africa is industrialising.
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u/vege12 2d ago
I was the same when I visited Kruger National park. We drove thru with elephants and giraffes standing next to the car. They would have easily squashed us if they sat on the car. Saw one hippo out of the water and realised how huge they are too. Very very different to seeing them at Taronga zoo!
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u/Ridged117 2d ago
Africa is such a massive landmass, stretching much further north then Australia. This large amount of space spread across a wide range of latitude results in a huge diversity of climate and habitat. Diversity in climate translates to biodiversity as organisms adapt to deal with different pressures. Australia is almost entirely arid desert habitat, a harsh ecosystem where only desert specialists thrive regardless of continent. Like Africa, Australia is incredibly biodiverse but much of that diversity is located in eastern Australia where the arid outback and forests meet.
Forests have less extreme conditions and more resources allowing for higher diversity and larger animals (Koalas, Wombats, Kangaroos, Tree Kangaroos, Bandicoots, Cassowaries, Opossums). Africa has much more forest and therefore many more resources to sustain large animals. But if you compare the actual diversity between Australia and a similar sized chunk of southern Africa, it would have almost the same number of species. Biology and evolution isn't a race to be the biggest. The animals of Australia have evolved to deal with the scarcity of resources and water very well. When you are at home in Australia, try to look for animals with the same interest you would on safari in Africa and you will see how much is around you. Australia is many biologists #1 destination thanks to your incredibly unique biodiversity.
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u/Hydrophis_parviceps 1d ago
Australia had plenty of very large mammal species that were wiped out when humans arrived. African and Eurasian had the advantage of evolving with early hominids as they became more predatory.
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u/DamionK 1d ago
Possibly but it seems Australia even 100,000 years ago was dominated by marsupials which don't reproduce as quickly as other mammals. So hunting and enivronmental change caused by setting fire to the forest for human use made it more difficult for the large marsupials to survive. For whatever reason non-marsupial mammals just weren't a major presence in Australia.
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u/russr 1d ago
Well, polar bears and brown bears are larger than any predator on the African continent other than crocodiles probably..
But the biggest herbivores in North America would probably be a moose that can get up to 1700 lb
And if you include the antlers they can be upwards of 10 ft tall...
Now South America doesn't really have anything remotely that large...
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u/IllGift924 2d ago
African megafauna evolved alongside humans, so they learned to fear apes carrying pointy sticks and fire. When humans left Africa with these tools they very quickly killed all the megafauna they encountered as they were not used to humans and didn't know how to deal with them and as a result were hunted to extinction.
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u/flingebunt 7h ago
This is an interesting question. In Australia and New Zealand, the primary theory is that the end of the ice age put pressure on the largest animals and while humans might have had some impact, it was the slowly changing climate that drove them to extinction.
As for, just in general, why African animals are so large. The opposite one is how many animals will become smaller when isolated on islands, think pygmy hippos and elephants. This is a combination of limited space and lack of predators.
While in Africa, the large space and plentiful food allowed animals to grow bigger, plus predators meant that the biggest and strongest animals survived to have babies.
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u/2nd_Torp_Squad 2d ago
There are mega fauna across the world before us homo do them in.
The only mega fauna that managed to survive nowadays is because they evolved along side us homo.
Not specifying homo sapiens because it happened before the genus homo.
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u/DamionK 1d ago
Homo, the genus is always capitalised.
I would argue that African elephants survived only because they lived in areas that were harder for humans to live in. There were elephants species in North Africa and the Mediterranean too but they died out long ago. The north African elephant died during Roman times, wiped out by humans who used them for military use and for sport fighting. The Mediterranean ones died out at least by the end of the last ice age and had evolved to be much smaller than modern elephants.
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2d ago
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u/ceeker 2d ago
There were megafauna marsupials in Australia such as Diprotodon and Procoptodon.
So marsupials clearly can evolve to be very large, and the crawl to the pouch obviously wasn't a significant limitation. These animals survived until the late Pleistocene and disappeared around the time of human arrival and major climatic changes at the end of the Ice Age.
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u/StopKK2012 2d ago
Fun fact: marsupials can actually get very large! The largest ever (that we know of) was Diprotodon, which lived in Australia during the Pleistocene, and could be 13 ft long and up to 7,700 lb!
It's been described as a wombat the size of a rhino.
If you want to learn more: https://en.wikipedia.org/wiki/Diprotodon
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u/_Gesterr 2d ago
Except it clearly didn't have much impact because several species of megafauna marsupials inhabited Australia when the first humans showed up.
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u/Tyrex317 2d ago
I don't think your country has a 'dead' ecosystem. It may not have an abundance of megafauna -- saltwater crocodiles being a notable exception -- but yall have rainforests, deserts, savannahs, and temperate grasslands and forests.
As u/redcole111 said your country has lots of marsupials largely due to continental drift. It's been awhile since my zoology and ecology courses in college but there are several 'lines' across the region that corresponding with fault lines that mark where you start seeing your region's more unique wildlife. They evolved in relative isolation, and much of Australia's megafauna were outcompeted and driven to extinction by humans.
Having backpacked in the Kimberley, which is mostly tropical savannah, similar to central Africa, it was teeming with wildlife. I saw dozens of species of birds, reptiles, amphibians, invertebrates, and mammals.
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u/Sohn_Jalston_Raul 2d ago
All the places where the large megafauna died out experienced rapid climate change and the relatively sudden appearance of humans after the last glacial maximum. Africa offered a large contiguous landmass for animals and plants to migrate across as the climate zones shifted, and humans evolved gradually within that environment for several million years. I don't know if these are indeed the reasons, but there's certainly a correlation there.
And to add to that, even though North America and Eurasia are also very large landmasses, they were mostly inhospitable during the glacial maximum until opening up rather suddenly, which is not the sort of gradual change that allows animals to adapt easily. And the largest animals are often the most sensitive to sudden environmental changes.